I had the bike out today. All was normal until it decided to start idling really low on the way home to where It's basically a T500 now. It idled kinda low, but seemed fine at speed. So, I was giving it some extra throttle when a car in front decided to slow down and turn quickly, so I rolled off and it died. A few cranks later and it was running again. The left cylinder isn't running at idle. It has compression. Around 105psi. It has spark. It's getting fuel. The plug will come out wet.
If I throttle it up the cylinder comes alive again. As soon as I let off, it's bupkiss. Also, strangely enough if I hold the cap a little bit away from the plug I can get that cylinder to run sporadically, and it's back to nothing with the cap seated. Rechecked timing and it hasn't moved.
Only thing I recently did was replaced the oil pump and set the float heights in the carbs. Which actually raised the fuel in the bowls a bit. The idle circuit was clear as well.
It has the original coils on it.
Crank seal perhaps?
Double post. Oops.
Sounds like it's flooding on that cylinder. So much fuel it can't fire at idle. Increasing the gap means the coil voltage has to build higher before it jumps the gap. Stronger spark helps it run.
Are all 3 as low compression as that one? It should be north of 120 and possibly closer to 135-140. I like to run at least 140 on mine with a few tweaks.
test compression and do a leakdown to see if the seals are also shot and pull the carbs again. Fortunately you have to remove them to do a leakdown test. And fortunately you can test one cylinder at a time without having to blank off the other cylinders - No lab seals on this high tech beauty.
I would start by trying a new spark plug in that cylinder. A combination of low compression and weak spark could make the cylinder drop out at idle.
lower fuel level on that one, or look for slight seep at needle. id bet its carb related when warm. drop it like 1-2mm and i bet it clears up.
or, the pilot jet fell out.
Quote from: m in sc on November 06, 2022, 06:49:18 AM
lower fuel level on that one, or look for slight seep at needle. id bet its carb related when warm. drop it like 1-2mm and i bet it clears up.
or, the pilot jet fell out.
The fuel level is definitely higher than it was... Also, the cylinder dropped out just like the snowmobile did when the float was set too high... Worth a shot as it ran fine before I messed with the carbs. Which figures lol.
Teazer,
All 3 are matched at about 105-110 PSI. She's a tired old girl that's for sure. I'm also fully aware that it's past due for a rebuild. I just need to acquire a set of cases. As paying a welder to repair my broken one seems like it could be a big pain in the dingus (though I do know a wizard with a welder, it takes months to see your stuff again). I have a line on a local set of cases, same year range and everything, including the cylinders AND potentially all the engine covers for around $600. Just figured I'd wait and try to get the last of the Fall season on this motor before baby arrives and kills my engine rebuild timeline. I figured the cost and promptly buried it into the recesses of my mind. :burnout:
Drop the fuel level a little and fit hotter plugs to see if that cleans it up a bit.
BTW, don't ever try to build a budget for rebuilding it. You may go into shock and never get around to it. I prefer the opposite approach of buying parts when I have some cash and eventually it gets done. :whistle:
With an older motor, it's really important to tweak things to get it to run as well as it can. A healthy motor can be way out of spec and still run OK but a worn motor needs more attention. If the exhausts have much carbon in the baffles, that could contribute to the symptoms.
If you are not running it hard, you go to a B7 or even a B6 plug which will tend to burn off excess fuel. I ran B8 or B9 in mine at the drag strip and dyno testing and they were fine.
The fact that it runs at higher loads and fouls at idle strongly suggests excessively rich mixture. Check the pilot jets, but also check the chokes. The plungers or whatever the correct Mikuni nomenclature is go hard over time and no longer seal properly allowing the "choke" to be active even when you have closed it. MikesXS has a plunger for a BS38 that is the same part at a reasonable price.
With the cracked cases, it's not hard to build that area up with weld but heat the cases before welding and obviuosly that has to wait until the motor is stripped. I have had a couple of cases done. For sure it's a lot of messing around to dress the case back so it looks perfect but worth the work.
And just a heads up. Check that the points and alternator leads are well clear of the exhausts. If the leads droop and melt on the pipes, the trail of destruction can be interesting to say the least.
Ok, I totally needed to put this info here but failed.
It has an Accent Ignition on it now. It's tucked up nicely in the motor mount points. The motor ran great until I set the float heights. They have around 2mm more fuel in them now. So, I'm gonna say that both you and Mark are correct. I think I dicked it up by setting the floats to stock with aftermarket needles and seats. As the bike ran absolutely fine before I did that. The chokes are all originals, but the rubber was good on them. Squishy, not worn in. I do have keyster replacements if necessary. But, running it on choke kills it, as it should.
I'll re-set the float heights back to where they were and throw a new set of plugs in it. Meanwhile, I stretched the Rd's legs today. Felt good getting on a bike that pretty much runs as it should... heh. Pretty much.
Try switching the carbs around if you can and see if the problem follows.
On my H1 500, it didn't fix the problem and I spent ages diagnosing poor running / idle from the left pot. A chap on a forum suggested to take the baffle it. That was it, a lump of carbon got dislodged. Clearly my efforts to decoke weren't good enough.
The carb trick would work if they were single carbs, but this is a bank of three, with the center carb tied to the other two.
Put the carbs back to about where they were and still won't run. New plugs showing up tomorrow. Leaving the old plugs out of the bike overnight, and disconnecting the fuel. I'll give it one last try tomorrow, but I think it might be a dead soldier.
Quote from: Striker1423 on November 06, 2022, 09:41:28 AM
.....). I have a line on a local set of cases, same year range and everything, including the cylinders AND potentially all the engine covers for around $600.
I don't think I paid that much for a complete bike... Just don't ask how much I sank into those cheap bikes though..
Going back a step, is it possible that the pipes are now full of fuel along with the crankcases? Pull the SRIS valves or plugs and see how much black oil/fuel mix drains out.
If the airbox is off, apply air flow to the carb inlets and see if the slides all lift at more or less the same rate. Did you do a leakdown test? It's possible that when it was running that a crank seal tore.
If none of the above work, please wrap it up and send it to me and I promise I won't charge you much to take it off your hands. If you happen to be headed to WI or states west or north anytime, drop the bike off with me and I'll see if I can work out what's wrong before you have to head home.
I don't have a leakdown tester. That's on the list too. But, yea, I can try pulling the SRIS plugs to see what happens...
Pull the plug on the questionable cylinder and crank the engine. At a minimum you can check for spark and see if it blows a bunch of fuel out the spark plug hole. Maybe not the worlds most decisive test, but you might learn something.
When you break it down, you need fuel, spark, and compression. Of course too much fuel won't work, but if that cylinder is blasting fuel like Moby Dick, then you know it is a fuel issue.
I tried this for a solid 30 seconds. Nothing came out of the hole except air. Put plugs in and the plug gets wet within a minute or two. Might be coolant. I'm going to see how much coolant left the overflow bottle later today too.
...
when wet, take out and see if plug tip can be lit with a lighter. (away from bike of course) if it burns, fuel, if not, coolant. might be ignition. :twocents:
Teazer is more of an authority on this than me, but the heads on these GT750's are not exactly amazing. A coolant leak is not out of the question.
Ha! Good point Mark, I already lit the bell mouth of the left carb on fire once by accident.
I'll try the few things today. Pending spark plug delivery, I need to get a coolant pressure tester that works on these bikes. Also, a pressure tester for the motor itself.
It could be something as simple as a stuck ring and low compression. We occasionally see this on our race motor if the rings get a bit too carboned up (we run a lot of oil because we don't like rebuilding engines). It is curious you aren't seeing much liquid when turning it over though. If it was a coolant leak you would probably see it in the coolant level and likely get a nice blast out of the cylinder pretty quickly. I suppose when at temp everything changes a bit.
Does the ignition run three separate sensors or does it use one and fire all three with wasted spark? We built our own ignition so I am not familiar with the system you are using.
The Accent ignition uses three separate triggers, and is timed off the center cylinder alone. It literally took me like 30 minutes to install.
See here:
https://www.oldjapanesebikes.com/blog/2012/07/30/elz2coil-accent-electronic-ignition-system/
And this video from Peter Ormrod. This chap's an inspiration to me haha.
https://www.youtube.com/watch?v=V9RH2kj8qho
It's unusual for an accent ignition to fail but it has happened on a couple. But before you send it back to Uwe to test it, double check the "points" lead to the coils and the 6 pin coil connector. It's possible one of the pins is loose or pushed out or corroded.
And check voltage at the coils. I usually fit a relay to feed the coils and that can make a difference.
I have not run an Accent ignition on the test rig but have run DYNA and Ignitech on our test rig up to 10,000 rpm. It's set up for Yamaha twins and I use it to check timing on Motoplat and Hitachi CDI systems but have an adapter that allows it to test GT750 systems as well.
I have a complete 72 GT750 engine if your looking for good cases.
Even have the radiator...
So the spark plugs definitely helped things. It pops and crack's more out of the left cylinder. I'll try pulling just the left carb and cleaning it first. Teazer, the ignition itself works fine. The plugs spark every revolution as it should... However, I will verify the connections as you suggested. I also ordered up a set of coils, wires, and new resistor caps. Those will trickle in over the next week, as well ordered a brand new water pump (new manufactured shaft and all new parts) from a Kettle Club member in anticipation of the eventual rebuild. Might as well start prepping for it now.
EDIT:
Also, don't use an electric ratchet to tighten the loose electrical panel stud nut. Cause it breaks easily. Heh.
Speaking of electric ratchets, which one do you have? I was thinking about buying one, probably one as a gift for my father as well.
I bought the Hazard Fraught (Harbor Freight) Earthquake XT. It's just OK. Their impact is much better. Though mines the first gen Taiwan made silver Earthquake XT not the new black one. Most folks recommend the Milwaukee fuel series. Look up the Torque Test channel on Youtube, or AvE for more teardown videos.
I use a 3/8" Milwaukee every day at work, Chris, and it's a fine tool. Home Depot has pretty good sale prices on them fairly often.
Took the top end apart. Someone's been into the motor. But, I'm guessing they did a base and head gasket swap. Everything just came apart. No need for puller blocks, etc. Just a bit of wood and light hammer taps. The cooling system has what I think is sand collected in a few spots in the head. Maybe they had it blasted and didn't get it all out of the motor?
There is no markings that say what size the pistons are, but from the looks of the underside, they are indeed Suzuki pistons. Measurements put them just under 70mm, so the stock bore. Bores are fairly clean with only the right hole showing slight scoring (just one line I can barely catch my nail on). A lot of blowby on the top and bottom ring end gaps. Head is in good shape. No nicks or pot marks except on the right hole. With only one small gouge I can see. Pistons had a few love taps with the left hole (trouble side) having a ding on the edge of the piston, but no scratches in the bore...
Crank rods are Suzuki original. Feel OK. Again the right hole has some minor pitting in the little end rod. Big end bearings feel just fine. The crank itself has a lot of surface rust. Wipes right off with a rag, but it's there. Piston pin was worn significantly on the right hole. But the bike sat and ran with no real loud engine noises.
If I wasn't too scared of wasting a top end, I'm tempted to just hone, fit new pistons and rings and run it. Flushing the crank out of course. Top gasket had a lot of shmoo come off and get all over everything.
You gotta center those plugs and get a proper combustion chamber. It's all apart...
I know a few guys...
As they said at the end of Shawshank redemption: You have come this far. Would you go a little further. Or words to that effect.
Top end is off. The PO used gasket goo on the head gasket? IS that what I read? That's not only not necessary, it actually makes it harder to seal.
Surface rust on the crank is OK but it suggests that perhaps the shafts might be rusty and may have damaged the seals. With the head off, you might as well go the rest of the way and send the crank to Bill Bune, or your favorite rebuilder. You might get away with new rings and if not, pistons are available from Mitaka, or Cruizin or even Wiseco.
A central plug squish head is a really good upgrade too. Raise compression and decrease the chance of detonation all in one neat package. Mr Livengood knows people who can design and machine a head after a short trip to the welder. And at a lower price and better idea than a head from RK-Tek with inserts.
BTW do not use stock or most aftermarket head gaskets. Get a head gasket from Cometic with say a 71mm finished bore and .043 thickness. OEM gaskets are about 76mm bore to allow for the fact that casting cores were not always in the same place, so bore to head spacing tends to be shall we say, imprecise. https://pinkpossum.com/GT750/GT750head.htm has more details.
The service at Bill Bune is perfect. Awesome work.
Teazer, I would say it might have been antiseize? Seems a good spot as you said to get some basic work done.
Does Bill Bune do full motors? Not that I want to send it to him necessarily. It's just a complicated mess compared to the Yamaha, and my propensity to feel like everything was done right only to promptly mess something up is higher than average.
Bill Bune did both my RZV cranks, and he bored my cylinders....beautiful work....very happy when I got the parts back.
Bill Bune Enterprises is essentially a machine shop that does great work at reasonable prices. They can source parts, but I usually send them pistons and crank seals. And sometimes I have to send them straight cut primary gears and new conrod kits but that's another story.
I don't believe they do complete engine rebuilds. You could probably do the rebuild yourself. It's quite a simple motor but as you can imagine it eats time like a hungry black hole gobbling up galaxies. The next issue with having someone else do a motor rebuild is that a complete motor weighs about 180 pounds and that means shipping on a pallet by truck or deliver it yourself.
i recently drove to IN to pickup a GT750 for a rebuild but I think you are even further away IIRC.
I'm in Southeast Michigan. I mean, don't get me wrong... I'll do the motor, just won't like it lol. But, I see Cruzinimage has full crank rebuild kits too. About $400 plus shipping. Would you run one?
The funny thing with these cranks is that they really don't wear out and that's probably a symptom of few miles relative to the ruggedness of the design. What does destroy parts is rust. If the balls or races are pitted, it will never run right and if the parts of the crank that the seals run on are rusty, then it will never seal.
BBE have called me a couple of times when rebuilding cranks for me to say, we need 2 replacement main bearings or a rod or a crank end because one or more parts are not good enough to put back in. But they can usually just clean the parts and pop them back in. Seals are always replaced, but bearings and rods, not so much. I have been very fortunate to inherit a few spare cranks and had a couple of other donated to the cause and I bought another one or two, so I have had cranks to use as donors, but quite a few contained zero usable parts and always rust was the cause.
What I would do in your case is to buy a set of seals from your local dealer or Cruizin and send them plus crank to BBE and ask them to strip clean inspect and build the crank. If the bearings are shot https://www.cruzinimage.net/2018/06/06/72-77-suzuki-gt750-crankshaft-rebuild-kits-oil-seals-bearings/
You could send the crank to BBE and ask them what parts it needs and then purchase what you need.
I believe that is the set that Roy Gibson uses and Paul Miller sells, but that's speculation on my part. It's unlikely to need rods but will need rings or maybe pistons. Cruizin pistons are perfectly good enough to run on the street if the bores need to be freshened up.
This is a bad example of rust under the outer crank seal.
This is more common and can usually be cleaned up and used.
If you pull the outer bearings you have to be careful not to score the crank at the seal surface. I usually send the whole crank. Pulling bearings doesn't save any money and you risk damage.
Teazer, I know it needs at least the right rod as its pitted and rusted. I figured the cost for everything from BBE and Cruzin' for parts. Crank rebuild, top end and decking the head to be $1250 or so before shipping. Josh told me over the phone that Suzy parts are increasingly hard to find and that Cruzin' was my best bet anyhow. I'll just fill in the shipping to go directly to his shop so I'm not double posting parts.
I don't want to spend a bunch of extra cash, but I also wouldn't mind just getting it over with in a sense either. I'll probably ask for the old bearings back just if they're OK. If they're rusty or worn out, then no.
So the top end the cylinder bores are offset so bad, I don't think they would even take a fresh bore job. Best bet seems to either send it off to Bill Bune, or just go with the next best thing. The whole setup from the guy I know. Then just send that top end etc to BB.
This is... really bad haha.
3mm overbore and sleeve it to a 900. :dawg:
These head gaskets are notoriously bad. The heads too.
That looks like it should be able to be cleaned up with a 0.5mm overbore.
Some barrels are worse than others but they usually bore OK. And order a head gasket from Cometic with say 72mm finished bore size and check to make sure it fits over the studs and does not overhang the bores.
An alternative is that you could buy that motor from Busa1300 and hope the bores are more central than yours. And the crank may be better than yours so you could save on a set of rods and probably main bearings too.
I just received a 71mm cometic head gasket in the mail. 100 bucks. Will that still work, or am I playing with fire? I guess I can just use what comes in the gasket kit I ordered off Ebay... same one that was on it basically.
Engine seals, and bolt kit showed up. Guy on FB in Canada has a set of cases that are in good shape too. We'll see if he delivers on what he said he has. Almost got the cases to the separation point. Just need to see if all the bolts come out OK.
That motor is a 72 correct? Aren't they quite a bit different than what is on mine? Or are the engine cases the same?
71 will be fine. That's what I order for stock or .5 o/s bores. You have to check for clearance though to make sure the fire rings do not overlap the bores at any point. You may have to trim the bolt holes slightly to make it fit.
For my money, a Cometic head gasket is the only way to go.
Yes, a 72/73 motor typically comes with old style crank and rods and old style cases depending on how late in the production run it was manufactured. Top ends have slightly different porting but on a stock bike the difference isn't huge and anything can be ported.
Well, it came apart. It's bad haha.
Not good but not as bad as it might have been. That's typical on a motor that sat for a long time. Sometimes they are like new but that's if the oil tank drains into the cases.
Looks like the alternator end seal spring failed and the seal allowed air and moisture in which caused the rusty end and rusty bearing. I would ship as-is to Bill Bune Enterprises and have them order a set of seals and main bearings or order them yourself and ship the whole lot up there.
You could also try spinning the other mains and see if they sound crusty or spin smoothly. Some may be OK, but if most sound gritty, I would recommend a complete set of bearings and seals.
The rest of the motor and transmission don't look bad at all, but check second third and 4th dogs on the output shaft. Clutch shaft dogs are usually OK but check them anyway.
And while it's apart, rebuild the water pump.
edit: I just checked the video again and expect the right (left on your bench) big end to be rusty but you might be lucky.
The transmission looks good. One set of the dogs has just the slightest nick on the edge, like it didn't quite go into gear once. Not sure if that warrants replacing it or not. Here's a picture of it.
I'm not a water buffalo expert by any means, but if that gear on the left is available, I'd want to replace it.
They all look like that after a few years. I have seen worse come out of motors that shifted flawlessly. If you do decide to replace it, Nova in the UK have them but for the JKL transmission gear sets. M/A models had a different 5th gear set and late model A and B had different second and third gears.
I have a list of all the gears and part numbers here from GT750L through GS1100 that I compiled when I was mixing and matching gears if you need any info on gears.
Yea, I think I'm sticking to the trans I have. Fourth gear for the M series is a yeti. Good news, the welder said he'd fix my cases. Also good news is the guy that was selling his sets had GT750-60185 with the transmission in it. Wants $400 CAD before shipping. Might consider doing it, but also fixing my cases just for S's and G's. The sellers cases will take even more elbow grease than mine.
I'd stick with what you have rather than having two sets of parts that need work. i have had a couple of sets built up with weld where a chain came loose and they both ended up fine. Took a but of work to grind/sand them back to the correct profile but that's why we have winter....
Yea, that's the plan. He wants another $150 CAD for shipping. Ouch. I'll be dropping it off to the welder this week.
Quote from: Striker1423 on November 29, 2022, 02:25:05 PM
Yea, I think I'm sticking to the trans I have. Fourth gear for the M series is a yeti. ................
And by some shear coincidence, the 8 valve GS750 has basically the same transmission with one or two better gears and a 16 valve 750 from say 82/83 has different dog design on the troublesome gears. I ran a GS trans with GSX gears in one of my GTs and IIRC, those same GS and GSX gears will fit of a GT shaft with little or no machining required.
I am fitting a GSX1100 trans in my drag bike motor and apart from a couple of wider gears and longer shafts it is the same design as a GT but with updates. To fit that I needed to have bearings and shafts machined and a few other changes as well, but GSX transmissions are available.
Don't tell anyone. It's a secret... :whistle:
Haha, well, working on a big update thread now. Looks like the bikes are on a massive backburner list for now!
I have the GT750 crank and parts kit from cruzin all boxed up and ready to ship. $46 shipping. Not bad.
Still waiting on the pistons before I send the top end over.
Next major purchase will be done Delkevics. Maybe . Lol.
For more or less the same sort of cash, you could have a set of shiny stainless pipes from Mr Lomas.
The guy that bought the Phat Trakka managed to throw it on the ground a couple of times and the last time destroyed the Jemco pipes and did some other damage, and while i was rebuilding it again, he bought a set of JL pipes. They arrived fast and are beautifully made. They are also the best sounding individual pipes I have heard on a GT other than 3 into 1s which always sounds awesome.
Not stock of course.
True teazer, however, there's a set of Delkevic pipes on Ebay for 900 bucks, brand new in the box, I don't think I can pass it up. Plus, stock on this bike is basically the goal. Think Peter Ormrod rebuild like here:
Maybe not quite as perfection, but similar vein.
Stock is nice too and Delkevics at that price sounds too good to be true. if you can get then close to that price, they are a steal.
Just as I was pulling out of the drive to run to UPS with the crank, the piston box was sitting in front of the garage door. Wife was like "You're back already?!" Yup, and leaving with another box to ship. This time $26 for the top end with pistons. Both should be in Anoka by thursday.
As is customary, I ran the pipe purchase by the wife. Typically anything over $500 I bring up as a "Hey, guess what I need?" conversation. Well, that got shot down pretty quick lol. Not surprised, but they're there... taunting me. What was it? Something about asking permission, then asking for forgiveness?
I always thought it was: "It is sometimes better to ask beg forgiveness than to ask permission", but someone here clarified it as "It is sometimes easier to ask forgiveness than to ask permission". Either way, you're not getting those pipes unless you find the cash outside the household budget. Good luck!
Anybody hear bad things about the cruzinimage crank seals?
A few guys on FB said their motors has problems shortly after installing these.
Also, I was wondering if anyone has ever successfully gotten a wrong order resolved from them? They sent over the wrong carburetor slides. Dang it.
I have had no issues with CI parts. I suspect that some of the cranks may have had rust pits where the seals run and that can ruin seals. It's not unusual to have to ship two cranks to Anoka to get one good set of parts out of it. Usually, minor pits and scratches can be polished out but if they are too deep, parts need to be replaced and use a bearing sleeve.
Bill Bune's team are familiar with our cranks and know what to do to ship back a good crank that should last for years.
Some people just don't like CI parts I guess.
Josh told me they'd do a more through assessment when he actually starts the work, but the cylinders look the way they do as they've been welded up and sanded down on both left and right cylinders, probably after a crash. Hard to tell on my end, but believable as the side cover has a huge welded crack that didn't get sanded down as nicely. He also said the bores looked normal to him... for a GT750. Although badly off-center it is far from untouchable. So... that's good I guess lol.
He stated there isn't any way to fix the exhaust holes where the sealing surface is non-existent. My welder might disagree, but he has yet to call me about the top engine case or side cover. This is the same it was when I had my snowmobile pipe over at his shop. Slow to do the work as he doesn't really make money on side jobs.
Will see how much is good, bad or otherwise on the crank hopefully next week? Josh didn't really give me a timeline.
Misplaced cylinder sleeves are common on GTs and some are a long way out. Some match the heads but on many there is some offset between bores and chambers.
https://pinkpossum.com/GT750/GT750head.htm
That's why Suzuki and aftermarket suppliers supply head gaskets with 76-77mm bores so they don't overhang the bores. My preference is to use COmetic head gaskets with say a 72mm finished bore and then gently open up the stud holes as needed to let the gasket move to the correct position.
On a stock motor, oversized (stock) gaskets are rarely a problem but if compression is raised they tend to detonate in that area and blow out the fire ring.
Tell us more about the crash damage. I don't remember that being mentioned before.
Well, the first inkling of damage I noticed was the right side charging cover looked kinda wonky on the bottom from rod scrape. I figured someone just smoothed out a few rash scratches until I took the motor apart and the cover had been cracked almost in half and welded back together.
Josh said the cylinders were welded and repaired due to a crash most likely. I didn't know exactly what he was talking about, but he thinks the outer exhausts were welded up which is why the gasket sealing surface is gone on both sides.
When the fall on that side, the cover usually falls apart. It's wide and thin. Nice casting work but zero strength when a big fat bike lies down on it.
What happens next can be more serious. I have one in the shop that was crashed on that side and it not only destroyed the rotor, but managed to bend the crankshaft. In this case, the end was out of round by about .065" and had to be replaced. The rest of the crank was fine though and the outer crank wheel was still round and it was only the part outside the bearing that was tweaked. If anything is wrong with yours, Josh and his team should be able to make it right.
Welded barrels sounds more serious though and most unusual. Damaged exhaust threads are common enough and usually can be repaired by opening them out and welding in fresh metal and then drill and tap back to size. But I guess if a crash was bad enough and ripped off the pipes, that could cause substantial damage around the exhaust port.
Did you have any pictures of that damage or welding repair?
https://www.2strokeworld.net/forum/index.php?topic=4581.msg38748#msg38748
I don't know if I agree with his sentiment on it, unless I'm just missing something...
So, just for S's and G's I ordered from Babbits a new temperature gauge for the GT750, figuring the thing was just showing it was in stock, but not actually... Well, it shipped! Lol, I guess now I get to see what a new gauge looks like!
I remember that picture but couldn't find it when I was looking the other day.
That exhaust is a mess for sure. The small pits are not an issue but it would be best to have that floor welded or machined to take a spacer to replace the damaged metal.
I doubt that damage is from a crash. It looks to be eaten away by caustic soda or someone put an oxy torch in the port to burn off carbon. Either way it should be repaired or replaced. if anyone can repair it it's probably Josh at Bill Bune Enetrprises.
Quote from: teazer on February 02, 2023, 11:20:30 AM
I remember that picture but couldn't find it when I was looking the other day.
That exhaust is a mess for sure. The small pits are not an issue but it would be best to have that floor welded or machined to take a spacer to replace the damaged metal.
I doubt that damage is from a crash. It looks to be eaten away by caustic soda or someone put an oxy torch in the port to burn off carbon. Either way it should be repaired or replaced. if anyone can repair it it's probably Josh at Bill Bune Enetrprises.
Josh told me it's unfixable. I might just have to have my local guy attempt it if he will. The welder doesn't really take side jobs anymore.
It is fixable, but will probably cost much more than finding a replacement cylinder.
Which was my only other thought. I doubt he has any extras laying around his shop though. And getting the right year, or later model cylinders might be hard.
its def fixable, you just need a BIG welder to get it hot enough.
What year/model? I might (long shot) have a set in my stash.
Quote from: teazer on February 04, 2023, 11:16:35 AM
What year/model? I might (long shot) have a set in my stash.
Would also need to pre-heat the block and probably cut away a lot of metal just to get in there. I would be more tempted to machine in and press in an insert and ignore the rest of the pits.
1975 M Model.
I can give up my idea of turning this into an end table, .....
....and let it be used for what is was designed for.
Well, if worst comes to worst, I could get the exhaust to seal using the goop shit in the hole method I did last time. Teazer, if you do have a set, I'd be willing to pay you for it and the shipping to get it over to Bill Bune. But, you might have to call them and let then know. I don't believe they've started on any of my work yet. So, that's going for us for now lol.
Busa, I appreciate the look, the problem is the cylinders are slightly different from the early to later models.
Crank and top end are back from BBE. I think a few good weekends and the bike will be together. So, times that by the sporadic working hours I get for this project... spring's cutting it close!
:cheerleader: :cheerleader: :cheerleader: :cheerleader: :toot:
For exhaust port repair consider an epoxy like Coltronics Durabond 7025, or maybe Devcon F. You'll need to get the pitting very clean for it to adhere properly. The Durabond 7025 is supposed to be good for 1000 degrees F. You'd use like body filler then grind or sand smooth. Might want to grind out the pits to good metal if you can.
Devcon F doesn't have the same temp resistance but it will fill pits and sand out invisible in aluminum. Temp resistance is only 250F. I've fixed oil pan and valve cover casting flaws and "PO pry damage" to gasketed surfaces with it. It is not affected by oil. When it fully cures it is much harder than pure aluminum.
Devcon F is expensive but a 1lb can lasts for many years.
IR8D8R
Devcon F is ideal for repairing crankcases on TZ or RD motors when a rod punches a hole in the bottom end to let all the big end rollers out.
And no sign of it going soft or leaking years later. It's a great product but not for exhaust ports. I went through my stock but didn't find a stock L or MAB set of barrels.
I would try JB Weld 37901 High Temp which is also rated to 1000F and is cheap. They claim it is good for exhaust manifold repairs.
or find someone that's wiling to weld it up. :whistle:
Might take you up on that Mark. At this point, I'm just breaking shit left and right. With another screw extraction in the mix, I can't actually make progress. I'm just happy the Yamaha isn't like this. Shitzuki isn't a term I used to throw around, but with this bike it's growing on me.
Finally to a point where general lower-end assembly can begin. I keep repeating...Triples are sweet. Triples are sweet...
Hang in there. It will be worth it.
The GT750 is a convoluted mess of a motor, but they sure are sweet when they work.
Ok, many moons and updates later... The GT750 is in process of reassembly! Second set of crankcases (three total now) showed up off Ebay. Cleaned and in good shape. Crank and second top end are back and aside from cleaning the top end good, the lower crankcases are basically ready to go together.
The transmission, crank, and new water-pump is in, all the little bits are in as well. Just need to glue the cases together, then focus on the top end.
She runs! But she also leaks coolant all over. Fixed all the external leaks (drain plug and upper head stud), but unfortunately she's also leaking from the new cometic gasket. I just lined it up and bolted it down, I did not coat the gasket in any kind of sealant, so I think the plan will be to drain down the coolant below the head a bit, remove the gasket, clean and dry it, then permatex copper spray it before reinstalling. The gasket is $100, so it would suck to eat the cost and have to go with the Athena spare.
was the head checked for straightness? im sure it was but...
Would you believe me if I said no? :whistle:
First thing I'm checking now though. It didn't leak before the rebuild so I figured I'd get lucky.
Quote from: Striker1423 on March 21, 2023, 03:49:43 PM...Triples are sweet. Triples are sweet...
Yes. Yes, they are!
The head is gonna have to come back off. I'm getting water from center and right pipes. A bit rpm the left pipe as well. But the white smoke hasn't stopped.
Is it possible for the o-rings on the bottom of the block to leak? I have to drain the coolant and pull the head again, but I'm curious if it could be pulling coolant from under the barrels.
Is it possible? Anything is possible. maybe an O ring is undersized or split or is out of place, but that's really unusual. If they are aftermarket O rings I guess that's possible.
That could cause a leak into the bottom end and that would be on the serious end of the undesirable scale.
Quote from: Striker1423 on June 05, 2023, 10:03:09 PMWould you believe me if I said no? :whistle:
First thing I'm checking now though. It didn't leak before the rebuild so I figured I'd get lucky.
. Yeah. Right....
Do a leakdown test and see if you can detect where the leak is coming from before you tear it down. The head is easy to check. Pull the head, clean off any gasket mess left and place it on a dead flat surface. I use a granite surface plate but a decent old thick mirror works well too. Put a thin smear of bearing blue on the head and press it down on the flat surface. Lift it and see the imprint on the plate. Anywhere it didn't sit flat will be obvious.
Will do. I admit I was being lazy but that's because my time is short in the garage lately. So is summer...
Oh well, should have checked and that's that. :bang:
She runs well! Not the biggest issue I thought it was. Pipe just collected a lot of shit. Just needs the anti-surge jets. I already have them, just need to tap the holes and install. Put 45 miles on it with no real issues.
^ Excellent! :thumbs: Yes, the anti-surge jets will smooth out any issues just past tickover. Richard's site (Pink Possum) has some great info and instructions on all things about GT750 carburation.
for those that dont speak buffalo, whats an anti surge jet?
The GT750 is known for off-throttle and low-throttle surging. Sounds like engine gallop. Causes erratic stops a bit too if you engine brake as the motor loads and unloads.
Excerpt from here: http://pinkpossum.com/GT750/carb/BS40carbs.htm
Surging on large capacity two strokes is a common design problem. With the BS40 carbs, Suzuki had hoped that surging would not be a problem, but unfortunately many bikes still surged at low throttle openings.
The fix was described in a Suzuki Service Bulletin and is quite simple. The passageway in front of the pilot air jet is tapped to take a screw in Mikuni air jet - the same type as all VM series carbs. Part number is BS30/97. The new air jet is either 0.8mm or 0.9mm depending upon model and effectively changes the fuel slope across the pilot jet. Order from SUDCO or your local Mikuni supplier.
At idle, there is no change in fueling, so it works just the same as before the modification. At higher revs on a closed throttle, it richens the mixture enough to eliminate that lean surge condition. The way it works is that on overrun or at a steady at say 3,000 on a closed throttle, the motor creates a relatively strong vacuum which on a stock motor, pulls in too much air via the air jet and it creates a lean surge.
By restricting the air jet slightly it causes the mixture to become slightly richer under those conditions. At idle, the vacuum in the carb is much lower, so the change does not really affect idle or slow running.
First attempt before installing the surge jets is to increase the fuel screws rich by a quarter turn. Idles even better now, will report back after I ride it again. I can safely report the bike does the ton. Gotta bed the rings somehow.
sweet! :clap:
Idle still hangs at around 2k on occasional stops. Comes down and stays if I just barely let off the clutch for a second at a stop. Maybe the carb sync is off.