So I finally had a chance to take my RD400 to the track. It's been modified a little- original heads with reshaped dome and a light skim, mildly ported cylinders, TDR reeds on a hogged out stock reed cage, reed spacers, VM28 carbs with Dave F mods (P-4 needle jets, 240 main jets), Y-boot with UniFilter foam filter, custom chambers probably equivalent to Wicked pipes. Installed BR9ES plugs last week. For fuel, I was running ethanol-free 94 octane. Timing is 1.9mm BTDC with HPI CDI. I'm still using the stock oil injector shimmed to 32:1 with Yamalube 2S. I squirted another 20cc's of 2R in the tank for good measure.
Motor was running perfectly. Took the bike to Thunderhill Raceway in N. California. It was my third session and I was ripping down the front straightaway at 90+ and went well into the redline. I let off as I headed into Turn 1, then suddenly I ran out of power and the rear tire locked up!! I was able to skid it to the outside of the turn and stop. I was thinking that I seized the motor. A minute later, an instructor came over to check on me. He asked me if the bike will start and I said I didn't know. I kicked the motor and it wasn't locked up. It started again on the second kick. What the heck??
I gently and cautiously rode the bike around the track and pitted in to my paddock space. I checked out the bike and everything seemed ok. I did finish the subsequent sessions, but I stayed away from the redline.
Any ideas what happened? First I was thinking I need to bump up a size on the main jets, but I wasn't at WOT. So I next thought maybe I need to raise the needle a slot. I had considered that maybe I was in the redline too long and maybe I didn't get enough fuel, since no port timing had been done. But now, I'm just wondering if my bowls were empty because the petcock couldn't keep up with the consumption.
The bike is home safe and sound. It seems to be okay, but I'm still scratching my head about what happened and would like to address the problem, so it doesn't happen again.
Any insights would be appreciated. TIA
did you shut down the throttle? and on premix?
Running oil injector, plus I added additional oil (2R) in the tank and gave the tank a shake. No, the throttle was still opened about halfway.
You better at least take off the pipes and look at the piston skirts.
maybe. me id up the pilots one size and adjust the air screw to compensate, even at half throttle. John Aylor tells a story of locking up a triple doing the exact same thing and turned out it was the pilots. even on partial throttle shut down it will still suck oil/fuel thru the pilot on decel :twocents:
Quote from: m in sc on June 19, 2024, 09:55:29 AMmaybe. me id up the pilots one size and adjust the air screw to compensate, even at half throttle. John Aylor tells a story of locking up a triple doing the exact same thing and turned out it was the pilots. even on partial throttle shut down it will still suck oil/fuel thru the pilot on decel :twocents:
Cool. I'll do that. I'm still thinking about getting a Pingel petcock to rule out the fuel starvation. Do you think that's a good idea? or a waste of money?
honestly on a race bike id def go pingel. i've starved a motor before but had more to do with needle and seat size vs petock and it wasn't fun. you'll feel a starved motor just go flat like a revlimiter. mine would do it only going into 6th gear wide open, totally repeatable. bumped up to 3.0 seats and problem resolved, but this also has (2) aftermarket petocks so that was never an issue. (fwiw)
Thanks for the suggestion. Sounds like cheap insurance. I'll look into new seats.
Are you sure it wasn't the back brake locking up?
Quote from: Hawaii-Mike on June 19, 2024, 05:21:46 PMAre you sure it wasn't the back brake locking up?
I hadn't thought about that. But there would've been resistance leading up to the lockup and there was no smell associated to the event. I've reviewed it on the GoPro video and there was definitely a loss of power before the lockup. Additionally, I ran another four sessions after that with no incident, since I stayed out of the redline.
Didn't you pull in the clutch when it locked up? That would have told you if it was the motor or gearbox/brake.
Complete top-end lockups usually leave plenty of evidence (like aluminum) in the bore. Another danger if the lockup was hard enough is the chance of ovaling the rod. Doesn't happen if the brake locks.
I have had rear brakes lock up on track (well once), and it comes on fast. I fixed the problem by not using the rear brake at all unless experiencing off-tarmac excursions.
At Moroso riding an RD400 I broke a rearset on like lap-2, which disabled the rear brake but the peg was fine; my wife always timed my laps, and suddenly my times dropped 1~2 seconds, and I actually had better control going into corners. From then on, I quit using the rear brake altogether and permanently placed 1 or 2 positions higher. Try it!
Yes, I did pull the clutch. Hmmm...that's an interesting point. Didn't really think about that. Everything happened so fast.
So I just reviewed the video again and after skidding and hopping, the motor does spin again as I'm slowly approaching the rumble strip and the skidding is no longer audible. Maybe it *was* the rear brake. I recently switched my rear setup from disk to drum. But it's still curious to me why I didn't experience more hiccups for the rest of the day. And could the brakes cool that fast to allow me to ride again just 2 minutes later? :umm:
they definitely can. weird. hopefully that was it :olaf:
Here's the video clip of what happened. I'm still a bit baffled. If it was a rear brake lockup from overheating, why did the engine die? I think I might take off the top end and just check things out for yucks.
that's definitely a soft seize. you can hear it in the motor. Probably ok overall but yeah id still suggest a bit of fuel.
Quote from: m in sc on June 20, 2024, 04:59:36 PMthat's definitely a soft seize. you can hear it in the motor. Probably ok overall but yeah id still suggest a bit of fuel.
What's a soft seize? Not familiar. I already ordered 3.0 needle/seats. I've got 35 pilots, but I can bump to 37.5- I reviewed my spreadsheet and it ran pretty good there.
when the piston will seize (swell) just enough to stop the motor but not nec hurt anything too badly. Ive done this on street bikes, have seen it at ahrma races as well. Hell, even did it on a borrowed bike at deals gap once :shocked:
other factors come into play. the needles and seats are just good insurance.
So what is the remedy? That was scary as f**k! More fuel? Richer mixture? It had a ton of 2T oil in it. Did it basically run out of petrol and was just sucking air, hence the overheating?
More oil is not the same as a richer fuel mixture.
If the piston has some scuffing you might think about changing it. Maybe you can save yourself from honing or reboring the cylinder. Muriatic acid works great for cleaning embedded aluminum from a steel cylinder bore.
I would expect that to need a new piston. Post up pictures of everything after you take it apart to help figure out what caused it to happen.
More oil makes for a leaner fuel mixture.
Quote from: Hawaii-Mike on June 21, 2024, 03:50:01 AMMore oil is not the same as a richer fuel mixture.
Yes.
Quote from: Kawtriplefreak on June 21, 2024, 09:50:20 AMMore oil makes for a leaner fuel mixture.
Yes!
Wasn't even thinking about that when I added more oil.
Yeah, I figured a new top end might be best. Shopping for parts. Base gaskets already in the mail. I've been on stock wrist pin bearings, as that was part of my original rebuild, before I decided to go bigger on mods. Going to upgrade those while I'm in there. Likely to just go with Pro-X pistons.
The flashback I just had to the 35-mile freeway run is all too vivid. My RD350 stayed locked for over 5 minutes though. Still ran and got me home rattling away at 25mph. Damn Mustang cutting me off lol.
I soft-seized my old Kaw G3SS a dozen times before I had a new bore done. It would shut off and then refire straight away. Was the weirdest thing. Piston had what looked like a "four-corner" seizure. Somewhere on the net is a piston seizure chart that Arctic Cat had out for snowmobile techs to reference. It helps to visualize the damage from various issues.
Although that's tiny, so try this:
https://www.scribd.com/document/44454041/Two-Stroke-Piston-Diagnosis
Thanks for the chart, Striker. That's helpful. I pulled the head/cylinders off the motor yesterday. Looks like the seizure occurred on the left side. Piston scuffing at outside exhaust and inside intake ports. Top of pistons look good. Haven't taken pistons off yet. Going to retrieve my bore gauge tools back today, then do some measurements.
Quote from: svgarage on June 24, 2024, 11:56:02 AMThanks for the chart, Striker. That's helpful. I pulled the head/cylinders off the motor yesterday. Looks like the seizure occurred on the left side. Piston scuffing at outside exhaust and inside intake ports. Top of pistons look good. Haven't taken pistons off yet. Going to retrieve my bore gauge tools back today, then do some measurements.
What does the dome look like, and underside of piston crown?
Intake and exhaust side seize with normal looking dome could be no oil. If the dome is really dark it could be overheating.
post some pics of the parts.
Quote from: rodneya on June 24, 2024, 12:07:38 PMWhat does the dome look like, and underside of piston crown?
Intake and exhaust side seize with normal looking dome could be no oil. If the dome is really dark it could be overheating.
post some pics of the parts.
I'll pull off the pistons sometime this week. I am stuck in Jeep world for the next couple of days, getting ready for an outing. I'll get some pictures up after I do that. I hate posting pictures to this forum, it's such a PITA and I have to hunt down which ones of my accounts haven't closed yet...
Just hit reply and at the bottom in the middle you can attach pics directly to your post
Quote from: rodneya on June 24, 2024, 11:52:26 PMJust hit reply and at the bottom in the middle you can attach pics directly to your post
Oh, cool. I guess I forgot about that function- think I used it once before.
Here's some pics of the left side.
4 pt seizure, due to heat. i still think it could be remedied w the pilot.
Almo
Quote from: m in sc on June 25, 2024, 10:04:46 AM4 pt seizure, due to heat. i still think it could be remedied w the pilot.
Almost zero wash on the piston crown, I would go up on the mains as well.
Definitely do a leak down test after putting back together.
what does the underside of the piston look like? color above the wristpin?
Quote from: m in sc on June 25, 2024, 11:14:20 AMwhat does the underside of the piston look like? color above the wristpin?
Thank you to all for the input. I haven't taken the pistons off yet. Maybe today. Just got my bore gauge tools back.
Yup. 4-corner seizure. My tuner is going to do a quick cleanup hone on the holes.
oil looks a bit cooke dbut not bad. was def getting a bit warm but not ridiculous.
Quote from: m in sc on June 20, 2024, 04:59:36 PMthat's definitely a soft seize. you can hear it in the motor. Probably ok overall but yeah id still suggest a bit of fuel.
yep. It nipped up.
I should have read to the end of the thread, but you can 'hear' it tighten. I would fit larger float needle and seat plus larger pilots and better fuel tap as suggested earlier.
Got 3.0 needle/seats in the mail today :like:
Does the other piston look like it was getting hot too?
Interesting anecdote and a grain of salt; for some odd reason, it's usually (almost always) the left side that seizes on ALL Yamaha 2T twins. Even back to the YDS/TD1 days, left cylinders and heads were in short supply due to detonation and seizure.
At the Yamashop back in the 1970's when RD's came in looking like this one, we would often just bore the left since the rights were generally fine. When racing, I've seized a couple 2-cylinder 2T motors, both RD and TZ, and it was always the left that was the worst.
Even more telling was when buying a few retired race team bikes and parts over the years, there was always a shortage of left cylinders and mostly good used rights in the piles. Neither I, nor other Yama-riders and mechanics never could figure out why, and after a bad seize of a RD400 at Daytona that almost put me on my head, I jetted the left cylinder rich and ran a higher float level on that side which helped; that was the last one I stuck.
Warren
Quote from: Yamanatic on June 27, 2024, 09:58:56 AMInteresting anecdote and a grain of salt; for some odd reason, it's usually (almost always) the left side that seizes on ALL Yamaha 2T twins. Even back to the YDS/TD1 days, left cylinders and heads were in short supply due to detonation and seizure.
At the Yamashop back in the 1970's when RD's came in looking like this one, we would often just bore the left since the rights were generally fine. When racing, I've seized a couple 2-cylinder 2T motors, both RD and TZ, and it was always the left that was the worst.
Even more telling was when buying a few retired race team bikes and parts over the years, there was always a shortage of left cylinders and mostly good used rights in the piles. Neither I, nor other Yama-riders and mechanics never could figure out why, and after a bad seize of a RD400 at Daytona that almost put me on my head, I jetted the left cylinder rich and ran a higher float level on that side which helped; that was the last one I stuck.
Warren
That is indeed interesting! During normal operation, it is my right cylinder that usually runs 10-15 degrees hotter than the left. I'm getting ready to make adjustments to the carbs, but I'll wait till I get the new rings seated first. This is really a street bike and I don't plan to wind the motor up like that on a routine basis. I have two more days booked for the track in August, then it's possible that'll be it for the old girl. But it's always nice to know that the bike is 100% sat and ready for any/all situations. I'll be moving to Reno, Nevada in a few more years. Who knows? maybe Fernley will get it's act together and I'll do some track time out there?
another weird anomoly, just as a point of interests, is when there's low voltage or such on a stock type ignition, the RH coil is always the one that seems to fail 1st.
Quote from: m in sc on June 27, 2024, 01:19:19 PManother weird anomoly, just as a point of interests, is when there's low voltage or such on a stock type ignition, the RH coil is always the one that seems to fail 1st.
Interesting idiosyncrasies :umm:
When I had a shed full of RD400s, the first one I bought had the left cylinder 1mm O/s and right was stock, so I gathered up a few spare motors and most had larger left cylinders or were missing a left. I put that down to the left crank seal behind the alternator drying out and leaking, but I suppose it could also have been crankshaft whip on the side with the heavier rotor compared to the small primary drive gear.
Quote from: teazer on June 28, 2024, 09:37:37 AMWhen I had a shed full of RD400s, the first one I bought had the left cylinder 1mm O/s and right was stock, so I gathered up a few spare motors and most had larger left cylinders or were missing a left. I put that down to the left crank seal behind the alternator drying out and leaking, but I suppose it could also have been crankshaft whip on the side with the heavier rotor compared to the small primary drive gear.
With all this talk about left cylinder issues, I looked back on my records to check things out. I remember than when I had the engine rebuilt, I had to shop for replacement jugs. The previous owner had left cylinder problems too! The right measured as standard bore, but the left was at 66.0mm!
crank whip on the LH side is interesting theory, makes sense it can 'push' the seal out of shape.
Quote from: m in sc on June 28, 2024, 01:22:18 PMcrank whip on the LH side is interesting theory, makes sense it can 'push' the seal out of shape.
If that's the root cause, then a Vape or HPI ignition should help, as the rotor is lighter, and much closer to the main bearing (so less leverage for any bending forces)
On that note, I have read somewhere that the heavy stock RD rotor can cause bending oscillations of the crank Stub at high rpm (say well above the stock redline), which in turn gave erratic timing due to the points cam being even further from the main bearing.
Good theories. Glad I have the HPI unit, which may mitigate the problem.
Another interesting find on my part. I got the 64.50mm Pro-X pistons in the mail. I measured them against the ART CruzinImage 64.50 pistons. The Pro-X measures at 64.36, while the CruzinImage measures at 64.44. NOS Yamaha pistons measure exactly the same as Pro-X. The holes were originally bored for the Yamaha slugs. When I replaced the NOS pistons and installed the CruzinImage pistons, we just did a quick cleanup and in the went- and they ran great till I really pushed them. Now that I'm back to the smaller pistons, wondering if that alone will alleviate future overheating issues?
that would def explain it by expounding the issue. yeah, don't ever mix brands between bores. aside from dimensional, there's also material composition differences that may affect clearances when hot. art/pro-x are interchangeable though.
Mine killed the left side too. BRP remedied the left-side seizing issues on their snowmobiles (Something to do with dwell time after the rotary valve rotated around) by upping the main jet on the primary (clutch) side two sizes over the right. I remember my 670 Ski-Doo had a 320 main on the left and a 300 on the right. The right-side of course having the transfer case (oil bath).
Honestly wouldn't hurt to do something like this to a track bike if this issue repeats itself.