Cylinder + Piston advise.

[350GUY]

Hi all:

I bought a pair of RD350 cylinders, the pistons were stuck/frozen in the bore. The cylinders measure at 64.08mm and 64.06 mm, each. I had to drill holes into the pistons to get them out of the bore as they just wouldn't budge even after 2 months in all sorts of oil, heat etc. etc.  New pistons will be required.....
From the looks of it there was barely any mileage done as the cross hatch hone marks are still visible along the bottom end of the cylinder skirt. However, the area around mid-cylinder wall and TDC had some rust from the pistons + moisture that effectively glued them pistons to the cylinder wall. I tried scrubbing the rust off with soapy water & scotch brite...... attached are some pictures.  What do the experts recommend, what are my options here since new pistons are required anyways?

- Light hone + new (STD?) pistons
- Bore to  (1ST o/s?) size pistons
-Just drop new (STD)pistons without honing

Thanks in advance!

B/R,

Daryl

[Jspooner]

Bore to clean up then bore/hone to the next appropriate piston size.

[gwcrim]

What's your budget?

I'd hone them first and see what they look like.  Measure them and go from there. If you don't ride much or very hard, maybe you can go STD bore.

Obviously, a fresh bore sized to the pistons will always get great results. 

[Yamaha 179]

Daryl:
It appears from the pictures that these cylinders have been modified.  We can't tell about the port timing, but it looks like the main transfer port entries, at the base of the cylinders, have been raised to improve mixture flow.  That doesn't really mean a great deal to
how you treat the cylinders but maybe you should evaluate the porting to see how much effort/money you should pay to restore them.  Joe has given you the only right way to approach this; bore them clean, determine the piston size needed, install the pistons/rings and you and done. 

As an  alternate you can use a Sunnen mechanical hone to clean up the bores and then buy a forged piston to see if it will fit the piston.  Forged pistons have looser clearances and might work.  I don't like them as they are noisy and they should be thourghly warmed up before you ride off, but that would be a cheaper way to get the bike on the road.  A ball hone, glaze breaking hone, will not work as you have to clean the bore or it is likely to seize. 

If you want to keep the cylinders, engine, and bike I suggest you get an expert to evaluate the cylinders.  Joe can do that.  Chuck Q can do that.  Maybe your local shop can do that but many shops don't have a lot of experience with two strokes and are not familiar with piston to cylinder clearances. 
Lyn Garland

[motodreams]

What you are trying to do here?  You have the 'right' approach above which, from a mechanic, typically has no consideration for someone's budget.   

How bad is that rust in the bore?  If it has caused pitting then yes you likely need a bore.  If it is surface and there are no major gouges etc. You may be able to get a hone.  Your venier calipers are not accurate enough a measuring tool but you will have to determine if you have too much clearance at current bore size.    Ultimately sending them to a specialist that deals with bore/honing cyls is needed.  My guy typically gives me the honest options on whether you can get away with a hone and what the best approach would be and we go from there.

Every city I have seen has these people that can handle boring a cylinder.  i'm not sure why you would need to send them half way across the country.  2-stroke snowmobiles and dirt bikes are still common.  This is not a job that should require sending to another city.

[quocle603]

Unless you're a machinist with the right tools. Should really let the professionals do this for you.

[EE]

 I use a wire wheel on a die grinder to take the rust off quickly without damaging the bore, you can't tell how deep it is before you do that. A hone will only knock it down flush with the bore.. and it wastes the expensive stones and with a hone you always want to knock what you can down first anyway or your honing crooked as the hone just rides on top of the rust until it wears it down. As far as having anyone bore your cylinder.. I wouldn't, seen to man bad bore jobs, use someone that knows our bikes, aircoolers at least, modern 2 stroke guys barely put a chamfer on their ports at all and our air coolers need good chamfering. Ed

[SUPERTUNE]

What you are trying to do here?  You have the 'right' approach above which, from a mechanic, typically has no consideration for someone's budget.   

How bad is that rust in the bore?  If it has caused pitting then yes you likely need a bore.  If it is surface and there are no major gouges etc. You may be able to get a hone.  Your venier calipers are not accurate enough a measuring tool but you will have to determine if you have too much clearance at current bore size.    Ultimately sending them to a specialist that deals with bore/honing cyls is needed.  My guy typically gives me the honest options on whether you can get away with a hone and what the best approach would be and we go from there.

Every city I have seen has these people that can handle boring a cylinder.  i'm not sure why you would need to send them half way across the country.  2-stroke snowmobiles and dirt bikes are still common.  This is not a job that should require sending to another city.

I'll disagree with you...I have bored over 15,000 cylinders in my lifetime and I have seen some real crap from some locals that did a bore job with sub-par equipment and knowledge.
A bore job is very precise work.
When not done right, you have a very short life span.
I have to always rebore ones that were just done and after under 500 miles were crap!
Chuck

[SUPERTUNE]

Hi all:

I bought a pair of RD350 cylinders, the pistons were stuck/frozen in the bore. The cylinders measure at 64.08mm and 64.06 mm, each. I had to drill holes into the pistons to get them out of the bore as they just wouldn't budge even after 2 months in all sorts of oil, heat etc. etc.  New pistons will be required.....
From the looks of it there was barely any mileage done as the cross hatch hone marks are still visible along the bottom end of the cylinder skirt. However, the area around mid-cylinder wall and TDC had some rust from the pistons + moisture that effectively glued them pistons to the cylinder wall. I tried scrubbing the rust off with soapy water & scotch brite...... attached are some pictures.  What do the experts recommend, what are my options here since new pistons are required anyways?

- Light hone + new (STD?) pistons
- Bore to  (1ST o/s?) size pistons
-Just drop new (STD)pistons without honing
Thanks in advance!
B/R,
Daryl

Hi Daryl!
Glad to see you made it over to the new forum...

If needing to try to determine if the bore is good you need to use a ball hone first to knock off any rust on the walls for measuring with a dial bore gauge. (mine is a Sunnen Dial Bore Gage and is over $1000 new now)
The RD's have 2 places that have high wear in the cylinders...just under the exhaust port is one point from heat and piston rocking and the other point is just below the intake port where any dirty air comes into the engine and the bottom of the intake skirt rocking more there because off that part of the skirt is farthest point from the pivot of the wristpin.
Measure these 2 points and also check for out of round halfway up from top of exhaust port to TDC.
Most of the time a good indicator of what the original bore size was, is to take a measurement at the wristpin sides of the bore and 1/2 inch below the transfers.
This is a place you rarely see wear and is a good indicator point.

There are a few of us that are specialist's on 2 strokes and with RD's...
I had 3 of my engines in the top five last weekend at the AHRMA Barber Vintage Festival is the F-500 race!
Also dyno tuned a few RD's while there. (4)
Chuck

[SUPERTUNE]

What you are trying to do here?  You have the 'right' approach above which, from a mechanic, typically has no consideration for someone's budget.   

How bad is that rust in the bore?  If it has caused pitting then yes you likely need a bore.  If it is surface and there are no major gouges etc. You may be able to get a hone.  Your venier calipers are not accurate enough a measuring tool but you will have to determine if you have too much clearance at current bore size.    Ultimately sending them to a specialist that deals with bore/honing cyls is needed.  My guy typically gives me the honest options on whether you can get away with a hone and what the best approach would be and we go from there.

Every city I have seen has these people that can handle boring a cylinder.  i'm not sure why you would need to send them half way across the country.  2-stroke snowmobiles and dirt bikes are still common.  This is not a job that should require sending to another city.

Here's why I disagree...
Look at this bore job that was done by a local on a Daytona special...
Customer had some issues with a carb setup that was too lean and experienced detonation on the pistons as the 2V0 engines have to have a special work for them to run on today's fuels.
After some acid washing and glass beading of his cylinders, it's apparent this LOCAL machine work was not up to par.
1st and 2nd pic...has a step in the cylinder as they were using a setup that started boring too big and it left a .002 oversize of a step in the cylinder!





Bore was also too big for cast pistons (.0045) and now is needing bored again by someone across the country to do it correctly...(ME)






More to come on the subject here:

http://www.2strokeworld.net/forum/index.php?topic=1175.0



Chuck

[Hawaii-Mike]

It's great having several professional tuners/racers contributing their knowledge to this forum.

[quocle603]

It's great having several professional tuners/racers contributing their knowledge to this forum.

Yep precision work like that would need professional work, not DIY individuals

[Organicjedi]

My grandpa was in the snowmobile tuning business for years and only had two or three places he worked with for boring.

He found that many places had issues with cylinders coming back not round and with incorrect tolerances which would not work well especially for his drag setups.

You've got to be picky especially when your livelihood depends on people winning races.

Millennium and oddly enough the local NAPA did good work for him.

[quocle603]

My RD buddy mentioned to me that NAPA did good work.

[350GUY]

Hi all: My apologies for the delayed response/follow-up. I was out of commission after my above post and I am back to base now.