YTM200 re-ring

[jbennett]

I just bought an '83 YTM200, she smokes really bad right at startup and continues while riding, basically never stops. Compression is at 100psi. I'm not really an engine guy, but did a little research and am leaning towards thinking it should be ok with a re-ring. Am I on the right track? Are there any good youtube videos or build threads I can reference? I can find a ton of info on the Hondas, but these Yamahas are not so easy to find info and build threads on. Any help would be greatly appreciated!

Also, should I get this gasket kit? Vesrah - VG-2003 Do I need anything else besides new rings once I tear it down and figure out the size? Could I most likely get away with a quick hone and not have to take it to a machine shop? I want to do this on the cheap, but also want it done right.

[fabiodriven]

You don't plan the rebuild ahead of time unless you say "Frig it, I'm doing everything". If you're just looking to replace what you only have to, a re-ring is feasible, but you have to get it apart and measured first. Measure the bore and you might just need a hone and rings and that's it, or you might find it will need to be bored to the next size up. Either way, it's probably a good idea to do valve seals while you're in there assuming the rest of the valve train doesn't need attention as well.

[jbennett]

You don't plan the rebuild ahead of time unless you say "Frig it, I'm doing everything". If you're just looking to replace what you only have to, a re-ring is feasible, but you have to get it apart and measured first. Measure the bore and you might just need a hone and rings and that's it, or you might find it will need to be bored to the next size up. Either way, it's probably a good idea to do valve seals while you're in there assuming the rest of the valve train doesn't need attention as well.

Good point, guess I was just looking for the most common possibility and options of what I'd need to do.

Tore it down today, cyl bore is 67.050mm, piston is 66.600mm. Piston moved around quite a bit, I'm sure it is supposed to be a pretty tight fit, but I've never gotten this deep before. Manual says max difference can be .045mm, I'm at .450mm, way out of spec.

Since my bore is 67.05mm, does this mean I can just get a 67mm standard bore piston and hone the cylinder and be good to go? That seems too easy, but I'm hoping that's a possibility. Is the taper limit the difference from top and bottom of bore? I think I'm right at that limit, the bottom of the bore is about 67mm.

What am I missing here or what else should I be checking? Is it common for the piston to wear and not the cylinder? Is a 67mm piston actually 67mm od or does that just refer to the bore size? It seems I'm still at stock bore size.

[yaegerb]

Good point, guess I was just looking for the most common possibility and options of what I'd need to do.

Tore it down today, cyl bore is 67.050mm, piston is 66.600mm. Piston moved around quite a bit, I'm sure it is supposed to be a pretty tight fit, but I've never gotten this deep before. Manual says max difference can be .045mm, I'm at .450mm, way out of spec.

Since my bore is 67.05mm, does this mean I can just get a 67mm standard bore piston and hone the cylinder and be good to go? That seems too easy, but I'm hoping that's a possibility. Is the taper limit the difference from top and bottom of bore? I think I'm right at that limit, the bottom of the bore is about 67mm.

What am I missing here or what else should I be checking? Is it common for the piston to wear and not the cylinder? Is a 67mm piston actually 67mm od or does that just refer to the bore size? It seems I'm still at stock bore size.

You need to measure with a dial bore gauge. I am sure that cylinder is out of round. Get it bored and save a headache. Get the next size piston, take it with you and have the machine shop set the bore to the piston.

[fabiodriven]

As Yaegerb said, it's very likely tapered or out of round. If you measure the cylinder from front to back in the bore and start at the base of the cylinder, then halfway up, then again at the top, it's likely the top and bottom will measure more out of spec than the middle.

[jbennett]

Thanks guys, I was hoping to be able to do everything myself, but I was afraid I'd have to have it bored.

Next size up I can find is 67.50mm, is there much difference between Shindy and Wiseco? At only $15 more, I assume Wiseco is probably the better option. Going .50mm over, what does that up the cc's to?

Oh, and I measured the piston wrong, I think it's actually about 66.90mm, so not as bad as originally thought.

[fabiodriven]

CC's gained will be minimal, probably just a couple I'd guess. It's your choice between Shindy and Wiseco. Wiseco obviously has a heritage and is known to be good stuff. On a YTM200 though I'm sure Shindy would work just fine.

[jbennett]

Now I'm a little confused. I've decided to get a 67.50mm piston kit and have my cylinder bored to match. Problem is the Wiseco only shows fitting 1984-1985. There is one website that shows it fitting 1983-1985, but all the rest and Wiseco themselves don't show the '83. The equivalent Shindy shows fitting all years.

Does anyone know for sure if the 4292M06750 Wiseco is the correct piston for 1983 YTM200?

[ironchop]

Now I'm a little confused. I've decided to get a 67.50mm piston kit and have my cylinder bored to match. Problem is the Wiseco only shows fitting 1984-1985. There is one website that shows it fitting 1983-1985, but all the rest and Wiseco themselves don't show the '83. The equivalent Shindy shows fitting all years.

Does anyone know for sure if the 4292M06750 Wiseco is the correct piston for 1983 YTM200?

According to Babbitt's OEM Yamaha parts fiche, all years of 83-85 YTM200 models which would be YTM200K, YTM200EK, YTM200L, YTM200EL, YTM200N, YTM200ERN use the exact same part number for std size piston (probably oversize numbers are the same between yrs as well, but I only looked at std size part numbers)

All are listed as 21V-11631-00-Y0

I would guess the Wiseco are the same case. Odd that they had no YTM200 category on their website to select (I looked too)

Sent from my Z958 using Tapatalk

[jbennett]

According to Babbitt's OEM Yamaha parts fiche, all years of 83-85 YTM200 models which would be YTM200K, YTM200EK, YTM200L, YTM200EL, YTM200N, YTM200ERN use the exact same part number for std size piston (probably oversize numbers are the same between yrs as well, but I only looked at std size part numbers)

All are listed as 21V-11631-00-Y0

I would guess the Wiseco are the same case. Odd that they had no YTM200 category on their website to select (I looked too)

Sent from my Z958 using Tapatalk

Thanks for the response and checking into it as well!!

Yeah, I find it odd that they exclude the 1983. I sent Wiseco a message, but of course I have to wait until tomorrow to hopefully get a response. I figure I'll just wait to confirm with them just on the rare occasion that theirs actually won't fit the '83 for some odd reason.