Old Yoshimura 816cc Big Bore piston kit for GSX750ES has a ring missing

[GSX750ES junky]

Hi All,

New here. Since I was young there is a motorcycle that captured my heart like no other ... The mighty GSX750ES
I'm re-building one now with great attention to details.

I recently got from ebay an old Yoshimura 816cc Big Bore piston kit that has a ring missing in each piston.
Yoshimura doesn't produce these anymore and I would like to use a Wiseco set of rings.
The wiseco rings and Yoshimura are both 816cc and both have an outer diameter of 70mm. Not sure about the other dimensions.
A rumor says that Wiseco was the one that produced the rings for Yoshimura.
Is it true ? How can I figure out which ring fits the Yoshimura piston without purchasing it ?

http://www.wiseco.com/ProductDetail.aspx?AppID=&ItemID=2756XC&ModelYear=1983&ModelID=551

 

[Guest]

I would try to contact someone at Wiseco. I'd bet their rings would work. Welcome to the forum, there is a bunch of us with these beasts here.

 

[posplayr]

Hi All,

New here. Since I was young there is a motorcycle that captured my heart like no other ... The mighty GSX750ES
I'm re-building one now with great attention to details.

I recently got from ebay an old Yoshimura 816cc Big Bore piston kit that has a ring missing in each piston.
Yoshimura doesn't produce these anymore and I would like to use a Wiseco set of rings.
The wiseco rings and Yoshimura are both 816cc and both have an outer diameter of 70mm. Not sure about the other dimensions.
A rumor says that Wiseco was the one that produced the rings for Yoshimura.
Is it true ? How can I figure out which ring fits the Yoshimura piston without purchasing it ?

http://www.wiseco.com/ProductDetail.aspx?AppID=&ItemID=2756XC&ModelYear=1983&ModelID=551

Look up RapidRay or call him; he would most likely know.

 

[Guest]

Look up RapidRay or call him; he would most likely know.

Now why did'nt i think of that. I'm kinda stupid sometimes...

 

[GSX750ES junky]

I pinged RapidRay.
Wiseco doesn't reply to my emails.

 

[Nessism]

I don't have personal experience with this but have read that Perfect Circle will make rings for most all applications...not sure how much it costs though.

So missing one ring you say? Does that mean you have one compression ring, and the pistons take two, or do those pistons only use one compression ring? Guess what I'm driving at is if you have one compression ring you could measure the dimensions so you will know exactly what to look for. For example, the ring thickness is critical, and of course the OD. The ID is less important. At any rate, if the ring requirements were known it would be easier to search I think.

Good luck

 

[GregT]

I would suspect that std GS1000 rings will fit.They're 70mm
Critical dimensions are the ring thicknesses.
Measure the groove widths and post the results here
as example - maybe, top ring 1.2mm 2nd ring 1.5mm. oil ring 3.5mm.
Yoshimura would have used what they could get easily which is why I think GS1000 rings will fit.
A PO may have run without the 2nd ring for race use - not uncommon.

 

[GSX750ES junky]

I just received the Yoshimura kit I bought on ebay for 80$.
I think I'm ****ed up . No free meals they say...
There are 4 issues:

1) 3 pistons have 2 grooves (1mm + 2.5mm) and 1 piston has 3 grooves (1mm + 1mm + 2.5mm)
2) This different piston has a CNC error on its top as you can see marked by a blue arrow.
3) One groove has one side machined to a lower level than the other side (also CNC error ?)
4) Another piston has a 2mm crack on its edge (red arrow on second picture). Can this be machined to turn the crack into a round hole ?

As for the rings, there are 4 sets of ring in the package.
Widths are 2mm (jagged one) ,1mm , and about 1/3 mm.
The seller said one is missing. Which ?

 

[GSX750ES junky]

Here is the crack...

 

[Nessism]

Your photo shows one set of rings: three piece Oil control ring and one compression ring. Do you have four sets just like this? If so, you should be fine. For the piston with two grooves, I'd leave one groove empty. And that crack I'd trim the skirt to remove it, should be fine.

 

[GSX750ES junky]

" Do you have four sets just like this?"
I have 4 sets like the one you see in the picture.

"And that crack I'd trim the skirt to remove it, should be fine."
I agree that "rounding" the crack will solve the problem and prevent it from getting bigger.

"For the piston with two grooves, I'd leave one groove empty"
You meant to say... For the piston with three grooves, I'd leave one groove empty. right ?

To prevent confusion let's call piston with 3 grooves P3 and piston with 2 grooves P2.
In each ring set there is one compression ring and 3 oil rings (1 thick + 2 thin ones).
Oil grooves can accept 1 thick oil ring or 2 thin ones.

Please describe which oil ring you think should go in P2 and which in P3
​

Is it safe to ignore the groove ? Is it OK to have one piston that has its grooves not exactly aligned with the grooves of the other pistons ?
In the picture you can see that the grooves of P2 and P3 are not parallel.

 

[Nessism]

For the oil rings, that convoluted ring is the expander and the thin rings are the scrapers. Three pieces make one ring. Each piston needs these three pieces. The factory service manual details how to install these rings.

For the compression rings, it wouldn't hurt to try to find an extra ring for P3 so that would be my first attempt. If you fail, I'd use the compression ring you have and put it into the upper groove. The P2 pistons have the compression ring lower on the piston crown to shield them from heat, which obviously won't be the case with P3. Nothing you can do about this other than try to find one extra ring if possible. If you can't find one, I'd throw it together as already mentioned.

 

[Guest]

Those are cast pistons. Wiseco didn't make them.

 

[Billy Ricks]

This guy works for Wiseco if you get to needing rings or info. I have an old Wiseco catalog around here that has ring specs in it. If you get to needing rings I can dig it out and see what series of rings match your specs. The 816 kit is probably Wiseco. Some of the Yosh piston kits were Cosworth but they were standard bore sizes. They came in .05mm, .5mm, and 1.0mm oversizes. The .05mm was just to get closer tolerances in a standard bore cylinder. I have a set of Cosworths that I had to send to Total Seal to have the grooves recut to accept a set of their Gapless rings. I never could find rings for them and Total Seal was a last resort.

 

[SqDancerLynn1]

The gold ring is part of the oil control ring There should be two very thin scraper rings that go with it into the wide ring land. The piston with the single ring groove and oil groove I would guess is a race only piston

 

[Nessism]

Those are cast pistons. Wiseco didn't make them.

Yup, cast. Yoshimura has used a lot of cast pistons over the years.
GSX750, What made you think they were Wiseco?

As far as only having one compression ring goes, that was not unusual for high performance piston kits back in the day. Some companies use a dykes style single compression ring. Using pistons like this on the street will work but obviously, the pistons will develop blow by faster than if there were two compression rings.

 

[Billy Ricks]

Wiseco had an 816 kit for the 750. I kind of assumed Wiseco too without paying attention to the pictures.

 

[GSX750ES junky]

OK... I read all your replies and think I got the point.
I'll sum it as I understand it and I'll try to offer a (crazed) solution...

Rings should be installed as in the picture below.
The oil ring consists of 3 actual rings (the gold one sandwiched by the 2 thin black ones). The other 2 grooves should house 2 compression rings. Since I have only one I need to order another one.

 

[GSX750ES junky]

There is a very renowned workshop in my area that deals with pistons and cylinders of motorcycles.
They said they can add a third groove to the 3 P2 pistons which I have for 40$. As you can see in the picture below it is going to leave a safety margin of aluminum (A) which greater the safety margin of aluminum of the stock P3 (B).
On the other hand one could claim that A is located at a more critical area close to the combustion chamber...
After I do this I'll need to order a total of 4 thick rings.

What do you say ?
I can of course save the hassle and return the pistons to the eBay seller but adopting the solution detailed above means I'm paying a total of 230$ instead of buying a Wiseco kit which where I live sells for ~ a 1100$

 

[Nessism]

Those P2 pistons have the ring groove in a different location than P3. Since, as you say, there is a good shop in your area you might want to take the pistons in to them so they can examine them first to see if there is room for the extra groove without getting too close to the valve clearance cutouts on the piston crown. There isn't anything wrong with running them with the single ring though. And if you are using one ring on P3, use it in the groove nearest to the piston crown, not the one in that photo.