Need Help With Piston ID

[TwoManyXS1Bs]

I finally dug deep thru my long-ago-sealed boxes, and found my old 750 pistons and rings.


Haven't seen them for 35 years. And was in for a shock. The ringsets DID have 3-piece oil control rings after all. Guess my memories are messed-up, must've been thinking about some other big-bore kits from back then that used 1-piece oil rings, dunno.

But your TX750 measurements are EXTREMELY helpful. I found that I had hoarded away some of the last of the Rocky Cycle ringsets, for the first oversize. Then noticed that the ringsets appear to be relabled Yamaha TX750 rings.


So, let's compare ring dimensions.

...This is what I found, measured with the finest Chinese Vernier known to mankind so +- 0.10 mm i'm afraid.
TX750 Rings, Thickness, Width, Piston Groove Depth.
Top Ring 1.5 mm 3.6 mm 3.75 mm
Middle Ring 1.5 mm 3.6 mm 3.8 mm
Oil Ring (3 piece ) 2.8 mm 3.6 mm 3.65 mm

This is what I got from those relabled Rocky rings, and my old piston groove depths:
ROCKY Rings, Thickness, Width, Piston Groove Depth.
Top Ring 1.46 mm 3.60 mm 3.80 mm
Middle Ring 1.48 mm 3.60 mm 3.80 mm
Oil Ring (3 piece ) 2.72 mm 3.42 mm 3.90 mm

AND, these measurements MATCH my old ringsets. So, I'm thinking that the TX750 rings are indeed the correct rings for these vintage '256' 80mm bigbore pistons.

Many many years ago Don Vesco was selling 80 mm pistons for the XS 650 with TX piston rings but the oil ring tells me its not one of those either.

Well, now that I'm reversing my earlier statements about 1-piece oil rings, I think we're locking-down this TX750 ringset applicability.

Some time ago I gave a Guy in Durban a good pair of TX pistons for a Laverda750 SF a direct fit apparently, be interesting to know what the Laverda rings are like?

Also on the TX750 forum a German Guy rebuilt a TX using Fiat 126 pistons Part No. 92050610, the pistons of course are flat topped and no good to us but the rings are another posibility?

Great! I'll add the Laverda and Fiat 126 to my research list.

... I have no idea what changes the TX piston rings underwent in its poor short life...

What I've been able to tell so far is that the TX750 rings parts numbers were superceded thus:

341-11610-00 superceded to 341-11610-01 - STD size
341-11610-10 superceded to 341-11610-11 - 1st over
341-11610-20 superceded to 341-11610-21 - 2nd over
341-11610-30 superceded to 341-11610-31 - 3rd over
...etc.

And that's all I've got. So, if the superceding numbers are compatable, maybe not an issue.
Maybe the subtle difference in your oil rings measurements to the Rocky relabled rings ARE the only differences...

 

[jonesey]

Hello again Gents.
Took a look again last night at the TX parts manual and the four sets of TX pistons. I cannot see any deserable difference in the rings, but bear in mind all are worn to a certain degree and my part manual only lists the 341-11610-01 although it covers the TX 750 &
TX 750a, both years of the model, it must of been a very early change.
Whats the posibility of it being a material change?
Like you say Too Many my brain is hurting now and I suppose i have to go do some work now. If i can be of further help don't hesitate to ask . Cheers