TY250 Twin Shock OEM Ring P/N

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CoolCat250
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TY250 Twin Shock OEM Ring P/N

Postby CoolCat250 » Mon Nov 02, 2020 11:20 am

Hi everyone,

I apologise if this has been answered before: I am new to the world of TYs and I haven't been able to find an answer yet.

I am looking for some clarification around TY250 OEM ring part numbers.

According to my TY250A Yamaha parts manual, the part number for rings for the TY250 begin

434-11610-XX

and I am lead to believe that this is the p/n(s) also given in the TY250E parts manual.

Again, according to my manual, the part number given for pistons begins

438-11XXX

and again I am lead to believe that this is the p/n(s) also given in the TY250E parts manual.


Now, from my limited understanding of Yamaha parts numbers, I am lead to believe that the first three numbers refer to the base bike model: i.e. 434 refers to TY250 and 438 refers to DT250. Based on this, one would assume that rings with a part number beginning

438-11610-XX would also be suitable.

I am 99.99% confident that 434- and 438- rings both have a 'Dykes' top ring to suit the L-shaped ring land in the top of the 438-piston .

So my questions:

1) Are 434- and 438- rings the same and/or interchangeable?
2) What are the differences?
3) Which ones should I use in my TY250A (with a 438- piston)?

Thanking everyone in advance,

Kind regards,

Brad



David Lahey
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Re: TY250 Twin Shock OEM Ring P/N

Postby David Lahey » Mon Nov 02, 2020 8:29 pm

I thought the :yamaha TY250A model had a non-dykes top ring :? My memory was that they went to the dykes ring design on the B model.
I'll have a look in my wonderful shed and see if any useful information can be found


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David Lahey
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Re: TY250 Twin Shock OEM Ring P/N

Postby David Lahey » Mon Nov 02, 2020 9:00 pm

Well that was interesting.
I looked in three different TY250 parts books (TY250A, TY250 A/B, TY250C)
All three listed the 438 piston as the standard piston type and the 434 as the alternative piston type, which seems odd because 434 is the TY250A prefix. Those prefixes are for Yamaha models that came out very close together in time. 438 DT250A 1974 and 434 TY250A 1974.

All three TY250 books show line drawings of pistons with dykes type top ring groove.
It's only a theory but maybe they both have a dykes top ring but differ in that one of them has ring grooves that suit the use of ring expander springs and the other doesn't.

All the parts books list the 434 rings as being something different to the 438 rings and one book listed the standard piston as being the 438 type and the standard rings as being the 434 type :? :shock:

Anyway why are you just replacing the rings? The usual thing nowadays is to re-bore rather than re-ring.


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brent j
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Re: TY250 Twin Shock OEM Ring P/N

Postby brent j » Mon Nov 02, 2020 9:14 pm

I don't know if you guys know but Yamaha use the 3 digit alpha numerical code for each different model.
Every part introduced for that model starts with that code and no matter what or hoe many models that part is fitted to it never changes it's number.



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Re: TY250 Twin Shock OEM Ring P/N

Postby David Lahey » Mon Nov 02, 2020 9:49 pm

brent j wrote:I don't know if you guys know but Yamaha use the 3 digit alpha numerical code for each different model.
Every part introduced for that model starts with that code and no matter what or hoe many models that part is fitted to it never changes it's number.

Yes and Yamaha also does cool things to keep old bikes going like making an old design part in a different colour for a more model model and updating their on-line parts listings with the superceded numbers so if you ask using the original part number they will say "Well we have that part but in a different colour. Do you want it?"
I'm thinking of things like bolts, nuts, control cables, switchgear, even wheel hubs.

The trick with these pistons and ring kits though is the old parts books lists both piston numbers as being correct without saying how they are different


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CoolCat250
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Re: TY250 Twin Shock OEM Ring P/N

Postby CoolCat250 » Mon Nov 02, 2020 11:42 pm

Hi everyone,

Thanks for the replays so far; it seems that I am not the only one doing a little head scratching.

I have continued my research and thought that I would share what I have found thus far in the hopes that it might stir some 'grey matter' into action amongst others.

And before we start; I am planning a rebore for my TY to 2nd O/S. I have a NOS OEM 438-11636 piston, I just need to find the right rings now.

New tidbits
1. My TY250A parts manual was published June 1973
2. The manual lists the following part numbers for O/S pistons and rings

Pistons:
1st: 438-11635-00
2nd: 438-11636-00
3rd: 438-11637-00
4th: 438-11638-00

Rings:
1st: 434-11610-10
2nd: 434-11610-20
3rd: 434-11610-30
4th: 434-11610-40

3. Alongside the O/S piston and ring part numbers Yamaha flags *Alternate Parts* which correspond to O/S 'Piston Assemblies' with the following part numbers.

'Piston Assemblies':
1st: 434-11630-10
2nd: 434-11630-20
3rd: 434-11630-30
4th: 434-11630-40

4. A quick Google/eBay search suggests that a Yamaha partial part number of '-11630-' corresponds to a 'Piston Assembly' which (now correct me if I'm wrong) is a kit that contains at least a piston and a set of rings (and possibly other bits that are inconsequential to this discussion).

So, from the above I would hazard a guess that a 434-11630-XX is a kit that contains a 438-1163X piston and corresponding 434-11610-XX piston rings. Or perhaps even a 434-1163X piston with XXX-11610-XX non-Dykes-type rings from another bike (perhaps a DT2?) Maybe this why early TY250A's are found to have non-Dykes-type rings. Either way, my guess is that a 434-11630-XX is a kit with a matched piston and set of rings.

So from this I suspect the following (again correct me if I'm wrong)
1. 434-11610-XX rings suit 438-1163X pistons
2.'Early' TY250A's used 434-1163X pistons with XXX-11610-XX non-Dykes-type rings from another bike (perhaps a DT2?)

So, I guess I still haven't answered all of my original questions, but I am feeling confident that 434-11610-20 rings will be what I require for my rebuild.

(But I'd still like to know the differences between the 434 and 438 rings).

Kind regards,

Brad



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Re: TY250 Twin Shock OEM Ring P/N

Postby David Lahey » Tue Nov 03, 2020 6:40 pm

I thought I'd post these photos of TY250 parts manuals up to hopefully help with solving the mystery
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CoolCat250
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Re: TY250 Twin Shock OEM Ring P/N

Postby CoolCat250 » Wed Nov 04, 2020 7:57 am

Thanks David

FYI my parts manual looks the same as your ‘TY250A’ only manual




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