Piston rings - help!

[ac3_snow]

Soo in an attempt to avoid starting assignment I instead pulled head, barrel etc off my bike. First thing i checked was the piston ring end gap, only to find they are in need of replacing (no big surprise there) but the spare set I had purchased with the false hope of them fitting are in fact not 'tall/thick' enough.
So my question is what is the best way to determine the size rings I need? I have no idea if it has ever had a oversize piston or rings before and do not own a internal diameter measurement tool.
What I do have is the old rings, some numbers stamped on top of the piston, feeler gauges and some digital calipers. Have been told this is not sufficient to solve my problem but hope some one out there may have some advice or extended knowledge re backyard mechanics?!
any tips or hints very much appreciated.

[TZ350]

Clean the top of the piston and rings and post any numbers markings you can see there. If its oversize there will be something like 0.25 or 0.5 stamped on the piston and rings, 0.25 or 0.5 that means quater or half of a millimetre etc oversize.

[ac3_snow]

So I have discovered that its a 1973 engine and believe it or not after 37 years is still on its original piston. So I even have a part number for original yamaha rings but at $100 a set is more than I have to spend. So I need a set of rings for a 52mm bore, and that are 1.9mm thick. So there must be alternatives out there that I could potentially use,

How can I find out or where could I go to figure out what alternatives I could use??

Have checked barrel/piston measurements and it doesn't yet need oversize.

[F5 Dave]

Yeah old Yamaha parts have gotten expensive. You'd have been better to get a Wiseco piston kit, but that will be more expensive again.

With rings you also need to have the right type of ends as well & there is no rule saying that different rings need to fit other manufacturers pistons.

In short there is little chance you will find alternative rings that will work properly & cheaper. I think my 50's rings are $60, so you might just have to get a paper round & stump up the 100 clams, or find some on ebay & hope the conversion & shipping doesn't burn you.

[quallman1234]

Perhaps you could find a TKRJ piston kit? I've forgetten who but a guy on here used to import them in. Was it "Dangerous"?

I have a AX100 TKRJ Piston kit hanging round i don't need. Doubt it would be anywhere near. have a look at the TKRJ catalog on their site. Its quite a big pdf, but has a shit load of information.

Now that i think about it, give Pete Jones a ring, he has a bunch of YB100's.

[Squiggles]

Perhaps you could find a TKRJ piston kit? I've forgetten who but a guy on here used to import them in. Was it "Dangerous"?

I have a AX100 TKRJ Piston kit hanging round i don't need. Doubt it would be anywhere near. have a look at the TKRJ catalog on their site. Its quite a big pdf, but has a shit load of information.

Now that i think about it, give Pete Jones a ring, he has a bunch of YB100's.

Oooh, I have 2 AX100's hanging around that might need one of those in future

[ac3_snow]

sweet checked out the TKRJ listings and they do have a piston kit and/or rings listed for my bike. only info for them in NZ i could find was for the supplier - kiwix, have just emailed them asking if they are willing to deal direct or if not where the nearest retail shop is that I can visit.
So will wait and c what I can discover will keep you posted.

[F5 Dave]

TonyB used to bring in TKRJ stuff, but they changed the policy so you had to bring in a real large amount & it wasn't possible to maintain that on the NZ market so he had to let it go. Pity, was a top bloke & cheap for bucketeers.

[Dutchee]

http://www.wemoto.com/bikes/Yamaha/YB_100_P/76-78/
around 10 quid, for standard rings

[quallman1234]

Oooh, I have 2 AX100's hanging around that might need one of those in future

Its 0.5 OS, send us a pm, if you ever need a kit, and ill sell you it cheap.
Great stuff about the AX bits is no one wants them, i also have a engine/with spare barrel and head.
Which i don't really need and cost me fuck all. Pretty sure skunk has one too.

Tell us how you go with the TKRJ stuff.

I would also PM TonyB on here as i know he will probabaly have some piston kits still laying around.

[ac3_snow]

Well TKRJ were about 100ish for a piston/rings kit and approx half that for just rings. But thanks heaps for the recommendation the brochure was real informative.

Any way after a bit of searching and waiting my new piston turned up today, ended up getting a 'piston/ring kit' for $27.50 found some NOS on trademe, Yamaha had never heard of the part numbers but it is a perfect match. Gentlemen I got the piston off was even nice enough to throw in the circlips for me.

Soo my next and hopefully final question is that once I'v got it all back together do i need to 'run it in' or anything similar before its ready to race?

[Henk]

Running in race bikes has always been a bit of a tough one in my opinion.
I tend to take the dirt bike approach.
Take it easy for a couple of practice sesions and get a couple of heat cycles on the motor and then go for it. Probably not the best from a long term point of view but I'm impatient and can't see myself running a motor in for half a season.
You are only trying to bed the rings in in any case so as long as you have given it a light hone things should be fine.

[ac3_snow]

haha yup I would fall into the impatient category as well. if I can restrain my self will take it easy saturday and bed it in. Might be a good excuse to take it out the beach on friday for a put around too. cheers, not long now!!

[Buckets4Me]

Running in race bikes has always been a bit of a tough one in my opinion.
I tend to take the dirt bike approach.
Take it easy for a couple of practice sesions and get a couple of heat cycles on the motor and then go for it. Probably not the best from a long term point of view but I'm impatient and can't see myself running a motor in for half a season.
You are only trying to bed the rings in in any case so as long as you have given it a light hone things should be fine.

running in my gp125

was a case of wheeling it up the road (didn't know it was a new engine was just told to try this)Friday
and then a few practice laps around Mt Wellington then into a 2 hour race Sunday

was always told to run them in like you intend to use them (but dont thrash them hard strait off)


the bike survived and 4 years later is still running good