Finally I’ve bought a 500...

[silverstrom]

Hi Jon, I'm using offset keyways on two of my bikes. I think the pistons have a lot to do with the vibration.
Genuine yamaha pistons 1st oversize front 154 grams rear 145 grams. Bill Wilson used Wiesco pistons machined to be
all the same weight on a my street fighter build, a lot less vibrations than the other bike.
Cheers Ron.

If you use 4 TZR pistons you can avoid the weight discrepancy. The TZR pistons are available as piston and ring kits.

You can also use Yamaha RZ500 pistons and lighten the fronts to match the rears. That has been done with an engine here.

[JonW]

Cool, didnt know the TZRs were weighed the same, but I guess they are all the same windowed pistons rather than the 2-with-n-2-without of the original 500? I'm not sure if i said, but I actually do have OEM TZR piston kits to fit to this engine, but i've not looked in the boxes at them, maybe i should lol. I will weigh them anyway as Im intrigued now

Thanks to everyone for their input on the balancer and the balancing, or lack thereof from new lol.

So back to my original post, any thoughts on the other things I noticed?

- Upper pistons were both cracked across the inlet window bridge and one actually fell apart when I pulled on the crank out, so those were minutes away from failing Both those pistons had obviously lived a very long and hard life...

- There is some damage to valley under the crank case on one of the upper cylinders. This looks like some kind of pockmarks, not from anything exploding through there (there is no evidence of that on the piston or head etc). Its more like water damage you get on magnesium, hmm... these cases are normal cast aluminium arent they?

- There was a vast amount of fuel / oil mix in the middle of both cranks, under the labarynith seals. I assume that' s to be expected?

[JonW]

Hmm, ive never know this forum silent when questions are asked or opinions sought, so this is a new one for me

I trudge slowly forwards... my fixings and brackets are back from the platers. Im now (its taken days!) going thru my pics to put the right fixings back in their places so this resto is done right. Its not helped by the fact the plating has all sorts in it, and the balance of RZ350, LC and XT stuff in there as well as car stuff (for my Evo) and odds and sods like my grandfathers old dividers from the 2nd world war which were all rusty and unusable before.

[jackson.40]

Post up a photo, I love plated parts

[JonW]

Sadly no pics of the buckets of zinc, I spent ages sorting out the bolts and brackets, springs and washers, nuts and screws etc etc This was made all the harder as mentioned that along with the car stuff there were XT500, RZ F2 and LC parts in there as well, plus some of my grandfathers WW2 era measuring tools that i inherited and a load of bits and bobs. I reckon Ive got most of it where it belongs now which is good, but its taken ages!

In other news...

Pistons... I said I had 2YK pistons, but it seems the only ones of those I have are the Fronts, the rears are the original 47X units. This means the fronts have the drilling, but the rears dont. Should I add some, or leave them as they are? In my engine when i took it apart the rears had seized and cracked the bridge

[JonW]

....Buler?

Ok, how about another thought... My bike has done 42k kms on the Original bore. My new OEM pistons are 0.5 over. Am I wasting a bore size I wonder...?! Should I instead be looking to buy TZR250 0.25 pistons? What do people think? And... if i do, what brand is best other than OEM?

[silverstrom]

My 2 cents worth: if you are on a budget, then using what you have on hand makes sense. If money is not a concern I'd do the 0.25 bore and get new pistons. Cast or forged is the question. Cast have worked for the past 35 years. I don't see a reason to change that. Mitaka kits work well and are well priced. They are in my current motor.

[JonW]

Thanks for your thoughts John, its appreciated as ever. To be honest using what I have was my original plan, but I hate throwing bores away if I dont need to...

I looked at the Yambits listings and didnt see a +0.25 piston, hence my thoughts about TZRs etc. Of course if there is no sensibly priced 0.25 option then I may as well fit the OEM +0.50 units I have in stock...

... and then my question about the drillings still stands. I do worry about how trashed the uppers were in my bike, but it had done 42000 kms and the PO did say he used it hard. I'd like to help the pistons live longer in the hot rears if i can.

EDITED TO ADD:

I see your piston kit was Yambits PTK090; their website says those fit "This kit is +0.50mm (56.9mm Bore size) and suits: TZR250 (Parallel Twins 1KT, 2AW, 2MA, 2XW1, 2XW2 Only)"
https://yambits.co.uk/tzr250-piston-kit ... p-290.html

I assume that was for a lowers as it has no windows and the uppers were another type?

Interestingly the 0.50 pistons for the 500 as now listed by Yambits as:
- PTK163 - lower - https://yambits.co.uk/rz500-piston-kit- ... 54679.html
- PTK167 - upper - https://yambits.co.uk/rz500-piston-kit- ... 54691.html
(These look like the Taiwanese version of the Mitaka units to me, see below)

There are no 0.25 pistons for 500 fitment listed by Yambits, but there are some for the TZR...and... I believe that the same unit as PTK090 in +0.25 is PTK134 - https://yambits.co.uk/tzr250-piston-kit ... 49070.html
These say that they fit: "This kit is +0.25mm (56.65mm Bore size) and suits: TZR250 (Parallel Twins 1KT, 2AW, 2MA, 2XW1, 2XW2 Only)

So that would do the lowers?

As as aside: Yambits also offer TKRJ as an option in that size (and others for the TZR) - https://yambits.co.uk/tzr250-piston-kit ... 55494.html - With the same fitment.
FWIW the TKRJs are my preferred unit these days as the box on the TKRJ units states 'Made in Japan' as seen in the pic, the pic of the Mitaka's does not and for good reason as not all Mitaka pistons are now. I raise that point as I bought TKRJs for my RZ250 and Yambits sent me Mitakas in totally the wrong size by mistake. They swapped them no problem but what was interesting when I looked at them was that they were (horribly) made in Taiwan, with casting that looked like a 5yr old did it in his sand pit as his first attempt for an art project. They do not look like the older Japanese made Mitaka units at all. Food for thought.

So... Are our 500 lower pistons the same as the 1KT, 2AW, 2MA, 2XW1, 2XW2? and what about the uppers? are they the TZR250L version? They dont look to have windows in them in their pics tho...

[phildu31]

As previously said, at 42 000 kms it is great time to rebuild your cranks !!...
For the rear pistons, you can look at original TZR kits in +0.25 that now come in replacement for the front ones.

[JonW]

As previously said, at 42 000 kms it is great time to rebuild your cranks !!...
For the rear pistons, you can look at original TZR kits in +0.25 that now come in replacement for the front ones.

Fear not Phil, the cranks will get looked at and maybe I'll just buy new ones from Gus etc. The bike was taken off the road by the PO for that very reason. He was afraid the crank bearing that fails would let go and decided to catch it before that happened and Im glad he did, the pistons were done by then for sure. The bike came with 2 new outer bearings that he wanted to fit, along with OEM piston kits (+0.50) and all top end gaskets and small end bearings etc.

Do you have part numbers for the TZR +0.25 pistons at all?

[JonW]

Ok... Just found this thread:
http://www.rzrd500.com/500phpBB3/viewtopic.php?p=65403

Do these piston part numbers still hold true? 99999-02109 for piston and rings for the uppers but I couldnt find anyone supplying the OEM lowers... Aftermarket info might well be more useful at this point?

Im still feeling very new to the 500 and its complexities to be honest, its not helped by the fact that the terms front and rear seem to be used all over the place on sales sites rather than upper and lower etc.

[phildu31]

Yes 99999-02109-00 is the +0.25 TZR piston replacement kit for the front/lower ones.
You can mount them into the rear/upper cylinders as I did.
Piston kit comes with rings set at a lower price than original ones ( 81€ ) and have holes for lubrication.
Don't bother with other sources.

[JonW]

Thanks Phil, In all the photos I saw online I couldnt tell if they had the windows in them, youve answered that question, thanks.

[ns86]

TKRJ all the way! From page 3 of thread. I keep posting this as I consider this the best available currently but no one seems to notice? Available in .25 increments up yo 2.00. Made in Japan! https://www.tkrj.co.jp/goods/m-AY8010X-2YK-47X.php

[JonW]

I am also a TKRJ fan, they make a better piston than Mitaka Japan, dont even consider Taiwan etc.

What I need to work out is which of the TZR options from Yambits I should be looking at really, TKRJs 500 versions are $400+ for just the rears, Yambits TZR TKRJs are about $100 a set of 2.