Rear Cylinders

[ChequeredFlagRacing]

Curious as to why is there a lack of rear cylinders for sale on ebay and other forums? (Seems to plenty of the lower front pair about.)

Are they more prone to failure due to seizing / overheating and therefore are trashed more often?

What should I watch for if they are prone to failure?

[Speed Freak]

Yes, often the upper left seems to be an issue.
Good that rear left and right are the same.

One theory is that it is the first one which doesn't get fuel when the tank is empty because it's the closest to the fuel tap. Then this one runs lean.
Other theory is bad cooling of the rear cylinders.
I'm planning to do a CFD simulation as soon as I have the complete engine in CAD.

[ChequeredFlagRacing]

Thanks the reply
Didn't know the rears were the same

[tacky1]

My cylinders are over with Bill Wilson getting rebored as we speak, Top bloody cylinders ran lean or overheated up in the mountains and lost a piston, Bottom two are still like new, Had to bore them all out to the last bore to get the damage out......
Its a problem with them...

[silverstrom]

And then there is the issue with the rear timing being off by 2 or 3 degrees causing them to run hot.

[tacky1]

And then there is the issue with the rear timing being off by 2 or 3 degrees causing them to run hot.

Exactly, I picked up a degreed woodruff key on here to help put it back in line, Ill take timing measurements and see how much it is out before I fit the key..

[silverstrom]

I bought 2 of them to correct the 2.5 degree retarded rear timing.

I have read here that if you use 4 TZR (2MA/1KT) pistons this is no longer an issue as the rear pistons are no longer offset on the pins.

[motosapien]

I am using tzr pistons on my build and I have an off-set key as well.
I'm planning to start the rz500 engine build during thanksgiving, will keep you all posted

[tacky1]

Bill is fitting Wiseco pistons as the cylinders are pretty well ported, 34mm carbs etc.

[silverstrom]

I am using tzr pistons on my build and I have an off-set key as well.
I'm planning to start the rz500 engine build during thanksgiving, will keep you all posted

Please do. I am interested in how the rear timing measures with the TZR pistons before the offest crank key is used.

[phildu31]

You will see a difference of 0,5 degree before and after by changing the pistons.
The original pistons pins have an offset of 0,5 mm toward the exhaust.
The corresponding new TDC will be at X where sin(X)*50 = 0,5 for a stroke of 50 mm and an offset of 0,5 mm.
This offset of the piston pin is not the main reason of the offset between the cranks.

[ChequeredFlagRacing]

I had the bike new in 1985/87 and can't recall overheating issues or Yamaha doing a recall to fix the issue. So is it something users are doing with mods to the engine tune that are causing the issue?

[tacky1]

The rear cylinder happens stock bikes also, I had 3 of mine blow up back in the day and they were stock, Rode hard on the country roads of Ireland

[Twidget]

I had the bike new in 1985/87 and can't recall overheating issues or Yamaha doing a recall to fix the issue. So is it something users are doing with mods to the engine tune that are causing the issue?

I think the biggest difference between then and now is pump fuel quality.

Has anyone heard of a burned up rear piston on a properly tuned bike running race fuel?

[marrcel]

I remember i did use different jetting for the rear barrels