88 RM250 Cylinder Bore Question

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10/9/2017 2:36 PM

I need to have a second cylinder I have bored up to the first step - 67.25mm. It needs about .008 taken off. My question is when the cylinder is bored to this next step, will the boring effect the power valve clearance when they are installed? Would the power valves also need to be cut down???


10/9/2017 3:12 PM

They need to be checked for clearance and may need to be cut.

Paw Paw


10/11/2017 5:25 AM

If you are considering boring an 88 rm cylinder it must have been sleeved at one time... You will want to send it to a qualified cylinder repair shop...millinium or Powersealusa. They will tell you if the sleeve is installed correctly & how to proceed. My 88 rm had been sleeved also & was done correctly, I had Powersealusa replate the sleeved cylinder to stock specs & used a standard bore piston, powervalves remained stock. If the sleeve was installed incorrectly the cylinder is junk.


10/12/2017 12:48 PM


New member here with a 1988 RM250 I just bought. I plan to tear it down this winter and rebuild the engine.

As part of the prep I have been scouring eBay to see what's out there. In every picture I see of a 1988 cylinder a sleeve is present.

Was the 88 RM cylinder definitely plated?

The bike I bought has an oversized piston so I don't have a plated cylinder. Of course it may have been sleeved.

Sandman how does your bike run with the sleeved cylinder?

Nice to meet everyone. I look forward to learning a lot.



10/12/2017 2:23 PM
Edited Date/Time: 10/12/2017 2:25 PM

Welcome, Mdesmond.

FYI, join this Facebook group as well. Lots of good people over there to help.

My 88 build, I was able to locate quite a bit of new parts using Partzilla and eBay. The cylinders are a hard find and you have to be really quick on the spot to get one on eBay. The 88 model uses a lot of specific parts made only for that year which can be a bit of a hassle. The swingarms are an instance of this. They only fit the 88 model. They are also known to crack on the pivot points requiring a welder to weld the aluminum. It's almost a given you'll have a cracked pivot. I personally have three arms that were all cracked!

That 88 cylinder is a bit different as well although an 87 and I think and 86 cylinder would work on the motor. The 88 had larger ports. Another thing different with the motor is the clutch. A true 88 motor will have 15 clutch plates where the 87 has just 11. I found this out the hard way when I tried putting 15 plates in my motor only to not be able to squeeze the clutch lever.

Pay close attention to part numbers also! The 88's have 26C in the numbers while the 87's have 00B. Just a tip there!

sandman and paw paw are two great guys who helped me tremendously! Find sandman's 88 RM250 build thread and read through it.

Good luck!


10/13/2017 5:39 AM
Edited Date/Time: 10/13/2017 5:41 AM

Mdesmond wrote:


New member here with a 1988 RM250 I just bought. I plan to tear it down this winter and rebuild the engine.

As part of ...more

My 88 cylinder is sleeved, it needed a piston replaced as cylinder was scored. when I rebuilt it I could have taken it to the next oversize piston, likely requiring exhaust valves needing to be cut back. since I"m no expert on looking to see if the sleeve was installed correctly, I sent the cylinder to Powersealusa and asked them to inspect cylinder & advise on best repair option. They said cylinder sleeve was installed correctly & they could replate the sleeve and their plating is better than what was originally on the cylinder. This enabled me to keep the stock bore, stock exhaust valve parts and get the benefits of plating, cooler temps, better lubrication, longer cylinder wear. They also sell piston kits & will match piston to your cylinder...I have no affiliation with Powersealusa, just very pleased with their services. I would also check head & cylinder top & bottom surfaces for warpage. Old bikes that have been blown up, overheated & worked on by hacks will have all sorts of surface issues...my 88 runs very good and the 88 rm cylinder was definetly plated from the factory...of course none of this is real without photos......