RZ250 Bore sizes and tolerances

[exup]

Hi,[/div]

I picked up two second hand RZ250 barrels without their old pistons, and I measured the dia of the bore as well as I can with my calipers.

I found them to be 54.25 which is not the usual 0.5 mm over sized steps.

Do you think someone has picked up custom sized pistons that are .25 increments or its worn.

What is the tolerance for the bore on most 2 stokes +- 0.05,mm?

[midlifecrisisrd]

All LC and YPVS bikes (250 and 350) have 0.25 increments in bore size so 54.25 is first oversize

I'd just be getting them rebored with new pistons

And beware 250 ypvs pistons are different to 250 lc pistons.

Not just like 350 lc and ypvs that are slightly different but fit, the 250 ypvs has a different pin height

Steve

[jon]

You’re not thinking of forged pistons are you? Some of those only go up in 0.5mm increments.

I had a set of very worn original bores that had to go from 64mm to 64.75mm to clean them up. As I was going to use forged pistons they ended up going to 65mm.

Jon

[exup]

Thanks for clarification for some reason I thought it was in .5 increments.

Next question where to get the pistin kits from. Not worried about performance more just reliability bang for buck.

And what tolerance should you look for in the barrel dia. Comparing the piston. Eg reborn of 54.50 to 54.55

[jon]

www.pjme.co.uk/acatalog/Yamaha-RD350-YPVS-Piston-Kit-Mitaka-380.html#SID=287

Jon

[midlifecrisisrd]

Can't remember the bore clearance, it will be in the manual

PJME sell them

Steve

Beat me to it Jon 😁

[JonW]

Lots of places sell pistons. PJME is a good choice, but Yambits and others also sell them.

I like the TKR kits from Japan for my 250s.

[exup]

I did check out Yambits thats why I thought they were in increments of .5, thats how Yambits and PJME are selling them. Where as the old microfiche for Yamaha has them as 0.25. Anyway, looks like I need to rebore them and stick 54.05 in them.

I went through my collection of PDF scanned copies from the internet aka RD350.NET and found the 83 service manual which is the YPVS range and has piston clearance tolerances for the YPVS range of engines.

If anyone has any newer RZ250 workshop manuals 84 and above please post a link.

That is a tight tolerance range. +/- 0.005mm, using their own example calculation below its too big a clearance. (0.13mm)?