RD250 to 350 questions,

[Tommo]

Looking for some advice here. I found a running RD250 for really short money.  I originally picked it up because I want to put a 350 top end on it, along with changing the primary gearing but other than that what else should I consider to make it work?
RD350 cylinders are hard to come by.  The one set I have has a broken skirt on one side.
I read through the Kveldwulf thread and TBH I'm not afraid to try it, I can't imagine the quality has gotten worse and I don't mind having them bored to whatever.  Can I run actual RD pistons in one of those cylinders? 
Full disclosure, my intention is to put this on the track, and just sell the whole 250 chassis off without a motor because I have a 350 roller I'll use.

[m in sc]

leave the 250 gearing in it will spin up quicker. ive run the kvekdewulf cyls for almost 4? years now no probs. yes you can bore them and run whatever you want

[38special]

I run Kveldwulf jugs with Banshee Pro-X pistons on my 250 turned 350, and I use the 250 primary.

A tip with the Kveldwulfs - make SURE you are getting the US/UK spec.  I ordered what was listed as US/UK, and was sent India-HT spec.  The same seller on ebay sells both styles.  Measuring the port heights is an easy check.

[Tommo]

What's the us/uk port height spec for the exhaust? that's the only spec i ever see mentioned.

[m in sc]

this one specifically https://www.ebay.com/itm/284796177040

[JKV45]

this one specifically https://www.ebay.com/itm/284796177040

Everything (cylinders, pistons, rings, etc) for $169 and free shipping?

And they are decent?

There are even some similar kits out there for half that!

Wow!

[m in sc]

i have a post on here about those in particular. look in the tech library for 'cheap cyls' post. the ones half that, i cant say for certain but 170 is suspiciously cheap. 80 is very very suspiciously cheap. there are different versions for sure.

[RD7]

I have some experience with the Indian spec cylinders. The biggest problem apart from the ports is that they are manufactured in such a way that the liners can slip down inside the casing in use. The head gasket then fails.

This can be fixed but my advice is to avoid them if possible.

It would be good if to know if the new US/UK spec cylinder liners have a flange or some other feature that stops the liners slipping. An X ray (aluminium is radiolucent) of the cylinders would show any flanges in the liner.

[m in sc]

ive heard of those issues. these def arent them

[2t Fan]

is there an India spec cylinders by Kveldwulf ? I doubt. He has one type which has exhaust port at 29.5mm.India spec is at 32mm. India spec original Escorts Yamaha cylinders were as good as Yamaha ones, if the liner is loose that means the liners are replaced by someone 

[m in sc]

there are chinese copies of the indian lt ones, those are the ones to avoid, and that seller does not carry them

[Tommo]

Just a follow up with a couple questions.  Joined the Kveldvulf club the other day, cylinders arrived with pistons as advertised, found one piston was .75g heavier than the other, does that even matter, I don't know what sort of tolerance I should accept.
I read through a lot of threads about these cylinders and could've sworn that it's okay to run them with the pistons provided but couldn't find that particular comment. The porting is US/UK spec, but all the edges are wicked sharp so I'll spend some time on those.
So is the conventional wisdom to run the provided pistons or ProX?  If I get other pistons should I send them out with the cylinders to get them to fit perfectly and if so is it going to be such that I just by the first oversize ones or stick with stock bore?

[m in sc]

conventional is to change them. me, i run the, cut the tab in the center off or radius it back, it needs to be addressed.

[Tommo]

I measured the pistons and they seem really tight.  IIRC it's supposed to be .5mm clearance? 

[38special]

It's nice to be precise, but these old 2 strokes are very forgiving and will run under pretty bad conditions.  If the piston slides up and down through the bore, I'd run it and just break it in super carefully.

That said, I'd only run Pro-X pistons in my bike, after checking the bore.