I got a 350 two stroke bottom end. can i use top end of a 400, if so what modifacations . I would be thankful for any coments

You'd need a 400 cylinder,head,piston and head gasket. Bottom ends were the same,both used the same rod and carbs had the same stock jetting when the 400 first came out. Main difference is that the 400 had a counter balancer dip stick the 350 didn't.

sleeve seems to b to thick to seat n 350 bottom, any sugestions ?

Yep you are correct.. I've never tried swapping parts like this at the shop(350 was repaired as a 350,400 as a 400) even though the rods are the same and much everything else on the bottom ends of both machines appear to be the same, but several people have tried and forum member Rick Ritter that works on these day in day out came across the same thing.

"Ok fellas - I took a base gasket from each off the shelf today . The bolt pattern is IDENTICAL - ( I didn't remember that) - the transfer port openings are different - and I can see the sleeve on the 400 is quite a bit to big . Anything is possible with machine work (you can get a 400L jug onto a 250r Honda with some machine work and welding) but I can see you just can't drop a 400L jug on a 350L bottom.

Cylinder heads - a 350 head will only fit a 350 and a 400 will only fit a 400 . The bolt pattern is different .

And there we have it .............. :-)

Rick Ritter

You could possibly take each cylinder to a machine shop and see if the lower part of the 400 sleeve could be machined down to match the 350 without loosing strength or taking a chance on it shattering under pressure.

the bolts match up perfectly with 400 to 350
side walls on 350 (bottom) to narrow for the 400 sleeve .
what if i cut off sleeve flush with 400 jug

Of course id rather use 400 bottom but when i pull it it jerks my arm out of socket .
Fly wheel boogerd up, from cheap after market starter. new fly wheel is too expensive.
is it normal to have this much trouble pull starting my machine?

NO.. Then you'd have extreme piston wear and could shatter. The sleeves on both cylinder are extended like this and on most engines for piston support at the lowest point of the piston travel. Stock compression isn't all that high. Try cupping your right hand under the left on the handle when pull starting,can save the fingers,or better yet get the electric starter working.

thanks for ideas enjoyed it

We both learned something new.. I never got a chance to experiment on cross breeding engines( really didn't have to or wanted to) since I was in a Polaris shop with a lot of parts at hand. Hard enough at times just to keep stock machines up and running.

while im sitting here my 800 rzr spits and sputters over 30mph. I replaced plugs and exhaust/gasket. what might i try nxt?