Where can I get a cylinder new for $280?

 

ATC250;
I've been told that 20hrs. is a good time to re-ring a single ring piston. How's your compression?

Livewire;
If you're serious about a cylinder; drop me an e-mail. I have a Polaris dealer friend. Sport400@earthlink.net

 

I picked up a cylinder, head, reed cage, intake boot and exhaust spigot. I'll have to make a new exhaust spigot, but having the original as a guide helps. I'll use V-Force reeds and need a bigger intake, but I can get everything assembled first before making further improvements. I was able stretch the intake over a 38 PJ I had laying on the bench. I would probably want to run a 41.

I don't see that I'll need to change to the long rod, but I don't have a piston to compare crown height. Eyeballing it, the 400 cylinder looks about 5mm shorter than the FL350.

Wow, that's a thick sleeve. I'll have to hog out the cases a lot more than I thought. The entire inner gasket sealing surface will be removed so the voids in the cases will have to be filled in with weld. The cylinder is narrower at the transfers requiring the barrel be widened or the case transfers partially filled.

AZ400L, do you have a piston laying around that you could measure from the wrist pin hole to the top edge of the piston? Do you know if when using a YZ490 piston on the Polaris if a spacer plate is used? There are two different year ranges for the YZ490 pistons as well as the YZ465 piston. Do you know which year is used?

What is that little hole above the exhaust port?

 

That hole in the exhaust port is a compression release. I tapped it an ran a set screw from the hardware store. Don't tap the entire hole go in only maybe 7-9 mm. then run the set screw in with lock toght and snug it up against the untapped part. That should wedge it in good. Doing that gives you 10 psi compression increase. You can weld it too I guess.....I didn't know if I wanted to keep it that way, that's why I tapped it.

 

I now have someone local to do the case mods. He did the work to put one of those PSI 425 kits on a 250R.

The instructions with the PSI cylinder said to just fill the cases with JB weld or an equivilent. I will do the same. I have decided to switch to the long rod. It will require a spacer plate either way. I think a thick spacer plate is better than a thin one because it will add strength to the bored out cases. One of my spare cranks needs a rebuild so I'll send that off to the longer rod put in.

I still need to know what year YZ490 piston to use. There is an 83-84 and an 85 up. If all else fails, I'll get the newer one and hope for the best. I figure the newer one is more likely to be made in future years. Once I get a piston, I can start figuring out port timing.

 

We have a rigid chassis that I believe had the that setup in it before but we do have a David Moore sticker on the fuel tank and he build the engine we have now but it’s a regular 250r cool head tho still pretty fast