82 250R low compression

[Hrobertson1]

Hi all,

I bought a decent looking 250R a few weeks ago. When I got it, it wasn't running, low compression. The guy I bought it from was running the Dunes and it just slowed down and shut off. I took it home and pulled the top end. Rings were welded to the piston and there was some wear. I took it to the shop and they bored .20 over and I got a new wisco piston and rings. I took it home and put it back together, but still low compression, about 60psi after 5 kicks. I would get a pretty strong pop through the exaust, enough to blow papers off of my bench 6 feet away. I took it apart again, checked the rod, no up and down play, and very minimal side to side. I did notice the top gasket was wet all the way through and the bottom was slightly too. My reeds looked fine and sealed. the carb has been taken apart and cleaned. I do not know a ton about 2 strokes, so I am appreciative for any knowledge lent. The new piston doesn't seem to have any play, but I am used to the rings sticking out from the piston more than they do, they look almost flush. I torqued the heads down to 22lbs, maybe I should have went more?

[yaegerb]

The shop matched the piston to the bore? Did you install the piston with the arrow towards to exhaust port and the numbers on the rings facing up?

[Hrobertson1]

The shop matched the piston to the bore? Did you install the piston with the arrow towards to exhaust port and the numbers on the rings facing up?

Thanks for the reply! The shop (Mikes Moto) told me the piston was matched to the bore. I did not see any marks on the rings, and the instructions in the box said they could be installed any way. I did notice after putting the rings on that I had to turn them to get them to seat flush.

[yaegerb]

They can be installed either way if there are no numbers. Are you 100% sure yours didn't have numbers? Also did the piston get installed with arrow facing exhaust port? The reason you had to turn the rings is because of the ring alignment dowels. On a fresh bore your static compression will be a little lower than spec due to rings not fully sealing. 60 lbs is really low for a new set of rings. When you performed the compression test did you hold the throttle wide open and kick until the needle stopped moving...it may take more than 5 kicks. If that all checks out you may have a head leak. I would advise performing a pressure test to see if you have any leaks. Look up pressure test in the search function, upper right hand corner.

[Hrobertson1]

Thanks for the info :) Yes, I made sure the arrow was pointing to the exhaust port. I looked over the rings a few times thinking there would be a number or letter, then I opened the instructions and read they go in any way. I did hold the throttle all the way open, and seemed to get less compression than with it closed. I am going to clean it up and put it back together tomorrow and put another 5lbs on the torque and see if it will seal. I will run it through a pressure test if I can put together one from the searches.

[Hrobertson1]

So I got a leak down tester and other than a small leak at the reed gasket it held 8lbs for the 4 hours I had it hooked up. So should I tell the machine shop that did my bore, piston and rings are not right?

[yaegerb]

I would think that something is wrong with the bore. Do you notice any scratch marks or any wear on the four corners of the cylinder? Also, did the machine shop camfer the ports (cut a bevel on the port openings)?

[Hrobertson1]

I don't see any wear marks. I also noticed when I took it apart there was a think layer of oil on the cylinder wall. Shouldn't the rings scrape most off?

Thanks for helping me out

[yaegerb]

I don't see any wear marks. I also noticed when I took it apart there was a think layer of oil on the cylinder wall. Shouldn't the rings scrape most off?

Thanks for helping me out

Yeah, the cylinder should be fairly clean. This is odd. Have you checked the ring gap by putting the rings in the bore and putting a feeler gauge in the gap? Do this and compare to manual specs.

Are the ports chamfered?

[Hrobertson1]

Yea, I am pretty sure its the rings. I took them off to check gap in the cylinder, and they dropped right thru the bore. I am worried about taking it back to the shop, they keep insisting it cant be the bore, and its the bottom end seals.

[yaegerb]

Best advice I can give you is to call, chat and then send the cylinder to either of the people below and let them get the right parts for you.

http://farmandsandtoys.com/ocart2/index.php (jeff is the owner)

http://www.smallenginemachineworks.com/ (john tice is the owner)

[atc300r]

The rings should not drop right threw the cylinder.Check your piston to cylinder clearance should be .002-.004 thousands.Bad or leaking crank seals wouldnt have much of an effect on the compression.

[John Tice]

You’re getting good advice from everyone so far.
Did you check the end gap in the rings? Wiesco has at times put the wrong ring sets in the box. Generally speaking the ring end gap should be .003-.004” per inch of bore diameter.
Is your new cylinder bore job round & straight? The skirt clearance for forged Wiesco pistons is printed on the box; Wiesco piston requires a .002” skirt clearance for a 250cc cylinder,

http://i1152.photobucket.com/albums/p497/johntice1/January%202015/P1011615.jpg (http://s1152.photobucket.com/user/johntice1/media/January%202015/P1011615.jpg.html)
This type of hone mandrel is our ultimate for small engine cylinders.

Many shops use a ball hone for finishing cylinders. Ball hones are great to deburr & champher your ports; but not much more. Other shops use a break cylinder hone. (Egg Beater)
Break cylinder hones have a tendency to snag in ports when in the BDC area of the cylinder on 2 stroke cylinders.

http://i1152.photobucket.com/albums/p497/johntice1/Album-2/P9190423_zps949781ad.jpg (http://s1152.photobucket.com/user/johntice1/media/Album-2/P9190423_zps949781ad.jpg.html)
If your machine shop used an incorrect method of finish honing, the piston may catch the cylinder wall in the BTC area around the transfer port cut outs. We always slide the new piston up & down the finished bore while finish rinsing the bore.

Our finish hone mandrels use a 280 or finer grit stone set. If everything measures out correctly on the cylinder, you’re maximum cranking compression should show up almost immediately.

John Tice
503-593-2908 Alternate 541-508-3944
www.smallenginemachineworks.com & www.nwsleeve.com
Turning Custom Cylinder Sleeves Since 1971
http://forums.everything2stroke.com/threads/49513-How-It-s-Done-Projects-around-the-Shop.com

[Hrobertson1]

Well Its up and running. The shop fixed what ended up being their mistake. Someone at Wiseco got dyslexia and sent the wrong rings with the piston. The shop fixed everything and assembled it on the trike, compression is 160 now. Starts up now with one kick. Quite a bit of smoke now, but I think I went a little heavy with my 32/1 mix. I have done 2, 5 minute idles with a cool down in between, tomorrow I plan on a short ride keeping the rpms down. I want to thank you all for the help and info. I got 2 trikes up and going now :)

[atc300r]

Glad to help.Also glad you didnt give up on it .These aircooled 250Rs are fun to ride.

[jvining]

235455
Love my 82 250R! Like you I also am new to 2 strokes.

[Hrobertson1]

Update! Well I read a few posts and did what I thought was the correct break in. I started and let idle, cool down. Then the next day idle and cool down, both times about 5 minutes. Went for about a 10 minute ride keeping throttle under half, twice with a cool down in between. The second ride though the engine seemed to slow then cut off, like the piston was seizing. I did not try to restart it and got a tow back. Let it cool, then started right up on the first kick and seemed to run great. Every now and then I hear and feel a clunk come from the engine. Is this normal for a new piston, or should I be taking it back to the shop?