Engine problem: need diagnosis help

[Chevy454]

Little bro was riding his newly acquired 250R last night, and he said it all of a sudden *died*...never could get it to restart. We figured it was a plug, so we hauled it back to the shop...but the plug looked decent, but we installed a new one just in case. Still no go, and it didn't seem to be drawing any fuel...pulled the carb, cleaned it all out, and still no fuel being drawn...but, we went ahead and did a compression test, and it's way, way down...like down to ~60psi.

My question is, will it need to draw fuel (and I guess oil) to seal the rings, or is that still too low even for that scenario? I understand a 2-stroke relies on some sealing to get the vacuum to draw the fuel, so is this a "chickin or the egg" kinda deal? Can I do it like my 4-cylinder and put a couple drops of oil to see if the rings will seal? It turns over, so he didn't stick a piston...maybe a ring? Or could we have popped a head (or base?) gasket? This thing has a big bore kit in it...how tough is it gonna be to get gaskets?

Any/all help is appreciated, as he has a race tomorrow...!

[Tom TRX250R]

That low of compression is way too low. The compression should be at least 170lbs. so he needs to tear the top end off and have it bored and new pistion kit put in it. It should cost about $175 after boring, piston kit, and gasket kit. To answer your other question it should be really easy to get a gasket kit for the big bore. If he has an aftermarket top end then I would go through the company to buy gaskets. If it is a stock cylinder with a big bore sleeve then you should be able to get it from any local race shop or any reputable motor builder such as ESR or LRD. Good luck!

[wilkin250r]

I'll tell you right now, he's probably not racing tomorrow.

There are several things that can go wrong even with a simple compression test, so the first thing is to make sure your test is accurate. You kicked several times, until the guage stopped moving? Throttle wide open? Guage in good shape?


You can certainly do like your 4-stroke and put a little oil in to seal the rings, but I bet it doesn't make much difference. If it was running decent, then died, the rings should be sealing well enough to get more than 60psi.

The "some sealing to get the vacuum to draw the fuel" is to draw fuel into the crankcase, and pressurize it to send it into the cylinder. It doesn't have anything at all to do with the compression of the motor.

Sounds like it needs a top-end rebuild.

[Chevy454]

Ok...stopped by on my lunch hour, and put a couple squirts of oil in it, and gave it a few whirls...was int he 150 neighborhood, which is better, but not stellar by any means. We tried 2 guages, a Snap-On and a Mac...both within a couple pounds...choke open, throttle pegged, 4-6 kicks.

I noticed it's a tad wet underneath...would the base gasket allow enough pressure to get by to keep the rings from sealing?

[Tom TRX250R]

If he is intent on racing tomorrow I would tell him to pull the head off and split the stock head gasket (3 pcs.) And use one of the outside pieces. It is the same size as a CR head gasket which should bump up the compression about 15-20 lbs. which should give him enough to ride tomorrow.

[wilkin250r]

No, the base gasket would have NO effect on engine compression reading.

[Chevy454]

Got the top end torn down...both rings are stuck, and there are a few aluminum bits on top of the piston. Also, the piston and cylinder walls are scuffed just a bit above the upper *outer* corners exhaust ports...is that normal? Probably from being a hot spot? Anyway, looks like *at least* a new piston/rings are in our immediate future...

Also, one gentleman we talked to told us that the aluminum shavings are more than liking from the rod bearing (cage bearings?)...said that's pretty common on big bore/stroke engines like ours (330)? That sound right??

Anyway, THANK YOU for the help, y'all...and I gotta send a shout out to http://www.totalperformance-llc.com for the great help over the phone...