Tomos A-3 Compression numbers? Gaskets?

Matthew Yeah /

My Tomos A-3 was recently re-honed by a local machine shop. It had be sitting outside exposed for WAY to long, and the upper surface (where the head bolts on) had somewhat rolled at the edge, so the piston couldn't move through the cylinder completely. I purchased a new piston, and had the cylinder rehoned.

I can't seem to find reference to any gaskets for this motor on any website, but I'm starting to think that maybe I'm either missing a gasket, OR the machine shop bored the cylinder too much. My compression numbers are only 90 lbs. Do I need a head and base gasket? If I do, this number will probably go up some.

If not, I'm guessing I need a new cylinder. Does this sound right?

Thanks!

blytz

Re: Tomos A-3 Compression numbers? Gaskets?

See Ya Moped Army /

Only a base gasket. There is no head gasket on a Tomos.

Re: Tomos A-3 Compression numbers? Gaskets?

Don Pflueger /

only a very few tomos engines used a head gasket. and it was only about .002-,002" thick. it wouldnt change your compression at all. sounds like too much material was removed from your cylinder.

Re: Tomos A-3 Compression numbers? Gaskets?

Don Pflueger /

hey larry, i have two tomos heads here from different engines, an a3n and an a35 that each have a gasket. look really close cuz they are so thin they are hard to see and often overlooked. even ike had a hard time believeing it but he found some on a few of his heads too.

Re: Tomos A-3 Compression numbers? Gaskets?

See Ya Moped Army /

I never knew this. I personally have not seen a head gasket on any of my Tomos motors.

Re: Tomos A-3 Compression numbers? Gaskets?

Don Pflueger /

i'll have to send you some pics. like i said, they are hard to see. they are paper tho. and i only found them on the early 90's models of the a3n and a35. no others have them.

Re: Tomos A-3 Compression numbers? Gaskets?

Matthew Yeah /

Thanks donp. The base gasket shouldn't affect compression (I don't think), so I bet that is it.

Actually, you know, I have 2 different cylinders, I think that they both register about the same numbers (it's been several months since I messed with it). If a brand new piston, and 2 different cylinders (one all original) both have the same compression, could I be doing something wrong? Is it possible that the base gasket is indeed causing my problem?

Re: Tomos A-3 Compression numbers? Gaskets?

Base gasket leaking wouldn't change cylinder compression... leaking at the head mating surface or spark plug hole would.

The piston at it's widest part (usually just above the bottom end of the skirt) should be about 0.002" less than the bore. The bore should be straight and perfectly round. Expect pistons to be tapered ovals.

I can't imagine accidentally honing a bore so big that compression suffers. Check your rings and their lands for junk and check the ring gap... some soapy water around the head might reveal bubbles during cranking. If so check mating surfaces for flatness, cracks, defects.. Check the compression gauge for accuracy.

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