Date: Sun, 30 Apr 2000 13:19:12
Subject: Re: 1991 Tomos Bullet TT head gasket
From: Hans Hartman
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Hello Mike, fellow mopedeers,
At 10:28 29-4-00 -0700, you wrote:

>Does anyone know if a 1991 Tomos Bullet TT has a head gasket? i took the
>head off because i felt i wasn't gettin good compression only to find no
>head gasket. Spark is good, carb is clean, timing is good.

Tomos didn't use head gaskets on most of their models. The combination of
an alloy head and cast iron cylinder works fine.
If the moped was losing compression, you'd hear that, and you'll see a
black spot on the cylinderhead where it leaked air.
Use a piece of sandpaper (<180) on a flat surface (a piece of glass or a
mirror) and grind the head until the black spots are gone. And don't forget
to clean the cylinder surface too with the same sandpaper (no need for
removal, just be sure to clean well around the cylinder studs)

In another posting of yours, I read that the moped didn't perform very well.
Check your exhaust pipe first for heavy carbon deposits. While you have the
head removed, check the outlet port of the cylinder too, I have seen them
with just an 8mm-hole left in them.
When I read your story, there are a few possibilities:

1: Clogged cylinder/exhaust; clean exhaust pipe, scrape the carbon out of
the outlet port.
In most cases, these problems arise due to two faults; too much oil in the
mixture (should be 2 percent) or a leaking oil-seal on the right side of
the crankshaft.

2: In some cases, the piston rings get stuck in their spleens, and it
looses compression that way. This problem is typical for too much oil too.

3: A leaking reed-valve; these were of poor quality in some years, (was it
1991-93?) the rubber gets thick, thus opening the reed-valve, which should
be closed.
Remove the valve, and hold it to the light. If you can see some light
between the seat and the valve, throw it away and replace it.
4: Worn cylinder, piston and/or rings; replace.

Tomos cylinders are very good, if this is the first time it doesn't perform
very well, you could replace only the piston.
You can determine pretty easy if the cylinder is worn or not; just scratch
your nail in the cylinder top, if you feel a significant edge, it is worn
and needs an oversize piston and rebored cylinder.

Hope this helps,


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