My son has been running his st-15 for almost 2 years now with out a problem, the other day
it refused to start ,new plug gas bat nothing would work.
I kinda think it needs a top end kit but was wondering if anyone has a rule of thumb they go by
as far as compression is concerned.
We installed a long plug without a gasket and it ran for 1 tank and that was it.

Greg

If you can feel compression when you flip it through briskly, they are usually OK.

Enjoy,

Jim

If it's been running fine for 2 years then suddenly not working then there's either something very simple wrong like a flat glow starter or on the last run something drastic happened like too lean and seized, mechanical failure etc. It's possible the head screws have come loose too. My rule of thumb for reasonable compression is to have a little fuel up in the cylinder then with a slow flick the prop should spin fairly quickly past the point where the exhaust port gets opened. An older rule of thumb was that it should hold some compression when held at TDC for about 5 seconds.

When you say it's an st-15 do you mean a Super Tigre G20-15 or maybe G15? If so, these have a cast iron piston so they need a fuel with at least 20% castor. Always use a gasket under the plug though.

It's an st-15 truck with a tower hobbies .15
HAve already ordered a new top end kit for it, the comp was almost nill you can turn it over from the crankshaft with almost no effort.

Thanks for the help
P.S.
Just wondering if a compression gauge is out there somewhere for these motors?

Greg

Hobbico markets two compression gauges. HCAP2600 is for .10 to .60 engines. HCAP2601 is for .60 on up. I bought one when I was just starting out, and never used it much. Flipping the prop through will tell you the same thing. It was suggested here at RCU, that a good way to use them is to check the reading on a new engine, keep this on file, then use it as a benchmark to document wear.