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how can I increase compression ... Answered

How can I increase compression  in a small (5-10 hp) engine without buying a new piston or head?



8 years ago

There are some oil additives that you can buy that will help compression, STP comes to mind, but there are many others on the market.  Just check the motor oil section at any of the automotive supply dealers, Pep Boys, etc.
Don't expect miracles though, if the rings are bad, sooner or later, they're going to have to be replaced.

the rings are good, it has good compression (for a lawnmower) already, but i want to try to convert it to kerosene or even diesel, i know it can be done, and i know it may be difficult...
 I have an aluminum head so i cant weld anything to it, it IS a flathead though so i may be able to make a new one out of steel?
I had the idea i could weld some finder washers to the head but seems how it's aluminum that would be a little hard, that's why i was wondering if i could make a head out of steel
 if i can make this work i will surely make an instructable on it

The is engine a tacmsech  6.5 hp

 If you're talking about some kind of typical Briggs and Stratton (or similar) motor for a go-kart or minibike, to get more HP out of it, they're pretty basic engines. You could (potentially) weld thin filler plates (fender washers?) to the underside of the head, as long as you absolutely prevent any collisions with the piston when it's running.

Aside from that, you can adjust or replace the cam or valves to remove any gaps during the compression stroke.

These ideas are best taken with a few grains of salt, as the potential for mechanical damage and even injury does exist.

since we dont know why you want to do this it is a little tricky to answer !

If it is a repair ,  you already have some good answers ,  If you are tryin' to boost performance you can shave th' heads or th' deck to reduce th' combustion chamber size !

Be cautious ,  if this is a lawnmower engine ,  that little aluminum connecting rod wont take much  abuse at all

A ring job and a valve job would get the compression back up to where it should be.  If you do the work yourself these are not very expensive.

Back in the olden days of cast iron flat heads races used to add metal in the combustion chamber of the head and grind it smooth.  That would increase the compression.  That might not work on a modern engine with a shaped combustion dome.

.  The only thing I can think of is using a thinner head gasket.

You're asking how to change the physical structure of the engine without changing it... For what purpose? - Maybe you want to do something else instead like changing the fuel / air / exhaust?