Re-surface cylinder head for more compression?

[fairracing31]

I used to re-surface my cylinder heads on my dirt bikes and quads when I was a teenager to bump up compression. It really helps on low and mid range on the powerband. Has anybody done it on a chinese motor? I'm afraid to try it, I'm not sure these motors can handle it.

 

[Herrmanator8]

i would say no...we have a few polaris snowmobiles and the heads have been shaved by a professional, it works great i must admit, but if its not done by a professional and its not precisionly flat, if it is somewhat on and angle, it will lose compression. too much compression is bad for these tiny putt putt motors, theyhave thin walls which only have a thin chrome layer then cast iron, the engine is so small that the pressure will cause extreme wear and will dramatically reduce the life of the engine.

but, maybe you should refer to a professional. i would not recommend it, i think it would risk the life of your engine. cool ideal though.

jon

 

[fairracing31]

My uncle owns a machine shop, so thats no problem. I've never been inside my motor yet so I have not seen how well its built internally. If its anything like the outside No way will I try it.

 

[andyinchville1]

HI,

I like the idea of a little boost in performance So I am just curious but does anybody have any idea what the compression ration of a stock 70 CC engine is?

I have heard that when an automotive engine has its compression raised, that only a very minute amount of material is actually removed...Any Idea on how much material would have to be removed from the head to increase the compression ratio by 1 point....(probably mere thousandths of an inch I would imagine?)....and if the head is made of as soft a material as the motor mounts I would imagine it would be fairly easy to shave off using some fine grit sandpaper attached to a smooth level piece of glass?.

Thanks

Andrew

 

[fairracing31]

I used to use a file and a straight edge, but dont do it!! I did that when I could not get to the shop, Take it to a machine shop, must shops will do it between $45-75. You have to mesure between the head and piston to see how much you could take off, its usually a few thousands of a inch. A good machine shop can help you with that. We do it all the time for are race cars, but we take it right to the edge, on our race motors we take out alot depending on how we want to tune the motor.

 

[rcjunkie]

You can shave off up to 12 thousanths of an inch on the head. To play it safe, try 10 thousanths first.

Engine compression ratio is about 6.5:1 or so.

 

[srdavo]

You can shave off up to 12 thousanths of an inch on the head. To play it safe, try 10 thousanths first.

Engine compression ratio is about 6.5:1 or so.

can you estimate what 12 thousanths, shaved off, would do to the compression ratio?

 

[gone_fishin]

start here and figure it out for us: http://www.nightrider.com/biketech/calc_displacement.htm

 

[srdavo]

start here and figure it out for us: http://www.nightrider.com/biketech/calc_displacement.htm

homework? lol

 

[fairracing31]

Sorry guy's, leaving for Mexico tonight for my race Saturday. Dont have enough time, be back somtime next week. Will be happy to have all that info for you when I get back.