Exhaust ports

[Glitch]

Hi,
I was wondering about exhaust port height as a sit there staring at my '87 CR125 because its too muddy to ride, and annoying to clean. I was wondering if you were to lower the height of the port by lets say 1mm, would you have significantly more power at low rpm. I was thinking of taking 24hr epoxy and filling in part of the exhaust port so its shorter, using my old piston as part of the mold, making sure its flush will cylinder wall.
Jim

 

[marcusgunby]

I dont think any epoxy will hold in that area.You need to machine the base of the cylinder-it should make a difference to bottom end power-dont forget the head will need modifying.

 

[Glitch]

Thanks marcus. I don't really want to mess around with getting the cylinder machined and stuff. Just something to do in my spare time so that I dont bore myself to death. Lets say I did use epoxy to lower it 1mm or so. Would I have to worry about it coming loose and coming in contact with the piston, or would it just shatter and do nothing, or blow out the exhaust.

 

[jmics19067]

any or all of the above?

 

[marcusgunby]

It propably would just blow out the exhaust port but i wouldnt like to take bests on it.If it did get stuck somewhere it will take alot of work to strip the engine down.How about trying a cometic thin base gasket-or even better get some really thin paper and make a gasket.You will need to double the head gaskets-you should aim for a gap of 1mm from the piston to the head.Use a piece of plumbers solder and place it down the spark plug hole-make sure the solder is 90 degrees to the exhaust port, kick it over and then measure the squashed solder thickness.

 

[jmics19067]

Use a piece of plumbers solder and place it down the spark plug hole-make sure the

wow I like that idea :worship:

 

[marcusgunby]

Its a old trick passed down the generations:)

 

[jmics19067]

sounds like it is a lot easier to measure than clay

 

[Glitch]

Awesome, thanks alot marcus.