How far can the Cylinder base be shaved?

[thumper135]

no mr. here, i wish...

it´s pretty consensual from some 50 years that mirror finished ports don´t work. they are better finished smooth, but not polished. from my point of view it´s worse on four strokes but it´s really a "no no"! :nod:

thats the first cylinder i heard of ring gap pass a port. i´ve seen ring gap on exhaust side but not right on a port...

the squish clearance is mostly based on squish velocity. if you don´t have the means or knowlege to calculate it the best way to get around the problem is to get the compression ratio right. if you really want to go on squish clearance and forget CR, 1,5mm is a good start, i assume, for that engine.

I'm sorry I meant i got the ports cleaned up since there was loads of carbon build up on it, no polishing was done apart from fixing the downward angle.

the stock piston with the stock cylinder had ring gap ends going in the intake ports too.. maybe nowadays ring manufacturers use angles on the rings that don't risk them catching in the ports?

thanks for all the help :-)

 

[thumper135]

Update

So now have over 1,000 miles on this engine with no issues what so ever, despite both the ring end pins lining up in the ports. :cool:

So now I have another engine being rebuilt with the same piston, Should I go with the same 2mm cylinder base shave as was done on this engine or would you guys suggest anything different this time?

 

[helio lucas]

great news!!!! :cool:

well, if you have easy access to parts and engines you may want to build the new engine with another spec. more top end. or even more torque to make it a fun play machine.
just a idea... :debil:

 

[thumper135]

great news!!!! :cool:

well, if you have easy access to parts and engines you may want to build the new engine with another spec. more top end. or even more torque to make it a fun play machine.
just a idea... :debil:

parts, this is the only piston that I can use, infact the bore is ready, only thing needed to be done is the shaving, shave it from the cylinder base or top? or both? approximately 2mm is what needs to be shaved.

I'll do whatever you tell me to do, trust me. :nod:

 

[helio lucas]

thumper, if you have the oportunity check the wear of the ring and piston near the place where the ring pass the port...

i am not im position to tell what to do, hope you understant. i can only do my best to answer your questions :cool:

if you want to shave the top to get more top end power you have to be sure that the distance between the top of exhaust port and TDC is not smaller than half the stroke. also the tranfers should not have less than 3\4 of piston stroke between the top of the port and TDC.
this is the ABSOLUTE maximum before the spec fall down in wild timing (do not increase power or torque, just make the engine agressive) with out some serious equipment and knowlege to fine tune the engine.
you really want to get some 2 or 3mm less than this.

hope it helps :blah: