rvd

After my last post where I advised against grinding the inside of an engine I was accused of being somewhat trivial. Now, here we have somebody who actually wants to attack the inside of his engine with a grinder. The original suggestion to grind the crankshaft was to make it lighter. Where to grind was rather vague, whether any balance or strength was affected was such a trivial matter that was not worth mentioning I suppose.

Most crankshafts are made from tensile steel that has been case hardened. Case hardening results in a hard outer skin (Case) for wear restistance and bearing surfaces. The inner core is softer and tough, to prevent the end from snapping off every time you hit the ground. If you start grinding away somewhere you will remove some of the hard skin. It is quite likely you will have localy weakened areas. By removing material You will also have affected whatever balance the crankshaft may have had. You are attempting to increase the RPM remember which will emphasise this condition

The inlet and exhaust openings on a two stroke can be compared to the valves on a four stroke. They are never open at the same time. If you grind the leading edge of the window in the shaft the intake is now opening sooner. Grinding the trailing edge will keep the intake open longer. It follows that if too much is ground off the window will still be open when the piston is on it's down stroke. This will result in fuel being blown out of the venturi rather then sucked in. Hardly a performance booster. The window creates a weak point in the shaft (One of the drawbacks of F.I. engines) opening it up does not improve this situation.

If you are new to engine rework I would suggest the following

If you have a good medium performance engine, leave it alone.

If you want a high performance engine then buy one of the many available similar to the one you alredy have and compare the differences.

If you realy must experiment, and who does not, collect a whole pile of junkers and go to it.

I realise this post was rather long winded and, no doubt, I will be accused of spending too much time on a trivial matter, but you did ask for help.

Ed S