Are you referring to the TAPERED COLLET ? If the ends of the split meet before the collet takes up all the clearance on the shaft it will slip. If the taper or the tapered bore are worn it can also be a source of slippiing. Take it apart ,look it over real well and get an understanding of it's function and you should be able to come up with a proper fix. Good Luck,LF

Since this is a continuous problem...(you indicate it "keeps slipping" Tried a new one with same results?)

Possibably something is wrong with the machining of the crankshaft. The work around is to take a file and make the split in the tapered "collet" wider, allowing it to seat better around the crankshaft.

The taper inside the "flywheel" (thrust washer) could be machined too large (OPPOSITE PROBLEM from above!) The fix here is one or more of: 1) replace the thrust washer. 2) file off the top (narrow end) of the tapered insert. 3) put a shim washer (usually a glow plug washer fits smaller engine crankshafts for this) on before the tapered piece.

If you don't know if its the taper not gripping the crankshaft or not gripping the thrust washer.. stick the glow plug washer on before the taper insert... you'll know right away. (assumes the crankshaft isn't tapered... and has a definitive step in size that the taper piece rests against.)

This is a car engine ,right ?

Doesn't matter if its a car engine or an aircraft engine or a boat engine. If the taper insert between the crankshaft and the trust washer/flywheel is bad... the same fix works.

Note that if its the taper needing the gap to be filed open slightly... you may need to then correct the fit to the flywheel/thrust washer, as narrowing the inner dia when compressed will also narrow the outer dia and might make it no longer grip there. (which is a good reason to try a new taper insert...)

I was asking crazy racer if it was a car engine. It may not matter to you,but you MAY be missing something . Thanks anyhow.