Large Model Association Forum

Hi,
I bought a used petrol engine a few months ago.
On checking , it has approx 7 thou run out at the prop driver,( measured with an accurate digital DTI) .
Do you think it's had a bump or is this the norm / acceptable ?

Advice appreciated please.

Shaun

More than i would like, but not worth the strip down Shaun, ive seen new engines with more than .1mm at the propdriver, could it have been bumped? maybe, but i dont think it will booger the running up at all, run it, see what is like, i would not strip it down just yet

i m just about to post one back to a guy, the crank was out of line, but it was also bent on the taper part,(yes kieth, it happens) with a new flywheel, best i could get was .015mm, it will run prefectly at this, if you decide to strip it, make sure you give the crank to someone with more than a 3 jaw chuck, and a big hammer, (insert smiley here)

Cheers Al,
I was hoping you would come along...
Thanks for the advice...

Shaun

Hi Shaun, Just noticed your posting - for some reason I missed it on the 30th.

You don't say what type of engine it is however it may run ok but I would do a couple more checks with your clock gauge before you do decide to run it.
Also Zenoah specify max allowable crankshaft run-out at 0.07mm or 3/1000". So at the moment you're more than double this.

Put a spinner back plate on and rotate the c/shaft through 360 degrees and check the back plate at the periphery - both radially and axially. You may find that the run off here is too much, and vibration will cause problems.

You can then ascertain if the run off is caused by the crankshaft, and/or mag flywheel, and/or prop adapter by first removing the prop adapter and checking the flywheel both axially and radially through 360 degrees. Then remove the flywheel and check the crankshaft through 360 degrees with your clock gauge.
Just take care when removing the prop adapter and flywheel and use a puller.

If you do this you'll be a bit wiser before you decide to run the engine as it is.

I can go into a bit more detail with you if you wish to email me.

regards, Ken

Thanks for the advice Ken..
I'll do as suggested re the checks.
Rgds

Shaun