Al T

Dave
I have A YS engine with the performance upgrade, Shadel Piston and liner. It's mounted in an Xcell Se. About 200 plus flights on the engine. I never did a runout on it bcause it has the uniball clutch and self aligning hub to the engine with the tappered collars (maybe I should have). Anyhow, I had to drop the engine out and decided to dial indicate the hub. I'm getting about 10th runout at tdc. where the piston and liner have the interference fit. Is this normal or is there a problem with a worn bearing or something? Is there anything else I should be looking for?

Al

Dave Shadel

Where are you checking the runout? If it's .010" just in front of the front bearing, you have a big problem. Were you having problems with the operation of your heli before you pulled it apart? If not, I would not worry about it, but since it's apart it's easy to put a new set of bearings in it. Cheap insurance!
Dave

Al T

Dave
The readings on the runout are being taken at the hub, after the cooling fan which would be equivalent to being at the end of the threaded portion of the crank shaft. I have not figured out how to position the dial indicator on the shaft at the front bearing or how I can turn it over by hand with the fan assembly off(It's a good interference fit at TDC so you can't turn it by hand but I guess I could put a nut on the crank shaft). SO what should the runout be at that point? Bearings replacement, pobably best to do both front and back at the same time?
Thank you in advance for your reply

Al

Dave Shadel

It's difficult to know whether you are measuring actual runout or a combination of tolerances. The part that the dial indicator is bearing on may be out of round, it may not be concentric with the shaft. Normal runout on the shaft should be near zero, by itself. If you install it in a case with bearings, .002" would be good. If you are going to replace the bearings, do both.

Good Luck,
Dave