Bump without glow plug, is it normal?
 

I have an OS 40LA (from my trainer) which was in a crash from a radio glitch some time ago, it seems to have no damage, actually the crash was no big deal, broken apc prop, bent landing gear, crack in fuse.

After the crash i removed it from the airplane (got it repaired and donated it to the club for the new students who don't have an airplane yet and wanna "taste" the hobby before putting money into it), got it cleaned, oiled and stored

Today i was looking for some stuff and ran into the engine still in its bag, took it out to re-oil it and spin the crankshaft a couple of times

I felt a "bump", like compression but not as "soft" as compression bump, removed the carb and backplate and spin it, the bump is still there, it can't be compression cause it has no plug, carb or backplate

What do you think it is?

RE: Bump without glow plug, is it normal?
 

It could have some of the original "pinch" left in the piston/cyl like it had
when new....or it could have some hidden damage, a piece of foreign
material, or a burr from some damage. Remove the head and see if you
can see anything wrong. ;)

FBD. :D

RE: Bump without glow plug, is it normal?
 

The sleeve are tapered and the piston are tight in TDC, it is normal for ABN, ABC engines. When the engine are running, the sleeve will be more cylindrical.

In case there are crankshaft bended...
Have you tried to rotate the crankshaft without piston/sleeve?

Jens Eirik

RE: Bump without glow plug, is it normal?
 

Thanks Dave, i have the engine dissasembled infront of me, no visible damage or foreign particles, the crankshaft is not visually bent or something like that, but something curious:

It seems like the piston sleeve is "tighter" on the top, cause when the piston goes all the way up, it pushes the sleeve and it pops out about 1 or 2mm, when the piston goes down it pulls the sleeve back in.

What do you think? Do i "break it in"... AGAIN? :)

RE: Bump without glow plug, is it normal?
 

Motorboy:

I think you're right, the crankshaft/piston turns very smoothly without the sleeve, it just feels like the top of the sleeve is tight

So that might be it

RE: Bump without glow plug, is it normal?
 

That's the "pinch"....your engine is still in real good shape. You don't need to
worry about break-in....just run it without over heating it, and it will be fine. ;)

Motorboy had a point....with a crashed engine, you might find a bent crank.

FBD. :D

RE: Bump without glow plug, is it normal?
 

Thanks guys, you solved my life in about 10 minutes :)

I owe you both a beer (as long as it's a Corona :D)

I intend to use this engine in a World Models Extra Sport .32, you think it'll fit?

RE: Bump without glow plug, is it normal?
 

....sure, it will fit....cram that bad boy in there and let 'er rip !! :D

FBD. :D

RE: Bump without glow plug, is it normal?
 

Thanks Dave, let's hope i won't have to post in the crash forum :D

I'll see you around ;)

RE: Bump without glow plug, is it normal?
 

OK, Joe....good luck with the plane....:D

Dave. [sm=thumbup.gif]