I just taxid my plane the other day, and ran it at a low RPM, and I forgot to do a run up at the end to clear out the engine, and now it's hydrolic locked, it wont turn easily, and i can't get it started. I already took out the glow plug, put some fresh fuel in, turned it upside down and turned the prop (that normally works) but it didn't this time. I then took it to the LHS, and we took the engine apart, and cleaned up all the castrol oil gum, but whe we put it back together (we did everything right) as soon as I'd put the glow plug back in it still is stiff, it's better, but still locked. HELP!

Some info first. Is the engine fully broken in, or is it still new? And is it an ABC engine or ringed? I'm guessing that it's different now than it was before you taxied the plane around.
Engines don't hydro lock while they're running. That happens while you're trying to prime them. And unless you put the starter to your engine while it's hydro locked you won't hurt anything. Once you clear it up, there are no lasting effects (unless you did damage with the starter)
If I had to just guess, and I do, I would say you ran it lean. You should ahve seen some indications of it, though, when you dissassembled your engine. It might just be a combo of a new engine, good compression, and if the LHS assembled it with oil, that will have the affect of boosting yoru compression and make the engine very hard to turn over.

Does it turn with the glow plug out at all? If it gets tough with the plug in, chances are there's just excess oil on the top end, turn it over a bunch of times with teh plug out and see if that makes it better.

Let us know!

Andy

A hydro locked engine is when the combustion area is full of fluid and will not turn over because you can not compress a fluid, sounds to me like your there is something in the squish area in the combustion chamber not allowing it to go up to top dead center but if it turns completly over without the glow plug then it might be your glow plug hitting piston.

Right. If the engine was hydro-locked you wouldn't be able to turn it over. When the piston got to top dead center it wouldn't go any further. (Because the liquid in the combustion chamber will not compress.)

Stopping the engine after running it at idle (for any amount of time) then stopping it, will NOT result in a hydro locked engine, that only happens when you're priming the engine before it's running, so something else is going on.

We need more info to help, but I'm thinking that if it's a new(ish) ABC engine, then it's just tight (as it should be).
Dennis-

If it turned over fine before you ran it....and you cant start it now but could then...then you have done damage to the engine, bent rod ,wrist pin... scored cylinder walls or piston ......or a combination of them...sorry dude ,you may be able to replace just those damaged parts and not need a whole new engine...Rog

I agree with DBCherry... no way you can hydrolock that engine once it's fired up. However, as twostroke said, if you did score the lining or whatever else, it wouldn't matter if the glow plug is in or not. Is the engine "locked" when the glow plug is in? That would be useful info.

Honestly, it sounds to me like you have a really good ABC engine. ABC engines naturally have a very very VERY tight fit between the piston and liner at top-dead-center (TDC). The liner tapers down, and is actually a bit smaller at the top of the stroke than the piston is round. If the piston gets up there, it can be really hard to get this piston back down. THIS IS A GOOD THING, nothing is wrong with the engine. It's designed this way, really.

You should be able to free the engine up by grabbing the end of the prop in one hand, and something solid, the engine, or something like that iwth the other, and turn it. You'll never be able to turn it over any other way.

When the engine runs, the liner heats up and expands, creating the proper fit between the piston and liner, but when the engine is cold, you get this kind of effect. Once the engine has been run for a little bit, this will go (mostly) away as the parts wear a little.

my engine is OLD, like as in 12 years old 40 FP engine. The Piston didn't show signs of scoring, and isn't hitting the glow plug. But I cleaned it up, got some castrol gum out of it, cranked it with the glow plug out, and as soon as I finish my new engine mount (I make em out of plywood, but the keep breaking) I'm putting it back in and trying again, although I'm still not exactly sure what's going down

Well, because it's an older FP, a very good engine by the way, then it sounds like you bent somehing. Either the con rod or the crank.
Dennis-

Hi Walter,
The OS 40 FP was a economy engine that many flyers grew up on . Its a ABC (Aluminum,Brass,Chrome) type with out bearings. We used to say--FP meant Front Plain . After a day of flying ,I always take out the glow plug ,and put some after run oil in the motor. Looks like Automatic transmission oil (ATF).Put the whole front of the plane in a freezer bag ,or large plastic bag,with a wing hold down rubber band to keep it attached. Catches the oil that seeps out. Will also keep your mother happy.
If your engine is really gummed up--Find a old used crock pot . Fill it half full with car antifreeze (50/50 mix-1/2 half antifreeze-1/2 water).Put your motor in it ,turn on -plug in the crock pot ,and slow cook your motor for about 8 hours.This will dissolve all the gum,rust ,and make the motor look like brand new. COMPLETELY take the whole motor apart ,and wash in dish soap water,rinse,dry,then oil the motor with WD-40,or any good lite weight oil. Reassemble the motor,put in a new glow plug ,fresh fuel.I would bench run the motor. allow it to get nice and warm . Try to avoid running it lean. Peak the motor out -Hi speed ,then richen it by 1/4 turn of the needle valve. reinstall it in the plane ,and it should be fine--good luck--hope this helps you out some ......Amelia