I ran my Poulan 305 Pro for the first time yesterday and it ran fine, but it seems to develop a lot of play in the crankshaft bearings after it warms up. The play seems to go away again when the engine cools down. These are new main bearings that I got from Poulan. Could it be they are not a quality bearing? Would replacing them with a ball bearing of higher quality be a cure for this problem? The bearings fit tight on the crank and I used bearing mount in the case recess as I thought the fit was a little loose. I have not run across this problem before. Any ideas, guys? Thanks

There's two kinds of bearings in some of these. There is the kind with a seperate outer seal and then there's the kind with the extra seal made onto the bearing. According to what I've read in the manual, they are not interchangeable in a case?

Jim

Why do you think its a problem? Does anything negative happen in the way it runs over a period of a tank full of run time? For whatever reason there seems to be a number of people running converted engines and they think they find wobbles or hear pings yet cant find complaint with the way it revs a prop. If the motor starts up and turns a prop with authority then try not to look too hard for problems that dont seem to effect the power the motor is already making. Piper

The engine has seperate bearings and seals. I used direct replacement parts. I do not know if this is a real problem or not. My other conversion engines, mostly Stihl chainsaws, do not show this trait. I guess that is why I am seeking opinions. The engine runs fine and I have put several tank fulls through it. It just rattles at idle when it is warmed up and you can move the crank up and down more when it is warm than when it is cold. If I thought a different set of bearings would cure this, I might just change them again. I guess I could just run it like this, but am a little dissapointed after replacing everything but the crank assembly.

So long as there is no vacum leak past the bearings or anything else adverse going on just run it as is. Some engines run well with strange tolerances like that. It just might be built in for some reason. Each engine is its own beast and it sounds like you got it running strong so I'd just go with it. Piper

I'm thinking that if the play is the bearings in their crankcase fit, that eventually it will hammer out the crankcase. I would check closely to see if this is the problem. The bearings should be a pretty snug fit in the crankcase, bordering on being a press fit I would think. Or does this engine split the crankcase halves in two horizontally above and below the bearings like the 33 to 46cc Poulans?

Good luck,
AV8TOR

The engine splits verticaly and not like the newer generation of Poulans. The bearing on the mag end was too easy to slip into the case, so I used green loctite to secure it. It was the only cure for the loose fit that I could think of. I do not know if the gasoline will wash the loctite out or not. Even if it did I would not think it would do so in just a few minutes of running as the looseness in the crankshaft showed up as soon as the engine warmed up on the very first run. I am thinking I should tear it down again and see if I can find a problem. If the bearings are still tight in the case, then it would indicate increased play in the bearings when warm. Does anyone know how to pull a seal without damaging it? If I pull the seals I could see if the bearing moves in the case. If the bearing is loose in the case, then what? Is there a cure other than a new case?

Clean the bearing outside diameter and the crankcase with acetone, and install the bearing with a thin coat of JB WELD glue. Let it set up overnight, and have at it. I've seen JB WELD used to install cylinder sleeves in full size engines, so I'm sure it would hold. The engine will probably last forever and ever in an airplane, so don't worry about future changes of the bearing. Do check the bearing closely to see that it doesn't have any unwarranted internal play, and that it is a nice snug fit on the crank, but from what you describe it is loose in the case. When the engine warms up, the aluminum expands more than the steel bearing, and it gets looser. Also, it is fairly doubtful that you will get the seal out without damaging it. The seal is critical, as if it leaks air, it will lean the engine out. (NOT GOOD!)

Good Luck,
AV8TOR

easy fix shim the crank at the rear bearing must be caerful not to shim too much and get it too tight some of the poulans I have done had extra end play it doesn't take much kenneth

Thanks guys!! I will tear it down and check the bearings and endplay again. I may just replace the bearings with a better brand. They are not that expensive and as long as it is apart may just as well do it. I appreciate your input.