Hi,
I got an old OS 120 Surpass pumped engine from a local swap meet recently, and I noticed a very faint hairline crack between the rear cover to the the rear engine mounting hole. The crack is very faint, appearing more like a surface scratch than a crack.
I am wondering if a crack in 4 stroke engine case is as important as in
The crack is important because it was CAUSED by something. Usually a crash or failed bearings. In either case, there was likely other damage. Dismantle the engine and make sure every other part is OK, then replace the case.
This would never have happened if you had an electric motor to begin with!
(gravy suit on)
A smack in the ground that would crack one of those tanks would destroy an electric.
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You are 1/2 right. Lots of other things (armatures, gear boxes and the like) WOULD have been broken when the power plant leads the way to the ground.
Don't be too sure. Electric motors are TOUGH. Generally the gearbox takes the brunt.
Ok, shafts bend, but can be straightened.
Ot just by a new one. Can motors are Cheap. Its the packs you have to protect...
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All the inane electric comments aside, The answer to youe question is adefinite maybe. Try running the engine on a test stand. Is it is a leak in the same chamber as teh crankcase vent, it will probably be no problem. Measure it before you run it and again after a few runs and see if it extends. If it is interfering with the running, look around for a repalcement crankcase. I had an OS 90 4 stroke that was a remake of two dead engines. Ran it for about a year on my Tiger 60.
Good luck, let us all know if & how it runs. Andy
We can make a box of wood.....FLY!!
I took it apart and and checked the crank runout with a dial indicator, and it was running true, so I ran it yesterday. It seemed to run fine. The compression of the engine seemed to be as good as my other 120 Surpass engines I have. I did not think the crack on the bottom of the crankcase was all that important, sicne the crankcase was vented to atmosphere anyway.
.I thought the hairline crack might not be from a crash, but perhaps from metal fatigue.
I got the engine and mount for ~$100, mainly for the parts in the pump, as they are virtually impossible to get from Tower or OS. But If I am convinced the engine is reliable after a few more runs, I might install it in my GP Gee Bee and fly it!
Suppose the crankcase fails in flight. Is it worth the risk? I would just get another crankcase amd make one GOOD engine with it.
WHAT? And take all the risk, er fun out of it?
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