Magnum .61 RFS bottom end running temperature?
 

Hi,
I have a new Magnum .61 RFS 4 stroke. This is my first 4 stroke. Other than running it on the bench for about two tanks, the engine has not been used. I have installed it in a 1/5 scale cub. This afternoon I ran it for the first time in this airframe without the cowl on. I noticed after running that the bottom end of the crank case was quite hot. Not as hot as the head but almost. My other engines run with the bottom end nearly cool to the touch. Should I be concerned? I noticed the heat while running it the first couple of times and thought that it was just because it was new. I took off the back plate and everything looks normal. The crank also turns freely so the bearings seem fine. Any opinions?

RE: Magnum .61 RFS bottom end running temperature?
 

If the back plate inside or the crankcase inside has no rubbing marks from the connecting rod, it should be OK.

RE: Magnum .61 RFS bottom end running temperature?
 

The backplate only shows slight rubbing from the conrod, but barely enough to polish the aluminium, and about the same as i have seen on other engines. Except for rubbing, what could be the cause? I was thinking maybe I'm used to 2 strokes and this is a 4 stroke quirk? what should the temp be on a properly running and setup 4 stroke?

RE: Magnum .61 RFS bottom end running temperature?
 

How does the prop feel when you turn it. Is it stiff or free except for the compression of the cylinder?

RE: Magnum .61 RFS bottom end running temperature?
 

It is very smooth and free. I've looked for everything I could think of short of taking the engine apart.

RE: Magnum .61 RFS bottom end running temperature?
 

When you feel of the crankcase, you almost have to do it while the engine is running or the second you shut it down. Otherwise the heat will travel all over the engine and the crankcase will reflect more of the cylinder temperature. Even then you cannot hold your finger on it but a second.

I would say your engine is just fine. It is just your awareness of temperatures and concern for your engine which is good.

RE: Magnum .61 RFS bottom end running temperature?
 

All four strokes run with a fairly hot crankcase. If your other engines have been two stroke, yes the crankcase runs much cooler. Most of the evaporation of methanol takes place in the crankcase of a two stroke.

RE: Magnum .61 RFS bottom end running temperature?
 

You see, you're never too old to learn. I think I am just being paranoid. I will keep an eye on it but like you said, it is probably normal. Thanks guys for the insight and quick answers.