5.8 Precision Eagle motor
 

My son has a 5.8 Precision Eagle motor he got at least 15 years ago. I built a Z P-51 for him with this motor installed. It's got maybe five hours total time on it.

Just for the record these have the Sachs cylinder,piston,Rod and crankshaft. PE made a nice aluminum crankcase. They came with a mechanical spark advance and an electronic ignition. The first failure was the mech advance. We replaced it with a C&H electronic ignition which worked very well.

Within less than an hour of test running the prop hub came loose. It destroyed a new TruTurn 6" scale spinner,prop and prop drive. The aluminum crank hub stripped the key and needless to say it made a mess. PE repaired it by making a new aluminum crank adaptor probably out of 2024 or 7075 aluminum. This lasted about two more hours of testing and tuning. Then it failed the same way again destroying another $200 plus TT spinner and stainless steel prop drive.

All props and spinners were carefully balanced beforevuse. Each were also installed in the same position on the motor. The motor actuall ran pretty well. It would idle down to well under 1000 rpm and would turn 24-12 props over 7500 rpm.

The problem is that the stock crank has only a very small straight diameter and a short taper with a small Woodfruff key. The thread machined on the end is very small too either 8 or 10 mm. There was a special nut and washer supplied by PE. The assembly was carefully torqued with appropriate torque wrench during all assembly work.

The third one lasted a couple hours of testing and looked like it was going to hold up. We were going to go and fly the maiden flight and on warm up it promptly tore up the whole front end again thus time taking the cowl with it. Believe me when I say we very very carefully installed props and hubs. Everything was spotless clean and all nuts and bolts torqued correctly. We both were very disappointed with this motor. At this point the plane was placed in storage.

Please pardon this long story. Well now it's time to either fix this motor or replace it. I've designed a steel hub and aluminum timing ring that is actually lighter than the solid aluminum one. I also did some stress analysis on it. It will be quite expensive to make as it requires some tight tolerances. We can probably buy a DLE or DA motor for about what it will cost for machine work.

So so what do y'all think?....fix or replace?

Get a different engine . . .

+1, three failures is trying to tell you something. I like many of these old engines but some are becoming dated and it does come to a point where it is just not practical to keep them going.

The used Sachs parts probably have some value so you could possibly recover some of your costs.

Sorry to hear of all your problems with this engine. I think we all have gone through something like this.
If you decide to change the engine I would be interested in the old 4.2! I need some Sachs parts.

I've been just sitting back to see what others thought about this motor. It's a nice piece but the stock 5.8 crank simply can't handle the prop. These were industrial equipment motors in stock form with pretty massive flywheels but they were more centrally located than our props allow. Brison eventually made an overhung crankshaft with a better mounting surface but they are long gone.

ive been trying to convince my son to just sell this motor or park it and get a more modern 80-85 motor. Even selling the entire P51 would be better and maybe build a new one around a rear exhaust or an inline twin.

thanks for the input.