RBean

I had a plane that went in full power at steep angle. Buried the nose in the ground. (radio receiver failure). Totaled. Had a G-38 in it. Finally got around to this project. I had a collection of G-38 parts. Sent three crankshafts to Al at BH Hanson. He was able to straighten two of them. Rebuilt engine with new seals, bearings. It had good compression so didn't replace the ring. Wouldn't run at first because of faulty ignition coil. Replace that with one out of my parts collection. After that it started ok and ran smooth. Has good idle at about 1,800 to 1,900 rpm. Good transition. Only thing is it will only turn up 6,100 rpm with 18-10 Xoar two blade. I can lean until it sags and richen high needle until it four cycles, but can't get above 6,100 rpm. Other engines tach as expected so tach is ok. I took off the muffler off and inspected, suspecting an obstruction. None there. It has a new Walbro WT 338. Took it off an looked, no obstructions. Any ideas?

Of note, since I had the parts and another straightened crankshaft, assembled another G-38. New ring, new bearings, new seals. Rebuilt the carb as this one was on the plane that went in. It starts and runs ok. Good idle, good transition. At first top rpm with same 18-10 prop was 6,700 but after two tanks of gas through it, now tops at about 7,050. This is not the advertised rated power with 18-10 prop of 7,300 rpm, but I hope with more running time on the new ring it will come closer.

I think I will take the carb off the second engine and put on the first to see what the result is, other than that don't know what to do. The timing is not adjustable so it's not off. Compression seems good. Better than the one with the new ring.

w8ye

My Feedback: (16)

Put a new ring in the poor running engine.

On a piston ported engine - unless the piston still has all the machining marks on the skirt - replace the piston.

Even though the skirt is smooth. On a G38, they wear the bottom of the piston skirt smoothly right where the carb intake port is in the cylinder wall. Usually we just look for a scored piston to suggest replacement.

RBean

Thanks for the reply. I have a new ring but not a piston. I didn't realize a new piston would make that much difference. I'll order a new piston and see how that does.

Gizmo-RCU

My Feedback: (27)

Just an FYI, advertised specs. and actual performance many times are two different things......go figure

w8ye

My Feedback: (16)

I never seen a G38 turn a regular 18-10 at 7300.They will maybe with a Menz but are more like 7100 with a regular Zoar.

RBean

Yes I also had those thoughts. So turning an Xoar 18-10 at 7,050 rpm should be ok. May even increase with more break in. Advertise and actual can be two different things.

w8ye

My Feedback: (16)

+1

RBean

Just as an experiment, I took carb and plug off good engine and installed on weak one. Didn't make any difference. Total, about 6,000 rpm with the 18-10 prop. So I've ordered a new piston. I'll report back the results.

RBean

I'm reporting back, I ordered and installed a new piston and ring in the weak G-38. After one tank of fuel, it is turning the same 18-10 Xoar two blade prop 7,080 rpm. w8ye, thanks for the help. Both engines are now usable.

w8ye

My Feedback: (16)

That's like it's supposed too.

Enjoy