Author Topic: Compression Question (Read 804 times)

Joseph Lijoi · « **on:** July 11, 2013, 10:38:45 AM »

I have a used FP 20 with a steel piston and liner. The previous owner used castor fuel so it was difficult to turn over. I cleaned it with methanol/after run oil without taking it apart. The result was a nice healthy pop when I turned it over with a prop on it, however when I grab the thrust washer between my thumb and forefinger and slowly turn it over I can get it past TDC with quite a bit of resistance. Is this engine worn out or is this normal for a well broken in engine of this type.

RandySmith · « **Reply #1 on:** July 11, 2013, 01:11:59 PM »

"I can get it past TDC with quite a bit of resistance "

Hi
If it has a good pop over TDC and the above statement is true the engine should be OK

Randy

Dennis Toth · « **Reply #2 on:** July 13, 2013, 10:02:51 AM »

Joseph,
One thing you should check is the wrist pin/connecting rod area to make sure that the connecting rod is able to move on the wrist pin. Sometimes if a motor has had dried castor in it the wrist pin can be locked to the conrod and will rotate in the piston, which will cause lots of wear. To check it, remove the backplate, rotate the shaft to bottom center, at this point you should have good access to the conrod. Then grab the rod and try to slide it in and out. If it moves you should be good to go. If it is locked used a heat gun to warm the inside of the piston/wrist pin/ conrod. This will generally loosen it, put some afterrun oil on it and button her up. If after a couple try's with heat if it is still locked you may need to disassemble it or send it to one of the engine guys for proper cleaning.

Best, DennisT

frank mccune · « **Reply #3 on:** July 14, 2013, 06:32:11 AM »

Hello Dennis:

Are you sure that a wrist pin can be moved in and out? Aren't the held in place by a circlip, end pads or some type of tapered hole in the piston? What type of tool can I use to grab onto the wrist pin when just the backplate has been removed?

I worked on a Fox.35 that had been put in an attic 30 years ago without having anything done to it after it had been run. The wrist pin-con rod was stuck and I used a carrage bolt to get the rod to move on the wrist pin. I could not move it much, but I did get it to move. I have not run this engine since 'cleaning" it but it the conrod-wrist pin junction has been slathered in a penetrating oil. I used a bit of heat and penetrating oil to break these two parts loose.

Oh yes, how does one remove the wrist pin from a "stuck" engine via the hole in the back of the case ? Lol I hope that I never have to attempt this feat!
Stay well,

Frank

Dennis Toth · « **Reply #4 on:** July 15, 2013, 02:38:10 PM »

Frank,
Sorry if I was not clear, what you are trying to check is that the con rod moves along the wrist pin in the piston. The wrist pin should also be free to rotate not move in and out on most engines because of the keeper clips or end pads. Sounds like the heat and penetrating oil did the trick. On one of my old Foxes I had to pull the sleeve and piston then remove the X#@! keeper clips (tip - do this in a zip lock sandwich bag to not loose the clips), then heat and tap the wrist pin out. After cleaning off the baked on castor it all went back together and works fine.

Best, DennisT

Author Topic: Compression Question (Read 804 times)

Joseph Lijoi

Compression Question

RandySmith

Re: Compression Question

Dennis Toth

Re: Compression Question

frank mccune

Re: Compression Question

Dennis Toth

Re: Compression Question