Hello,
I purchased some used equipment from a guy who got out of the hobby.With that came two used engines.The one is a Magnum GP 40 & the other is a Magnum pro 25.The 25 was seized up but the 40 had very few runs on it.(the head,case & muffler arent even discolored)I called around to some hobby shops to see if I could get rebuild kits or gaskets for these engines because I wanted to open them up & check the internal condition because neither of these engines were stored with oil in them.I was told that these engines are no longer made & none of the shop could get me parts.The 40 turns over good with good compression & if I didnt know its been stored for 6 years I wouldnt even hesitate to start it up.Any suggestions on what to do , or any information about these two engines would be greatly appreciated. I did take the 25 apart to unseize it.I figured I had nothing to lose so I started it & it runs( kinda runs,but that will be another thread LOL ).I would like to put the 40 on a sig kadet that Im building so I figured Id ask for advice before taking a chance on ruining it.
Thank for any help.

The Magnum GP40 is no longer made. It was made by Thunder Tiger. It's a bushing type trainer engine but was well liked. There's a newer Thunder Tiger GP42 but no parts are interchangeable.

In your efforts to use these engines. Keep your disassembly to a minimum. I would only remove the back plate and inspect for rust. I would immediately put some oil in them. Use Auto Transmission Dexron or Marvel Mystry oil for now for lack of having anything better.

When you are going to run one, try to flush it with fuel right before you run it.

If you tear a backplate gasket, make one from a sheet of paper. If you want a heavy duty one, use a magazine cover page. Cut the big hole. Punch out the screw holes. Mount it all together and trim off the excess paper hanging out beyound the backplate.

Enjoy,

Jim

Thanks for your reply W8YE,
If I pull the back plate off and I do find rust what would you suggest I do? Since it is a bushing engine could I just clean the bushing off with some fine scotchbrite or is there a better method?
Or since this is a brand new airplane that I want to put it in should I just spend the $70-$80 and buy a new engine?
Thank you
Scott

With a bushing engine...there isn't much to rust save for the crank, and I'd be surprised if you found any there. (unless the motor was immersed in salt water before storage)

Sounds like a thorough flushing with fuel would free the motor up nicely and allow you to get it on the bench for some adjustment time.

Like W8YE said...minimize your disassembly. If it isn't broke...don't try to fix it.

Get the motor on the bench and get it running.

Chances are...you're in good shape.

Best of luck to ya.

'Race

The 25 might only be siezed from castor oil sitting in it and turned to a gummy or hard varnish. Brake cleaner dissolves that stuff like nothing. I would say take the back cover off and the head and then spray it into the cylinder from above and below the piston, and onto the conrod bushing and crank bearing. Heat alone may free it up but you need a cleaner/or some fuel to get rid of the gunk. Just make sure when bolting the head back on that you use a sequence like a star pattern as you would when tightening up lug nuts on your vehicle, only tighten them a tiny bit each time doing the sequence many times until they are all a little snug. The bolts don't need to be really cranked on otherwise you risk stripping them out. you want the head to go on flat and not slightly tilted, just take care doing it. I don't hesitate to take any of my engines completely apart including the four strokes, havn't screwed one up yet.

I forgot to add that the key to having an engine run just as good after a teardown as before is to put all parts back exactly as they were. Use a felt pen or something to put alignment marks on parts that fit into each other like the head and cylinder, cylnder and sleeve, piston and sleeve, piston and ring gap.