O.S. 20FP/25FP Parts Swap??

I need a favor from someone who has actually converted an 20FP to an 25FP. Or the other way 'round, of course.

It has been claimed to me that with the appropriate piston/cylinder set, head and gasket set, this is a simple remove-and-replace operation.

Confirmation or refutation of this is needed.

And I will kick in with information in return:

Those 2.5mm cap screws used to retain rear cover on these engines can be really hard to locate. Try a Du-Bro metric fasteners rack at Local Hobby, the selection is complete enough to offer standard-length back door screws or slightly longer screws to use in attaching bracketry for a remote.

The screws retaining stock mufflers on these engines will sometimes back out, at least I have seen this happen on RC models. To the point some will use a thread-locking compound. While at the Du-Bro rack pick out a pack of 3mm x 30mm cap screws. They seem to be harder, plus one can cinch 'em down a little better.

Might also want to get some 4mm flat washers, if using ST, PA or J&J Sales NVAs they work nicely in centering fuel outlet in venturi.

Thanks,

Your right about the muffler always comming loose. and the ##### threads strip if you really crank em down. So I have been drilling them out and tapping them for a 4-40 locking Helicoil. Now they stay locked in place and never loosen up. Not only that, 4-40 screws are a lot easier to find than the original metric hardware. I have a few hundred Helicoils so if anyoe wants to send me their mufflers,I would be happy to install them for you. Larry, NorCal Circle Jerks.

I did not do the 20-25, but I did a 35-40. I replaced the FP 35 cylinder, piston, wrist pin, head and gasket set with Tower 40 parts. It now runs just like I would expect a new FP 40 to run.

Regards,

>I need a favor from someone who has actually converted an
>20FP to an 25FP. Or the other way 'round, of course.
>
>It has been claimed to me that with the appropriate
>piston/cylinder set, head and gasket set, this is a simple
>remove-and-replace operation.
>
>Confirmation or refutation of this is needed. (snip)
>Thanks,
>
>Dan

Dan, yes, the piston/cylinder, wrist pin, head, and head gasket are the only "different" parts. The case is identical except for the number on the side. The crankshaft, con rod and back plate (OS calls it a "cover plate") are the same.

So if you are wanting to convert your OS from one to the other, it is easy to do. Also, the TT 25 parts fit as well. The TT uses a different type of venturi, but is otherwise the same. So, if you can't get parts for the OS, try to get parts for the Thunder Tiger. They are probably a little cheaper, and (to me) are better quality. I know the plating on the cylinder of the TT is heavier.

Oh, and the Thunder Tiger 25 back plate can be used to replace the "thingie" on the LA 25 if so desired.

Len,

Ooooh, thanks. Advice from someone who both knows and I can trust.

Also appreciate the extra effort: I had not considered the wrist pin, thought myself to be going the extra mile in remembering head gasket needs to be swapped out.

Now, my man, about those O.S. mufflers...