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Engine basics => Engine set up tips => Topic started by: Douglas Ames on August 18, 2008, 09:38:14 PM

Title: OS .25 LA and FP Piston/ Liner assy's
Post by: Douglas Ames on August 18, 2008, 09:38:14 PM

I have an older .25 FP and was wondering if the newer LA series cylinder liner and piston is a direct swap? Looks like two different part #'s but OS upgraded to ABN on the LA's.
Anyone try this?

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: Ralph Wenzel (d) on August 18, 2008, 11:14:19 PM

Unless the old Piston/Cylinder are truly worn out, I wouldn't bother with the transplant. From all I've read and heard, the older steel piston unit is to be preferred. Speak up, Brett and DD ???

Ralph

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: Just One-eye on August 19, 2008, 06:47:48 AM

Quote from: Douglas Ames on August 18, 2008, 09:38:14 PM

I have an older .25 FP and was wondering if the newer LA series cylinder liner and piston is a direct swap? Looks like two different part #'s but OS upgraded to ABN on the LA's.
Anyone try this?

The parts are not interchangeable.  During the comparatively long production life of the FPs, more were made with ABN than with any other metallurgy, and if you can find any replacement sets (for the FP) at all any more, those will probably be ABN.  There were some actual ABC versions of the engines, produced in parallel (and priced higher) with the iron motors, but those P&C sets are very unlikely to be found anywhere now. 

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: Bill Little on August 27, 2008, 12:20:53 PM

I am pretty sure Brett and Dirty Dan recommend an ABN engine for the BBTU.

The P/S assemblies do interchange for the 20FP and 25FP (a 20FP P/S fits in a 25FP case), but I understand they do not interchange with the LA.

Mongo

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: RandySmith on August 27, 2008, 09:25:12 PM

Hi

He was asking about the OS 25 LA P/S in regards with replacing it with the OS LA 25, of course  the OS 20fp will not work in the 25fp, even if  it was the same outside diameter the head would be a problem

Regards
Randy

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: Steve Helmick on August 28, 2008, 08:08:24 PM

Quote from: RandySmith on August 27, 2008, 09:25:12 PM

Hi

He was asking about the OS 25 LA P/S in regards with replacing it with the OS LA 25, of course  the OS 20fp will not work in the 25fp, even if  it was the same outside diameter the head would be a problem

Regards
Randy

Actually, Danny Dirt converts used 25FP's into 20FP's (actually 3.5cc's or .21's) on a regular basis. The head is a minor problem, cured with a little lathe work, or scrounging of a genuine .20 part. The sleeves are drop-in, just like the .35/.40FP's.  H^^ Steve

Title: Re: OS .25 LA and FP Piston/ Liner assy's
Post by: RandySmith on August 28, 2008, 10:34:27 PM

If you have a lathe  and  buy new parts  to make the engine into a smaller engine, not much question that can be  done, however  I still read the question was will a 25 FP take a 25 LA piston/sleeve
You could also make  Magnum 25 or 28 parts fit , or  machine whatever is needed  to use  Thunder Tiger  25 or 28 parts, and  remachine or make a matching head

Randy