I have a C85-12 with the O200 crankshaft, rods and pistons as per the appropriate STC. This work was done a while ago and several owners ago and I am getting ready for a new set of spark plugs. I currently have REM40E and am under the impression that the REM37BY are of a superior design for these small engines. According to the fitment guide the REM37BY will fit a C85, C90 and O200 but I can't find any details on the STC regarding changes (if any) to the clearance of the piston at TDC. I have read the overhaul manual for these engines and I see that the O200 has a 1/4" longer stroke than the C85 but without knowing how the final fitment is setup i am not sure on clearances for this slightly longer (0.165") plug.

Does anyone have the details on the clearance at TDC for this modification? Alternatively, is anyone running the REM37BY on a C85 that has been fitted with the O200 parts (and still retaining the 85HP, cam, valves and 2450 redline)?

Also, is there an initial gap that that is preferred for these plugs in this engine or should I just set it at the bottom end of the range?

THX

DJ, I sent you a PM.

flyingjack

The 37BY plugs are allegedly more resistant to lead fouling.
Has anyone here had a lead fouling problem with standard plugs which was solved by going to 37BY's?
I run standard UREM-40 plugs in the 180 and have never had a problem with them.
Ditto for my last two airplanes.
But I run 75% or more e-zero mogas, so very little lead to cause fouling to begin with.

hotrod180 wrote:The 37BY plugs are allegedly more resistant to lead fouling.
Has anyone here had a lead fouling problem with standard plugs which was solved by going to 37BY's?
I run standard UREM-40 plugs in the 180 and have never had a problem with them.
Ditto for my last two airplanes.
But I run 75% or more e-zero mogas, so very little lead to cause fouling to begin with.

The Lycoming guys at my local field swear by them for this reason. When I called Champion to discuss them they recommended the 37 as the better option assuming that it would fit.