Hello All:

      I got a 1949 Fox .35 out of my junk drawer today to get it ready for an OTS airplane.  However, the piston becomes very tight during the final .200" of travel in the compression stroke.  The question is now what to do if anything.  I made the following observations:


The engine is in great nick despite it looking that it has many gallons of fuel run through it.  All of the areas subjected to combustion gases are coated with a very hard and smooth coating.  The p&c are as smooth as black marble.  No scratches or any sign of use.


It started at first flip and ran very well at a very low speed.  The n.v. worked very well.


What to do if anything? Should I remove the "carbon" from the cylinder by crock potting?  Just run a mix of fuel with a bit of synthetic oil added and hope to clean the engine.  I use a bit of 0000 steel wool and carb cleaner to remove a very small amount of carbon.  This helped but it remains tighter than a fish's butt.


Perhaps it would be a great idea to leave the carbon and hope the engine becomes lose at operating temperature.  It has a pinch near the top of the stroke  per an ABC setup.  However, this is steel on steel and I suspect that the p&c will both expand at the near the same rate and remain too tight for safe operation.   The only caution that I have is that there may be an excessive load placed on the conrod if it  is running too tightly.


Suggestions/comments?

                                                                                                                                              Tia,

                                                                                                                                              Frank McCune

Hello Frank
I would put it in the engine sauna and boil it up to get that burnt on oil/carbon off. If there is no metal to metal contact from a distorted liner/piston , then something is there that shouldn't be and has to go...
bye Gerald

   I would beware Randy's admonition in his fuel post (pinned to the top of the forum and required reading - or should be). When you clean off all the carbon, there's a really good chance that you will have no compression left.

      There may be something else wrong, like distorted cylinder from a crash, improper muffler installation, uneven head bolt torque, etc (because it could be a bunch of reasons), but most are insoluble without replacement parts.

   I would just run it a while, see if anything changes. If it vibrates violently, er, more violently than normal, then look for a bent crank, bent conrod, uneven wear in cylinder bore carbon, etc, and replace the part/parts that are damaged.

      Brett