Cessna 120-140 Association

After several replacement front crank seals within 6 years, unable to stop fine oil spray from prop seal. Fine mist covers windscreen after 1 hour or less. Shaft appears smooth, not pitted, as best as one could see at seal location as per A&P. Any one with similar history or problem? Engine has 1400 hrs after initial overhaul. No history in logs for leak. Probable new shaft in future as fix...tks for any info, Fred

The seals between the crankcase halves could be the problem.

Have you tested the crankcase pressure? Is it a tapered or flanged shaft? Are you using the split seal? If so, how are you aligning the split and the spring ends?

Ditto on John's post.

I've done many crank seals.

I like the solid seals the best. (but have a split seal on my own airplane.........go figure)

1. Is the leak coming from the crank seal or the case split line? Once the case halves start weeping/seaping, the only fix(usually) is splitting the case.
2. If you have a split seal,
A. don't line up the split with the case half.
B. the tips of the ends of the seal need to match up perfectly.
C. Is the seal spinning in the case? if so you either need to find an oversized seal, or bond the seal in place.
3. One trick I use with stubborn seapers is to use a sandpaper tongue stick. (like a thin wooden ice cream stick with a sand paper finish) and put a rough finish on the crank at about 40 degrees to the seal knife edge as it rides on the crank. Doesn't take much.
4. if you have too much blow by past the rings (i.e. too much crank pressure) you can either re-locate the breather tube or start replacing cylinders.

I'm sure someone else will have some more tips.

529 wrote: ↑Thu Mar 07, 2019 8:38 pmput a rough finish on the crank at about 40 degrees to the seal knife edge as it rides on the crank.

Note that the scuffing must run from forward left on the crank to aft right, as viewed facing the crank. The purpose is to draw the oil away from the seal and back into the case as the crank turns. I believe there is a service bulletin on this subject, but can't put my hands on it right now.

Tks for reply, crank is not tapered, split seal put in with opposite; connecting spring opposed to split seal. Will check pressure, no leak or evidence on case joints. Will check for line up with split re case haves, do not think so, did not appear. Seal is not spinning. Engine is C85-12F, Direction as to locating 0200 crank, been looking in trade a plane, obviously rare $$ item. Very much appreciate info, member for years, first post however. Made Nj Sky Manor gathering, just missed the famous Hudson Mission, although flew it many times.

HAD THIS PROBLEM IN THE PAST. REMOVE OLD SEAL AND CLEAN ALL OLD GLUE FROM CRANKCASE RECESS USE MEK . GLUE SEAL WITH ONLY PLIBOND. TWO COATS ON SEAL AND CRANKCASE LET DRY COMPLETELY.DO NOT GET ANY GLUE ON CRANKSHAFT! PUT DIELECTRIC GREASE ON CRANKSHAFT WHERE SEAL RIDES. ACTIVATE GLUE WITH MEK USE ACID BRUSH WORKS BEST. PUSH NEW SEAL IN WITH SCREWDRIVER LET IN DRY 24HRS.