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- Aug 23, 2019
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Any of you engine experts ever heard of this:
C85 with about 1000 SMOH over the course of 30 years (plane recently purchased). Replaced a cracked #4 cylinder with a new cylinder at annual two weeks ago. Have been breaking in cylinder, so running at high power settings and air temps are now in the 90s. Noticed oil temp was well over 200 (probably 230 ish) had been running 185 or so, but attributed the increase to higher power settings and higher external air temps.
But... after shut down, I remembered I needed to set idle speed, so I grabbed a screwdriver and got to work. I had to reposition the prop and when I did, I noticed that there was excessive internal friction. Enough friction that when propping the engine, the prop just stops dead when you stop pulling - no bounce back after compression.
once the engine cools down, engine loosey -goosey again. So I flew her around the pattern and got her hot again and viola, tightened up again. This time temp was only 190 and the friction was a little less than when it was hotter, so the degree of internal friction is directly related to engine temp.
Checked screen, found a couple of very small flakes of shiny, probably attributable to the new cylinder, nothing profound. Pulled the new cylinder, re-checked ring gaps - all looks normal, no scoring, gaps good. And I would characterize the friction as ‘steady’ or ‘continuous.’ If it was ring/cylinder related, I guess I would expect it to vary (worst mid stroke, minimal at TDC/BDC), but since the cylinder was just changed figured that was a place to start. Sadly, I am not sure that I ever tried to start this thing while hot, so it may have been doing this all along, and is just worse because the engine is running hotter(?).
i plan to pull the engine and open her up, see what is wrong, in.ess somebody on here knows something that I don’t and this is somehow normal. Looking forward to seeing the responses on this one!
Thanks,
T
C85 with about 1000 SMOH over the course of 30 years (plane recently purchased). Replaced a cracked #4 cylinder with a new cylinder at annual two weeks ago. Have been breaking in cylinder, so running at high power settings and air temps are now in the 90s. Noticed oil temp was well over 200 (probably 230 ish) had been running 185 or so, but attributed the increase to higher power settings and higher external air temps.
But... after shut down, I remembered I needed to set idle speed, so I grabbed a screwdriver and got to work. I had to reposition the prop and when I did, I noticed that there was excessive internal friction. Enough friction that when propping the engine, the prop just stops dead when you stop pulling - no bounce back after compression.
once the engine cools down, engine loosey -goosey again. So I flew her around the pattern and got her hot again and viola, tightened up again. This time temp was only 190 and the friction was a little less than when it was hotter, so the degree of internal friction is directly related to engine temp.
Checked screen, found a couple of very small flakes of shiny, probably attributable to the new cylinder, nothing profound. Pulled the new cylinder, re-checked ring gaps - all looks normal, no scoring, gaps good. And I would characterize the friction as ‘steady’ or ‘continuous.’ If it was ring/cylinder related, I guess I would expect it to vary (worst mid stroke, minimal at TDC/BDC), but since the cylinder was just changed figured that was a place to start. Sadly, I am not sure that I ever tried to start this thing while hot, so it may have been doing this all along, and is just worse because the engine is running hotter(?).
i plan to pull the engine and open her up, see what is wrong, in.ess somebody on here knows something that I don’t and this is somehow normal. Looking forward to seeing the responses on this one!
Thanks,
T
