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Hold off doing anything until you do a bore scope inspection. If the piston had any kind of hole or or total ring damage other than a broken ring you would have much lower compression check than you did. What were the CHT's? A reading of 69 is nothing to worry about considering the others were in the 70's, (how high were they?) and where was the blow by EX valve or IN valve?
Warn the engine and do another compression check. Also it's possible for a crank seal to go out because is just worn out. Your engine is not the first engine to blow a seal, and the seal is not hard to change. So settle back and get a good borescope inspection done. Also a little metal showing does not constitute an overhaul. Get some opinions of other mechanics and a spectrographic oil analysis will tell you more about the metal you see and where it coming from with limits. Also check the oil sump suction screen on the lower part of the engine for larger metal parts.
it's hard to diagnose a problem when you don't have all the information.
Tom Smith A&P/IA
From: Tim Andres tim2542@... [canard-aviators]
Sent: Tue, Feb 12, 2019 6:48 am
Subject: Re: [c-a] Blowing the front crankshaft seal due to overheating.
Don, you will almost certainly find a scored cylinder when borescoped, probably #3 of course. The reason for the crank case pressure is the seal surface the ring rides on is probably totally shot and/or you burned a hole in the piston, combustion gas is being forced past the piston much faster than the vent can handle.
Sorry that your engine got too hot.... very glad you landed and avoided more damage. I don't know why the shop guy said the crankcase becomes pressurized during overheating conditions. That phenomena may be possible but it doesn't make sense. The only time I have heard of that the crankcase becomes pressurized is when the breather becomes blocked which is often from freezing engine condensate. I would guess you had no ice...
I would not use that mechanic unless you can verify that his "overheating = pressurized crankcase" statement/theory can be confirmed (if in fact that is what he was trying to tell you.... poor communication is often the source of misunderstandings).
Since your nose seal leak is excessive, you may have a worn out thrust bearing (and oil slinger clearance issues) according to the Lycoming tip in this link.... How to Avoid a Nose Seal Leak
It sounds easy to check and difficult to repair. I would get a second opinion before deciding what to do.
How to Avoid a Nose Seal Leak
Perhaps the first step in discussing this subject is to first get the terminology correct. The latest revision o...
Cozy MKIV #1273
While flying Calypso on a sightseeing tour with a friend, I suddenly lost power and Number 3 CHT read through the roof. I declared an emergency and landed at Torrance airport. After landing and taxing to a shop, I noticed that my speed brake was down. When
I built my Cozy, I installed the speed brake up and down buttons on top of my stick. Big mistake, I found that it was too easy to inadvertently drop my speed brake. To avoid this I installed a sliding cover over the down button. Despite the cover, I apparently
managed to hit the button. The few minutes climbing out was enough to overheat my engine. The next day the shop checked my compression. All cylinders were in the 70's except number 3 which read 69/80. They also pointed out to me that they noticed a leak
around my crankshaft seal. I decided to fly Calypso back to CPM, a short flight, if everything checked out so that we could look for any other possible damage/problems. The engine started right up and I I checked the engine at max rpm for a minute or so
and all CHT's rose more or less together within the normal range. After the regular ground check I took off and flew the less than the 10 minute airtime flight to CPM. The airplane performed normally.
After landing at CPM I found that the seal leak had worsened to a great extent. That short flight had dumped about 3/4 quart past the seal. we opened the oil filter can and found tiny metallic chip residue on the filter element. I showed the filter to a
nearby reputable engine overhaul shop. He checked the residue with a magnet and determined that it was aluminum. He indicated that it was probably a piston, and if so due to the different coefficient of expansion between the Al piston and the ferrous cylinder
wall under high temperature, the piston skirt could rub against the cylinder wall, usually in the 6 and 12 o'clock positions. The next step is to boroscope the cylinders to see if this is the case in #3 and any of the other 3 cylinders. The bad cylinder/cylinders
will be removed and brought to the shop. We will also have an oil analysis done to see if there are any unusual readings indicating bearing or other internal wear.
This is all background information leading into my question. He said that in overheating conditions, the crankcase becomes pressurized and the high pressure can cause the crankcase oil to blow by the crankshaft seal. There is no question that the seal leaked,
oil was over the inside cowling and prop. My question is just how does the crankcase become pressurized to such an extent due to overheating? The crankcase is not sealed. There is a crankcase vent, about a 3/8 inch tube. Wouldn't that relieve the crankcase
All you guru's and learned engineers please help. An inquiring mind wants to know.
Cozy IV "Calypso"
Long Beach, California