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Blow By Question

Brazoria, Texas
Brief Synopsis of Problem:
Lycoming 0-235-C1.
Fairly new engine, approximately 30 hours SMOH.
Ran fine with full 6 quart oil capacity with no leaks. Breather vent never even had a drip. Landed one day and belly was covered with oil. Not a drop of oil was in the baby bottle. Isolated the leak at the front crankshaft oil seal. Replaced seal. Ensured the oil sump was full with 6 quart capacity as usual. After a 20 minute warm up, no leaks on the ground. After a test flight staying in the pattern with three touch and goes, the belly was covered with oil. This time the front seal did not leak, but the baby bottle was full of oil and the belly was covered with oil again. With the baby bottle full of oil, the crankcase vent tube had blown a lot of the oil out of the top of the baby bottle and it was all over the belly all the way back to the tail wheel. Checked the oil it had 5 quarts left in the sump, so it blew a full quart of oil out on three touch and goes.
I pulled all four bottom plugs and all four of them were pink and dry, not a trace of oil on any of the plugs. Any idea's, thoughts, or suggestions? Thanks in advance.
 
ECI has some good engine troubleshooting tips on their web site under "technical articles". What color is the oil? Blackened oil is a sure sign of blowby by the rings which is a classic cause of crankcase pressurization. The hint of the blown nose seal and oil out the vent is the result. Jim
 
Upside down ring pressurizing the case? Make sure you have the slot cut into the breather line.
 
ok, how was the compression check?? sudden problem like you describe makes me think hole in piston from object in cylinder..
 
The breather hasn't somehow moved further into the airstream has it?

If not it's time to pull the oil filter and cut it open, or check the screen. Looking for metal bits.

Perhaps a broken piston ring.
 
1 what oil and weight
2 change oil clean screen or filter
3 fly it on a hrs climb with hig oil temps cylinder tents 225 245 oil temp range keep cylinder head tems about 400 plus work it hard for a couple hours the do normal let down land check it then , if you shoot a lot of landings the blow by increases till you get out of the pattern and use I mikeo
 
Gotta an A&P friend gonna come by and do a borescope inspection on all the cylinders this weekend. He suspects a cracked or broken ring because it only blows oil out after take-off but not on run-up. Said probably on the cylinder with the lowest compression, but he wants to take a look at the cylinder walls before we do anything else. I figure we will probably pull a cylinder because whatever it is has to be in the cylinder. Just wanna make sure we pull the right one. Will post findings when we figure out what it is.

The oil is Phillips 20W50 mineral oil.

Breather is not in slipstream. I have a baby-bottle on the end of the vent tube to catch the blow-by. When this started it blew a whole quart out in an hour and covered the bottom of the aircraft with oil. So I drained some oil from the sump, left 4-1/2 quarts in the sump (a quart and a half low) and flew 30 more minutes. On landing there was about a half inch of oil in the baby bottle this time, with no oil on the belly. It dosen't blow anything out while sitting on the ground, only when full throttle is applied on take-off.

We will find out what is going on this weekend.
 
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Problem appears to be a slightly glazed cylinder. Possibly two cylinders. The glaze appears to be barely noticable, but enough to cause some blow-by. Gonna pull all four and hone them and put a fresh cross-hatch and all new rings. Did not have any broken rings. Rechecked all compressions. 80/80, 80/79, 80/79, 80/80. All is good.
 
When you did the compression check, did you hear/feel a lot of air coming out the breather pipe exit? If the rings are leaking by, that is where you will find the answer.
 
With with compressions like that hard to believe Blow by is a problem. Maybe it threw the top quart out. I don't run more than 5 in my o235c1..
 
I have seen blow by with glazed cylinders before. It does occur and it can be a problem. After you re-hone with new rings and get a good break-in, you should be fine.

Bill
 
When you did the compression check, did you hear/feel a lot of air coming out the breather pipe exit? If the rings are leaking by, that is where you will find the answer.

No air coming out of the breather pipe, but a just barely noticeable amount of air coming out of the dipstick filler tube. The clue was a very barely noticeable wisp of smoke come out of the dipstick tube when the dipstick was pulled out during each cylinder compression test to see if I could hear anything in the oil sump. The borescope reflected a very slight glaze on a couple of cylinders. I was also alerted to the possibility of advanced ignition timing on a magneto contributing to blow-by as well, so will be checking mag timing also.
 
Compression tests have the piston at TDC. Cylinder glazing happens below that. Too low cylinder pressures are always a break-in concern and flat pitched/STOL props can be contributors. Run it hard.
 
Agree.
Compression tests have the piston at TDC. Cylinder glazing happens below that. Too low cylinder pressures are always a break-in concern and flat pitched/STOL props can be contributors. Run it hard.

Do you by any chance have a vacuum pump installed? If so, there is a possibility that it is pressurizing the case. Particularly if the garlock seal is backwards.
 
Don't forget to check the other rings, the compression test only checks the upper ring(s)
 
I have seen blow by with glazed cylinders before. It does occur and it can be a problem. After you re-hone with new rings and get a good break-in, you should be fine.

Bill
Can a person with an experimental, re-hone with one of those 3 fingered abrasive devices, chucked into a low speed drill, to break the glaze?
 
Are the ring sets for the O-235-C series still outrageous? You can use a manometer on a modified oil filler cap to check crankcase pressure as well. Can remember what is excessive.
 
Steve People are getting the blow by question and the Johnson creek poster mixed up !! The mysteries in life !! mikeo
 
Are the ring sets for the O-235-C series still outrageous? You can use a manometer on a modified oil filler cap to check crankcase pressure as well. Can remember what is excessive.

45-55 mph with a max of 100 mph on a Lycoming measured on an airspeed indicator according to Sac Sky Ranch.
 
Long shot - a bloke I know had similar problems with a new engine. It was discovered that the remote oil filter had been connected up in reverse flow. It took a lot of smart men to find out that the non return flapper/ valve broke loose and lodged somewhere in the engine.
 
Are the ring sets for the O-235-C series still outrageous? You can use a manometer on a modified oil filler cap to check crankcase pressure as well. Can remember what is excessive.

Steve,
The ring sets for the 0-235-C series are definitely outrageous. The price for a set of rings for just one piston is $180. For four pistons, it is $720 + tax (at .0825%) = $779.80 which is pretty high. $780 just for the rings alone for four pistons. The gasket set is only $15, so go figure. These prices are from J&J. The price just for the top two compression rings (on just one piston) if bought from Lycoming, is $190 just for the top two rings alone.

I will be pulling and honing cylinders and replacing rings this Monday. Figuring it to be about an 8 hour job to do all four.
 
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While you have it apart, give it a good looking over for anything else that may be out of place. Make sure that there isn't a piece of rag blocking a breather opening, or ???.
 
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