Question for Paul McBride, the General Aviation News engines expert: We have a Cessna 152 fitted with a Lycoming O-235-L2C engine.
Recently we opened the cylinders and serviced the valve leaks. Compression check was OK. Later we did a run-up and found everything was OK.
Today when we did a takeoff run check and mag drop check, we found full static RPM 2300 and a mag heavy drop with vibration.
I also noticed that the oil gets black very soon.
Then we opened the spark plugs and found the plugs are filled with oil.
Kindly guide us what to do further. May I do only an oil ring replacement to rectify the problems?
James Kumar
Paul’s Answer: Regarding your question about your Cessna 152 fitted with a Lycoming O-235-L2C, I will offer my thoughts and hope they will get you started in the best direction to correct your situation.
First though, I must point out that I’m once again dealing with a question that offers little information regarding the history of this engine, such as total time, etc.
However, I think there is enough information to allow me to offer a few suggestions.
We’ll start with the spark plug situation and the picture provides some concerns.
If I see what I think I’m seeing, it appears that there is a mixture of spark plugs being used in the engine. I can identify the REM 37BY spark plugs, but have no idea what the others might be.
Good shop practice would dictate using all the same spark plugs and avoid mixing different plugs in the engine simply because the heat ranges may be different.
From my experience, the best choice of spark plug for the O-235-L2C has been the REM 37BY, which was developed by Champion to alleviate spark plug fouling due to lead deposits.
I noticed the oil in several of your spark plugs and after reading your information, it appears obvious that there is excessive blow-by in the cylinders to cause the plugs to be fouled.
I’m not quite certain what you meant when you mentioned you serviced the valve leaks, but I don’t think that was the cause of the oil-fouled spark plugs. My suspicion of what’s causing the problem is that the piston rings are completely worn out. The oil turning black in a short period of time is also an indication of this.
In order to correct this problem, I’m recommending that all cylinders be removed and inspected, including a dimensional inspection. If the cylinders are within Service Limits, they must be honed in preparation for installing all new piston rings.
Once the cylinders have been honed and new piston rings installed, you can reinstall them on the engine.
Remember, you must use a straight weight mineral base oil for engine break-in as mentioned in Lycoming Service Instruction 1014 or its latest revision. You should also refer to engine break-in procedures as set forth in Lycoming Service Instruction 1427C.
I’m confident that following these recommendations, your engine will once again provide you with good operational service.
Oil. Control ring upside down
My guess is that the owner has been trying to do his own maintenance. Owners are allowed to change oil and clean plugs.
Mixing plugs is poor practice, yet I’ve seen it done. How about a mix of short barrel, long barrel and fine wire on a Turbo Comanche 400? Owners often think that they know what they are doing, but ……..
Mike Bush also recommends doing a ‘ring flush’ , to clean the ‘stuff’ from the ring grooves.
It’s not low cost, but a lot less that honing 4 cylinders and a set of rings.
I agree that given the small amount of information it is likely the cylinders and rings are simply worn. If time was low on the cylinders then the break in may have been improper leading to glazed cylinders and improperly worn in rings.
However I had a 1958 Cessna 172 with about 400 hours SMOH that used a lot of oil, fouled the plugs, and seemed to always have a lot of breather tube oil inside the cowl and all over the belly. Compressions at annuals were ok but uneven.
I started using Camguard oil treatment and anticorrosive.
I noticed right away that the engine seemed to spin over faster on startup, making for easier starts. Oil blowby out the breather tube almost entirely stopped and I finally had a clean airplane belly. A few months later at the annual the compressions on all cylinders improved significantly and were very even, and the plugs looked normal, not oily. I continued using Camguard for the hundreds of hours I had that plane, with the same result. In addition it is supposed to prevent internal corrosion of engine components. That would be especially appreciated in eastern or oceanside locations with humid conditions.
Note that I also used Alcor TCP fuel treatment to minimize lead fouling from 100 LL fuel.used
I have recommended Camguard to friends and they reported similar results. Even a friend who repairs Morgans began using the automotive version and now recommends it for all cars, based on his positive results.
Whether this helps in your case I can’t say, but once you have the problem diagnosed and fixed I recommend using Camguard following breakin, and to other owners who may wish to avoid blowby and corrosion.
This engine has been very susceptible to lead fowling, mainly in the lower spark plugs. The REM 37BY were recommended for the lower plugs. When servicing plugs in this engine as the plugs were removed the lower plug holes literally had lead by products from the fuel falling out of the holes. A common problem with this engine??………
You should also replace your A&P that does your annuals. Not good practice to install a mixture of spark plugs. No telling what else is misplaced.