Q: We have some problems in an R44 engine related to blow-by. We replaced all the cylinders a few months ago, but the problem remains. Lycoming support suggested we replace the type of oil.
We are thinking of replacing the pistons before we begin to use a new oil type. If we do remove the pistons, what would be the best way to choose a correct part number related to pistons and rings?
Antonio Costa
A: Antonio, with the lack of more detailed information, let me offer some suggestions.
When you mentioned that you recently replaced all of the cylinders on this engine, were they factory new cylinders or factory cylinder, piston, and ring kits, or were they used serviceable cylinders purchased from an overhaul facility?
I suspect from what you mentioned that the blow-by is caused by glazed cylinder walls. This could possibly be a result of improper break-in, so let’s begin there.
The most important thing that must be accomplished is to follow the requirements of Lycoming Service Instruction 1427C or its latest revision and the Pilots Operating Handbook (POH) from the aircraft manufacturer.
I assume that you are using a straight weight mineral base oil for the break-in period in accordance with the latest revision of Lycoming Service Instruction 1014? You should not be adding any type of oil additive at this time.
Typically, this straight mineral base oil is recommended for the first 50 hours of operation or until the oil consumption stabilizes.
Keeping the ground run time to a minimum is also a good idea, but once again, following the recommendations of Service Instruction 1427 for Rotary Wing (Horizontal Installations Only) is extremely important.
Before making any further decisions, I would like to suggest that you fly the helicopter at high power settings for a couple of hours to possibly get the rings to seat better.
Following the guidelines in Service Instruction 1427 exactly may be our one-time possibility of improving the situation. There is no guarantee that this will resolve the issue, but it’s worth the try.
With regard to replacing the pistons, I’m not convinced that doing that at this point is a good idea. My suggestion would be to try to get the current cylinder/piston and ring combination to seat in by following the above-mentioned recommendations.
Failing that, I would suggest removing all of the cylinders and having them honed to the proper specifications and install all new piston rings. Then once again follow the recommendations of Service Instruction 1427 and the POH.
While my suggestions do cause expenses for operating the helicopter, it’s much less expensive that just jumping in and changing things. If the flights prove that the piston rings are not seated, then you can consider what I have mentioned regarding the honing of the cylinders and replacement of the piston rings.
