August 17, 2013 at 1:00 pm #84402cochraneParticipant
I recently had a problem with cylinder compression that I thought I would share. I have ECI Titan cylinders on RAM VII engines with ~900 hours since new. Historically they exhibited 75 – 78 PSI during compression checks. During this annual compressions on three cylinders fell to the mid 50s – low 60s; I had performed a compression check 25 hours prior with those cylinders reporting 75 – 76. I asked quite a few people / organizations, including RAM and ECI, about it. The response, except for one, was that 50s to 60s are acceptable. Oil analysis did not show any anomalies.
The one exception was Steve Thomas from Poplar Grove Airmotive. Steve responded with an ECI service instruction, SI 96-4, that describes the ring design. ECI uses a top compression ring that has a plasma-sprayed molybdenum coating . The Poplar Grove engine technicians have seen this coating fracture and break off resulting in loss of the top compression seal. After inspection of the oil filter I have a small amount of ‘something’ ( non-ferrous) in the filter.
As far as I know, there was no causal event – CHTs have not exceeded 370 – 380 at any time. But it seems unlikely that 3 cylinders would simultaneously exhibit this problem unless there was a problem with the rings at the time of manufacture.
While it is not conclusive that the rings are the source of the problem, the probability is high. I am not quite sure what the next step is; I will either fly the plane to Poplar Grove to replace the cylinders or attempt to find someone good locally. That decision will be based on a borescope inspection of all 6 cylinders tomorrow and further analysis of the filter debris. I will most likely replace these cylinders with ECI Titans again or, depending on the condition, have them repaired.
For reference, Poplar Grove charges the following: $1,300 Labor + Parts to replace 3 cylinders on one engine in 2 working days; $3,800 Labor + Parts in 4 working days for a complete top overhaul on both engines.September 10, 2013 at 3:20 am #100584cochraneParticipant
Here is a follow-up to this post and some additional information on lifters. I realize that lifter pitting / spalling has been covered in other posts and articles but I thought the explanation as to the source of the problem might help one of you avoid a costly repair. I couldn’t embed the pictures into the post so they are contained in the attached file.
Last week we ran a compression test after running the engine for 25 hours after noting a substantial drop in compressions on 3 cylinders on one engine ( ~20 PSI in the previous 25 hours ). The compression results came back pretty good – no cylinder was lower than 70/80. But the oil was black and some particles of moly were still present in the filter. I decided to take it to a shop that had both engine overhaul and airframe repair capabilities – Poplar Grove Airmotive. When I arrived after a 2 ½ hour flight compressions were checked and all of the previously bad cylinders were 70 – 76 PSI / 80, 0.040 orifice. We decided to pull one of the cylinders that had reported sub-60 PSI 28 hours ago. As seen in the photo below, the moly had separated from the top compression ring and required replacement. We decided to pull all 6 cylinders and replace all of the rings while the engine is apart. ECI customer service has been a pleasure to work with, replacing the ring sets and providing substantial support for the labor as well. At ~900 hours I would not have expected any consideration from them. ECI identified this problem in the 2005 – 2006 timeframe.
Now for the bad news. When I arrived at the shop this morning, Steve Thomas, owner of Poplar Grove, took me for a tour of their engine shop. One of the first things they showed me were a number of engines waiting for overhaul due to pitted / spalled lifters that resulted in camshaft damage. Their shop manager explained that both lifter manufacturers, Continental and Superior, had significant problems over the past 10 years with the metallurgy and manufacturing technique associated with lifter manufacture. Continental fessed up to this in their SID 05-1 document. They noted Lycoming had the same problem. A new manufacturer has come on line that purportedly resolved this problem.
Below are pictures of two of my lifters showing early-stage pitting. This pitting was not significant enough to damage the camshaft. Had I let this problem go unattended for another 100 – 200 hours I would be looking at a teardown / cam replacement. We are replacing all 12 lifters in this engine along with the rings. For reference, the total cost ( pull 6 cylinders, re-ring the pistons, hone cylinders, new lifters, gaskets, oil, tax etc.) is about $4K.
The inside of the engine and all exposed steel surfaces look fine – there is no evidence of rust or pitting on any other surface. I have had these engines on oil analysis since they were new and there has been no indication of problems at any of the 25 hour oil changes. These folks suggested the best way to identify lifter problems in the early stage is to closely examine the filter for very small particles of ferrous metal by using a small diameter magnet to inspect the pleats.
Attachments:September 10, 2013 at 11:57 am #100594
Thanks for documenting this issue you had. Certainly concerning issues, I think what’s more concerning is the lifter spalling. Did they say when the “newer/better” lifters were introduced? We’ll need to keep an eye on that on our 520s.
I do somewhat wonder about what harm the moly coating flaking off would do. Devil’s advocate here just to open discussion. Obviously lower compression which is not desirable, but otherwise the flakes themselves I don’t think would cause a major problem. Just thinking out loud here. The good part for you is that you discovered the lifter spalling and saved a double teardown.
- You must be logged in to reply to this topic.