After replacing almost everything in my engine, why is there metal in my oil filter?

Question for Paul McBride, General Aviation News’ engines expert: I’ve inherited the infamous Lycoming O-320 H2AD engine.

In 2022, I had a prop strike — no damage to the engine — but did a bulk strip and nothing amiss. The engineer did notice the small-bore lifters were pitted and, of course, recommended replacing. As you’d be aware, the narrow bore lifters aren’t made any more, so I went down the path of a new crankcase, had the additional oil grooves put in, and new larger lifters, cam shaft, and replaced the rings. As we’re in Australia, the engineer also sent the camshaft overseas to have the oil tappets drilled for better lubrication.

Of course while we were at it we replaced basically everything else — the starter, alternator, prop, belt, mags, harness, baffle kit, plugs, air intake, exhaust, and harness. I should have bought a new engine!

The run-in process was followed meticulously.

The aircraft has been running like a dream. It has flown 34 hours since this major work but on the recent service, very fine metal (a super fine dust-like metal) was noted in the filter.

The mechanic has removed the engine and it is now back with the engine engineer for inspection.

I have not heard from the engine engineer as to what, if anything, has been found, but he is already blaming the mechanic for not flushing the oil cooler when the original engine work was done and wear was found on the lifters. The mechanic is already blaming the engineer for making a mistake.

As for the cooler, I am inclined to just replace it regardless, as I don’t know its history, except that it was installed in 2005. I also note when looking up the part number that it is for a Maule or Piper and not a Cessna 172N.

Some in our aeroclub have recommended going for a larger cooler than the “proper” part number as we live in a hotter climate. Temps are 23°F in the winter to 120°F in the summer.

Do you have any thoughts on coolers?

Ben Smith

Paul’s Answer: Well Ben, I’m not sure where to begin with this one. You’ve done so many things correctly, but on the other hand, let’s just say you could have done a little bit more.

First, after suffering the prop strike, you did the proper thing by removing the engine and having it completely inspected.

Stepping up and buying a new crankcase utilizing the large diameter tappets was another good decision. So far, everything is good!

I am familiar with the work done to the camshaft and would guess it may have been sent to New Zealand for that modification, which by the way has never been approved by Lycoming, but it has been approved locally by the proper authorities. Personally, I’m not certain if it provides any added benefits, but I also feel that it probably does no harm.

At this point, I’d say you’ve done everything correctly even to the extent of going above and beyond what may have actually been required. As they say in Australia, good on you!

Now comes the difficult part: After 34 hours of operation you’ve found some very fine metal dust. There is no doubt in my mind that you are suffering the results of not installing a new oil cooler and new oil lines at the time the engine was reinstalled.

Believe me, you are not the first to experience this situation — and certainly will not be the last.

However, since you have already returned the engine to the engineer for further inspection, I hope his inspection will conclude that no harm has been done.

If the information you provided is accurate, and the contamination is just some very fine dust, you may be able to save the engine without much additional expense.

If the inspection shows no serious contamination, the next step is to flush the engine as good as possible, and then install a new oil cooler and all new oil hoses.

Following that, I’d suggest doing an oil and filter change within the next five to 10 hours and inspect the oil filter very closely. Fly another 10 hours and do it again.

What we’re looking for is if the engine is still manufacturing metal or not.

My hope is that the fine dust will be less and less, but these results will dictate whether or not you’ve caught the cause of the contamination in time. I honestly believe you can possibly save it.

Now, let’s approach the blame game. I can tell you from experience that replacing the oil cooler and hoses when contamination is found in an engine becomes a financial decision on behalf of the owner, on the recommendation of the facility doing the work. However, the final decision should fall on the shoulders of the facility or individual signing the engine off to return to service.

Taking your situation in hand, the water has already gone under the bridge, so there is nothing to be gained by pointing the finger at someone now. There is, however, a lesson to be learned by all parties involved and that is not to be caught in this situation again.

My advice to all who have or will experience metal contamination in an engine: Replace the oil cooler and hoses rather than taking a chance. Even if the cooler can be flushed, why not just go with a new one?