Question for Paul McBride, the General Aviation News engines expert: I have a Lycoming O-320-H2AD installed on an experimental Piper Pacer. It has never had the T mod done to it. It recently started making metal.
My question is: Does the case need to be sent off to have the upgrade completed? Or is it simply an upgraded cam and lifters?
Joe Dory
Paul’s Answer: Joe, you’ve asked an interesting question and I could go a couple of different ways with my response.
Not knowing the past history of your O-320-H2AD, let me offer you a few suggestions and a couple of things to consider before throwing lots of money at this situation.
As you know, you’re not the first nor will you be the last person to experience this type of incident. So, let’s see if we can take a more practical approach to handle this.
I’ve got to depend on your judgment as to how much metal was found in the engine oil filter and what type of metal it was.
I suspect it’ll be something that you could pick up with a magnet, which could indicate cam and tappet spalling.
That being the case, the next thing I would suggest is that you remove all of the valve action from each cylinder, making certain to properly identify the location of each component.
Once you’ve removed these parts, then I’d suggest you remove each tappet body, one at a time, and inspect both the surface of the tappet body and the corresponding camshaft lobe for any indications of displaced metal on either surface.
I strongly recommend a very close review of Lycoming Service Instruction 1011N, which will provide you with the proper inspection criteria.
It’s important to understand that the results you get from in complying with this publication will dictate the next steps that you’ll take.
It’s a no-brainer that should the tappet body fail the inspection for spalling it requires the tappet to be replaced — period.
Now comes the next step, which just may be the saving grace in your particular situation.
If you inspect the corresponding cam lobe and do not see any of the discrepancies mentioned in Service Instruction 1011N as spelled out in Attachment 1 (Tappet Body Inspection Guidelines), paying close attention to Task 1 and especially the corrective action under Task 2, you may be in luck.
From my past experience, I have seen many spalled tappets on this engine model, but some have been continued in service by simply replacing the spalled tappet because there was no corresponding surface damage on the cam lobe. It’s very important that you really give this a close visual inspection.
Joe, what we’re looking at here is the investment of some man hours to do a close visual inspection on the cam lobe and tappet body surfaces. Should you find that you cannot meet the inspection requirements of Lycoming Service Instruction 1011N, then the decision has been made for you.
In my opinion, I think taking the time to do this close visual inspection is worth the time and effort.
Now, let’s look at your second question regarding the upgrade for the O-320-H2AD engine.
To my knowledge Joe, I am not aware of any FAA approved repair facility that can modify the original crankcase configuration to accept the larger diameter tappets that are standard on the -76T engine model configuration.
History shows us that Lycoming went through three modifications on the H2AD engine with regard to cam and tappet spalling issues. It went from the original design to a second configuration that introduced a wider lobe camshaft and then finally to an upgrade using a larger diameter tappet body, with the wider lobe camshaft.
However, the original crankcase design did not allow re-machining, due to lack of material on the tappet body boss, in order to accept the larger diameter tappet body, therefore a new crankcase was required.
Hopefully, the information provided will give you a common sense approach to learning just where you are with this issue.
If an engine is making metal, it’s time stop operating it, and it’s time to disassemble it and investigate.
At a Cessna dealer in Baltimore in 1977, we had several customers who owned new 172N aircraft, plus we had three new company aircraft. I can’t speak for the customer-owned aircraft, but ours flew at least every other day. Shortly, Cessna issued a series of service bulletins under Operation Blue Streak (I think that’s the correct term) with included numerous Lycoming bulletins on the H2AD engine, and Bendix bulletins on the D2000 magneto. On inspection, I found valve tappets to begin spalling at about 250 hours time in service. So, at each 100 hour check, I began pulling and inspecting all tappets. Doing this negated any camshaft lobe damage, but I replaced many tappets before spalling became critical, and we never had to take an engine out of service.
I never owned an airplane. So, I cannot give you good advice. But if you do noy keep up with the engine it won’t keep you up.
Back in the ‘90s I had two N model C172s with the dreaded H2AD engines (76 series). I ran them about 80 hrs/mo and got 2,200 hrs between MOH. I do think they were series 2 (by your definition these had slightly increased cam/lifter contact.). They are subject to failure IF they aren’t flown/lubricated REGULARLY. OH, each of those engines went to tbo twice each over the 8-9 years I ran them.