Maintenance question for engine over TBO
 

Can anyone point us in the right direction?

I am part of a syndicate which runs a C172P on a UK private C of A. The engine (O-360) is over Lycoming's recommended TBO (now with about 2,300 hours on it) and we are operating it "on-condition". We have run this aircraft for over 20 years and it is very well maintained and used very regularly. We regularly run engines to over 2,500 before overhaul (we are on engine number 3 so far), as long as the certified engineer (and we pilots!) are happy that it is safe and legal to do so.

Here is the question: we have identified low compression on one cylinder (still within limits), and the engineer says it is a very simple fix as the valve probably needs re-seating. However, he also says that as it is "on-condition", he is not allowed to remove the cylinder head, but that the whole engine must be overhauled. If that is true, fair enough, but I like to see these things in writing. I've looked through LAMS/CAP411 and cannot see the reference. I don't have the C172 log-books to hand to see if it is referred to in the specific maintenance schedule for the type. Can anyone point me to where it says no part-disassembly of the engine once over recommended TBO?

Thanks in advance!

I cannot speak for the UK regs, someone else will be along for that.... In Canada such a repair would be entirely acceptable on an "on condition" engine.

Refer to Airworthiness Notice - B041, Edition 4 - 31 March 2005 - Transport Canada for the Canadian perspective. See "Failure to meet standards" near the end....

Good luck.

I think you need to refer to CAP747

Have a look around page 388 (GR no.24)

How this all applies with JAA, EASA, CAMO .... I just gave up and went onto Permit to Fly.

First your engineer is telling you the truth, the engine is "on condition" and removing a cylinder is showing that the condition is not satisfactory under the regulations.

At 2300 hours the engine is telling you something so it is time to listen to it! you have extracted 300 hours extra flying from it so now is the time to get it overhauled.

The options are overhaul in the UK, or an exchange engine from the factory.

In the past I have done both and I have to say that the Lycomong exchange engine was the wrost thing I have ever done, it has been apart at 700 hours for piston pin plug failure and is now total junk at 1300 hours because of issues with the crank, I am sure that I got a Friday afternoon engine from Lycoming and they know it but you can expect ZERO product support from them even when your engine only just reaches half life (in hours & calender time)

My recomendation would be for an overhaul in the UK, but not a cheap one! the price should be IRO £10.5-11K, I know of one company on the south coast who say they will do an overhaul for £9K, this is little over the cost of the parts and I can't see how they do it for the price (well I can we had to put the valve gear right on an engine they had "overhauled").

My recomendation would be to take it to Nicolson Mcclarren ( who I use) or Eisenburg (who I have never done business with but who has a good reputation)

Or an overhaul in the USA, where there are a number of highly respectable engine shops. I have used Barrett Precision in Tulsa, Oklahoma and would use them again. They did an excellent job.

The $ exchange rate means the pricing is good even if you blow away £3000 on DHL for the shipping there and back.

In the UK there is at most the one company which anybody will honestly recommend.

I would read CAP747 para 3.2 and have an overhauled/new cylinder fitted as a maintenance action to make it airworthy again. (Subject to the rest of the powerplant being satisfactory as per para 3.1!)

I know of engines bottom ends that have gone to 3500 hrs, so a complete overhaul now may be a waste of another potential 1000hrs. Fit 4 new cylinders, and who knows - you might even get that far without any more trouble showing up on the regular assessments!

PS: "UK private C of A" does not exist.

I wouldn't mess around with patching it up with those hours, not in a SEP anyway. I second Nicholson Mclaren. I know of one down south I wouldn't touch with a barge pole and their prices always go up apparently as the "find things".

We got an engine rebuilt last year by NMA, the service was excellent and the quality was superb and the price was as quoted. It was higher than some of the others but it included dynamic balancing.

I did a lot of research prior to the rebuild and all those in the business recommended NMA. It was a toss up between them an Norvic who also seemed very good, and slightly cheaper, but we went for NMA purely on the recommendations.

There are some interesting things I heard about some engine shops giving a kick back to maintenance outfits who send an engine to them.

If I were you, I'd probably bite the bullet and go for the full overhaul, as you are merely a couple of hundred hours off the point at which you will have to do this.

In addition, given you have one of the lower compression Lycomings, you might want to see if you can find if there is an STC which will allow you to convert it to run on MOGAS at the same time, which will prob 40 save you time and money in the future.

There is one engine shop in the S of England I wouldn't touch with a long $h1tty stick. The general modus operandii is to give a very competitive quote and then, when the engine is in pieces on the floor, announce that 'all the grommets and giblets are clapped out' and the price rises by 50%. This is also the same chap who offers a £500 'referral fee' to the maintenance outfits who look after the aircraft.

I hear good things about Nicholson McClaren Engineering, and Norvic and Isenbergs also have their afficionado's.

Personally, for an O-360, I wouldn't opt for an overhaul in the USA; when you consider the cost of the overhaul of the 360 (say £13,000) as against the cost of overhauling a 540 (say £25,000), the shipping (which is broadly speaking the same for an O-360 as it will for an IO-540) will form a much bigger percentage of the cost.

Having said that, there are people who say that the quality of the work done in the USA is better than that done in the UK. I have no personal point of reference on that, but would merely say that Texas or Oklahoma is a long way to go to deal with any warrantee or paperwork issues!

Best response so far. Assuming no obvious signs of engine distress, operations beyond TBO become a cost/benefit calculation. If a cylinder repair is likely to result in another couple of hundred hours of use before more work is required than it is quite cost effective. If the other cylinders are also tired than you are probably better to spend the money on an overhaul. In any case as was mentioned above pulling the cylinder will allow a look at lifters and cam condition. If these are not in good shape than an overhaul is definitely in your best interests. The universal problem with private aircraft is they do not fly enough and thus it is not operating wear that kills the engine but corrosion damage resulting from lack of use. Lycoming specifies that the published TBO times are for engines that are flown at least once per week. Just running the engine on the ground isn't enough, in fact it is actually bad for the engine. Therefore the history of the engine is an important clue as to whether you want to continue its service.

Thanks for all the replies so far.

Silvaire 1 is so right! We are following the course we are because of program requirements and not common sense. The engineer is very happy with the engine and so are we. There is no oil leakage and nominal consumption; the engine is operating entirely within the manufacturer's specifications and our previous experience with our (regular) usage is that 2,500 hours is a good point to look for the replacement engine.

Thanks also for the suggestions for overhaul - pretty much the names we have come up with too.

I'm looking at CAP 747 this evening - it looks like a cure for insomnia!

Meeting the engineer soon for further discussions.

As has been said, 'UK Private CofA' doesn't exist for a C172. You will have an EASA CofA.

Lycoming recommend your engine is overhauled at 2000 hours or 12 years whichever occurs first. At 2300 hours your engine is into its 'extension' period which, under UK rules, is a max of 20% applied to both TBO (to 2400 hrs) or calendar time (to 14.4 years). Beyond these figures the engine is normally termed 'on condition'.

CAP747 GR No24 specifies what you have to do during the 'extension' period or when 'on condition' - includes monitoring oil consumption, 100 hr compression checks etc.

For what was 'Public Transport Passenger' use (Club hire/PPL training) an engine can be used up to the end of the extension period. It can then continue in use but only for 'private' use.

At 2300 hours you can have a cylinder replaced or reworked (note, the cylinder is an 'assembly' - barrel and cylinder head, mated at birth and not to be separated thereafter).

Truth is you might as well call it quits and put the money that would be spent on having the cylinder sorted, towards an overhaul - not worth waiting another 200 hours to your quoted 'normal' overhaul time.

If you go for an overhaul, ask around where to go. Visit the establishments and listen to those who have had work done before. Don't necessarily believe the adverts or websites. Some engineers are paid 'finders fees' to send engines to engine shops.

At work we have been using Nicholson McLaren Aviation for some years now. Good people. No problems.

I completley second Big Pistons, and by extension Silvaire's response. I ran my O-200 to more than 1500 hours beyond the recommended overhaul interval, while operating on condition. This included two complete cylinder exchanges. When I finally did overhaul it, it was because it was "making metal". It turns out that the metal was from a crimped on alternator coupling cover, and everything else in the engine was in excellent condition. As it was apart anyway, I zero'd it, but it would have happily gone on for some time to come.

"On condition" means just that. As long as the indicators of wear and potential failure are not present, keep running it. Regular operation is vital. There are not too many unknowns about these "legacy" engines any more. With compotent, and regular maintenance oversight, they will run safely for a long time.

My experience has generally been that mechanical caused failure of engines, is more condition or maintenance related, than associated with time in service. I recall more sudden failures of new and recently overhauled engines, that those with many, many hours of service,

Thanks everyone. We've discussed CAP747 with the engineer and we are all happy to do this very minor work as the engine is running as sweet as can be. (Hopefully NOT famous last words.....!)

One issue is that many MOs in the UK do not cut open the oil filter, and almost nobody does oil analysis. The "on condition" run is done on compression checks.

Personally I wouldn't do it. The money saving, per airborne hour, of running to say 2300hrs over 2000hrs, is negligible. At a £15k overhaul, I make it 98 pence per hour. Would you risk your life for 98p/hour?

That is true, which is why one should use only reputable engine shops (very rare in the UK).

This is also why there are few exchange engines of good quality. Most people overhaul their own until it is trashed, and only then do they pass it down into the exchange engine marketplace ;)

Just have the one cylinder done,send it to a reputable engine shop.Am sure Norvic will rework it for you.
I used to have a Pa28-140 ex CSE Oxford, with 4300hrs on the engine,ran great,made the climb performance when we used to have a C of A airtest every three years.
I think CSE used to have an excemption from the CAA to run their PA28 fleet engines to 5000hrs on the old Public Transport CofA.

Now, why do I find that absolutely hilarious (having had dealings with that company) ?

I am sure the FAA found it equally "hilarious" after inspecting the "procedures" in their prop shop...

TBO is only a manufacturer recommendation, as you know. This means that a new engine made on the wrong day can be much worse than any engine with 4000 hrs on it. Don't get paranoid and waste money on a completely new engine - that's just what Lycoming wants you to do, hence the TBO number they've set. Change what needs changing and continue flying. You'll know when it needs to be overhauled completely.

And as someone else said - you're highest likelihood of an engine failure is when they're new and not run in. I can't tell you how may times I've heard of engine troubles up in the first 50hrs after an overhaul, some with catastrophic results.

What you find is that many people who patch up engines, most often done on a twin, and try to run them as long as possible, invariably end up with an engine failure at some point.

I wouldn't want an engine failure, and particularly not in a SEP. So I play safe and had the engine rebuilt by a reputable engine shop, even though it was less than TBO when I had it done. The reason I did this was a) it was subject to a shock load inspection anyway and b) it had had a new cylinder bolted on recently which told me that something was possibly amiss.

As the engine was new to us, it was an unknown quantity. If however we get to TBO next time and the engine is running just fine, we will run it on condition, but at the first sign of trouble we'll get a major overhaul by a good shop.

I wouldn't mess around with bolting on new bits if you are beyond TBO, if the engine is running fine at TBO then yes, run it on condition. Bolting on new bits past TBO indicates that the "condition" of the engine is not really what it should be....

Adamfrisch
 

There is a lot of truth in what you say about a good old engine being better than one that has had a factory overhaul but it is not that simple, putting new parts on an old engine is likely to be costly in the long run.

An engine that has reached TBO is only worth the core value of the engine, if you put new cylinders (About £ 3K for a O-360) the engine is still only worth the core value and your aircraft value will be depressed by the cost of an overhaul (About £ 10.5K).

You will have to do 571 hours on the engine before you break even on the hourly cost of cylinder replacment, this of course is assuming that you have no other problems with the engine that result in you having to overhaul it, the chances of having a camshaft failure on an engine this old are high and this would likely wreck your new cylinders so that you could not overhaul them (less likely with a full flow oil filter).

As you can see the whole thing is a minefield but it points to not investing in a lot of money in an engine that is near or over TBO.

The only thing that I cant understand about your post is the term "run in" perhaps you might like to tell us a little more about this?