I overhaul mine at 500hrs – I have a spare (single shaft dual mag) on the shelf, at a cost of $2500, so one can be away overhauled (I would not use any company in Europe)
What’s the beef with UK piston power plant shops, Peter? You are pretty consistent with your attitude towards them…say having the same level of respect as something you have just trodden in 
Without doing anyone working on aero piston engines a dis-service, it’s not that hard is it?
In the UK, we build a great deal of the world’s most complex, most performant engines. Relative to these, aircraft engines are built to the nearest half brick.
Surely this isn’t beyond the skill of the native workforce?
Just curious 
An inspection is cheaper than an overhaul, but with an overhaul you get NDT of the casing which is probably important because cracks in the casing, near the point where the mag is secured to the engine, are not unheard of.
Or alternately, if they’re Scintilla/Bendix/TCM, you might walk them them over to the grumpy but actually pretty friendly guy who has a 40 year collection of overhaul parts in his hangar, and do the job there with his help and sign-off (for the price of parts). Unfortunately for me I have Slicks on both planes, so my approach has been to trade them in on new ones. If you’re really smart, you trade in a set of zero-value Eisemanns that have been littering somebody’s hangar for the last several decades and keep the old Slicks.
Masterofnone, Peter has quite rightly identified that there are a couple of quite well known outfits in the UK that have some pretty toxic history behind them which, seemingly, the CAA have chosen to turn a blind eye to. In addition, when it comes to some of the more complex machining processes involved with recovering damaged crank-cases and cranks, in nearly every single instance the repair is done by an outfit in the USA. All that being said, in many cases, if you want an engine overhauled, you might as well mail it to the States, as that is often where it will end up….
An inspection is cheaper than an overhaul, but with an overhaul you get NDT of the casing which is probably important because cracks in the casing, near the point where the mag is secured to the engine, are not unheard of.
I don’t agree, have worked some years in magneto shop (next to the avionics shop), and sometimes still do when the magneto shop is busy. The NDT / OH makes thinks actually worse then better. 500 hrs inspections however are a good idea in my opinion.
The problem with NDT inspection that is will have lots of indications (due to poor casting). Of the hunderds of magneto’s I have seen their where only two cracked, and these where obviouse. This mostly occurs (also from FAA data) on aircraft which have poor access to the magneto.
A lot has to do with craftsmanship when it comes to magneto’s. I would definitly rather have a proper inspected or overhauled one that a new one. Seen quite a number of new mageneto’s which damaged rotors due to far to much play on the axle, worn housings etc, damaged coil due to wrong installation, no point opening because the factory forgot the lubricate the cam.
The funny thing is, if you have these really big 1200 magneto’s, they are allowed to have serious cracks and still be serviceable. In my opinion it would have been better to stay with the visual inspection, using a 10x magnifier. Don’t forgot that the NDT process at a lot of costs as well, to no or negative benefits I would say.
you might walk them them over to the grumpy but actually pretty friendly guy who has a 40 year collection of overhaul parts in his hangar, and do the job there with his help and sign-off (for the price of parts).
I have been told (probably inaccurately) that none of the D3000 magneto casings remain in the overhaul market anymore. So if yours cracks, you can forget the magneto. I am sure there are some old mags sitting on dusty shelves but they need to be not corroded.
All the other parts either never break, or they are made under PMA.
Surely this isn’t beyond the skill of the native workforce?
I might recommend becoming an aircraft owner and exploring the maintenance business from that position
When the parts availability issue hit the news about 3 years ago, one of the worst was the impulse coupling spring. I then found a UK firm which “had them in stock” and sent my mag to them for OH. They later refused to let me have a copy of the work pack for it, and there are very few explanations for that which do not involve major dishonesty and possibly the re-use of previously condemned parts (an area in which that company turned out to have previous form – easily found on google and I think I posted the link here before). I later got a report on that spring which thought that it was an old used one, not the new one which it should have been.
One advantage of the US scene is that it is much bigger and it is much easier to do due diligence, and find a company which has a good reputation. In the UK it is almost impossible to find a company which has a good reputation. You can find one person who speaks well of one firm and then you find another who found the exact opposite.
For example the company which did this was highly recommended… and of course they have every imaginable approval. Some of what they did was actually potentially life threatening. And it wasn’t just one person there; the MD was quite happy to bodge some wrong size screws into the circuit breaker panel which was hanging off by 1-2" when I finally collected the aircraft, right in front of me.
The problem with NDT inspection that is will have lots of indications (due to poor casting)
What magnetos was this found on?
I would not use that as a reason to not do NDT. It seems to me that the argument comes down to value for money, and I can see that a “repair” is much better value. But, for me, the “magneto overhaul fund” is about $3/hr which is insignificant.
One could make the same argument, I am sure, about the propeller. There is no good reason to “overhaul” as that involves removing leading edge metal for no good engineering reason if there is no significant damage.
Does a D3000 magneto have any plastic parts which are common to both mags? I think the central drive gear is steel. If that is so, the lack of redundancy is really just in some material breaking off one of them and jamming the other.
I might recommend becoming an aircraft owner and exploring the maintenance business from that position
Point taken! It wasn’t that I doubted your perspective, more that I was curious as to how you got it
Looking at other forums, it is clear that you can never get consistent advice on MO’s
Whilst the concept of being a single, CofA aircraft owner looks good on paper, the realities of it are a total turn off. I just have no desire to expose a reasonable proportion of my life to the hassle and financial minefield that is CofA aircraft ownership. There are just too many horror stories. Its something that will have to wait until I have too much money to care (hopefully sometime soon )
The horror stories regarding maintenance are truly awful. It’s bad enough to be forced to have someone else work on the aircraft. But when they screw it up, and subsequent complaints to the CAA are met with the response “Sorry, that’s none of our business…..issues of airworthiness are the pilot’s responsibility” – that’s a red light to me!
Note, this has fortunately not come from personal experience, just stories I have heard several times, from different, unrelated people whom I have no reason to believe would lie
I have had three engines overhauled at Norvik and was always pleased with the outcome – so one vote for a UK established outfit. I can also think of overseas European customers who use them.
I am sceptical on the MTBF of 50,000 hours for piston engines – I tend to think 5,000 more likely.
I am sceptical on the MTBF of 50,000 hours for piston engines – I tend to think 5,000 more likely.
I am rubbish in maths but I am sure that if the MTBF was 5k hrs then of the order of 50% of engines would be smashed up in forced landings (of various severities) or lost in ditchings, before reaching the 2k hr TBO.
Can anybody work this out correctly?
Some of the old Rotaxes had a terribly bad name, and I have read accounts from microlight pilots who said they expected an engine failure every 200hrs.
I know I am critical of UK maintenance facilities but I could write a lot of stuff on my experiences. It has been suggested that I attract these people but I don’t see the mechanism which would explain that. I think it’s much more likely that, following some dodgy experiences, I tend to be suspicious, I know where the skeletons are likely to be buried, and when I see a bone sticking out somewhere I quickly go and dig out the rest of it. Whereas the vast majority of aircraft owners would never find a problem because they are totally non-pro-active until something actually falls off in flight. I used to be like that – everybody is initially – until things started to go wrong. It started with small things like all the Philips screw heads getting chewed-up by the use of power screwdrivers (CAA 145 company) and it went downhill from there.
I am sure there are good firms but as I said it is really hard to research them.
http://www.vicorpower.com/documents/quality/Rel_MTBF.pdf
The maths, density functions, may require some more thought. The link is quite helpful in describing the technique, however not related to piston engines.
Given the bathtub function and that a large proportion of GA installed piston engines are at the rising part of the curve, it is quite impressive that our engines are as reliable as they are.
Will see if Google throws up some more specific studies.
…and here is quite an interesting NASA paper:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.27.1020&rep=rep1&type=pdf
I don’t think the certified engines have this bathtub distribution curve.
I think there is significant infant mortality (probably caused mostly by defective workmanship of various sorts e.g. over-tightened bolts which eventually strip) and then the failure rate is probably a gradual increase, with nothing special happening around TBO, and I suspect most owners are dead long before the engine reaches an age where it would be assured to no longer run properly; maybe 10k or 20k hours.
The MTBF of a human is apparently easily calculated at about 800 years.
