On the other hand, peripheral items is another matter. A failing water
or oil
pump, ignition coils, injectors, oil cooler or radiator is a much more
likely
failure and just as serious than the much more unlikely failure if the
basic
engine itself. How exactly do you expect the engine itself to
catastrophically
fail?
Loss of compression, failed water seals, or a failed apex seal come to mind
without thinking real hard. High BMEP applications aggravate the situation.
Average horsepower usage for vehicle application is probably less than 50
hp. I'll bet average horsepower for aviation use is double that, at least.
IŽll grant that the first two items are not necessarily catastrophic
failures. However, an engine failure does not have to be catastrophic for it
to be a major problem in an aircraft. It just has to stop generating
whatever sufficient power you need to sustain flight.
I would be very skeptical about putting a junkyard motor with perhaps well
over 100,000 miles in an aircraft, where the load factor will be much
higher. The buyer has no idea if said engine has previously been starved of
oil, overheated, over-revved, otherwise abused, or just plain neglected.
Note that I'm not saying that these engines are inherently unreliable. I
think they are excellent motors, and very reliable -- provided they were
maintained. If the donor vehicle was maintained, you wouldn't find it in a
junkyard unless smashed, or just a rare find. The majority of rotary powered
donor vehicles, RX-7's, I see in the junkyards though, seem to be there from
problems that accumulated to the point where the previous owner could no
longer see the economics of keeping it running.
If someone were to ask me my opinion, I would say, sure get the junkyard
engine as a source of parts, but plan on rebuilding it with new rotor
housings and seals at a minimum.
Your point about the peripherals is good, but I would suspect that most
folks here would address these issues up front.
IMHO.
Regards,
Rob
They don't fail all of a sudden unless you fracture the apex seals and then
only one or two are broken. The engine still makes power. Leaking
water seals will give you plenty of warning.
I agree with the junkyard purchase. You won't find any bargains there.
The original thread was about buying a running car from a private owner.
Perry 120,000 mile engine would still be flying fine if he had not broken
a tension bolt. One can remove the tension bolts one at a time, coat them
with red RTV and replace them. Or replace them with new ones to be on
the real safe side. Perry's engine ran fine with the broken bolt for at least
30 hours and a 700 mile trip until the engine started leaking internally.
Even then it would still takeoff and fly as Perry proved several times.
Paul Lamar
David Sowers wrote:
I'm the one who is considering getting an engine from the junkyard. I assure you
that it will be totally disassembled, inspected, and rebuilt with utmost care
since i'm the one who wants to fly behind it. I have more time than money and
will take the time to ensure that everything is working well before it will be
airborne.
Dave Sowers
I got a real junk engine from the junk yard :-) One rotor was useless
as were the rotor housings. The point is you will probably get better
parts if you buy a running car for overhaul. I don't suggest doing what
Perry did. I always recommend overhauling the engine your self so you
know what goes in it. I think Ken also has some experiences along these
lines. I think you are more likely to get a better core for overhaul
if you buy a good running car.
Paul Lamar
Ken Powell wrote:
Just for the record, I have bought 3 engines from the junkyard, all from cars that were obviously not running when junked (no body damage). I also have owned 1 '86 RX-7, which I had to rebuild within the first 200 miles of ownership because of a collapsed coolant oring land which is a common failure on the '86's due to core ship when cast. From the 3 junk yard engines I have enough parts to build 1 engine that is completely within specs, a second engine that would be OK but really needs the housings lapped, and the 3rd engine would definitley need the end housing lapped and new rotor housing (plus a new/used rotor due to apex seal failure). So, as you can see a junkyard engine may not be all bad, but the odds are high that you will have to buy at least 2 of them and you need to be prepared to have the end housings lapped (this costs ~$200). I am also installing new hardened stationary gears from the '89 to '91 models.
Ken Powell
kenpowell@aristotle.net
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