What to ask when buying an engine?

[Marty_d]

Hey folks,

 

I'm looking at a 912ULS for the 701. Second hand, removed from a training aircraft at 2100 hours.

 

I've been told the following:

 

- Engine age: approx. 6-7 years.

 

- Rubbers: replaced around 2 years ago.

 

- Leak down: worst reading 76/80.

 

- Oil test: 25 parts per million (I assume this is the test for metal particles)

 

- Fuel pump: replaced prior to rubbers so due next couple of years.

 

- Gearbox: needs 1000hr test so probably $400-500 there.

 

- Serial number is in the 6700 range so would have the new casing (if I've read the manual correctly).

 

- Apart from one flight when new, never used 100LL.

 

All this, to me, says reasonable condition for the age and the price. However I am a total newbie when it comes to engines.

 

What other questions should I be asking?

 

Thanks, Marty

 

 

[old man emu]

What is the TBO for these engines?

 

I'd be wanting to have a real good look into the engine log-book if one exists. If one did not exist, I'd look elsewhere.

 

 

[bexrbetter]

- Does it run mate?

 

- Your Son ever use it on weekends?

 

I think you should do better than 2100 hours, it might be fine but it's right at the far end of time.

 

 

[Downunder]

New case was after 2006, so all is good there.

 

Hours are relative to price but I think 2100 is ok if leakdowns are ok. (BIG bonus that no avgas was run through it)

 

You might want to get the g/box inspection/ overhaul prices sorted before purchase. (Maybe strip and quote)

 

Rotax parts prices are horrendous. It could go 3 times the price what you expect but again, no avgas is good.

 

It should have the soft start modules from factory.....

 

The original oil pressure sender was the black honeywell around that time...... these are known to fail and they are not made anymore.

 

The latest "keller" works well for a few hundred dollars.

 

Would be good if it was still in the aircraft and running to inspect it....

 

There is a training aircraft locally coming up to 2000 hrs so it may have the engine for sale also.....

 

 

[Marty_d]

Thanks for your replies.

 

Engine log book - pretty sure he said it was complete. Will have a look at it. Engine came out of a training Foxbat so hopefully it will be. (Engine is located at the other end of Tassie, I'll have to plan a road trip to have a look.) TBO on this is 2000, which is why he had to replace it to continue using the aircraft for training.

 

2100 hours - yes that's high, but Rotax's are known to run on condition past 3000 and 4000 if maintained properly. Given it's put those hours on in the last 6 or 7 years (300 hours/year average), means it's been used regularly and not left to sit in a hangar for years on end. Last flight before he put in the new engine was over Bass Strait so he had confidence in it.

 

Gearbox strip/quote prior to purchase is a good idea Downunder. Unfortunately I can't see engine in the aircraft as it was removed 2 months ago and inhibited.

 

All good points! Any more?

 

 

[Downunder]

There's some engines with suspect cranks around that time.

 

Service bulletin SB-912-064R1

 

https://teveso.cz/content/wys_zpravy/SB-912-064UL_R1.pdf

 

 

[fly_tornado]

have a listen to it start up from cold without a prop on it and see if the valve train is noisy

 

 

[old man emu]

If the engine is "on condition" that means that the person who has serviced it over a good deal of its life has intimate knowledge of it and is prepared to put his neck on the block to allow its continued use after manufacturer's TBO has passed. You'll either have to take the engine back to the person who put it "on condition" or find another person who is willing to take the word of the former maintainer.

 

 

[facthunter]

If the price is right the usage seems as good as you would normally get. The training aircraft must have airframe /engine log book records that correspond and it's been regularly used in a non dusty environment and serviced? Now inhibited. You could check the valves and valve springs without going over the top. Carbs for float mods and mikuni pump kit. Nev

 

 

[rankamateur]

Engine came out of a training Foxbat

Was the Foxbat at Glen Innes?

 

 

[Marty_d]

Was the Foxbat at Glen Innes?

Nope, Tassie.

 

 

[rankamateur]

Nope, Tassie.

Good!

 

 

[Marty_d]

There's a story there?

 

 

[rankamateur]

When the prop is hard to pull through and the cause is a bent crankshaft!

 

 

[skippydiesel]

New case was after 2006, so all is good there.........................................................................................

The original oil pressure sender was the black honeywell around that time...... these are known to fail and they are not made anymore.

 

The latest "keller" works well for a few hundred dollars.

 

.....

A Speco oil pressure gauge & sender works very well and will only set you back about $80

 

 

[Blueadventures]

If the price is right the usage seems as good as you would normally get. The training aircraft must have airframe /engine log book records that correspond and it's been regularly used in a non dusty environment and serviced? Now inhibited. You could check the valves and valve springs without going over the top. Carbs for float mods and mikuni pump kit. Nev

Agree and add that its worthwhile if you go ahead with the purchase to add in servicing the valves.

 

 

[Lyndon]

At those hours I would bet the cam is gone. If you do buy it take off a barrel and have a look. 1200 for a cam plus lifters. Case needs to be split. Flat tappet valve trains don't last long. New rings for sure 600 bucks. . Barrels should be fine and the heads and valves should be fine as would be the bottom end. Gearbox service is easy as. You need some special tools which you can buy from bert flood.

 

Remember don't hone those cylinders. Crc and and a clean rag is all they need.

 

Also don't touch the valves. They are non serviable. Valve stem seals. New colets. Check your heads for hardness. Media blast them and if you want a very light hand lap on the seats.

 

Lyndon

 

 

[eightyknots]

All good info here! Next question

 

What fair price should one be paying for an 2,000-2,100 hour Rotax?

 

 

[Downunder]

All good info here! Next questionWhat fair price should one be paying for an 2,000-2,100 hour Rotax?

5 to 6 grand?

 

 

[facthunter]

Too variable a question to give an absolute answer. Some would be worth very little. Nev

 

 

[alf jessup]

About $1700 for a overhaul including new gear set replacement , pressure washers ect on a Rotax gearbox including labor.

 

2100 hrs on the engine, just run in, gearboxes are the weakest link on a very robust built engine.

 

2000 hr TBO is one way Rotax keep making money selling parts that most likely don’t need replacing , otherwise they would go broke.

 

 

[Marty_d]

The seller has emailed me pictures of the aircraft's maintenance log from the 1,000 hourly onwards. Looks pretty comprehensive and every 50 & 100 hourly is noted fully.

 

Oh, I don't think there's any chance of Rotax going broke - just by what they charge for a new donk!

 

 

[alf jessup]

The seller has emailed me pictures of the aircraft's maintenance log from the 1,000 hourly onwards. Looks pretty comprehensive and every 50 & 100 hourly is noted fully.Oh, I don't think there's any chance of Rotax going broke - just by what they charge for a new donk!

Marty

Good old adage.

 

You get what you pay for.

 

Rotax are expensive but they are robust.

 

50,000 or more 912’s built in 30 or so years.

 

Got to be doing something right considering most light sport manufacturers fit them.

 

But yes they are still an internal combustion engine and can have failures.

 

Clean fuel, clean air filters, regular oil & filter changes will go a long way to keep you running.

 

 

[facthunter]

If there was anything to replace them with they would hardly sell one they and their bits are too dear.. They are not a GOOD design from a few points. Built up crank is unnecessary and has been the source of. a few problems

 

It can't easily be enlarged. (more cubes).This is a fairly common aircraft engine situation.

 

The inlet manifold set up is quite bad..Fuel distribution is not good and is hard to improve. The existing manifold design is the problem. The Bing Carbs are a cheap thing and shouldn't be high up on the motor. especially with float equipped carburetters

 

Liquid cooling (only the heads) is a trick system with a lot of complexity for only cooling a critical part. Often they run too cool.

 

The oil return system is quite weird. I wonder who was so clever as to think the crankcase pressure is a good way to scavenge the oil.back to the tank rather than use a scavenge pump.

 

The engine cannot be zero timed. It life expires on a time since put in service as well as in use hours. One of it's saving graces is it doesn't need to be opened up very often. Working on engines is no problem if people know what they are doing. Unfortunately they rarely do so leaving your Rotax alone is a good point. Nev

 

 

[alf jessup]

If there was anything to replace them with they would hardly sell one they and their bits are too dear.. They are not a GOOD design from a few points. Built up crank is unnecessary and has been the source of. a few problemsIt can't easily be enlarged. (more cubes).This is a fairly common aircraft engine situation.

The inlet manifold set up is quite bad..Fuel distribution is not good and is hard to improve. The existing manifold design is the problem. The Bing Carbs are a cheap thing and shouldn't be high up on the motor. especially with float equipped carburetters

 

Liquid cooling (only the heads) is a trick system with a lot of complexity for only cooling a critical part. Often they run too cool.

 

The oil return system is quite weird. I wonder who was so clever as to think the crankcase pressure is a good way to scavenge the oil.back to the tank rather than use a scavenge pump.

 

The engine cannot be zero timed. It life expires on a time since put in service as well as in use hours. One of it's saving graces is it doesn't need to be opened up very often. Working on engines is no problem if people know what they are doing. Unfortunately they rarely do so leaving your Rotax alone is a good point. Nev

Seems to work though Nev