914 leak down

[BrendAn]

4 hours ago, F10 said:

Lots! 2500. But still returning great leak-down numbers and regular oil changes/oil filter checks, show no glitter! The Rotax 80 Hp 912 ULP engines are the jewel in the Rotax crown, if you as me. They are pretty unstressed and I have heard when opened up after 5000 Hrs, you can still see the honing on the bores. As I said, I have heard this. Anyone with more info, happy to hear it.

I know where there is a 912 uls in a box that has 3600 hrs and still passing all tests, it was only removed because the owner thought it was time but it still performed flawlessly.

[facthunter]

Limits of materials and physics apply to all engines. They are all capable of failure  The 80 HP Rotax will be the best of them.   You can't prove much with one engine. It's too small a  sample to be significant.. Nev

[facthunter]

They fact they are stretching and loosening hold down studs doesn't bother you?.  Nev

[BrendAn]

2 minutes ago, facthunter said:

Limits of materials and physics apply to all engines. They are all capable of failure  The 80 HP Rotax will be the best of them.   You can't prove much with one engine. It's too small a  sample to be significant.. Nev

Those big bores have been fitted to a lot of engines and you don't hear if any problems. 

[BrendAn]

I have seen a 912 uls standard that was fretting the case joint. The crank getting tight to turn by hand.

 

Actually my jabiru is like that when it's hot but turns easier once it cools down.

 

 

[facthunter]

It's crank run out or case warping causing those things.   Not something you want or should have with any motor. Nev

[BrendAn]

23 minutes ago, facthunter said:

It's crank run out or case warping causing those things.   Not something you want or should have with any motor. Nev

the 912 got changed out.

as for my jabiru, what i am feeling may be normal. i need to pull over another hot jab to see. it runs like a clock, smooth and quiet, doesn't mean it won't crap itself, sort of expect it to when you own a jab.

Edited May 28 by BrendAn

[facthunter]

Watch how they stop when shut down. A good motor will bounce back off compression.  Nev

[F10]

Yes I wonder about that? You seem to get all these cylinder head mods, power flow exhaust systems and bored out barrels for more power... But the bottom end, crankshaft and journal bearings or conrod big ends are never mentioned? Are they able to handle the higher power output? I feel engine life/reliability may be shortened. 

[facthunter]

You would expect so. Engines operated at higher power outputs have reduced TBO's Nev

[F10]

22 hours ago, BrendAn said:

I know where there is a 912 uls in a box that has 3600 hrs and still passing all tests, it was only removed because the owner thought it was time but it still performed flawlessly.

 

 

 

 

Yeah, running on condition is just that, I think. To my mind perfectly acceptable with the restriction on training etc. Most motors can bed in very nicely if not abused and should last as long as they show no problems. There are a few reasons I think the 80Hp 912's are pretty hardy. One, the liquid cooling trends to keep engine temperatures therefore expansion rates, far more stable than air cooled. If you handle them right, keep a bit of power on in descent and so on, no shock cooling occurs.  They are well made and the 80 Hp is fairly low stressed. The oilways are well thought out and it is well lubricated.

I am happy with compression tests but this coming annual I am keen to organize a  borescope check to have a look see. Certainly would do that at first sign of trouble. Also, piston engines will rarely fail and stop dead. You will normally get some sort of warning. Vibration changes, slight misfire or new noise. Temperature or pressure changes, from what you normally see, noticed in the cruise. Keep a look out for any change in behavior.

 

I guess one problem may be forcing yourself to accept something is not right! Because you know it will lead to $$$$$!! 

[facthunter]

You can WISH things were so because that saves money or making decisions. Nev

[Red]

15 hours ago, facthunter said:

You would expect so. Engines operated at higher power outputs have reduced TBO's Nev

Yea, the limiting factor on 912 series is the crank rigidity, its a multi piece pressed together crank and too much torque will twist it.

This is what governs the allowable boost on a 914 for instance though the Rotax limits are very conservative for arse covering reasons (there is a little dongle that can be purchased for the 914 that allows a higher boost , dubious legality )

 

[facthunter]

 Pressed  up cranks are highly strained when just sitting there . The later ones have a slight taper of the bit's that press together and a higher torque test figure  which can only be done at the factory with NEW bits. Nev

[rhtrudder]

On 29/5/2024 at 12:49 PM, F10 said:

Yes I wonder about that? You seem to get all these cylinder head mods, power flow exhaust systems and bored out barrels for more power... But the bottom end, crankshaft and journal bearings or conrod big ends are never mentioned? Are they able to handle the higher power output? I feel engine life/reliability may be shortened. 

I guess that’s why the the hot up mobs offer to weld up the crankshaft to take the strain of the extra power, I think I will leave it standard 

[facthunter]

Don't weld It. That doesn't work.  A Pressed up crank is an extra liability however you look at if. I would have done 1,000s of them in my lifetime.   Nev

[Red]

On 28/05/2024 at 7:23 AM, BrendAn said:

the 912 got changed out.

as for my jabiru, what i am feeling may be normal. i need to pull over another hot jab to see. it runs like a clock, smooth and quiet, doesn't mean it won't crap itself, sort of expect it to when you own a jab.

Mine did that and it was low hours it's supposedly common.

My theory was that the torque required to clamp the cases using just the through bolts is so high that when the aluminium cases expand (expands more than the steel through bolts  expand in length) the case  clamps down on the mains.

Noticeable that on something like a Continental engine the cases are held shut at the case edge by multiple bolts and don't exhibit this problem.

 

[BrendAn]

4 minutes ago, Red said:

Mine did that and it was low hours it's supposedly common.

My theory was that the torque required to clamp the cases using just the through bolts is so high that when the aluminium cases expand (expands more than the steel through bolts  expand in length) the case  clamps down on the mains.

Noticeable that on something like a Continental engine the cases are held shut at the case edge by multiple bolts and don't exhibit this problem.

 

Excellent info . Thanks for that.

[BrendAn]

4 hours ago, facthunter said:

Don't weld It. That doesn't work.  A Pressed up crank is an extra liability however you look at if. I would have done 1,000s of them in my lifetime.   Nev

Pretty sure edge weld their 912 cranks and they are not dummies.

On the downside I just found an article on the edge 155 HP 914.

It has to stripped and inspected every 500 hrs. 

Edited May 30 by BrendAn

[facthunter]

The Continental has big bolts too but also the smaller ones around the case edge. Your main bearing fits would have to be a bit on the tight side for that to happen. 

ANYONE Who welds up that kind of crank IS A DUMMY.   It ruins the whole concept of a pressed up crank. Destroys the heat treatment of the original parts, distorts the whole thing and creates stresses.. It's a Bull$#!t idea full stop..Nev

Edited May 30 by facthunter

[Red]

12 minutes ago, facthunter said:

The Continental has big bolts too but also the smaller ones around the case edge. Your main bearing fits would have to be a bit on the tight side for that to happen.  Nev

My point is that it doesnt wholly rely on through bolts to keep the cases shut they have sensibly placed bolts around the edge of the case and dont rely on overly clamping the central mass where the mains reside just to stop the case leaking or fretting.

Whats your theory on it Nev?, I'm sure you have one

 

Edit..sorry thread drift🙃

Edited May 30 by Red

[BrendAn]

11 minutes ago, facthunter said:

The Continental has big bolts too but also the smaller ones around the case edge. Your main bearing fits would have to be a bit on the tight side for that to happen. 

ANYONE Who welds up that kind of crank IS A DUMMY.   It ruins the whole concept of a pressed up crank. Destroys the heat treatment of the original parts, distorts the whole thing and creates stresses.. It's a Bull$#!t idea full stop..Nev

i would have thought the welding process would involve some way of protecting or re heat treating the crank.  i  will see if i can find any stories of edge performance cranks failing.

[facthunter]

. It would be better to have the extra small bolts  for case joint stability but the other bolts are similar. They resort to using some pretty strong sealant on the Jab. The Continental 0-200 series has big bore sizes and less main bearings.  Motors are never stiff and the cases are very strong on the bottom half.  .  Nev

[Red]

16 minutes ago, facthunter said:

The Continental has big bolts too but also the smaller ones around the case edge. Your main bearing fits would have to be a bit on the tight side for that to happen. 

ANYONE Who welds up that kind of crank IS A DUMMY.   It ruins the whole concept of a pressed up crank. Destroys the heat treatment of the original parts, distorts the whole thing and creates stresses.. It's a Bull$#!t idea full stop..Nev

You replied to 2 different posts from 2 different posters, in that single reply, gets confusing for readers. Can you try and make some indication of who you are replying to in your posts (most use the quote function) Thanks☺️

[facthunter]

No process can be available to stop ruining the original heat treatment and pin fit. If there's any carbon in the parent metal it will cause a line of hardening near the weld edge. IF you anneal that out it goes soft and loses some of the clamping interference fit. Be interesting to ask Rotax what their opinion os about that and the FAA.. (they probably would not have a clue either.  It's basic metallurgy and heat treatment lore.   Nev