Rotax 912s tight

[Ayecapt]

Not one brass bush 8 brass bushes and 7 out of 8 have visible wear. We cant understand the mindset of the person who was responsible ( irresponsible might be better) but there ya go, i have theories on this but i cannot discuss them here. There might be some official investigtion , after all this is a maintenance incident that could have had serious consequences

 

B.

 

 

[Lyndon]

I've never done a Rotax. But I'm doing mine now. Bikes and cars only. I'm sure your mechanic is onto it but in my experience. Use only three bond with an 11. It's rubber . Not a 12. It's silicon. All silicons worm. There is lots on that motor that uses sealer. Just my opinion. Ps three bond is with out a doubt the best stuff

 

 

[Lyndon]

Your quite correct. It's just insane. WHY. If you find out love to know why .

 

Lyndon

 

 

[Blueadventures]

Your quite correct. It's just insane. WHY. If you find out love to know why .Lyndon

Absolutely agree; add in- has this person done the same deviation to other 912's. If so need to let the owners know immediately.

Regards

 

Mike

 

 

[facthunter]

It's not bronze .It appears to be brass, which is a copper zinc alloy. rubbish for bearings..Some people can't tell the difference from bronze which is a far better bearing metal and there are many different bronzes. used for high load bearings. A good bronze would do the job but if the original does the job why change anything? Apart from anything else the engine is not airworthy if you just change things like that. Another point is I can't see why it would make much extra tightness. Some rockers don't even have a closed top. They run on a ball or a half journal. which is height adjustable. Nev

 

 

[facthunter]

The oil pump should be the only part not protected by the filter. Unless it bypasses due being part blocked it should protect anything downstream of it. That's what it's there for. I don't know what size of particle it will filter out. There should be a spec somewhere. Nev

 

 

[Lyndon]

For piece of mind I can send some pics of a 1740 hrs pump. Like brand new. Some housing marks a per normal but gear s perfect.

 

Did you buy this engine recently ????

 

 

[spacesailor]

Zinc is added to copper to make Brass alloy.

 

spacesailor

 

 

[ozbear]

Rotax 912 have a gauze filter in the oil tank and settlement area at the bottom if you've ever looked at a dyson vacuum cleaner which separate the heavier particles with centrifugal force it appears to work a little like that it would stop the larger bits from heading into the system a good reason to clean it at 100hrly or sooner.

 

 

[bexrbetter]

I would be interested if you could ask the oil experts where the zinc is from

Most modern engine oils contain zinc, it's one of the standard additives used and recommended for flat lifter engines (most pushrod engines).

 

Zinc is usually in extra high concentrations in many assembly lubes and after market oil additives.

 

 

[facthunter]

Zinc compounds . are different from alloyed zinc in the bearings. I would think the analysis would be sophisticated enough to pick the difference. The oil(s) recommended for the 912 have to be suitable for the drive so would have more additives than "normal". Nev

 

 

[Ayecapt]

Quick update our heads have been stripped down valves lapped and reassembled ready for fitting soon.

 

On the oil flow into the rocker area .....it does come up the push rod middle . Then it returns via the push rod outer tube . Oil must come in and back out. Otherwise it would heat and lose its properties with time.

 

The brass of course is caught by the filter and the pre strainer in the oil return cannister. But it is being worn off these faulty rocker bushes , therefor it travels through the rest of the engine to get to the filter. The filter reduces the concentration of brass in the engine. There were signs of brass on the cylinder walls ! But it actually wasnt bonded to the wall .

 

What i still cant come to terms with is that a brand new rotax rocker bush is very inexpensive , less than $10 yet someone made up brass ones .... Cant see any sense in that.

 

 

[Ayecapt]

Im no chemist so cant comment on the zinc questions other than we had heaps of copper in the oil sample and high ish zinc but no reference to brass. And since brass ia a alloy of copper and zinc then it fair to say the brass was being de alloyed ( is there such a word) by the combustion process. Giving copper , and zinc in the oil and chunks of brass in the filter which didnt get melted in the cylinders all theory but it sort of fits.

 

I am guessing that we will see highish copper for a while after rebuilding as the remaining brass is flushed out , but it will reduce. Our oil cooler was proffesionally flushed out and there was surprisingly little brass in the cleaning fluid afterwards. So maybe there is little brass left in there. Only time will tell.

 

Cheers all lots of interesting comments . thanks

 

 

[IBob]

Quick update our heads have been stripped down valves lapped and reassembled ready for fitting soon.On the oil flow into the rocker area .....it does come up the push rod middle . Then it returns via the push rod outer tube . Oil must come in and back out. Otherwise it would heat and lose its properties with time.

 

The brass of course is caught by the filter and the pre strainer in the oil return cannister. But it is being worn off these faulty rocker bushes , therefor it travels through the rest of the engine to get to the filter. The filter reduces the concentration of brass in the engine. There were signs of brass on the cylinder walls ! But it actually wasnt bonded to the wall .

 

What i still cant come to terms with is that a brand new rotax rocker bush is very inexpensive , less than $10 yet someone made up brass ones .... Cant see any sense in that.

It's a bad situation, that's for sure.

 

Obviously whoever did it thought it would be 'all right'. I sure hope you can find out who it was so that they can be made to understand that it's anything but.

 

All the best with the rebuild.

 

 

[facthunter]

A "decent " bronze would have been alright, but brass is not. It may have just been someone mis-identified the bar of metal BUT why change from the original which works and is legal? If they are $10 more the stupidity. Incidently, the presence of fine copper particles frequently act as a catalyst in the oil and and cause premature breakdown (oxidation). Nev

 

 

[IBob]

A "decent " bronze would have been alright, but brass is not. It may have just been someone mis-identified the bar of metal BUT why change from the original which works and is legal? If they are $10 more the stupidity. Incidently, the presence of fine copper particles frequently act as a catalyst in the oil and and cause premature breakdown (oxidation). Nev

With respect, I think that's the sort of thinking that has lead to this problem in the first place. Yes, some rocker bushings in some engines are bronze. And they perform and wear in certain ways.

 

But it's a dangerous and erroneous step to assume, from there, that 'A "decent" bronze would have been all right' in this particular case. Unless one is a specialist in the specification and performance of bearings?

 

 

[facthunter]

Most who start off "with respect" don't actually have any. You make many assumptions yourself. I'm not going to list my qualifications, but it's an area I've worked in for many years. Engine mods and rectifying faults in special motors. Rocker bearings are not rocket science, and I'm very familiar with the metallurgy and design of many types. Most engines don't have them anymore, and a lot run steel on steel which is a bit critical on lubrication. Many learned people would happy to replace the plastic with a good steel backed bronze, but I'm not suggesting that, because it's not a problem in that engine (as far as I know). Where the engine is Certified it's stupid,( as well as illegal.).particularly if they are cheap and available..Nev

 

 

[IBob]

Most who start off "with respect" don't actually have any. You make many assumptions yourself. I'm not going to list my qualifications, but it's an area I've worked in for many years. Engine mods and rectifying faults in special motors. Rocker bearings are not rocket science, and I'm very familiar with the metallurgy and design of many types. Most engines don't have them anymore, and a lot run steel on steel which is a bit critical on lubrication. Many learned people would happy to replace the plastic with a good steel backed bronze, but I'm not suggesting that, because it's not a problem in that engine (as far as I know). Where the engine is Certified it's stupid,( as well as illegal.).particularly if they are cheap and available..Nev

You begin with another generalisation, but I'll leave that:

 

I think my comment is valid, which is surely more to the point here than your personal experience and qualifications, or whether or not I make assumptions?

 

For the rest, I did not comment here in order to get up your nose, or to engage in any sort of technical pissing contest. I'm sorry if that has been the result.

 

 

[facthunter]

I thought your last line required having qualifications, otherwise I certainly would not have brought it up. I also thought I was essentially supporting your position of leaving well alone, if it works OK. The stuff posted here is for general information, and I though pointing out the non suitability of Brass (which I have personally seen fail in other motor situations) might alert some people. Nev

 

 

[storchy neil]

according the power at the top these sort off repairs don't happen in ga or raa

 

as I have stated before if you do not follow rotax manuals installation service repair you are on your own

 

rotax put out these manuals so as to cover there own arse had your air craft killed or maimed some one you have lost

 

I feel that these sort off repairs have to have more accountability for the sake off saving lives screem blue bloody murder

 

oh sxxx don't waste your time telling raa or casa tell the shxx house door

 

pss hey facthunter while I'm here can you find out where the letter is from rotax saying that persons have aurthourization to alter the installation manual for rotax 912 motors

 

searched but I cant find neil

 

 

[storchy neil]

Not one brass bush 8 brass bushes and 7 out of 8 have visible wear. We cant understand the mindset of the person who was responsible ( irresponsible might be better) but there ya go, i have theories on this but i cannot discuss them here. There might be some official investigtion , after all this is a maintenance incident that could have had serious consequences

 

B.

 

might be official investigation good luck with that they will send out blind fredy to do that neil

 

 

[facthunter]

Don't twist my words Neil. I've said leave well alone. Nev

 

 

[IBob]

I thought your last line required having qualifications, otherwise I certainly would not have brought it up. I also thought I was essentially supporting your position of leaving well alone, if it works OK. The stuff posted here is for general information, and I though pointing out the non suitability of Brass (which I have personally seen fail in other motor situations) might alert some people. Nev

I could have expressed that better. I was focusing on the 'how does this happen' part of it, because as a tech support contractor in various industries, I come across 'fix a problem and make a problem (or sometimes several)' quite a lot, and it's a constant challenge as to how to avoid that. On the one hand, we require initiative of maintenance staff, on the other, we don't want them making assumptions that lead to inappropriate fixes.

 

None of that should apply in aviation: the stakes are too high for anything but by-the-book, so far as I am concerned. But here is someone who probably thought he was fixing a problem, and has in fact made several others. So I was thinking that over, how it begins, and how one can avoid it....just as I do in my work. That's all.

 

 

[ozbear]

The good thing about bronze is it doesn't melt like nylon the 912 is the first engine I've seen with nylon rocker bushes and I'm an engine reconditioner

 

Having said that I would always fit the genuine part before thinking of any substitution

 

 

[Kiwi303]

I'd be Chary about nylon too... I had a MGF, needed to watch the temp since the thermostat was on the inlet not the outlet and the head gasket locating pins were nylon. Fine for the little Metro town commuter car the engine was designed for originally, in the Lotus and the MGF there were lots of melted pins and walking gaskets due to overheating and then shock cooling when the thermostat opened.