Dafydd Llewellyn

Sadly they could indeed be at risk, as I'm sure no sales will be going ahead after this. No income generally causes a business to go under very quickly.

is 'camit' .......... a jabiru engine ?

Well, THAT may be what it takes to get Ian Bent's mods moving. Here's hoping.

Non hydraulic lifters both roller or flat faced need ramps to unload the inertia loads on the valve train. This makes them quieter and less wear on valve ends etc. I'm not surprised the hydraulic lifters gave less power. There could be several reasons for that. I'm not a fan of hydraulic lifters in aero engines. Some Continentals have them. II had an 0-300 lifter fail on take off, rendering the engine well down on power. In fact it would not climb with only 2 on board.( C-172.)

I still make cams now and did good work with a very nice man, Merv Waggott, in the early 60's. Nev

Almost all Lyconentals use hydraulic lifters.

Dafydd, It's always been the case that the ramps vary, from solid to hydraulic in general auto practice. I have heard it stated specifically the same applies to the Jab cams which I believe were outsourced. It might be possible to have a design that would work with both. I have no knowledge of this being the situation though. A call to CAMit will sort it out. Certainly anyone changing over should get the full story.Just in passing, Roller followers are less critical on cam profile. Too rapid rise may result in the edge of the follower digging into the cam of a solid lifter, as it's essentially flat. (Very slightly spherical). Nev

Well, yes indeed, it does - but I was looking at the LAA note on the rear crankshaft flange bolts. Many people would not be aware that changing to the belt-driven alternator is of benefit to them; one thinks "Alternator - electrical system" not "Alternator - crankshaft flange attachment".

The common message seems to be run solid lifters and keep the engines temps down. Have you valve geometry right. Solid lifters need a camshaft change at the same time. Also putting those heat reading washes under the plugs could affect their heat range. Perhaps go one colder on affected plugs to be safe. . Nev

Rosshave a look @ LAA's safety newsletters about Jabiru distributors

 

http://www.lightaircraftassociation.co.uk/2014/Mag/June/safety spot June.pdf

If I were operating one of these engines, I'd replace the original permanent-magnet alternator with the CAMit belt-driven alternator. That has two important additional benefits, apart from the increased electrical power capability and the benefit of field-current regulation:

Firstly, it provides a substantial reduction in the "Flywheel" inertia bolted to the back end of the crankshaft. That substantially reduces the oscillating loads on those rear flange bolts, which is probably its greatest benefit. It also increases the natural frequency of the propeller/crankshaft/flywheel system, thus moving it further away from the excitation due to the firing impulses.

Secondly, it provides a measure of damping for torsional vibration within the crankshaft.

The 2200 engine that I've been running in the test cell, is fitted with one of these, and it's keeping the test-cell battery up with no more fuss than the alternator in a modern car. The installation in an aircraft may need a separate electrical approval, and heavier wiring between the alternator and the battery.

This sort of thing is an ongoing problem for any manufacturer that uses off-the-shelf items; unless they are "standard" items - e.g. AN bolts (and then we have the problem of "bogus" parts). That's one of the reasons why manufacturers of aircraft are required to generate and supply Service Bulletins.

It's not obvious to me whether the failure shown in the SB was a "cutting" effect or a "rubbing" effect; however what IS evident is that the turning effect driving the valve rotation is sufficiently powerful, in the hydraulic lifter engine, to overcome the friction between the spring retainer and the spring, whereas it would seem to be insufficient to do that in a solid-lifter engine, with its lighter valve springs.

Whatever, all this has come about because of the issue of hydraulic lifter pump-up; and that may be traceable back to excessive oil pressure - which would bring us back to the oil pressure relief valve. This would maybe explain why so many engines DON'T show this problem.

Hmmm. Too many "maybes". Needs research. Think I'll stick to solid lifters and the original valve springs. For what it may be worth, the CAE engine uses 4140 steel for its spring retainers; in the "as received" condition it's about 2.5 times the strength of the original Jab spring retainers.

Can't tell more until I get the thing in my hands.

The SB clearly shows a quite different condition. The valve was evidently not stuck in the collets in this instance; however some torque would still be applied to the spring retainer, and the digging in of the end of the spring that resulted has evidently prevented the retainer from turning in the spring, so the thing has just settled down and continued to run.

The end of the spring obviously makes an effective cutting tool; it's obvious why Jabiru switched to a hardened retainer.

One of the less voluble followers of this thread has sent me a photo of a valve spring retainer from a hydraulic-lifter Jab 3300, at around 700 Hrs TIS. See attachment. As you can see, it shows that the ground-off end of the spring coil has dug into the seat face to some extent. If this is representative of the condition of these components after 700 hours TIS, then I do not see this as a life-threatening situation. The retainer has clearly NOT failed and allowed the valve to drop - and is not likely to for a good time yet.

As far as I can ascertain, this is the original form of Jabiru valve spring retainer, made from C1020 steel (i.e. mild steel, not free-machining) as per the original Jabiru drawing. These retainers do not exhibit this sort of damage in solid-lifter engines, to my knowledge; however the hydraulic lifter engines have much stronger springs, to help prevent lifter pump-up (though they do not seem to be a complete cure for it).

More recently, in the light of experience, I am informed that Jabiru has switched to a bought-in spring retainer, which is hardened. The subject engine had these in one cylinder, and they had not been marked by the spring. The example in the photo might not show any significant marking had the end of the spring been de-burred.

That's as much as I am prepared to say on this forum at this stage; and if this were all there is to it, I do not see any justification for the emotive garbage on this thread on this subject. I don't think I have the full story as yet, but at least here is some factual information.

And may remove the principal means of valve rotation. Swings and roundabouts again.

A good example of the oversimplification of the issues by othersYep likely some valves have failed/dropped/whatever.

did they have washer problems? or it that just what people assume because of SB.

 

The valves can give problems for plenty of reasons, crook valve, excess leakage, burnt stem, most likely is sticky guides. A long term known problem. Detailed in manuals as long as Ive owned one.

 

Ive had a few of these, have sent back 2 heads on new rebuild to be looked at. tolerances are very fine. This is what daily pull through is looking for.

 

Was taught to look VERY closely for burnt oil in rocker boxes at service as this escaping gas gums up guide. Ironically maybe they are tight from new, loosen a little, then begin to gum up all maybe in 300-400hrs???

 

Theres some link to overheating too but cant think of it

 

Jabiru are aware of it and are doing things to make this type of failure less catastropic, recessed pistons is a recent one. Roller rockers and Camit rockers are to help side loading and guide wear???

 

Can valve problems be linked to detonation in any way?

Question ,Have these retaining washers been failing in "from new " heads , or are the failing in overhawled top end heads ,

Mike

1. Have these retaining washers actually been failing?

2. If so, what is the failure mode?

3. If we have an answer to Q2, who has the failed part?

4. Was the failed part analysed to determine its metallurgy & heat treatment condition?

5. If not, why not?

Well, Andy, you can get an answer to Q3, surely?

I'd observe that "valve bounce" is in fact what happens when the valve springs reach their critical surge frequency - i.e. normally an RPM well above what the engine was designed for. This causes the spring to momentarily lose its pressure. That would definitely cause mischief in the valve collet area - but I'd not expect this to be a likely cause in a Jab engine in an aircraft. See

Nev, my apologies - I know well that you have similar views to myself.

POST EDITED AS IT DOES NOT ADD VALUE - MOD

I've never come across a wear problem with valve collet retainers, in the taper; really, there's no reason why the taper should wear, unless the valve springs are surging, because there should not be any relative movement between the outer faces of the collets and the bore of the taper. Normally, I have to tap the collet holder with something to release the collets, in fact. So I really want to see one of these failures with my own eyes.

POST DOES NOT ADD VALUE - MOD

With the continual ongoing failures of the same internal components within the Jabiru engines, the time will be forthcoming in the not to distant future whereby if unfortunatley there is a fatality in this type of aircraft that is considered to have resulted from an engine failure & further more if CASA, RAA or Jabiru have done nothing about the known defects that may have contributed to the engine failure apart from tooing & froing & passing the buck & sitting on their respective hands, then in all probability they will be required compulsarily to give a PLEASE EXPLAIN to the Coroner in the event of a CORONIAL INQUEST being conducted, which may result in the CORONER making certain specific recommendations in order to prevent similar occurrences, which seems to be the only consolation at present to concerned Jabiru owners & pilots.

I'm trying to pin down exactly what components, and why are they failing. So far, no useful answers.

It's a critical part not because the springs wear them out. I've actually never seen that happen in any other motor. The collets sometimes pull through the body due to high loads and soft metal IF the valve springs are strong. and the taper expanding or wearing. Nev

OK, I saw that before. So, you have in your engine a set of washers (or Collett retainers) that you consider defective. Next step - beg, borrow, purchase or steal a replacement for one of them, install it, and send the one you remove from the engine to a laboratory (e.g. Alphatest, Brisbane http://www.alfatest.com.au/ ) and pay them to give you a material ident and a hardness. That will give you a certificate from a NATA laboratory that states the material and heat-treat condition of the part you have, whose history you know.

With that, you can do one of two things - either send the part, plus a copy of the certificate off to CASA with a filled-out CASA defect report; you will have to say that you consider the part defective because it wears too fast, and argue that the Jabiru SB proves your point. You could possibly consider having the lab. test an automotive equivalent part, to get a comparative composition and hardness.

Or, you can try to find out what the Jabiru drawing for that part calls for by way of material and heat-treatment. You could perhaps ask Ian Bent, if Jabiru will not answer.

If you can prove that the part is not in accordance with the drawing, you will have some solid evidence. If it is in accordance with the drawings, but inferior to an equivalent automotive item (as shown by test results) you will have a different argument.

This process is standard practice to justify a substitute component

POST EDITED AS IT DOES NOT ADD VALUE - MOD

So Dafydd, you say" put up or shut up ! " You are missing the point, Jabiru have a SB to check the washers, they know they wear out and drop valves ! Because the were ok to start with then changed them and now they are soft and wear out, the problem is a committed manufacturer would have recalled and replaced them and discontinued the part ! You are very quick to read out the rules like CASA, that's because you think like CASA ! but I think this way, if there is a problem fix it NOW not later or when someone gets hurt ! Maj, the Ibis was one but there were a few other Australian manufacturers.

Radials are the ones with substantial counterweights. Yes most aero engines don't counterweight where they can get away with it , to save weight, but a bit of extra bearing loading happens then, which stresses the crankcase more.. I think we could get away with a slight variation from even firing impulses in a vee. I notice most of the upgraded VW aero conversions run counterweights. Their cases aren't strong.. Nev

To the extent that one can "build up" a multi-cylinder engine (in principle) by "stacking" two-cylinder units, it will be possible to delete part or all of the intermediate counterweights - completely, in the V-4 layout - but the V4 firing order is pretty wild. You'd find the armchair pundits blaming it for all sorts of things.

Thanks for that. There is still a severe pulsing concern because of the lack of flywheel effect and common to all flat or inline four cylinder engines, That of having all 4 pistons stationary at the same time twice per revolution. A well designed Vee 4 is better in that respect and with the optimum Vee angle, particularly so.. Surely the starter helps the retaining screws/bolts on the flywheel to move also. Nev

Vee engines tend to need fairly substantial crankshaft counterweights. The flat four and flat-six layouts get away without counterweights, so they can result in a lighter engine. That's why they are so common, I suspect.

I'm aware of the specificity of the testing requirements. engine to prop.. Sensenich are a respected manufacturer but their composite has problems on the Jab and not other engines. If there were no issues with torsional vibration in the rev range why the prop damage and loosening problems and the flywheel retaining problems?. A wood prop forgives many sins. How much must it forgive on the Jab? Nev

The Jab 2200 shaft tested free of resonance in its required range; however the 3300 is another question, to which I do not have any knowledge. The CAMit belt-driven alternator definitely acts as a torsional vibration damper on the 3300. I have never liked the flywheel or propeller flange connections on the Jabiru engines; however they passed the required JAR 22H endurance run on the Jab 2200 J and C engines, so they work if everything is right. The 3300 has the same bore & stroke (uses the same cylinders) so its peak torque should be no greater.

Wood propellers must be driven by friction between the propeller and the flange; and again, I suspect the margin is not great - tho it certainly works if everything is right. On the Seabird Seeker, the propeller flange (Lycoming 0-360) is definitely too small to be reliable with a wood propeller (which the Seeker has, because it's a pusher and the propeller works in dirty air, which causes problems with metal propellers), so it has a propeller extension that has an 8-inch flange diameter, with eight bolts, not six - and each bolt has nine Belleville washers, to maintain the clamping pressure. Few manufacturers go to that amount of trouble - and the Seeker has problems, because well-meaning but ignorant maintainers persist in over-tightening the Belleville washers.