Dafydd Llewellyn

And in doing so, they would drag CAMit down with them. NOT the desired outcome.

You mean a CAE data-plate engine? No; and that's one of the first things to sort out.

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

Yep; I'm aware of that. I think Ivan Tighe was involved in the original Jabiru cam. Almost all Lyconentals use hydraulic lifters.

Nev, I'd agree this is normal automotive practice; however the power output of hydraulic lifter Jab engines with the flat-face followers was noticably down from the solid lifter engines that preceded them. My understanding is that that was a consequence of the cam profile NOT being altered to suit the hydraulic lifters. I think the roller followers were introduced to avoid the issues of cam profile/flat-face followers. As you say, anybody getting a conversion kit from CAMit would need to check this point, but I'm sure you will find that Ian Bent is two jumps ahead of you.

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".

Are you sure about the change in camshaft? I thought - tho I may be wrong - that the hydraulic lifter engines that do not use roller-followers, used the same camshaft as the solid-lifter engines, and can therefore be converted back to solid lifters.

In regard to the subject matter of this LAA engineering note: 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.

Thanks for that; I can't at this point do more than surmise that all these things indicate excess valve temperatures. The link to overheating is likely to be that the valve guides are "growing" inwards - bronze does that, and provided it's not excessive, it's useful in maintaining the guide to valve clearance. The stellite valve seats are poor conductors of heat, so the valve has to shed its heat via the guide - and obviously the guide clearances are critical to that. If the valve head gets too hot, it acts as a trigger for detonation, as Ian Bent has identified, and detonation drives the exhaust valve temperature even higher, so it's a vicious circle. The whole thing seems to go over the edge when the CHT gets up around 200 C (but Ian has first-hand info on that, not I).

Let's go back a step: 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

POST EDITED AS IT DOES NOT ADD VALUE - MOD I'm trying to pin down exactly what components, and why are they failing. So far, no useful answers.

do you have a failed one laying around?

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

I thought Jabiru put out an SB on them; what did it say? Are you chasing something that has already been dealt with? My point was, IF you have a part that you consider defective, PUT IN A DEFECT REPORT ON IT.

If you care to look up the crankshaft counterweight requirements for a 90 degree V-twin with common crankpin, you will find that it can have complete primary force balance (one per rev) and complete secondary (2 per rev) force balance in the plane of symmetry; but a small secondary out of balance force at right angles to the plane of symmetry. This makes it far superior to an "in line" engine, and also to a boxer twin; however this requires fairly substantial counterweights. Take a look at a Peugeot 604 crankshaft sometime. That had uneven firing intervals (90 degrees/150 degrees), but that's not really an issue with a direct-drive propeller, tho it evidently is with a vehicle transmission at low RPM, high manifold pressure. 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.

Yes, I like the Vee layout; but it does not really come into its own with less than six cylinders, because it's very difficult to get a good compromise between even firing intervals and optimum inertial balance. There's a definite advantage on the six-cylinder engine to having the ring gear at the propeller end of the engine. 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.

What other engines are we talking about? The 912 has much lower peak instantaneous torque input than the Jab, because of its rubber coupling; and also the frequency is much higher because of the gearbox reduction ratio. So it's much kinder to propellers. 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.