ianboag

I have the same problem in my 160. I have been toying with the idea of partly blanking the vent holes on the fast-draining side to see if that makes a diff. In a non-critical environment of course etc etc

Well that's all pretty blunt, but it's about where we got to ...... undersized bolts -> pull/distort threads -> relax clamp -> case fret/bolt break ..... We went to ARP bolts/nuts but anything with tight threads will work

True. A conservative version of the area ratio (at thread root) might be diameters of 3/16 and 1/4. That makes the area ratio (3/4) squared ... = 0.5 near as matters. So put 0.5 where I had 0.65. That says 1/4" bolts torqued to 15 ft-lb have much the same bolt stress as 5/16" ones torqued to 30. The bigger bolts will have twice the clamp force of course.

For what it's worth, the expert on our field (who has done quite a bit of Jab research) gets a bit worried about whether that sort of torque level would run the risk of bending the treads in the crank. I did some sums that suggested it would not. Enough other people have reefed them up the 30 (ft-lb - lubed even) and higher with no ill effects that it sems OK. Not for 1/4" bolts though - one would expect to "derate" the figures by the ratio of x-sectional areas - so (1/4) divided by (5/16) and squared is 16/25 = 0.65. So whatever feels OK for the 5/16" bolt torque-wise - 65% of that should work for the 1/4" ones. That will give the same STRESS in both bolts, but of course the bigger ones will have more clamp force because force=(stress) x (x-sectional area).

These units can freeze at random times if the power supply is a bit noisy/spiky. Generally it is not immediate. A big cap across the cig lighter plug can help.

4925

True. Less of an issue here in NZ. It's just a mod that I submit to the equiv of RAA which they will be quite reasonable about. The prop change was a non-issue. Even though ZK-BGY started life as an Adelaide Soaring Club 24-xxxx :-)

One takes the points about big tyres on sports cars and all that .... but I like my J160. It has excellent viz , plenty of room and is pleasant to fly. It's a bit slow off the ground though. So I have changed the 60x42 prop for a 60x40. Takeoff feels better (nothing scientific). I didn't really lose anything at the top end because I always used to cruise 95-odd knots at 2800 or so. Now I do it at 3000 which the folklore all says is better for a Jab engine anyway. Now I'm wondering about a 62x36 - same engine load as the 60x40 but more takeoff thrust and 5-10 knots off the top end. I don't mind the top end loss. I used to have a C172A which was working hard to get over 95 knots. I am wondering about some fatter wheels so I can use it easily in places where the surface is not so flash. It will never be a 701 but it will be happier on rough ground. So if some big wheels turn up for a 230 I'd be interested to know the source and the cost ..... Horses for courses. Nothing venture nothing win. Old men's toys and all that. So what if I have a sports car with Desert Duellers on ... IB

I would agree with that. Lubed or unlubed makes huge difference to the tension. Jabiru say you do it dry. I've never seen that anywhere else. Conti and Lyc say to use engine oil on the threads. ARP supply their own lubricant to be used on their stuff. Go figure. When we did some of the testing you describe, the bolt did not permanently stretch - the threads did. 30% over was about where we stripped one even. So I would also check that the bolt threads do not permanently distort ("pull") with the 30% overtorque. With the new longer nuts they probably won't. If you are bothered about the nuts being loose, you could check (google knows) what 1A thread tolerance means and what 2A and 3A tolerances are considered appropriate for. Call Jab (or Camit) and ask to speak to someone technical. Ask whether the bolts are made to a 1A, 2A or 3A tolerance ..... Cheers IB

Plain English Met disappeared there again. Airservices changed their web address. Naturally an unofficial user like me doesn't get to hear about that .... thanks to Ian Baker for giving me a headsup. It was a 10-minute job to fix :-) Would have been a 2-minute job except I haven't been near the site for so long (it just works) and I had to refresh my ageing memory .... Thanks again IB (Aus). IB (Kiwi)

Jabs are nice planes. Slippery though. On approach (LSA 55, J200, J160 are what I have flown) the general problem is that it is easy to slow down and easy to descend. It just gets a bit tricky trying to do both at the same time :-)

Make what you will of this. When we decided to use ARP studs/bolts/nuts there were some conversations with Jabiru because we had stripped/pulled TWO sets of newly supplied through bolts. Nobody seemed to be interested. It was just after this that the longer 12-point nuts were released. They were from ARP! They looked awfully similar to what we are using. Go figure. We went to 10mm through bolts because the only (correct length) off-the-shelf stuff that ARP had was 10mm rather than 3/8". They could have made a special run for a setup cost of something like $US500 as I recall. ARP make engine bolts and studs for a living - much of their stuff goes into race cars. The ARP stuff was not hugely dearer that the Camit bolts. I don't understand - Jabiru use lots of car bits in the engine but want to make their own through bolts. IB

My 2c. One problem (there may have been others) with through bolts was that they were undersize. They were done to 1A standard which is about the same fit as on rattly farm gate bolts you buy at Bunnings. The nuts were wobbly. We managed to strip a number of bolts when torquing them up. That's how we found the undersize problem. We also found bolts where the threads had pulled so they looked like Christmas trees. It is possible that this happened after the bolts had been done up - possibly they were very close to the limit anyway and a bit of thermal stress pulled them over it. If this happens then some clamp is lost, the barrels/caee start to fret and we are on the way to a fatigue failure. That's one where a bolt snaps off at the barrel/case point. I understand that is where the snap usually happens. I was under the impression that the Camit bolts were rolled anyway. Just rolled to be loose. 1A=wide tolerance, 3A=close tolerance. The longer nuts were a bit of a band-aid to spread the load over more threads. The new SB means that engines have to be disassembled anyway as they say you have to replace the crankcase dowels. Personally I am of the opinion that the problem is not enough clamp which allows things to move and fret. The old bolts/nuts were so close to max tension that there was no scope to reef them up any plus they were likely to relax in service. As they are welded up with 620 Loctite one would never know. Incidentally - this is not all bolts. We have seen ones of older engines that had no trace of this problem and torqued up just fine. IB

When we freshened up my 2200 (hollow pushrod etc) a couple of months ago we put in K-Line inserts. We were advised by the South African Jab dealer that this was a good idea. He also felt the oil hole was necessary. Our engine recon man thought it was a bit strange (he has put K-Lines into lots of engines) but relatively harmless. So we did it ....

Thanks Don. If I lived in NSW you'd get my vote for sure :-)

All go again. My ISP changed my IP without telling me ...... :-(

Yep. Movement. Not enough clamp. But the studs were prone to strip if reefed up. If one stud breaks from fatigue, the others are all moving down the same road. Arguably if one breaks, the right thing is to replace all of them. Not enough clamp. Movement. Fatigue ....... Nuts are not "specially designed". They are an off the shelf item from ARP.

They break at the interface. Fatigue - not shear - bending back and forth - not enough clamp.

My Trio in a J200 was like that. Easy enough to overpower if you felt you should .... and there was a "kill the autopilot" button ...

The Tauranga J230 that popped its bolts at 900 hrs TTIS had a Jab wooden prop and the starfish thingo and LAME maintenance every 100 hours (monthly) because it was an LSA being used in a flying school. When you have a substantial flywheel at the opposite end to the prop. ( which is another flywheel ) they oppose each other at times, and work together at other times. The aluminium disc on a Jabiru engine hardly qualifies as a "substantial flywheel" and neither (as you said) does a wooden Jab prop. All you have to do is strobe the motor and if you mark references (flywheel/crankcase and prop hub/crankcase) you will see things happening with crankshaft flexing as you move through the rev range. And if you clamp the prop end well enough and the "flywheel" end well enough then all will be tickety-boo. The crankshaft flex will be followed exactly by the things bolted to the ends of it and the clamp bolts will happily stay clamping ...... no movement of bolted on things = no bolt breakage. Interesting I suppose that (AFAIK) it's never the bolts at the prop end that break ..

I can't say how they arrived at this information but one has to assume they haven't just dreamt it up. Wish I shared your faith on that one. When bolts fail in a clamp joint it's because the clamp is not enough to stop the mating surfaces from moving back and forth and the bolts fail from fatigue. That's for ANY clamp joint, not just Jabiru flywheels. Google something like "clamp joint failure" to learn more. So whatever is going on with torsional vibrations (or phases of the moon or whatever) is enough to overcome the clamp joint friction. The answer is relatively simple - more clamp = more friction - so long as you don't start pulling threads out of the crank. The occasional set of flywheel bolts still croak, so there's your tests. However some basic sums say that you can torque the bolts up to 45 (not 30) with grease (not Loctite). That's what gregv is doing. Nothing will break from the torque and the bits won't move ..... Cheers IB

Which page in the flight manual tells me that? Can't be - there were no SBs or other attempts by the factory to get owners to rectify them the J200 got it after I bought it at 75 hrs TTIS - there was an SB that said it was a good idea so I bought the kit 2003. What's this about "old" cowls? Yes the oil cooler was silly - it was the same as the 2200 cooler. I replaced it with a big one. Thick-finned heads were how it came. Four wounded Jabs and five non-wounded 912's on our field. One of the wounded Jabs was fitted behind a relatively young dead one. I can appreciate that you are a very tolerant test pilot sort of chap. You are willing to instrument things at your own expense beyond what the factory feels was necessary. You are also willing to muck about with configurations outside what the factory knows anything about. I'm not like that. I just wanted to go flying and feel confident about the fan.

I suppose having 4/6 gauges for EGT/CHT is a good idea. Someone should tell the factory ..... J200 #1 was built by the NZ Jab agent at the time. It has a single CHT and a single EGT gauge. The new owner is fitting 6x6 stuff to see if he can avoid repeating the head crush he found at 400 hours. I just bought it and flew it the same way I had flown the Cessna I owned beforehand. One temp gauge seems to be considered enough on Lycs and Contis. Noone (including my mate the Jab agent) told me I needed 12 temperature measurements to avoid cooking the engine. Pioneer 300 #2 just had one of each. At 600 hours it was cooked too. To be fair, the cowling was not the best. Jab 230 #3 had single gauges - the owner bought the kit from Jabiru and built it as per instructions and flew it. Jab 160 #4 is a factory-built 160C. It came with one CHT gauge and no EGT gauge. Go figure. None of the 912 powered aircraft ( Zenair, Sky Arrow, Sting, Avid, Gazelle) have 4x4 temperature reporting. That's water-cooled heads for you I suppose. One of them is at 1500 hrs TTIS and still has 80/78 leakdowns. The others are younger. I was there - none of this is hearsay. I freely admit this is a small sample.

Now there's a challenge. Here is the story of five Jab-powered planes on our field in the last two years. A 3300 (solid lifter) in a J200 had a pot go soft at 200 hours. Honed and ringed while I owned it. I sold it and it is now having a full top overhaul at 400 hours. A 3300 (early hydraulic lfter) in a J230 burned an exhaust valve at 160 hours. Others were all pitted and had to be replaced. A through bolt stripped during reassembly. Owner had built the kit and installed the engine that came with it. A 600-hour 3300 (solid lifter) had through bolts strip during reassembly. My J160 (early hydraulic lifter) that I bought from the Adelaide Soaring Club with about 900 hours on the engine. It almost made it to 1000 hours. The top overhaul we just did includes cylinders and pistons and a conversion to the latest lifter configuration. It was actually the second engine in this plane - the first one had been replaced at 500 hours because of case fretting. I owned/own and fixed two of these aircraft and watched the other ones being fixed. Then there is a J160 (early hydraulic) which has done 220 hours with no visible issues. I can think of four 912-powered aircraft on the field which in the same period have pretty much just had petrol fills and oil changes and just flown .... Cheers IB

I went back and had a look at the site to get rid of the error where "as" gets translated to "altostratus" when it shouldn't. I may have missed some possibilities so will act promptly (truly!) if anyone points these or other translation errors out to me ..... the TTF METAR one is a bit more than I feel like taking on right now though. Cheers IB