ianboag

Yep. We had threads stripping on several engines at torque values of 30 with a calibrated torque wrench and knowledgeable user. The first time it happened, Jabiru blew smoke at the issue and sent a set of bolts. They were no different. Some of the bolts that did not strip just bent the threads so they looked like a Christmas tree. I think Roger in the UK was right ... there was a batch issue with through bolt threads. There were some undersize bolts .... Predetermined clamp force. For a given clamp force (torque), bolt stretch will be less for larger diameter. The ARP guys are all over this and how things are all standard and reproducible with their proprietary lubricant. And let's not forget the benefits of looking at the cylinder base. If there is any oil weeping, the joint is moving and things are heading toward the fret/fatigue/pop situation.

I had it done about 15 years ago to an O-300 in the 172A I then owned. While doing a strip (ex prop strike) a crack was found in the crankcase. I was told that crankcase cracks in old O-300's were not unknown. It was welded up, then the case was machined and line bored. Didn't cost an astronomical sum as I recall.

When this stuff started hitting the fan a year or three back, a group in NZ found that torquing beyond 30 ft-lb produced a serious risk of stripping (or at least bending) the BOLT thread. Turned out that the bolts were undersize. The "12-point" ARP nuts helped because they were longer, but it's a pretty ugly "solution" .... So the group found some 10mm ARP bolts (for a Suzuki motorcycle) (closest off-the shelf to 3/8"). Torqueable to 80 ft-lb before the stud broke. This info was all passed to Jabiru at the time and totally ignored. After considering the crush issue, 35 ft-lb was selected as a suitable (?) torque. Seems to be working ..... The 3/8" vs 7/16" bolt thing is a bit strange. The key factor is the amount of clamp force holding the joint together. This is proportional to the torque, no matter what the bolt diameter. A 3/8" bolt and a 7/16" bolt torqued to 35 (or 40 or whatever) ft-lb will have essentially the same clamp force. The only difference is that the stress in the bigger bolt will be less. If the smaller bolt can take the stress, who cares? Just one other point - ARP (fasteners are what they do) stress that bolts should be torqued using their proprietary lubricant - if you look on their website, the logic (based on a LOT of testing) is pretty convincing. They compare it with dry torquing and "lube oil" - Loctite does not get a mention.

A rectracted ballpoint pen works fine as a stylus. You can knock up a sunshade easy enough from black cardboard.

If this is in a Jab powered plane, the electricity can be a bit spiky. Mine used to regularly freeze up GPS's until I put a big fat capacitor across the ciglighter socket. As you noticed, a simple power off/on doesn't restart it. Normally it would go again from a hard reset - the stick the probe in the hole type.

Get a grip. Ian B runs this site as a (sort of) commercial venture. It's his to run as he sees fit. End of.

Sigh. The old mud-wrestling-with-pigs problem. Moderator please note - this is getting personal ..... New fatter pins as a long term solution didn't cut it as the (ally) hinges were flogged out. Jab had sent me some new stainless ones that didn't fit the old holes. The (fatter) brass pins were a stopgap so I could keep flying for a couple of months until I could organise fitting the new hinges ... but I said all that before anyway .... Back to the point of all this. If a Jabiru aircraft needs an all-singing EMS to get a reasonable life out of the engine, then one might wonder why the factory doesn't see it that way. Funny you should mention the Xtreme - I put one in my Rotaru. Amazing how you can fit it all on a 5" screen .... I'm a fan. (watching thread Ian...mod)

Good on yer mate. The factory has an "option A" on factory-built aircraft with just one CHT and no EGT. How is a buyer supposed to know that this factory option is (in your opinion) dumb? Could there be other dumb ideas from this factory? Perish the thought.

On the Jab site it's called the "Option A" panel. I didn't find the bit where it says that if you buy this one you are either a cheapskate or an idiot and that you should not be surprised if you have overheating problems .....

Tell that to the Jabiru factory ......

I'm just telling it how it was. Not all the users - even ones with Jabiru airframes - were as clever as you .... seems that Rod wasn't either.

So long as you didn't mind tightening up the overheated heads every 25 hours and having them pull in until the tappets hit the cover ....

ARP make through bolts etc for a living. Zillions of them - all sizes and shapes. They go into high performance engines. ARP reckon that if you use their "ultralube" you get random variation that looks like under 5%. They compare results for other lubes as well. Their claims appear to be based on a simply ginormous heap of testing. They don't just say it. It's all there - summaries, graphs, comparisons in http://arp-bolts.com/p/arpultratorque.php. These folk appear to have a seriously good knowledge of all this. FWIW in the early days of the (ongoing) through-bolt hooha Doug and Sue were pointed at all this. We took their subsequent silence as disdain. Go figure.

Who knows? OTOH if there's room to reef up the torque some more (and use proper lubrication on the threads) that might just sort it. This problem does not happen after 10 hours and not every engine does it. So it would appear that the present setup is close to being OK. "More clamp" would seem to be a sensible place to start ......

It's getting bashed back and forth (in a torsional sense) by the pulsating load that a piston engine puts on anything attached to its crankshaft. If the joint is not sufficiently well clamped, then there will be (a tiny amount) of back and forth torsional movement which will eventually snap a bolt or two. If there is enough clamp then the flywheel and crank act as a single unit. If you remove the flywheel and you can see thread marks in the bolt holes, this is not a good sign ......

I understood Jabiru have had a starfish setup for a while .... I could be wrong.

When tensioning up a bolted joint, normal practice is to lubricate the fastener. This gives a reproducible relationship between the torque and the bolt tension. I am told by people who should know that dry-torquing is a total nono. You can get galling of the mating surfaces and the torque-tension relation is all over the shop. ARP (who ought to know) supply their own special lubricant - Continental say threads should be lubricated with engine oil etc etc. When a thread is lubricated and not welded, you can check for loss of tension .... and you know that x torque is y tension. Torquing it up with a non-lubricating substance that sets like concrete in a few minutes is - I am told - unusual. Not really hard. People have been doing it that way forever. Go figure.

The oil is 'pumped' out because the pots are moving.....

Back in the bad old days of breaking through bolts, I did some sums about a starfish configuration and concluded it was no better or worse. The sensible solution seemed to me to be - biff the Loctite (a unique Jab thing) and reef the bolts up some more. I had a local mate on the field who wondered about pulling the thread out of the crank, but some more sums indicated this was pretty unlikely ... The (former) NZ dealer who flew his (brand new) (starfished) 230 across the Tasman subsequently had the bolts break .... aircraft became a kitset, but noone was hurt. So I guess that makes it OK ... and the J120 he had also flown across the Tasman didn't throw a pot until a month later ... it was in the circuit so noone died. Anecdotal. That's why we don't have an NZ dealer any more. Noone wants it.

You get oil leaking from between the crankcase halves when they start to fret. Because of insufficient clamp. And of course once the fretting starts - some metal disappears - which reduces the clamp - which makes things move some more ..... yadda yadda yadda Pop! More (initial) clamp (torque) required. What's hard about this concept?

Dowels schmowels trowels ... friction is what holds a joint together. Think of it as a zillion tiny dowels. Dowels can be handy for location but not much else.

There's a basic point here that gets a bit lost in the noise. The flywheel setup is a clamp joint - also known as a bolted joint - a sandwich where the bits are tensioned together and friction keeps them that way. Not dowels, not Loctite, not sellotape - FRICTION. The bits in the sandwich should have no relative movement. If they move, then as they move the clamping bolts get bent backwards and forwards a tiny bit lots of times. Eventually the bolt(s) snap from BENDING fatigue at the junction between the moving parts. Rolled threads, cut threads, waisted/shanked bolts are not the issue - the fastener fails from bending (back and forth) fatigue because the bits of the sandwich move relative to each other. That's how clamp joints fail. Google "bolted joint" or "clamp joint" if this is hard to accept. So if a bolted joint fails, it's because there was not enough clamp. It's that simple. Detonation, harmonics, phases of the moon, phooey. Not enough clamp to handle whatever happens. Same analysis holds for the through bolts - another clamp joint. If you can see oil round the base of the cylinders, the joint is moving ....... Shoot me down someone ...

I'll rephrase that. Two Rotaxified J160Cs ....

I used to have a reward on offer for the best take on "bogey", "bogey-up-your-nose", "bogle" .... etc etc. The world ran out of new ones sometime in the 1960's. I was in my teens ... :-)