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gregv

3300 Flywheel spacer mod

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I've asked plenty of questions of late, and added little. Thanks for the helpful comments from members of this board. All have been very helpful in the top end rebuild process I am now near completing.I thought I'd post a few photos of the flywheel spacer modification I have used.

 

In short, my assessment is that flywheel bolts break because the 'friction joint' between the crankshaft, the ali spacer and ali 'flywheel' gets loose and the bolts subsequently get stressed and break. Maintain the friction between the parts by maintaining bolt preload and the problem is solved. Dowels won't stop this from happening. The new steel centred 'starfish' flywheel on newer engines removes the relatively soft aluminium centre which the flywheel bolts tended to recess into, losing their preload and loosening the sandwiched parts.

 

Old flywheel centre is pictured below with Unbrako 5/16" 1-1/4" long cap screws tighened up against the ali flywheel. Two were loose, and all were recessed into the flywheel by up to 0.3mm.

 

[ATTACH=full]13723[/ATTACH]

 

I machined up a steel replacement spacer, but dispensed with the vacuum drive extension. I also machined a 4.5mm steel disc, and replaced the bolts with ARP brand 5/16" 1-1/2" long bolt (to counter the new compression disc and provide a few more threads into the crankshaft). The crank bolt holes were cleaned out and checked for adequate depth.

 

[ATTACH=full]13725[/ATTACH]

 

Replacement steel spacer with compression disc and new bolts

 

[ATTACH=full]13724[/ATTACH]

 

The aluminium flywheel is now sandwiched between two steel discs. The bolts are spec'ed to to tightened up to 50+ft/lbs into steel. We settled on 45ft/lb as a compromise figure.

 

[ATTACH=full]13722[/ATTACH]

 

With the vacuum pump drive no longer sitting in the hole in the alternator spider, I can use a mirror to check the witness paint on the bolt heads during regular inspections.

 

This idea was developed by a local Jab owner who generously spent many hours with me going through the rationale for why these bolts break and how he thought one could prevent it - basically get rid of most of the soft aluminium in the sandwich of parts. We'll see how things go...

 

Greg v

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Hm,

 

You may know that there has been a lot of discussion on the Yahoo Jabiru engine group lately about the 5/16" no dowels flywheel bolt attachment. It seems that the rest of the world is finally catching up with the situation experienced in NZ a while back. So far the only promising solution I have seen, is the flywheel steel centre boss/crush plate you developed.

 

The interesting thing for me right now is how is it holding up? Any more related problems? This particular solution was engineered for the 6-cyl: have any been installed on the 4-cyl as well? Any operational and/or maintenance experience?

 

Thanks

 

Kai

 

 

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Hm,

You may know that there has been a lot of discussion on the Yahoo Jabiru engine group lately about the 5/16" no dowels flywheel bolt attachment. It seems that the rest of the world is finally catching up with the situation experienced in NZ a while back. So far the only promising solution I have seen, is the flywheel steel centre boss/crush plate you developed.

 

The interesting thing for me right now is how is it holding up? Any more related problems? This particular solution was engineered for the 6-cyl: have any been installed on the 4-cyl as well? Any operational and/or maintenance experience?

 

Thanks

 

Kai

Hi Kai

 

The 3300 I installed the steel spacer mod on was retired last year at 481hrs TTIS. No problems noted with the flywheel end at that time. The other 3300 I know of in NZ that had this mod had no flywheel bolt problems but ingested an exhaust valve (near enough to an airfield thankfully to make a successful forced landing) at around 1200hrs TTIS and they bought and installed a CAE engine.

 

I think the airframe is a superb cross country cruiser (J200B) but psychologically was struggling with my perception of the engine's reliability. My 3300 never stopped, but I had problems with valve guides grabbing valves, recessed thick fin heads and just before removal, leak downs were increasing towards limits via leaking exhaust valves again. So I have installed a new 100hp Rotax 912 with CS prop.

 

The 3300 might go on a project in the future. Probably one that isn't an aircraft. The second hand market for 3300 engines in NZ has mysteriously evaporated since November...

 

It is possible I have switched one set of problems for whole set of news ones. Cowling is being modified now, test flight planned for Feb all going well.

 

Greg v

 

Northland, New Zealand

 

 

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Some modern applications torque to permanent stretch. ( single use bolts). I can't see the logic in that but there you are.. Nev

The bolts are deliberately tensioned beyond their elastic limit into the `plastic' range (ie. while further deformation is possible, it results in relatively little increase in bolt tension. If you keep going, then eventually the bolt's ultimate tensile strength is reached and it snaps). The advantage is that the bolt's maximum (and known) clamping force is achieved, but due to the permanent stretch the bolts can only be used once. It's commonly done in building structures using methods that don't involve torque wrenches. However, aircraft bolts are typically torqued to less than their elastic limit and so can be re-used. The downside with that approach is that there are so many variables involved in applying a tension using a torque wrench, that you are never quite sure how much tension is actually in the bolt. It's also important to compensate for prevailing torque when installing bolts into nutplates, or using nylok or other types of friction fasteners.

 

rgmwa

 

 

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Hi KaiThe 3300 I installed the steel spacer mod on was retired last year at 481hrs TTIS. No problems noted with the flywheel end at that time. The other 3300 I know of in NZ that had this mod had no flywheel bolt problems but ingested an exhaust valve (near enough to an airfield thankfully to make a successful forced landing) at around 1200hrs TTIS and they bought and installed a CAE engine.

 

I think the airframe is a superb cross country cruiser (J200B) but psychologically was struggling with my perception of the engine's reliability. My 3300 never stopped, but I had problems with valve guides grabbing valves, recessed thick fin heads and just before removal, leak downs were increasing towards limits via leaking exhaust valves again. So I have installed a new 100hp Rotax 912 with CS prop.

 

The 3300 might go on a project in the future. Probably one that isn't an aircraft. The second hand market for 3300 engines in NZ has mysteriously evaporated since November...

 

It is possible I have switched one set of problems for whole set of news ones. Cowling is being modified now, test flight planned for Feb all going well.

 

Greg v

 

Northland, New Zealand

Greg,

 

Thanks.

 

Several of us are struggling with this issue now. Why now and not much earlier, is a mystery. The engines concerned must be 2003-2008 vintage or thereabouts, all fairly lightly loaded with well balanced wooden props and no prop extensions. Still, when failing, the engines are well below 500 hrs TT. Norway is very much Rotax country, so the total Jab population is fairly small- maybe some 40 engines. And with Sweden and Finland altogether 90 units. Not very much on which to base statistics.

 

However, not many of us consider the Jab an inferior engine. True, it is overly sensitive to installation errors of all sorts and they have had their fair share of manufacturing deficiencies. The worst is probably total absence of anything from the lot at Bundy. On my own 4-banger I have installed liquid cooled heads, forged pistons, fuel injection, longer and stonger through bolts (!), the 40 Amps CAMit alternator plus plus, and I seem to have it licked save for that awful flywheel attachment joint that keeps on failing the bolts. Presently I know of four other engines in this country with the same issue. Unless you can tell me some horror story I am going to recommend the installation of your mod, which I believe should be fairly easy to manufacture locally, jus like you did.

 

I see you used ARP bolts. Do you remember to what torque you set them?

 

Regards

 

Kai

 

 

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How long have you run the CAE belt driven altenator?

 

It is supposably dampens vibration linked to flywheel issues

 

 

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Kai,

 

When you say " total absence of anything from the bundy mob", do you mean from Jabiru and CAMit. Or just Jab? If you haven't contacted Ian Bent @ CAMit it might be worth your while.

 

 

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Well,

 

The CAMit generator has been on the engine for some 5 hours now; not nearly enough to draw any conclusions of course, but as they state on their website- the engine just feels different and I am full of hope. However, until winter releases its grip on this country (global heating is a great disappointment to me!), I will not be able to report on any development. Nevertheless, while I am happy, the others with this flywheel bolt issue are not, and with this rediculous thing from CASA hanging in the air and just waiting to hit the desks at our national CAA, I just cannot risk that one of the engines throw a flywheel (mysteriously, we have not had any through bolt issues). They will surely ground the rest of the fleet immediately.

 

Just to emphasize; my only experience with this flywheel bolt thing is the 5/16" no dowel version. The others, i.e 5/16" with dowels, 3/8", 3/8" with dowels, 3/8" with dowels and starfish (when will we have the octopus?), I know nothing about.

 

Let it be known, for the record, that in 2004 I visited Jabiru, Bundy. Phil Ainsworth was very kind to show me around, including the machine shop. That was before I had my 22A airborne. After the issues started to pop up: nothing, nada- niente! Apart of course a request to turn in the engine nameplate as it could no longer be considered to be a Jabiru. Surely, it is not a Jab any more, but before 2010 it was as standard as it could possibly be, and running itself to destruction. I will not deny that presently, with all my mods and power upgrade, I might be helping- but so far it is still in one piece. Imagine my complete surprise when I got in touch with Ian Brent at CAMit. They actually act like normal, communicative, socially trained humans in this company, responding politely and swiftly to queries and suggestions, helping to solve issues, keeping their promises; you know- like the rest of us. I am convinced they will be able to get this thing back on track, given some time.

 

Kai

 

 

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Kai, a few small observations, if I may.

 

Ian Bent at CAMit is developing a new flywheel attachment mod. which is now in late testing phase. He agrees with pretty much everybody that inadequate clamping pressure is the issue; however his experience also says that the 3/8 bolts (and especially in a crankshaft with dowels / dowel holes drilled), presents a concern that there is inadequate metal in the shaft area around the threads to prevent micro-cracking of the shaft around the bolts, which may be exacerbated by over-tension of the bolts. Your 5/16 bolts and no dowels is probably the optimum compromise, though if others are experiencing bolt breaks at /very close to the head of the bolt, the load of the starter on the flywheel in low temperatures may be part of the problem there. He is developing a different approach entirely to securing the flywheel and no doubt the details of that will emerge when he is satisfied with the testing work.

 

The fact that through-bolt issues seem to be non-issues in Norway is interesting: do you guys have consistently good-quality fuel available? It can be a real lucky-dip here in Australia. The major problem for through-bolts comes from detonation caused by one / both of fuel quality and operating temps. in use. I'm guessing here, but I would imagine that in Norway, the normal ambient temps are generally a bit kinder than we routinely get here.

 

 

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Oscar,

 

Anything is welcome! I am well aware of Ian´s plans concerning the flywheel attachment and I am sure it is going to be a good, solid, permanent fix. However, I am scared stiff our national CAA could act on the CASA paper any moment now. Should they start to investigate, no doubt both the flywheel and the through bolt issue will emerge and, reasoning like all other CAA´s in this world (flying is not neccessarily dangerous, but it could kill you), they are liable to stob Jab flying up here- 40 airplanes grounded! I just can´t have that; I can´t wait for Ian´s development to materialize and must be able to present a sound solution to the problem, preferably yesterday. We have a regional distributorship for Jab up here, and how I wish they would shoulder some responsibility, however, no go (what else is new!). Consequently this falls on little me :-(

 

A bit kinder? As I write I have minus 15 centigrades right outside my window. The snow throwers are going full blast everywhere to keep mother nature at bay- in vain of course. Believe me; there is nothing kind about this. Our mogas, which we are presently forced to use because 100LL is rapidly disappearing, is a can of worms. We have summer fuel and winter fuel. Some northern areas are cold in the extreme (minus 42 centigrades the other day; yes- the kids STILL play outside), so they have a special fuel quality. Phase separation is a constant threat, we are running a neverending battle with at least 5 and often 10 % ethanol in the fuel, and the oil companies will only warrant their product´s octane rating for 6 weeks once it has left the distributor hubs (not the fuel pumps, mind you). But, it is comparatively water free (!)

 

Common to all types is that the vapour point is nothing to boast about, and we were sorely plaged with vapour locks, lean running, detonation and what have you during the laughable short period we call summer. However, we saw this one coming and were somewhat prepared. As a curiosity, the Jab engines with their low mounted carby and lesser chance of heat soak, were far less affected than the R912 fraction (justice, for once!), which were really struggling. Many of these installations will only be able to solve the issue permanently by getting rid of the Bing things and hanging on some kind of EFI system. Something else to consider is that light aircraft flight instruction is solely carried out in flying clubs- the moment we go commercial the intensity of this activity would increase dramatically- then we would see the split crankcases!

 

The broad finned heads were something else again. During maintenance and head bolt retorque compression ratios would habitually rise ever so slightly as the cylinder sealing surface slowly embedded into the now "plastic" heads. This, in combination with poorly understood princioles of air cooling by both aircraft manufacurers and individual builders (not the engine´s fault for sure), has forced quite a few head replacement issues. I am told the new narrow finned heads are a boon- but so expensive! The Rotec LCH´s seem to offer the best of both worlds- with some added complexity.

 

Cheers

 

Kai

 

 

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Kai - you must be keeping in very good touch with Ian, since this work has mostly happened over Christmas! He's busy on I think the Mk.3 version, basically tidying up the actual installation details, and there are some tests to be run to check that there won't be any shaft cracking. (magnafluxing with the full tension on everything).

 

But for that work, his first engine (a 3300) for testing to ASTM certification would probably have been bolted up to the test cell rig for that to commence this weekend ( the bolting-up, not the testing - there's a bit of sensor installation, testing and some cooling airflow mods still underway for the cell). I'm glad it hasn't, as my own engine, which has been being both run in and used as the test cell development 'mule' for several months now, will be stood down and the delay has given me a chance to build some 12mm thread dehydrator plugs so we can do a full inhibit on it when it is stood down - as the aircraft has several months of work to go before we can think of bolting it in.

 

Re vapour lock - getting the aux. fuel pump as low (preferably, the lowest point) in the delivery circuit is the most critical factor; the ux. pump will add pressure to the fuel to the carby and help with vapour lock. Because of the ethanol hygroscopic problem we will be adding a gascolator to our own fuel circuit. It never ceases to amaze me that just about anybody in Australia has stories of 'dud' fuel loads in their cars, where the EFI systems can just barely cope with handling the problems but their car 'ran like a dog' until they got a new load of fuel in the tank - but it seems to never occur to many that the fuel they are putting into their aircraft tank from a mogas pump might just be as 'dud' as some they get in their car tank... and then blaming the engine for poor performance.

 

 

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It's pretty poor to sell a product (Mogas) that lasts such a short time, and you don't have any figures on it. I've many times mentioned this problem. With a hot running aircooled motor it could be an engine killer. Nothing else needed.. Nev

 

 

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Nev, I'd say that at least in Norway the fuel companies are being more fundamentally honest than they are here. At least they (de facto) ADMIT that the octane rating goes to hell in just 6 weeks! Has anybody, ever, here tried to ask a service station 'when was your (95/98) tank last filled?' before filling their containers with mogas to pour into their tanks? ( and no, I haven't, either..)

 

 

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I have been testing the specific gravity of both Avgas and Mogas over the last two months and the deterioration of Mogas over two to three weeks is quite dramatic.

 

No wonder Jabiru and others are having detonation problems.

 

Do not store fuel - particularly in plastic jerry cans.

 

John.

 

 

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OK the SG changes but I don't know how this affects octane numbers. Fuel can be tampered with so easily . Nothing is sealed (except avgas drums and once opened they have no valid release note, subsequently). Legally it should all be used on opening. Nev

 

 

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Kai - you must be keeping in very good touch with Ian, since this work has mostly happened over Christmas! He's busy on I think the Mk.3 version, basically tidying up the actual installation details, and there are some tests to be run to check that there won't be any shaft cracking. (magnafluxing with the full tension on everything).

But for that work, his first engine (a 3300) for testing to ASTM certification would probably have been bolted up to the test cell rig for that to commence this weekend ( the bolting-up, not the testing - there's a bit of sensor installation, testing and some cooling airflow mods still underway for the cell). I'm glad it hasn't, as my own engine, which has been being both run in and used as the test cell development 'mule' for several months now, will be stood down and the delay has given me a chance to build some 12mm thread dehydrator plugs so we can do a full inhibit on it when it is stood down - as the aircraft has several months of work to go before we can think of bolting it in.

 

Re vapour lock - getting the aux. fuel pump as low (preferably, the lowest point) in the delivery circuit is the most critical factor; the ux. pump will add pressure to the fuel to the carby and help with vapour lock. Because of the ethanol hygroscopic problem we will be adding a gascolator to our own fuel circuit. It never ceases to amaze me that just about anybody in Australia has stories of 'dud' fuel loads in their cars, where the EFI systems can just barely cope with handling the problems but their car 'ran like a dog' until they got a new load of fuel in the tank - but it seems to never occur to many that the fuel they are putting into their aircraft tank from a mogas pump might just be as 'dud' as some they get in their car tank... and then blaming the engine for poor performance.

Not, not really- but just before x-mas he was unlucky enough to be the focus of one of my frustrated outbursts. That was when he mentioned he was working on a new flywheel hookup. However, he told me to keep it under wraps- to which I agreed.

 

Overall, it would probably seem reasonable to assume that australian mogas is even lower on the quality scale than the stuff sold here. After all, in winter the whole car population could feeze up to an immecdiate standstill if there should be too much water in the fuel. Still, we are very carefull not to leave mogas in the tanks during winter periods of inactivity- the spectere of a lump of ice in the tanks is always with us.

 

Up here EFI is seen as the solution to all our fuel related problems. There is one company specializing in this (Edgeperformance), and recently I was told some 90 kits had been sold worldwide; mine and around a dozen other Jabs among them. The rest is R912. Kits are very complete, but of course on the Jab the induction pipes have to be shipped to his shop for welding of the injector bosses (hardly worthwhile living in Aus) While there is a slight performance increase (not much), the engines run much smoother with even egt´s and no more fuel related problems.

 

 

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Kai - I have seen Jab engine intake pipes with injector bosses installed - for drone engines.

 

 

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Nev, I'd say that at least in Norway the fuel companies are being more fundamentally honest than they are here. At least they (de facto) ADMIT that the octane rating goes to hell in just 6 weeks! Has anybody, ever, here tried to ask a service station 'when was your (95/98) tank last filled?' before filling their containers with mogas to pour into their tanks? ( and no, I haven't, either..)

Interesting!

 

We in the NLF (Norwegian Airsports Society), where I am chairing the technical committee of the microlight section, specifically instruct our members to purchase their fuel exclusively from pumps with an above average (high) turnover. That way we hope to avoid fuel which is out of specs. I´ll be the first to admit that hoping just is not good enough, but I can´t see what else we could do.

 

And I would like to emphasize that the fuel is not neccessarily dud after 6 weeks; the oil companies just say that they will not warrant the octane rating after that because long time pump tank/end user storage is beyond their control.

 

 

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I have been testing the specific gravity of both Avgas and Mogas over the last two months and the deterioration of Mogas over two to three weeks is quite dramatic.No wonder Jabiru and others are having detonation problems.

 

Do not store fuel - particularly in plastic jerry cans.

 

John.

Buy your mogas from a high turnover pump station, use it immediatly, don´t leave it in the aircraft tanks or any other ventilated container for that matter subject to conditions that cannot be controlled.

 

 

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Kai - I have seen Jab engine intake pipes with injector bosses installed - for drone engines.

Yes,

 

It´s a tight fit for sure. But should you in addition run your otherwise standard off the mill Jab on these "iridium" plugs, it really makes your day to see your Jab idle smoothly at 350 rpm: it will make you smile for days on end!

 

 

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It's pretty poor to sell a product (Mogas) that lasts such a short time, and you don't have any figures on it. I've many times mentioned this problem. With a hot running aircooled motor it could be an engine killer. Nothing else needed.. Nev

If not an engine killer, at least it brings the planes down. I have 6 documented cases from 2014. No fatalities, just a few bent aeroplanes. The norwegian terrain is very rugged; mountainous and heavily wooded. Pilots are instructed to always plan their course in such a way that they could take the plane safely down when the engine stops. Because it will stop.

 

Now, if you ask me how we cope in winter when all landable fields are covered in feet of snow, I will probably stare at my shoes and scrape them in the gravel :-( You just have not lived before you have experienced the plane overturning in a snow field on landing. Getting out of the plane is a question of motivation- and the smell of dripping mogas is a great motivator!

 

 

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OK the SG changes but I don't know how this affects octane numbers. Fuel can be tampered with so easily . Nothing is sealed (except avgas drums and once opened they have no valid release note, subsequently). Legally it should all be used on opening. Nev

We were explained that the moment you put mogas in an unsealed container (your aircraft fuel tank), things start to happen. Lighter fractions (octane enhancing ethanol) start to evaporate, it draws moisture from the air, phase separation could start to set in quickly etc etc. Rather quickly the octane rating is not what it was :-(

 

 

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There is a direct relation between SG and octane. Fuel mixture also changes as the weight of the fuel changes.

 

John.

 

 

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...my own engine, ... will be stood down and the delay has given me a chance to build some 12mm thread dehydrator plugs so we can do a full inhibit on it when it is stood down - as the aircraft has several months of work to go before we can think of bolting it in.

Oscar, Why would you build dehydrator plugs when you can but them from the Skyshop or Aircraft Spruce. Too much time on your hands?????

 

 

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Saw those, didn't like the colour... and I thought, geez, if I'm going to have dehydrator plugs, then ones that would actually screw into a Jabiru would be probably more useful than ones for Lycontinentals...

 

 

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