Jab engines

[kgwilson]

If a flywheel bolt is loose or is broken then the mating surfaces should be loctited/sealed from oil ingress. This is a major task and requires the engine to be removed and the entire alternator & flywheel assembly & oil seals to be removed. Every 50 hours the flywheel bolts should be checked for correct torque. With nordloc washers that is 35 ft/lb for the later 3/8 bolts or 30ft/lb for the earlier 5/16 bolts. If any move then they must all be replaced so that is an engine removal process. If not then there will have been no possibility of oil getting on to the mating surfaces.

 

Originally the flywheel bolts were loctited in & getting them out was a major problem as they had to be heated up and at the same time the rare earth magnets in the alternator rotor had to be protected from the heat. I replaced mine when I had a minor prop strike as a precaution and was sh!t scared I was going to break them as they were so tight. I replaced them 1 by 1 with new bolts with Nordloc washers & cleaned up the thread each time with a 3/8 tap then did the bolt fit check. Each was perfect & there has been no movement (as you'd expect) with each torque check since.

[zodiacpilot]

When l purchased my plane the 3300A had 525hrs up, all on avgas. At 580hrs it started pumping the bottle full of oil in about 1.5hrs. Had to break all top rings & 3 seconds to get unstuck from lead carbon in grooves. Approx 1.5mm carbon on pistons & valves. New 40thou over commodore ringset($50) with endgaps opened up & valves cleaned/lapped. Changed to 98mogas, now after 620hrs in 5years have gone to 50hr oil changes due to oil not dirty 'nuff before then. Using 40-50ml ph & at each service approx 15ml in bottle, of which 5ml is water/condensation. Runnin like a swiss watch.

[facthunter]

Yes I don't see loctiting the BOLTS as the answer. Why would you recheck them when they have been "cemented" in place? It's hard to expect an already stressed fitting to like/survive the hammering it gets from starter engagement. (of the inertial type particularly). Anyhow you shouldn't have a flywheel at both ends of a crankshaft ideally. The prop is a flywheel( even a wood one) but wood is one of the most forgiving. Nev

[Kenlsa]

BTW, looks like the Gen 4 only needs inspection of the flywheel bolts to ensure the torque seal is intact (page 34) nothing further is mentioned. and if the seal is broken then the procedure is on page 41. No need for replacement at 500 hrs. I had confirmed this some time ago with our LAME/L4. Ken

[kgwilson]

I think the mandatory replacement is a precaution based on some of the earlier 5/16 bolts breaking which is why they were replaced with 3/8 bolts and then changed from being loctited with standard washers to not being loctited and with Nordloc washers. The Gen 4 flywheel has 3 locating dowels on the crankshaft and 3 flywheel bolts with belleville washers which are used to press the flywheel on to the dowels. These bolts are not used in the final engine assembly according to the manual so I guess new bolts are installed and torque seal applied at that time.

 

The Gen 4 overhaul and parts manual is very well detailed, far better than most other engine manuals I have seen.

[kgwilson]

When l purchased my plane the 3300A had 525hrs up, all on avgas. At 580hrs it started pumping the bottle full of oil in about 1.5hrs. Had to break all top rings & 3 seconds to get unstuck from lead carbon in grooves. Approx 1.5mm carbon on pistons & valves. New 40thou over commodore ringset($50) with endgaps opened up & valves cleaned/lapped. Changed to 98mogas, now after 620hrs in 5years have gone to 50hr oil changes due to oil not dirty 'nuff before then. Using 40-50ml ph & at each service approx 15ml in bottle, of which 5ml is water/condensation. Runnin like a swiss watch.

I have always used Mogas, originally BP 95 then after that got hard to get, changed to 98. Oil consumption is minimal so no topups required between changes & the oil catch bottle only has about a tablespoon of condensate in it at oil change time. I change every 25 hours. I only use Avgas when away from home as that's all they have in the bowser. Otherwise I will take a jerrycan with me & fill it in town. Don't have to do that too often as I have 3 tanks & 170 litres.

[Yenn]

I bought a factory zero timed Jab 2200, to replace the Jab 1600 that I put in the Corby years ago. The replacement was also years ago. When I got the engine I also got the Instruction and maintenance manual. Tyhis gives a good run down on the Bing carbie.

I had mine reconditioned recently and since then it has been running rich, so I decided to lower the needle in the fuel metering system. Easy job, just remove the top and the piston and the needle needs to be turned 90 degrees and moved to the new groove location. That doesn't work, the needle is free turning and will not disengage from the spring clip. Looking down the piston I see a large screwdriver slot, so I remove the screwed in part. Lo and behold it is holding the needle in place and the needle is noting like all the Bing manual depict. There is only one groove for the spring, not 4.

Leith at Jabiru tells me that it has been this way for years, even before my engine was sold to me.

I wonder if anyone else has tried to re locate a needle, or did they have the correct info in the engine manual?

[Old Koreelah]

...I wonder if anyone else has tried to re locate a needle, or did they have the correct info in the engine manual?

Yenn I didn't even get that far; couldn't budge the device that locates the needle, so gave up and put it all back together. It ran well for years after that.

This morning I removed the iridium plugs. First time they've been out for years and they all show the colour of rich running, with a few tiny fingers of carbon starting to grow from the ring. Might lower the fuel level in the float bowl as a first step towards addressing this. Not in a big hurry to risk running too lean.

[planesmaker]

I would not lower float as at full power you risk running short of fuel and engine will surge.

[Old Koreelah]

I would not lower float as at full power you risk running short of fuel and engine will surge.

Agreed, Planey. Just trimming it back a smidgeon, within tolerance.

 

Yesterday arvo I poked my inspection camera down the plug holes. Wish I hadn't; up close, the encrustations on top of the piston look like massive geological structures.

I've been religiously using AvGas for a decade, mostly for it's known quality, but would love to get away from lead. Is there any additive I can use to clear those internal deposits?

[kgwilson]

I would not lower float as at full power you risk running short of fuel and engine will surge.

 

The fuel pump should always be able to deliver more than required for full power because if not, even with a full float bowl you will eventually starve the engine of fuel. The electric pump should be able to deliver 50-60 litres per hour. This is part of the Jabiru fuel flow test. In flight the mechanical pump is in use so add the electric pump & you will have a lot more than required for full power.

 

As an aside one of the guys at our airfield, an ex Qantas captain owns a Tiger Moth. At a flyin he was designated to go and pick up a photographer. The Cirrus engine uses Mogas but at the pickup only Avgas was available so he filled up. Part of the way back the engine stopped & the prop windmilled. At only a hundred or so feet above the trees it started again. This happened 8 times on the return flight. He told me that day he nearly gave up flying. The problem was the cork gaskets in the system were attacked by Avgas & the debris had partially blocked the fuel line so the flow was insufficient and the float bowl emptied but the engine restarted once it had refilled sufficiently.

[kgwilson]

I use Mogas 98 exclusively and the engine stays clean. Plugs look brown at low level but black up high. The oil stays cleaner longer too. The only issue is Mogas deteriorates quickly so I always put some fresh in if I have not flown for more than a week or so. BP did a study some years ago and this was all that was recommended. Interestingly the RON number increased to 99.5 after 5 weeks after the aromatics had evaporated somewhat but the fuel then began to induce detonation & pre-ignition at high engine speeds causing piston damage. The BP study is attached.

petrol-life-vehicle-tanks.pdf

[Bruce Tuncks]

Like you, old K, I have used avgas but the guys who use mogas have cleaner engines. What endoscope do you use? Can it look back at the valves?

On flywheel bolts... my engine has the first-generation 1/4" bolts and no dowels.

I rang jabiru once about how come this was ok and they told me that they had no problems with engines of my batch.

Well I'm still worried a bit and I use epoxy to ensure that there is no hammering from the prop.

[Old Koreelah]

Thanks for that, Kevin. Donation is to be avoided at all costs, (correction; that sounds like some of Australia's wealthy class- I meant to say detonation) hence my use of AvGas and putting up with lead deposits.

If I could burn 98 without risk of detonation I would.

Edited June 10, 2020 by Old Koreelah

[Geoff_H]

I use Mogas 98 exclusively and the engine stays clean. Plugs look brown at low level but black up high. The oil stays cleaner longer too. The only issue is Mogas deteriorates quickly so I always put some fresh in if I have not flown for more than a week or so. BP did a study some years ago and this was all that was recommended. Interestingly the RON number increased to 99.5 after 5 weeks after the aromatics had evaporated somewhat but the fuel then began to induce detonation & pre-ignition at high engine speeds causing piston damage. The BP study is attached.

CASA produced a warning about using 98 fuel in aircraft some years ago. It has dissolved gasses in it. Their vapour pressure is low. On a hot day it is possible for these gasses to come out of solution in fuel lines and starve the engine of fuel. Each aircraft design needs to be checked for 98 in fuel lines at altitude on hot days.

[kgwilson]

Vaporisation is the main known issue in using Mogas over Avgas. Even at 40 degree temperatures on the ground I have never experienced issues and it is much cooler at 10,000 feet. At the standard lapse rate it would be 20 deg C. Location of the electric fuel pump is a consideration as well. Mine is directly below the main fuel tank in the fuselage so it is pushing fresh cooler fuel through the firewall into the hot engine compartment & so should reduce the likelihood of vaporisation wheras the engine driven pump is in the hot environment and sucking fuel also in that hot environment which could include vapour. Even so like most people who use Mogas I have never experienced it.

[facthunter]

The Avgas also gives you a bigger margin of octane . The two ratings are not the same. The aviation spec is higher for the same stated number. Usually the avgas has two also, a lean and rich figure. The RICH figure is the HIGHER one,

Avgas has an additive to remove the tet. lead. That's what makes the exhaust go white in the end of the pipes. (IF it still does).

Jabiru has played around with comp ratio (lowered it) and also retarded the ignition timing to stop detonation so there is an issue there, at least potentially. If there's significant build up of carbon deposits or such that's a potential source of a hot spot and also putting anything under the plugs, like a temp sensor or not having them correctly tensioned can effect their heat range. Nev

[Old Koreelah]

Good point, Nev. My sensors are screwed into the head between the plugs. Yesterday I removed them for an overhaul. No. 2 has been showing consistently cooler temps, so I bolted the four rings together and hit them with the heat gun. The MGL gauge showed identical readings from all four, up and down thru the temp range.

 

To reduce errors from blast cooling of the senders, I had fitted Ian Bent's little insulating hoods. Based on a suggestion from the Jab/CAMit forum, I've also covered the sender wires with a couple of layers of shrink wrap and conduit.

 

Now, if only I could buy AvGas before they add the TE Lead. During WWII the additive was stored separately and mixed in just before use.

[spacesailor]

O K

YES, there,s a spray can that Subaru uses in their motors, ( we all know why ) to decoke them,

Works a treat, lots of alloy in Subi motors, so should be good for most engines.

" upper engine cleaner " thats their name !.

spacesailor

Edited June 10, 2020 by spacesailor

[onetrack]

The Subaru Upper Engine Cleaner makes no claim to decoke combustion chambers, only to clean the intake tracts.

[Old Koreelah]

The Subaru Upper Engine Cleaner makes no claim to decoke combustion chambers, only to clean the intake tracts.

They claims it cleans the combustion chamber as well and there seems to be a Nulon product as well.

 

I'd love to hear from aircraft owners who have used it; I'd be cautious because none of these car engines burn leaded fuel like some of our planes do.

Edited June 10, 2020 by Old Koreelah

[facthunter]

There was some kind of solvent they were using on the competition cars. I reckon water/methanol will do it. Use it for take-off. Lots of competition cars used avgas . You could get a permit from Customs for certain vehicles for road use, even. Nev

[skippydiesel]

CASA produced a warning about using 98 fuel in aircraft some years ago. It has dissolved gasses in it. Their vapour pressure is low. On a hot day it is possible for these gasses to come out of solution in fuel lines and starve the engine of fuel. Each aircraft design needs to be checked for 98 in fuel lines at altitude on hot days.

 

Rotax 912 range tend to have fuel lines running over the top of the engine. Makes them prone to vapour lock on hot days (exacerbated by using ULP). Can be managed of course -avoid take offs during hottest part of the day, do extra long run ups befor take off. This will tend to clear the vapour (may produce some rough running/ rpm drop), use a good long runway (dont be tempted to do an intersection take off and do not persist with take off if engine not purring) and have a plan if the engine stops/looses power. Once up and away NO PROBLEMS AT ALL.

[Bruce Tuncks]

Thee was a time when avgas was mandated in aboriginal settlements because it ( avgas ) was less attractive to petrol-sniffers.

They ran their cars on avgas for sure.

[Bruce Tuncks]

Personally, I was never attracted to petrol sniffing. But I loved the smell of model plane dope and diesel fuel with ether.