Jabiru Pistion pin offsett

[gwillimm]

Gooday all i am in the prosess of top end over hall on my jab 3300 humm.

 

I have a question ?

 

 

 

 

 

 

 

 

 

 

Jabiru use a holden piston, the holden motor rotates in the clockwise direction the jabiru rotates in a anty clockwise, thus should mean on a Jabiru the pistion notch on the piston crown should be fitted to the rear.

 

,

 

Offset is always to the major thrust side of the piston, as the Jabiru motor rotates the oppsite direction the pistion notch should face the rear. 'Not the front' as stated in the manual.

 

Quote' from Jabiru manual

 

Note: Arrows on inside of pistons point in direction of rotation. Oil Rings and

 

 

 

 

 

 

pistons and bore well. Notch on the piston crown faces the Propeller Flange.

 

When i arsked Jabiru engine shop they told me in short that the thrust is from the propeller on a plane and a car it is from the flywheel and according to them the manal is correct.

 

I for the thrust is from the power stroke ???

 

"humm" :hittinghead: I dissagree.

 

All the reserch i can find states that,

 

"Most engines today utilize pistons with an offset pin bore. That is, the pin

 

bore is "moved" a specific distance from the centerline of the piston. In gas

 

engines the offset is always to the major thrust side of the piston. The

 

piston thrust side is the part of the piston perpendicular to the pin bore

 

that carries the majority of side loading during the power stroke.

 

The primary reason for pin offset is to prevent the piston from slamming into

 

the cylinder bore after the connecting rod journal passes top dead center.

 

This problem is referred to as piston slap. The desired scenario for piston

 

movement is to gently rock from side to side within the bore. This rocking

 

motion eliminates slap. "

 

by Hunter Betts

 

Can any one else shed some light on this

 

Thanks Mick

 

 

[Tomo]

That is all correct Mick.

 

GM - Detroit pistons are all symmetrical as those engines can run both directions.

 

The others as you say are offset slightly to eliminate piston slap, and or excessive bore wear. I haven't a lot to do with Jabiru engines, but I would just do as the manual states. As any other way your are becoming a test bench.

 

The torque loadings on a propeller compared to a flywheel/gearbox set up is very much different. So as they say, it must have something to do with it.

 

From what I'm aware, They aren't "Actually" holden pistons, they just look very similar.

 

 

[facthunter]

Piston pin offset.

 

the ONLY thing to consider would be the direction of rotation. Which end of the engine you take the drive from is irrelevant.

 

The way the offset works is to cause the piston to 'rock", because of the pressure acting on the crown. The piston wants to rotate on the piston pin axis. This puts the top part of the skirt against one side of the cylinder wall and the bottom part against the opposite side, and helps to eliminate the "clack" when the piston moves over TDC, under load. Nev

 

 

[Harthy]

Mick,

 

With many years of experience in rebuilding engines, you need to do as the manual says.

 

As for rebuilding the jab engine. You are not first person to do so. All of the others that have rebuilt jab engines would have followed the manual or instructions. I'm sure with the experience of the Jabiru engineers, they would have it right.

 

With no exception from what I have seen, the notch or the arrow on the piston goes towards the front of the engine unless specified other wise. I also have heard that the jab pistons are not Holden pistions, as are other parts that have been dobbed with the same title.

 

In the end that is your decision. I for one would be following the manual!

 

If you don't already have a contact, I can give you a contact number of a LAME that is certified to rebuild Jab engines in Bundaberg.

 

Harthy

 

 

[thommo]

So what way did you put those pistons in?

 

 

[Yenn]

Even if the pistons are Holden I think you will find that they have been reworked. I know they reworked the gudgeon pin retaining ring groove in early models.

 

 

[gwillimm]

Motor running well

 

Gooday all after a lot of research us and other LAME when you draw up the cranckshaft, direction the pistion offset we fitted the pistions with the notch to the rear.

 

Thanks for all your feedback. :hittinghead:

 

Yours in flying

 

Mick:rotary:

 

Look at the pistion direction humm

 

Contrails ! Inside a Jabiru

 

 

Photo Pete Krotje

 

Anatomy of the Jabiru 3300

 

Jabiru engine lovers will enjoy this little "journey inside a Jabiru".

 

Those Jabiru 3300 and 2200 pictures were provided to Contrails by Pete Krotje from Jabiru USA Sport Aircraft, and Jabiru owners, and are published here with their kind permission.

 

The 4-cylinder Jabiru 2200 technology is quite similar to that of the 3300.

 

Top

 

Jabiru 3300 6 cylinder tear down

 

Bottom end

 

Photo Pete Krotje

 

Note how the engine is secured vertically on the bench with two bolts through the propeller flange. The Loctite 515 tube is for sealing the crankcase.

 

Near the top, the mechanical fuel pump pushrod protrudes from the crankcase.

 

Further down are the pushrod holes and and oil orifices to cylinder heads.

 

At the bottom is the oblique oil pump pickup tube with its skewed end.

 

Photo Pete Krotje

 

The fully machined crankcase splits vertically.

 

At the top of the camshaft, in front of the #6 piston, the fuel pump eccentric and its pushrod passes through the right crankcase half.

 

This model has solid lifters. The oil return holes machined in each lifter housing are clearly visible.

 

Photo Pete Krotje

 

The top cylinder has one of the through-bolts holding the crankcase half and the cylinder base flange.

 

At the bottom is the oil filter adaptor with its thread and the oil pressure relief valve nose, washer and retaining ring.

 

The main oil gallery runs down the length of the left crankcase half at the level of the cylinder head lubricating holes.

 

Crankcase

 

Photo Pete Krotje

 

Matching crankcase halves are fully machined from solid light alloy. The machining is fine.

 

A serial number can be made out in the #1 piston passage in the right crankcase half. See also the oblique oil pickup tube.

 

The crankcase has 7 bearings. The #1 bearing shows the recessed thrust bearing washer housing. Note the positioning dowel at each through-bolt passage. Sealing is with O-rings in grooves machined in the dowel bores.

 

Photo Pete Krotje

 

Note the waisted through-bolts (10 long, 4 short, 2 very short), and the intricate oil passages to the main bearings.

 

Looking closely at the lifter housings, the pressure lubrication holes and oil return holes are visible.

 

The camshaft bearings seem to be splash lubricated.

 

Top

 

Moving parts

 

Camshaft

 

Photo Pete Krotje

 

The camshaft installed in the left crankcase half.

 

The 7 journals and 6 pairs of cams are clearly visible.

 

At the rear near the timing pinion, the fuel pump eccentric is located between the two #6 cylinder cams.

 

Also note the two thrust bearings machined in the camshaft near the pinion.

 

Crankshaft

 

Photo Pete Krotje

 

The hollow crankshaft is machined out of solid 4140 chrome molybdenum alloy steel. It features 7 main bearings (48 mm diameter). There is a double bearing for the propeller.

 

The steel shell bearings are of automobile type. The generous oil holes in the crank pins and main bearings are visible.

 

Lubrication of the big ends is ensured by oblique channels drilled from main bearings # 2, 4, 5, 7, the bearing shells of which have a groove and hole. The #1 bearing shells have no hole, as the oil is fed via the hollow crankshaft main bearing.

 

The crankshaft seems very light and its finish is outstanding.

 

Photo Pete Krotje

 

Hollow 45 mm diameter crank pins have plugs closing the oil circuit.

 

Thrust faces are machined at the front of the crankshaft and the front face of the #1 crank throw. They bear on thrust bearings housed in recesses in the crankcase.

 

Each crankshaft end takes a lip seal. Those seals are removable without splitting the engine.

 

The propeller flange is removable to give access to the front crankshaft seal.

 

Pistons

 

Photo Pete Krotje

 

The slipper type pistons come from General Motors Australia.

 

The very short pin is floating and maintained by circlips in re-machined grooves in the bosses.

 

The classical 3-ring set includes two cast iron top rings and one expander-type scraper.

 

Note how the piston passages in the block are narrow, ensuring better crankcase rigidity.

 

Connecting rods

 

Photo Pete Krotje

 

The I-section connecting rods are machined from 4130 alloy steel.

 

The big end caps are tapped for 1×5/16 UNF screws, so disassembly implies removing the pistons and splitting the crankcase.

 

© Jabiru

 

Matching big end caps are positioned with two 3×14 dowels [1].

 

The steel shell bearings [2] (45 mm diameter) are of automobile origin.

 

Top

 

Top end

 

Cylinder heads

 

Photo HJ

 

The heads are machined from solid aluminium alloy.

 

The combustion chambers are wedge shaped, with the spark plugs located on the thick side.

 

Note the squish surface (see below) with an "X" mark.

 

Doc Jabiru/GTH

 

The wedge shape gives a very compact combustion chamber.

 

This arrangement results in parallel valves, with inlet and exhaust ports on the same side.

 

Photo GA

 

The head shown here is from a Jabiru 2200 4-cylinder engine.

 

The different diameters of the shrunk in seats are visible : smaller exhaust on the left, larger inlet on the right.

 

One can clearly see the turbulence generating squish surfaces below the spark plug holes and above the ports.

 

Please note that the finning is larger on the exhaust side, as thermodynamics dictates.

 

Valve gear

 

Photo GA

 

The picture shows the valve gear components.

 

The parts are the same as in the Jabiru 3300 6 cylinder engine.

 

Below the head are the valves with their single coil spring (40 mm long), spring seat washer, spring retainer and split collets.

 

In the forefront are the two manually adjustable rockers (solid lifters) and their 12 shaft.

 

Rocker pushrods are visible on each side.

 

Valves and guides

 

Photo GA

 

The valves are manufactured in England for Jabiru.

 

Stem diameter is 7 mm, and head diameters are 33 mm exhaust, 41 mm inlet.

 

The original valve guides are manufactured from aluminium/bronze, and have an oil hole.

 

Maximal allowable valve/guide tolerances : inlet 0.10 mm , exhaust 0.12 mm.

 

Top

 

Timing gear and accessories

 

Rear engine plate

 

Photo Pete Krotje

 

The rear plate is machined from a light alloy plate. We can make out the trace of the timing gear housing, sealed with Loctite 515, as well as its two positioning dowels.

 

On the crankshaft end, the 6 tapped holes for the flywheel screws, and the small bore of the pinion indexing pin.

 

In the forefront, the large 44 tooth camshaft gear, the thinner pinion above is the distributor drive gear (30 teeth).

 

Near the s/n two timing marks are showing in white.

 

In the corners, the 4 silent blocks mounting lugs are integral with the rear plate, which also shows the starter motor aperture.

 

Timing gear

 

Photo Pete Krotje

 

The gear housing is machined from a light alloy plate. The timing gear lip seal (50×65×8) is pink.

 

In front of the seal, the 22 tooth timing gear which slips onto the crankshaft end. We can see the 6 screw holes, and the 3 6×24 dowel bores, as well as the indexing pin maintaining the pinion on the crankshaft during assembly.

 

On each side on the housing, the two pinions (30 teeth) are riveted to the distributor shafts. Behind are the distributor cap mount plates, the left one showing its lip seal (15×24×7).

 

Flywheel

 

Photo Pete Krotje

 

The flywheel has 3 assemblies of 3 15×7 rare earth magnets and pole plates, as the the engine has 6 cylinders (engines fires 3 times per revolution) .

 

In the middle, the alternator rotor has 12 cylindrical magnets, which have attracted some screws.

 

The internally splined part is the light alloy vacuum pump drive.

 

Alternator

 

Photo Pete Krotje

 

The spider stator mount standing on its 4 L-shaped mount blocks.

 

The black sleeve coming out of the spider protects the alternator leads.

 

Photo Pete Krotje

 

12 pole stator on its spider mount. The two ignition coils are screwed to the 4 L-blocks through their pole plates.

 

Induction manifold

 

Photo Pete Krotje

 

The 6 lower induction pipes are inserted into a fully machined two part plenum.

 

The manifold assembly is attached under the sump at the rear of the engine.

 

The rubber carburetor coupling is visible on the right.

 

Top

 

 

[thommo]

So you didnt follow the Jabiru manual and went and fitted the pistons in backwards?With the notch to the rear?

 

 

[deadstick]

Well interesting that this topic is being discussed ATM, I have recieved advice from 1 race car engine builder, 1 engine reconditioning shop owner and 1 person that has built a few jabs for people that I should reverse the pistons from what Jab says as they have it all wrong (All in one day) and after listening to the logic I think they are right. The engines that were built with the pistons reversed to Jabs manual run quieter so why have Jab done this?

 

 

[gwillimm]

Humm

 

Well when the Jabiru engine shop told me the thrust is taken from the propelor flange on a areo plane not the flywheel as a car they lost me,

 

I agree

 

The ONLY thing to consider would be the direction of rotation. Which end of the engine you take the drive from is irrelevant.

 

The way the offset works is to cause the piston to 'rock", because of the pressure acting on the crown. The piston wants to rotate on the piston pin axis. This puts the top part of the skirt against one side of the cylinder wall and the bottom part against the opposite side, and helps to eliminate the "clack" when the piston moves over TDC, under load.

 

From Nev

 

Thank you

 

Legally you should assemble your enging in accordance to the Jabiru manual.

 

Yours in flying

 

Mick:rotary:

 

 

[deadstick]

Well when the Jabiru engine shop told me the thrust is taken from the propelor flange on a areo plane not the flywheel as a car they lost me, I agree

 

The ONLY thing to consider would be the direction of rotation. Which end of the engine you take the drive from is irrelevant.

 

The way the offset works is to cause the piston to 'rock", because of the pressure acting on the crown. The piston wants to rotate on the piston pin axis. This puts the top part of the skirt against one side of the cylinder wall and the bottom part against the opposite side, and helps to eliminate the "clack" when the piston moves over TDC, under load.

 

From Nev

 

Thank you

 

Legally you should assemble your enging in accordance to the Jabiru manual.

 

Yours in flying

 

Mick:rotary:

Yeah legally I have assembled per spec as its cert, But the whole thrust thing from Jab I dont get it? its more to do with rotation of the crank per power pulse, as far as I understand. I would really like to see some engineering info on the design philosophy for this plant.

 

 

[deadstick]

Another thing why would you design an engine with a cylinder and piston at its max oversize and then pick a generic piston and not a forged one, I recieved a piston today that was 5 grams lightr than the others and they have gone to circlips instead of the round wire type, what the? I am advised that the circlip design is prone to failure, why is Jab so reluctant to tell us why they change design?

 

 

[Vev]

Guys,

 

Hate to say it, but if you have fitted the pistons with the notch to the back (fly wheel) you have put the pistons in wrong way around .. the Jab manual is quite correct.

 

Forget about rotation for the moment and fit the pistons as per the manual... try marking the centre line of the piston on the underside of the piston crown ... you will see the pin is off set to the centre line.... now assume the rod part way down the power stroke 90% ATDC, now draw a line through the big and little ends ... you will note that the line between the two centres will intersect with the centre line you have marked on the underside of the crown. If you put the psitons the other way around it will be way off set which will drive the piston down the bore sideways during the power stroke.

 

Cheers

 

Jack

 

 

[deadstick]

Guys,Hate to say it, but if you have fitted the pistons with the notch to the back (fly wheel) you have put the pistons in wrong way around .. the Jab manual is quite correct.

 

Forget about rotation for the moment and fit the pistons as per the manual... try marking the centre line of the piston on the underside of the piston crown ... you will see the pin is off set to the centre line.... now assume the rod part way down the power stroke 90% ATDC, now draw a line through the big and little ends ... you will note that the line between the two centres will intersect with the centre line you have marked on the underside of the crown. If you put the psitons the other way around it will be way off set which will drive the piston down the bore sideways during the power stroke.

 

Cheers

 

Jack

Hey Jack, I am hearing what your saying and they were installed as per jab manual but every engine builder I speak to including those that rebuild 2200s and 3300s both overseas and here, are saying they are fitted incorrectly. One local gent has built three 2200s now with pistons reversed, no probs so far and he say's they are quiter.

 

I was also speaking with a KIWI the other day who was telling me that the standard pistons are being ditched in favour of forged items over there.

 

I am not sure about others but all the Jab engines down here do not make the slated TBO with mine spitting the biscuit at 230 hrs, and on dissasembly it had advanced scuff on the pistons and bores. Locally they are developing a bit of a rep for unreliabilty to the point people don't fly over tiger country without a paddock to FL in. would be agreat little plane with a 914 rotax LOL

 

 

[Vev]

G'day Deadstick,

 

You may want to check on what is current with Jab as there has been many updates on the new top end that has made a significant improvement on engine durability.

 

They have fitted new pistons with more ring grove clearance and a bigger slot for the oil drain back, new cyclinders, new heads with 50% more fins along with a new shape to the combustion chamber and new over head gear and push rods ... the new pistons dont have the notch on the crown (they have also removed the centre dome on the crown) and only have a tit over the piston pin mount which faces the front (prop)... I guess what I'm trying to say is there are many changes to the current engine that you can retro fit onto your older engine and dont use the old bits to compare what is now available as standard from Jab.

 

In my view the new engine bits has made a good engine great.

 

Cheers

 

Jack

 

 

[deadstick]

Gday Jack, by dome do you mean the dish in the piston? are they flat top pistons now? Mine is an 08 model 3300. A picture of a piston prior to my overhaul is here: post 5 http://www.recreationalflying.com/forum/jabiru/98599-3300-cylinders.html

 

This was after a mere 230 hours and as I said the bores and piston skirt's were badly scuffed. Also the exhaust pushrod was eating its way into the rocker (hydraulic lifters)

 

and was going to cause a real bad day prior to reaching TBO. I just don't get it, the bottom end seems fine but its the top end and carburation that is letting them down, if Jab were serious about the customer they would offer a fuel injection solution (they have purchased one of the RO-TEK units) and a better prop (only has to be an option). One of the jab reps at Temora told a friend that they wont certify another prop as they make too much money out of propellers, that attitude is what is earning them the rep. All the Jabs down here suffer from carb icing and different CHT and EGT per cylinder and Jabiru engine department have told me they are aware of the CHT and EGT problem but could only suggest moving the one thermocouple around till I find the hottest CHT and use that from then on. If its such a well known problem I would think they would fit a 6 CHT/EGT monitor as standard, I am currently researching one at the moment and looking at the MGL units. A certified 3 blad prop ould be a dream on the 3300 and inflight adjustable:clap:

 

 

[brilin_air]

If you are going to turn pistons around you might want to consider the raised compression ratio in the combustion chamber due to the piston pin offset and the damage that it could cause through detonation damaging pistons, heads and breaking through bolts.

 

Brian

 

 

[gwillimm]

pistion offset

 

GEE that sounds like the standard problems that Jabs have normaly.

 

Hummmm.

 

Yours in flying

 

Mick

 

 

[Vev]

Hi Deadstick,

 

The earlier piston had convex domes .. you have flat but these are not the latest pistons.

 

Cheers

 

Jack

 

 

[gwillimm]

This is from Brumby A/C Thread

 

Hi

 

The first new engine run for about 30min andthen when we removed the cowls and doing checks when we seen paint peeling from one barrel.When we removed the paint it was blue fom heat.

 

This was also making a noise as well on that cylinder. So was replaced

 

Next engine

 

We repalced engine with another new engine that jab supplied and it lasted 15-20 hours and then one day in downwind the engine made loud bang and the prop stoped.

 

After a forced landing i went to retreive the plane and the engine had locked up.

 

I then removed plugs from engine to find a smashed plug.We are not sure what happend in the end with the engine Jab replaced with another new one.We think a piston let go or a rod.

 

After a few phone calls to Jab they then told us that they had changed there piston supplier.

 

Next engine Still running but owner has little trust in Jab motors.

 

 

[brilin_air]

The most critical thing to maintain in a jab motor in flight is the EGT and CHT if you hang off the prop and have low air flow through the ducting and high engine temps then you are doomed for a failure, do that with any engine and it will not last.

 

Brian

 

 

[Vev]

Spot on Brian ... 90% of these problems are over heating issues.

 

The magic numbers is to keep the EGT below 1250 deg F and CHT in the middle of the green at around 275 F ... need to make sure the carby jets are fat to keep EGT's down and that air flow through the engine cowl are correct .... tooo much pitch on a prop will kill them very quickly too .. as you said good airspeed and plenty of air flow works wonders.

 

Cheers

 

Jack

 

 

[bushpilot]

Our colleagues over at the FTF at Orange - "Orange Flight Centre" - have put more than 4,000 hours on Jab. motors and have never done anything more major than the maintenance books prescribe.

 

The CFI there - Ken Pidcock - is an L2 and does all his own servicing. He does oil and filters and tappets at 50 hours and the 100 hourlys by the book. He pays special attention to backing off, lubricating with anti-seize and re-torquing the head retaining bolts every 100 hours. Jabiru have inspected 2 of his engines at around 1000 hours and said that they were in such good order they could have gone straight back together.

 

I think durability is a combination of usage (circuits are better for a motor than long flights at constant revs) and proper maintenance.

 

 

[Jack Donsen]

Gooday all i am in the prosess of top end over hall on my jab 3300 humm.I have a question ?

 

 

 

 

 

 

 

Jabiru use a holden piston, the holden motor rotates in the clockwise direction the jabiru rotates in a anty clockwise, thus should mean on a Jabiru the pistion notch on the piston crown should be fitted to the rear.

 

,

 

Offset is always to the major thrust side of the piston, as the Jabiru motor rotates the oppsite direction the pistion notch should face the rear. 'Not the front' as stated in the manual.

 

Quote' from Jabiru manual

 

Note: Arrows on inside of pistons point in direction of rotation. Oil Rings and

 

 

 

 

 

 

pistons and bore well. Notch on the piston crown faces the Propeller Flange.

 

When i arsked Jabiru engine shop they told me in short that the thrust is from the propeller on a plane and a car it is from the flywheel and according to them the manal is correct.

 

I for the thrust is from the power stroke ???

 

"humm" :hittinghead: I dissagree.

 

All the reserch i can find states that,

 

"Most engines today utilize pistons with an offset pin bore. That is, the pin

 

bore is "moved" a specific distance from the centerline of the piston. In gas

 

engines the offset is always to the major thrust side of the piston. The

 

piston thrust side is the part of the piston perpendicular to the pin bore

 

that carries the majority of side loading during the power stroke.

 

The primary reason for pin offset is to prevent the piston from slamming into

 

the cylinder bore after the connecting rod journal passes top dead center.

 

This problem is referred to as piston slap. The desired scenario for piston

 

movement is to gently rock from side to side within the bore. This rocking

 

motion eliminates slap. "

 

by Hunter Betts

 

Can any one else shed some light on this

 

Thanks Mick

Hi Mick,

Your assessment is correct. The reversal of the crank rotation effectively moved the wrist pin offset to the wrong side of the centreline. Jabiru Sth Africa have been reversing pistons from new for over 10 years and are getting great results in achieving 1000 hours TBO. If you record your T's and P's prior to correcting the offset and comparing them after, you will drop CHT by 30 degrees F and the oil temp will drop about 10F and you will pick up an extra 50 RPM at full static.

 

 

[Camel]

Hi Mick,Your assessment is correct. The reversal of the crank rotation effectively moved the wrist pin offset to the wrong side of the centreline. Jabiru Sth Africa have been reversing pistons from new for over 10 years and are getting great results in achieving 1000 hours TBO. If you record your T's and P's prior to correcting the offset and comparing them after, you will drop CHT by 30 degrees F and the oil temp will drop about 10F and you will pick up an extra 50 RPM at full static.

I'm very interested in a way of confirming that Jabiru Sth Africa actually do this, Jabiru have published a bulletin on why it is the way it is, would love to see confirmation on what you say !