Shell bearing diagnosis.

[geoffreywh]

I was just dismantling a late model 2200 (roller lifter) for a top end (1000) hr overhaul. The top was not pretty. Replacing the big-end shells is part of a top end o/h. The shells have a unusual look to them. Namely the only place to show any noticable wear is a point of contact on the half shell directly below the wrist pin. The waer point is about 10 mm dia and almost through the lead. The bottom of the shell shows little wear. Not happy with what I was looking at I pulled the crank out. The mains are even odder. the front two journals show each side the same and considerable wear. The third journal (from the front) has copper showing on the r/h side and the l/h/side is UNTOUCHED. I can see where someone has measured the shell i.d. with a dial gauge. .. The fourth journal has copper showing on one side and just normal on the other the reat are just rubbish... The crank looks OK...and has about 0.03mm max runout...The cam journals are very similar. I guess at a warped crankcase... What do you think?????

 

 

[jetjr]

May not be at all relevant but there is a point of view that the method Jabiru specify to assemble case halves can lead to enven clamping

 

I believe the recommended methods and sealants is very difficult to get right.

 

 

[DrZoos]

I would be extremely happy with what your looking at...you safe, saved a fortune compared to a parts failure.

 

 

[Aldo]

Geoff

 

I'm no mechanic and don't pretend to be one, if all the items you have described are due to be replaced in a top overhaul I would say you have got a pretty good result if there are items in there that are not supposed to be in a top then you have some other problem.

 

Aldo

 

 

[bexrbetter]

Geoff,

 

Doesn't sound excessive although I would be checking the clearance of the big ends and ultimately ignition timing as it sounds like the big ends are being thumped a little at TDC.

 

As for the Mains wear, sounds like the prop might be out of balance causing a little torsional end whip and /or the crank itself, a balance for individual parts, then complete assembly might be advisable.

 

Overall, your bearings are doing what they are there for.

 

 

[Oscar]

In the factory assembly ( i.e. by CAMit), dial-gauges are not used to check bearing fit; the cases, shaft and rods are laser-measured. The cases are pulled down together to full clamping pressure and the tunnel laser-measured, in a controlled-temperature measuring room and only when they have been left to settle to ambient for a goodly number of hours. Had that engine had through bolts / 12-point nuts changed in at some time? It sounds as if that engine had had the cases split at some time -necessary, obviously, to get dial-gauge access to the mains - and as mentioned above by jj, the Jabiru case-joining technique is hard to get correct.

 

 

[facthunter]

Also the bearing metal itself is copper-lead, with an overlay (usually indium) which aids in bedding in during the run in period..The overlay is a very thin plated surface. Align bored bearings don't have an overlay so they are copper coloured all over the wearing surface, from the start. Jabiru probably don't align bore the bearings, but someone else may have . I would have thought alutin might have been used as bearing metal. Copper lead with overlay is one of the best, but do better on a nitrided shaft. Nev

 

 

[Oscar]

On CAMits recommendation, I used Clevite MS-1776AL mains, which I believe are alutin.

 

 

[jetjr]

if the through bolts have been replaced without case separation, this could cause plenty of problems

 

I think Jab specify using spring gauge on prop to check if bearings too tight after new bolts installed........

 

I was recommended that replacing bolts in assembled engine was a pretty poor idea. Many older Jabirus have had this done or should have

 

 

[facthunter]

They are all wrong about that advice. Both the bearing materials available need a positive running clearance for the correct oil flow and fit, and just turning if free enough is not on. If the studs have let go, The engine needs dismantling and any fretting would mean remachining and rebuild. The bearings need an interference fit in the tunnels, which must be right, or it won't run long. Nev

 

 

[jetjr]

Correct, but letting your customers know they are up for full engine tear down, even those just shipped, would be pretty unpalatable.

 

Also why persons recommending this type of fix need to be totally sure its the root cause not a symptom.

 

Plenty of engines - since # 900 onwards, have had throughbolts replaced this way. see JSB 031-3. This only applied to flight training AC. as they were seeing most problems.

 

http://jabiru.net.au/images/JSB031-3_Through_Bolt_Replacement_and_Upgrade.pdf

 

Details of spring test methods are in there. Using 50g accurate scale but still a bit questionable.

 

Previous to this was recommendations to replace nuts with longer versions, some nuts needed radiused back egdges, then longer bolts, now longer AND larger bolts AND washers and nuts. This applied back to # 500 or so. The spring tension test wasnt mentioned for any of these.

 

Only recent versions since # 2574? have had larger bolts and nuts from new.

 

Its quite possible some engines went through this process more than once, each time loosening case halves and retensioning.

 

Id be surprised if at least some of the early rebuild or maybe even failures are not linked to this problem.

 

 

[geoffreywh]

The engine was new from the factory no major work on the engine apart from recommended maintenance. (7/16" thru' bolts from new) The shells are a whitish lead colour ( Babbit Metal) same as every other shell I've ever seen. Except where the bearing surface has worn away. The one shell shows where a dial gauge has been ,absolutely no doubt ....I have photos now, if I can post I will. I would normally set up crank clearance with plastigauge and different thickness shells ( motorcycles.) But this c'case will need line boring and big ends sized............ I just don't know if I want to go on with it...It's like hanging the sword of Damocles over your own head....It's sad as the owner assumed that a top-end at 1000 hrs will get him another mille. (As the Manual quotes) ... But a new motor will remove the sword from above my head and hang it above his!....Shame about all the $K spares he bought....BTW it also needs barrels and heads!.....Eng serial 22B 299

 

 

[jetjr]

Its an old solid lifter engine Id guess, Might have missed the whole throughbolt debarcle being old as it is.

 

Do some serious numbers as with labour a whole new one isnt too bad

 

Get a price on CAE core - most of the good bits new, fully assembled case, heads and barrels. Still solid lifter like existing engine

 

Then again a fully new one isnt that much more and you get more upgrades inc altenator and flywheel mods too

 

Edit, seems you get flywheel inc fastning mods and fuel pump too now on core engine

 

 

[SDQDI]

Its an old solid lifter engine Id guess, Might have missed the whole throughbolt debarcle being old as it is.

I think he said in his original post that it was a 'late' model and post 12 says 7/16 throughbolts from new?

 

 

[jetjr]

Yeah but Ser #299 is pretty early........maybe why it made 1000hrs without much work

 

7/16 didnt come in until 2013/14 I think

 

 

[geoffreywh]

the original post said Roller Lifter.......The engine is from a flying school.

 

 

[jetjr]

Righto, then it aint ser 299

 

And CAE isnt an option, guess hes stuck rebuilding what hes got

 

Wouldnt be many roller lifter models with 1000 hrs

 

 

[biggles]

Yeah but Ser #299 is pretty early........maybe why it made 1000hrs without much work7/16 didnt come in until 2013/14 I think

Jet the serial no is 22 B 299 which I think would be a fairly recent build ... Bob

 

 

[deadstick]

Hi geoffreywh, where are you located? Can you provide a little more detail? Did th engine have 4 channel CHT? What airframe was it in? ( J170?). What oil was being used? (Aeroshell W100 or multi grade). Cylinder blue around the top? Are the exhaust valve guides worn? What is the roller surface on the cam like? Sorry for the questions!

 

 

[geoffreywh]

Located at Tooradin, Vic....Yes it's a 170. Just two channel CHT .. on 3 and 4 . Oil was aeroshell 100w... fuel 100LL exclusively. Cylinders not blue , lots of blow-by on the pistons, nearly all 2nd and 3rd rings stuck. Rocker shafts and bushes totalled. Roller rockers beautiful as is cam. Bore wear reasonable, BUT barrels too short (170mm ) and have been superceded.(now 170.50mm )........ Loss of head material between valves (granular disintegration?) Heads on 2 AND 4 have sunk onto barrel too far. Valves too deep into the head, ( 1st time removal).....some valve guides worn too far. .............................Report from Crankshaft Experts. Too large big-end bearing clearance. Wear spots are evidence of detonation.. Crankshaft bearings not in line. Heads cactus. Barrels superceded. Recommendation...........Throw away and buy a new one....Thus......1000hrs, engine finished..

 

 

[deadstick]

Hi Geoff,

 

does sound like she has been hot, just about all the head and valve train issues you describe point in that direction, the cylinder length should be 107.0 mm nominal and surprisingly Jabiru still allow shorter cylinders to be used with a shim under the base ( never seen one that seals and causes allow barrel to case chaffing ). May be economical to buy a short change over engine and transfer your ancillaries over.

 

 

[Oscar]

Geoff, it sure sounds to me as if that engine had a hard life and was fairly routinely operated at right on the cusp of overtemp.

 

The owner might find it a prudent investment to install 4-channel cht with recording capability AND to a) calibrate the cht probes back to the instrument, and b) utilise a cht instrument that has cold-junction ambient temp compensation inbuilt. The MGL 'Extreme' is the cheapest (and well-regarded) of the readily-available options there, I think you will find. However, Jabiru may not have approved the MGL, it tends to prefer Dynon. Professional test-pilots involved in GA certification work have less than 100% confidence in Dynon in anything but a calibrated installation - you can't just 'chuck in a Dynon' and it necessarily reports accurately because of the brand name, any more than for an MGL.

 

There are some intriguing anomalies in the saga of this particular engine which suggest to me that it was opened after manufacture but before delivery and modified; at one stage Jabiru held a considerable stock on hand of new engines and I wonder if this one was actually manufactured with the 7/16 through-bolts (the CAMit build record would show that, but that's proprietary Jabiru information) or upgraded at Jabiru's workshop before being released. I am aware that Jabiru had to tear down and repair - twice - engines that had installed a dud batch of pistons from China, due to the circlip groove being incorrectly machined and then the accompanying circlips being found to be out-of-spec. The Jab. workshop simply does not have the capability of CAMit for laser-measured accuracy, which might explain the dial-gauge evidence.

 

I have to ask: since you found severe blow-by, had ANYBODY picked up low compression on the D.I's? Carbon impaction of the rings doesn't just happen overnight; is there no record of leak-down testing over the last few hundred hours of use? Is the operational environment in which this engine was operated characterised by the D.I's being undertaken by different people every time ( i.e. students) who do not have a reference for acceptable compression on pull-through? These are the sort of questions that do need to be addressed for everybody involved with operating Jabiru engines (in particular) so that the entire Jabiru-operating community can learn what NOT do do in regard to sensible operation of the engine. They aren't Fergie 35 tractor engines, which are almost by definition fine if they start...

 

 

[geoffreywh]

Sorry Oscar. I am a late comer to this engine. I will certainly be recommending a new bare motor + 4 cyl CHT....Thanks for the input everybody....General Consensus ............Overheating leads to ruin.

 

 

[Oscar]

Geoff - I'll take London to a Brick that Keith Rule would endorse your decision, and I couldn't think of anybody better to advise. That engine was a dead engine walking.

 

FWIW, I spent about half an hour earlier this week talking to a J160 owner at Camden about and looking at his progress on cooling set-up mods. A really clued-up guy who is doing all the best sort of development stuff: calibration, testing step-by-step, recording and analysing. His first engine was changed for a new one at 1000 hours, because he's a careful and conservative owner, though it was running fine and had never indicated high temps. on the standard single CHT on #4.. When he installed the new engine, he upgraded to full cht monitoring - and was horrified to find that temps across all four varied by up to nearly 40C - with no. #4 being always the coolest!.

 

By patient and fully-tested and recorded changes to baffling etc., he now has all four CHT's within 10C of each other, across the range of revs and ambient temps. and his highest CHTs are around 140C even on a 25C ambient climb-out at around 75 kts. He has 600 hours now on the second engine and it's running like a Swiss watch (and that comes from an engineer, the most critical of human beings on the planet for mechanical performance!) He does a heap of touring, lots of hours/year - no circuit-bashing. A very happy Jab. owner - and his engine installation is impressive, eat-your-lunch clean and tidy and a paradigm of good practice.

 

We all know that Jabiru has tended to place the blame for engine problems on 'operation' - and we all know, I think, that that is not a reasonable response. However, I believe that the truth is nowhere near black-and-white.

 

The laws of physics ARE black-and-white. For example, the temperature exposure at which Jab. heads suffer permanent degradation can be narrowed down to a +/- of around 10C for a period of less than 5 minutes. Once that has been exceeded, the heads will continue to degrade over time, even at lesser temps.

 

Without adequate, reliable and recorded monitoring, an operator will not KNOW that the limits have been breached - hence it is correct for BOTH Jabiru to say: 'you have exceeded the limitations' and the operator to say 'No I haven't'' - because the operator has had no evidence to the contrary. Neither are wrong, but neither are right.

 

Every bit of cogent information about the operations of Jabiru engines is valuable to a whole lot of owners and operators. Please, for the sake of all of us Jabiru owners, continue to post the experiences you have with the most information you can provide.

 

 

[deadstick]

Hi Geoff,

 

do you have some pics? id expect the barrels to be out of round but am interested mainly in the ring issue. Do the pistons have fly cut valve reliefs in the crown? The reason I ask is the ring lands were enlarged to prevent Carbon deposits from causing the rings to stick IIRC. A pic of the head recession would be good too, will give an idea if its been hot around the exhaust valve's ( mixture, leaking seat, worn guide) or from inadequate cooling. Unfortunately Jabiru's in the ab-initio training environment cop a hammering, not intentionally but nevertheless its a harsh environment for any engine. Without warming orbits and constant monitoring its easy to shock cool! With full monitoring, watch the CHT plummet during a PFL or EFATO evolution, its not uncommon to see less than 60 degrees C if not managed correctly. Then imagine the strain on components as the differing expansion rates between the case to barrels to heads plays its hand when the throttle is advanced to max and the nose raised to VY, they really need a soft touch in these circumstances.