dmech

dieselten can you tell me which bolts failed top bottom and on which side thank's A.D.

How do you arrive at that figure bob , holden manual quotes 1.00mm , are they wrong!!

Ornis Offset is neither towards or away from lump lump is on pin axis looking at bottom of piston with lump towards you the offset will be to the right of pin axis, and is obvious by just looking at open end /bottom of piston

NOT SURE ,if fly cuts are the same size,then you would have to swap from one side to the other to change piston orientation , will look at this but sure that can be done

holding the piston upright and arrow or lump away from you,or forward , , the pin will be offset to your right , that side also happens to be the major thrust side when fitted to the holden. Please note : jabiru 's engineering paper's quote offset of only .05mm [ .020"] . Offset that I have measured is 1.00mm [ .040"] this is also confirmed by the holden vn engine manual. Pistons with valve relief 's is still the same holden piston . A.D.

will talk to night or tomorrow, off to fly behind one of those modified motors today. would like to upload holden engine manual but must be to large for this site if you have an email I can email to you / would prefer every one could see it though ,if you know of a way to get it onto this thread/ forum, please let me know how. A.D.

YES Factory fitted wrong way, offset IS relevant to rotation ,has nothing to do with prop thrust, or flywheel , thrust , because this engine rotates opposite to the holden engine that these pistons were originally designed for and since adapted by jabiru for their engine, the arrow should go towards the flywheel . This will definitely improve smoothness of engine and performance . The conrods are way to short also 1.53:1 c.r.s.r, I have made longer rods and barrels for my engine ,but have not had it running as yet. offset was originally introduced in the auto industry to correct angularity problems due to shorter c/rods as the demand for more compact engines were required by the auto industry. Piston slap is certainly caused by fitting these pistons with offset to minor thrust side , and this would have to be happening in the jab engine ,absolutely! Offset has often been thought to control slap, but its main roll to correct angularity of c/rod at max cylinder pressure ie. 15- 17 deg atc. There is a number of modern engines that don't have any offset on pins and these do not suffer from piston slap , 2 examples are Subaru ea81 /ea 82. I have both of these engines ea 81 176k and a ea 82 282k and these engines don't have any piston slap noise. some engines ,Honda for example have actually offset the cylinder centre line to the c/shaft centre line by as much as 14mm t achieve simular results . I made up a model 20 months ago which clearly demonstrates the effects on the engine with pistons fitted wrong way around, since then a number of engines have been changed with good results . and no detrimental effects at all!. The piston used in jab engine has 1.00 mm [.040] pin offset . jab claim .05mm [.020"] offset [see pin offset link ] on jab site. see attachments below. Changing pistons creates a more favourable angle of rod between piston and crank centre line for the smoother transmission of load. With piston wrong way ,it imparts a more jerky motion into crank ,which then is absorbed by the engines rotating mass which results in abnormal loads on flywheel/ prop hub/ prop/and their fasteners, it also imparts an opposite and equal force to the engine block and accessories ,which to some extent is restrained by engine mounts[ vibration felt in air frame]. A recent survey indicating top thru bolts on oil filter side and lower bolts on opposite side failing , tend to indicate that this opposite force may contributing to the bolt failure Piston pin orientation does not change max piston velocity but does change the position that max velocity occurs . Changing pistons around will retard ign tming as it will bring tdc earlier . however as the piston dwells longer as it travels thru tdc this would have a correcting factor, and does not appear to have effected the engines that have been changed , as they seem to have a small increase in power, and run cooler , side benefit of changing pistons is better oil control [ less oil in catch can].Changing pistons according to my model indicates a small effective change in valve timing [ retarding ] , however this engine has long manifold runners and probably results in less flow thru of a/fuel mix into the exhaust during valve overlap resulting in lower egt. Another indication from model is that more of the power stroke is used before ex valve opens ,should result in less stress on ex vale and contribute to lower egt These engines have a history of valve problems , mainly when using avgas , im sure I have a simple fix for this , I mentioned this to Ian Bent some weeks ago & he indicated he would try it out , so wont mention that tonight. Another problem I cant under stand ,is why jab have fitted the oil pressure switch between the pump and filter instead of the main oil gallery this would give error readings especially when cold , also fittings for oil cooler at filter are to small. Also using a sealer over the complete crank case halve is an invitation for disaster, as is the use of Loctite on certain other parts could not load holden manual or jab pin offset link . Could be checked at your holden dealer manual for vn commodore v6 A.D.

Thank's deadstick , would like to hear from other jab owners ,re bolts. Had a few replies so far involving 11 bolts , seems to be a pattern emerging , all bolts on filter side are upper bolts and other side are lower bolts, I think I know whats doing this but more data would be helpful Thank's A.D.

Hi dazza, Jab runs higher rev's

Hi deadstick would be interested to know your experience's with thru bolt issues , in particular , which side and whether top or bottom on each side ie oil filter side or dipstick side A.D.

HI JIM, I would like to advise our steps to eliminate problems , however there would be jab owners wanting to modify their engines , since this would require dismantling of engine, it might lead incorrect assembly and resultant problems that could be blamed on the modification it self , as we have seen . L2'S might not want to do the job as they are supposed to adhere to the manufacturer build instructions, this may put there privilege's at risk, could end up in a legal system , then expert witness's ,probably from j... and we know what they would say, and all in front of a judge who wouldn't know where a tow ball goes!! . I contacted rs jan 2013 and was told that there was no problems with their engines , before I could explain any thing he bought my call to an end. A letter was sent to casa regarding the fix march 2013 , not by me but by owner of first engine modified . I believe CASA contacted jab end of 2013 but nothing productive resulted . I believe the present action is a shot across the jab bow, next shot might be direct hit [ really hope it doesn't come to that]. I have sent a letter to CASA detailing the fix , and a fix for valve problems. that was last week. I'm about to send another letter to CASA with supporting engineering data , today or tomorrow.So with the above in mind and the fact casa has my info , I think it's probably best to wait and see how casa deal with it . after that if nothing eventuates, I can make our findings available. However, any mods you do are at your own risk, however I know you wont be disappointed. The engines mod. here so far, are going fine. A.D. [email protected]

yes it will make problem more pronounced , increased flywheel effect ,ie your spinner will put prop hub bolts under increased stress as it is trying to smooth out irregular motion that is created within the motor, will also impact more on thru bolts, a harmonic damper of any kind mounted on crank won't help either , prop should be as light as possible, at least until problem is sorted A.D.

yes 2 accelerometers and interface to dual trace cro , mine is a TECKTRONIX 488 DIDGITAL STORAGE, , however one from jaycar or alltronics / labscope or sim d trace, however I already know where these torsional movements and spacing's. are happening within the engine cycle and I think they are responsible for almost all of the problems associated with this engine incl.[ exept valves], fly wheel prop hub fasteners , comp. props ,c/case fretting , although we have seen some of this after mods were done but engine did have 80 hrs on it before mod , so time will tell on that one [ except valve 's] but they are also easily fixed , as are the vibration probs which we have already sorted, just need more data re thru bolts so that I can positively associate these failures to the above vibration issues, with info so far, it looks very much like it is . WITH all the bolt problems reported, there must be a lot more data out there . I need to know side and if upper or lower bolt incl studs, to get a definite pattern indication . [email protected]

but then second thought's it is actually abnormal cyl pressure that's causing ,as we have found and mostly eliminated in more than a dozen jabs, no broken bolts in 2 yrs so far 800hrs on one engine fts 160

hear hear dead right there bex

Thanks Planesmaker we just need to see if there is any pattern to these bolt failures . we have found the resonance problem and eliminated about 90% of it in several jab engines , since then [18] months ago we have had no trouble 1 eng 800 hrs at least 2 others around 700 hrs all still operating, engines run smoother /50 deg cooler climb small increase in power, 200 hrs was about all you could expect out of these engines before a major repair, used in F.T.S . 2200 hydr lifter . the way the bolt has broken certainly indicates[ cyclic loading ] , even if they increased size to 5/8 would probably still fail. the base cause needs to be addressed, rather than just beefing up bolts , seems to be an Australian manufacturers trend, if it breaks , just make it bigger. Your bolt failure position and the other one I have ,ARE ALLREADY indicating a pattern that I suspect would be associated with this resonance . bit like the violin and glass trick. I'v been engine remanufacturing since 1976 full time , I have seen large diesels have ends break off cranks 4"diameter all because of resonance. So again , thank's for your reply. ALL other bolt failure position indications would help ANYONE !. Could be a goose chase , but who knows , has to start some where. A.D.

Hi Planesmaker the top bolt u mention which side was that on oil filter side /dipstick side would appreciate your reply on this A.D.

Can anybody inform me which thru bolts are the most common to break ie. upper or lower and on which side of the engine , any bolt size. Just doing some research on this. thanks A.D.

yep its the fuel ! if the engine didn't have fuel it would nt snap bolts

whats happened with this thread, look's like an engine failure . thrue bolts snapted, prop come off, what!.I'V had a lot of response via email several l2's and owners , even a law firm from usa.

yen . that grey stuff on the pistons is lead!. av gas here is loaded with it. this will also play havoc with your valve guides then valves. most jab owners i know don't use it, use 98ron and a little flash lube to protect valve seats in cars we use about 500 ml for 5000 kms . to much will cause soot build up under rings and may cause them to jam in grooves dmech

Hi ANDY CAN YOU FILL ME IN A BIT ABOUT THE CLASS ACTION TOU MENTIONED PLUS ANY LINKS PLEASE. I am interested because i have located a significant fault that jab have unwhittingly applied to there engines due to lack of knowlege.this problem has been inherent for more than 10 yrs and should have been sorted by now. i'm supprised there hav'nt been more legal action against jab. REGARD'S dmech [email protected]

Rick, i have looked thru most comment,s re jab engine . Have there been any comment's posted by Jabiru?, i would be interested in what they have to say with the numerous failures that have plaqued this engine over so many years , and still not resolved.I have done a lot of research my self since i would like to see an ausie engine make the grade. I believe i have found the smoking gun, which i am 100% sure is responsible for 9o% of problems like thru bolts breaking, excessive brg. wear, flywheel bolts coming loose , heating problems, high fuel use. detonation problems , high ring loading causing prem. ring wear,problems relating to head seal leak's, head bolt problems, prop. hub problem's etc. ALL caused by one simple easy to fix low cost solution and this simple oversight would be embarrasing to jabiru factory. I can't elaborate any further at this stage because it would be to hard to ex plain why this is happening , in this post. allso i need to contact jab.first to see if they will listen to me , and i need to verify some other details. I have been a engine reconditioner since 1976 and involved in speedway with many successful engine build's with 4 state titles and many other major win's All the post's [ not including valve related problem's, that's another issue which i'm still looking at]don't go any where neer to the actual cause. if you would like to contact me you could by email [email protected]