dmech

JAB PISTONS ARE BREAKING TO ,all the ones i'v been associated with are gen jab pistons , one engine was mine 260 hrs. another one in our area went at 268hrs . these were the valve relief type. dmech

I use P.C.D tooling piece of cake and very fast ,expensive but just about lasts forever ,[ impossible to grind ring grooves economically ] , diamond hone for silicon ally cylinders . These pistons do flex and are designed to flex, so long as flex dose not go beyond design limits , in this case only a few thou,[like a spring has limits to] in the jab application I have measured consistently, the flex is over .014" this is what breaks the piston ,marks in barrel show this also. There is absolutely no problem with hyper pistons if operated within limitations , which works in the holden engine, the jab engine has not been designed for use of these pistons , but could easily be. Another thing, the piston top dose not match the cylinder head combustion chamber , but close , probably the saving grace there is the long intake pipes , runners. dmech

Yes , still the same piston style with very little slot would be better owing to a different heat path from crown but not a fix. I believe they had problems with tips being broken off the end of cylinders, they being weaker than the 4140 barrels. The full slotted pistons would still be the better way to go because they flex better. the slotted piston can be modified to work in the jab engine, steel or ally. there is a much better option , but this would require changes to cylinder and con rod.

Jab piston is a slab sided piston you cant use a round skirt in a jab engine , so can not be same style as lycoming . I have 8 Lycoming 0360 pistons in work shop at the moment .Can you show me a picture of the new piston , the one I saw looks like a reversion back to the old A.C.L style, still same skirt problems but not quite as bad due to less slot under oil ring still has off set as well ,which lycoming don't. dmech

Crown temp. can be estimated fairly accurately by testing the hardness of the crown against the hardness of other cooler part of piston ,or another good piston, is how we do it. Centre of crown usually the hottest. These pistons contain more than 13%silicon which is more than can be dissolved by the aluminium, which is then frozen in solution by a heat treating process , [T6] this process increases strength , makes piston lighter ,more heat tolerant , trade off is it also makes piston more brittle , same as carbon does in steel, after various heat treatments . Heating of the pistons past the transition zone which starts at about 600deg. f , will start the softening process . The disintegrated and cracked pistons I have seen [ 16 so far ] don't show indications of over heat on crown, in fact 4 at 120hrs from new, showed no colour under the crown at all, and this engine had one disintegrated piston and 3 pistons showing 2 cracks on major thrust side and 1 crack on the minor thrust side. This engine was repaired which included a line bore , has done over 500 hrs. since In my opinion the piston is ok for purpose if the engine is operated properly . My extensive heating test show piston does fit cylinder well once piston becomes fully heat soaked along with cylinder. Cold engine take offs .extensive circuit work ,engine failure sims. Will cause piston failure of some sort in this engine , but can be fixed. dmech

have seen this report many times. No reason for piston failure

On 6 / 2017 a jab 430 had a forced landing due to piston failure [ I refer to page 14 aircraft incidents & accidents / light plane down Bundaberg QLD ] . It appears the ATSB has closed this investigation , with no real outcome, as to what has caused the piston failure. In RAAS incident reports , it seems that there are still a number of piston failure's happening under certain conditions . [ some as late as 2019 ] . On looking through latest engine manuals for both gen 3 and 4 it appears as though there isn't any rectification in this area, there is another piston that jab are using for gen4 , which looks like they have reverted back to the style of the old ACL piston skirt ,probably Asian manufacture ,[ ACL stopped making pistons some time ago] and different metallurgy process than ACL. ACL made good pistons but these would fail eventually in the jab engine under certain conditions. I'm sure we have found the cause and its not down to metallurgy or die grinding of skirt but more to do with the style and the application and skirt profile. It is my opinion that these original pistons can be made more reliable with little modification. My Question is has any one heard of the ATSB investigation out come with regard to why the piston failed. DMECH

mahle .040 forged available from precision international in aust all states nice piston, can be circliped easily no off set pin

sticking ex valve will increase egt moisture will expand the carbon on the stem ,causing the sticking , this can happen regardless if hyd lifter or not jab engines get carbon build up on stem when run on leaded fuel , problem not so common when run on unleaded car fuel. old tappet engines valves stick to but not as much but still enough to burn valves

went to a seminar years ago, presented by two manufacturing engineers from usa , one from GM the other from sealed power corp [ well known hyd. lifter maker] . they talked on ,so called pump up with lifters , they stated that in normal auto engine set up it would require 300/ 400 psi to act like a hydraulic ram to over come valve spring pressure , also taking into account rocker arm ratio. I don't know lifter piston area , or installed valve spring pressure used in the jab, to do the maths . in high rpm race engines 7-8 k rpm. its common to use anti pump up lifters in these engines , the lifters only pump up as a result of valve float, which leaves a gap in the valve train and the lifter does exactly what it is designed to do , fills the gap , which results in the valve not closing fully until the lifter returns to its normal position .[ rev limiter] by carefully dimensioning the components of the valve train we have been able build engines with better than 8k rpm ... with std off the shelf lifters. However since the jab only runs 3000rpm there abouts , I cant see the above causing the problem . The problem I see with the jab engine ,is more likely due to valve stem to guide interference [ sticking open momentarily ] causing the gap I mentioned earlier and then the lifter adjusting to compensate, and then ???. The valve stem or the valve guide can easily be modified to eliminate this , as was done up until lead was phased out in truck and auto engines , but still exist's in diesel engines because of soot build up on lower valve stems. Also I might mention , the solid lifter engine had issues with valve guide /stem interference , causing burnt valves /missing etc . I sent some photos of how the stems should be modified to jab , over a month ago , hav'nt heard any thing from them , but hope they are investigating it . our club jabs only run unleaded mo gas , in the 5 years i'v been a member and I have over 60 hrs flying them my self , although I know there is still a small amount of carbon build up on the v/ stems, I have not heard of a single problem regarding valve issues.

Hi Jim , you would have to ring me 0437511002

same thing , same cause . Can you tell me which side and if upper or lower bolt/stud, just doing some study on through bolt/stud issues , would appreciate any input regarding through bolt on jab engines . A.D.

Hi jetjr , The new case is for a future engine, rods and barrels as well , but I can use the new rods and barrels on my existing case. existing engine can be modified easily to be reliable , as we have already done back in early 2013.

With out prejudice. also to add to your question info sharing , JAN2012 a senior member of our club contacted casa and ASTB, as far as I know he didn't get a reply. I have contacted casa and Repcon recently and they have acknowledged my email , and have requested my permission to send my email complete to their or casa investigation team , so at the moment I feel I cant say to much, but will, after Repcon have finished with it.

I did contact jab back in JAN.2012 and talked to Rod Stiff , however got the same treatment that everyone else seems to get , he stated that they sorted all the problems and had to go flying . I left all my contact details , but never heard from him or anyone else from jab since . I have talked to Ian Bent at Camit, on several occasions , [much better person to talk to] and I can say that their engine is a much better engine , and I would be surprised if they have the same through bolt issues that are experienced on jab engines. The case halves and bolt structure on both engines, is still very fragile , in my opinion . In my spare time , I've started to design another crank case , which wont be split will still have through bolts ,so that all other jab parts can be used, there could be a slight increase in weight , but then as improvements to jab engine and .CAE. are gradually increasing the weight anyway , I don't think that's going to be a problem . I have manufactured my own longer barrels and con rods , which are ready to go . I've been researching this engine since I started flying behind one 4 yrs ago j160 . I was fortunate to be able to buy the eng. out of this plane after engine stopped dead in the air after a circlip /piston issue. for a reasonable price , but after I discovered the main problem with these engines . Up until then I hadn't seen inside of these engines , except on utube . I made up a model which demonstrates what is going on in the engine , I'm sure if you were able to see this model , you would be convinced , as has every one else that has seen it . I was recently asked to demonstrate it at the Serpentine aero club [ jab members] which was well received . I posted in the jabiru aircraft engines problem solving thread JAN 2012 almost 3 yrs ago No I cant think of away of getting jab .to listen to me . Hopefully /perhaps through this forum it might happen. I've also posted on the zenith forum, on this matter 2 yrs ago as well. Still need some numbers on the through bolts!! All the best for Christmas [ whats left of it] and more peace and confidence in flying the jab next year A.D.

Hi geoffreywh, Thanks for info ,we sorted out some problems 3 yrs ago with a number of jabs within our club here in W.A., and these have been running very well since. Its just recently since I have started to assemble my own engine , and this casa intervention , that I decided to research the bolt situation ,which I have read as being a random occurrence . but looks like it isn't at all , there seems to be a definite pattern, which looks like its directly linked to the problems we sorted out 3 yrs ago, possibly why we have not had any bolt issues . I'm still working on this , so would appreciate hearing of any bolt failures. Thank's A.D.

Hi Camel, I do have a very strong opinion on the cause. IT is not caused by detonation, I'm very sure of this , have a good look at this engine, the breakages and their location line up exactly with another problem within the engine ,cylinder for cylinder . Its a geometrical problem , which is easy to fix, within reason . I have data involving 12 bolts so far. I read a lot on this site regarding through bolt issues , so I would appreciate some more data from those unfortunate owners that have had broken bolts /cylinder's etc. I need to know , side that failure occurred and if on the top or bottom ie oil filter side ,l/h , or , other side , r/h, top or bottom for which side . with the extra data I should be in a position to give a more accurate and detailed reasoning. However .... forget about detonation as being the primary reason , I know detonation doesn't help , anywhere! . I have looked at several engines and can see no sign of detonation , I 'm not saying that it doesn't happen.... as it can with any engine given the right conditions . Even if detonation was present at the time ... its not the primary cause. Any more data re bolts please..... would be appreciated!. A.D.

Hi geoffreywy, I will take a punt here , that cracked barrel , I reckon it was on the oil filter side of the engine, could you let me know also which side your bolts broke and wether top or bottom, the indications I get is that it is top bolts on oil filter side, bottom bolts on other side, same with barrels, most common. this is not caused by detonation !. A.D

Tell me, why are hydraulic lifters causing problems, we don't have problems with them , or valve issues in the jab engine,are they not being set up properly?. I' have set up thousands of lifter's over 40 yrs in auto engines ,when reconditioning . I've also seen plenty of problems with solid lifters over the time . there is a lot of auto engines that don't get the tlc that jab engines do .I went out to a ford truck on a farm [300 ford 6 cyl petrol hyd. lifter,] recently [ ignition problem] . This is an engine that I reconditioned , April 1979, still had the same paint that I painted the engine with on the oil filter! never changed , I don't think the oil had been changed either in that time , this truck is used on a daily basis , no valve issues , little bit of blue out the ex pipe though

exactly correct, camit needs to be careful THEIR engine doesn't become a noose around THEIR neck 2000 engs . or so, down the track, sim to jab now. experimental or not.

400 hrs! time to start praying

Leyland trucks were the best in the world once, sold every where, we had two , comets , What happened ! Government , the biggest ostrich farm ,took over factory .other's invested in technology , listened to product owners, left Leyland for dead. Haven't seen a Leyland truck on the roads for yonk's . IF they were still operating , would be probably be consistently booked for going to slow

I agree!. computers!! and good design engineers ,competition, they have to get it right or they are history . computers look after the engines, if they knock, computer takes action in nano seconds to limit damage. ect. we recondition automotive engines ,since unleaded computer engine management , we hardly see cylinder head work and even after 400k klm it's hard to find wear in car engines , most of my work is now with heavy diesel and diesel fuel injection systems repair . jab have problems that could be easily solved , but they have a bit of a stiff problem to over come in the engineering department .

Jabs letter , all true, fuel aint what it used to be . We should have mtow of 700 kg, so engines could be run on lpg mutch higher octane