Yet another Jab down.....

[facthunter]

You have to run more clearance on the exhaust guides on any engine. Gumming up of exhaust guides has generally been caused by excess of an antiscuffing oil additive plus high temps occurring. The stuff formed is fairly soft and gummy and will ream out easily without damage to the guide inner surface finish or size if done carefully. Reaming cannot be done with the K line process, because it is split along it's length.. I have spoken out against this method of repair before, as in a high temp situation it will collapse a bit and tighten up on the valve stem. The K line is burnished,( expanded) to a size when fitted. It also has one more discontinuous surface for the heat to go through.

 

All rocker bushes should be a good fit and the geometry correct. Roller rockers reduce side thrust on the valve stems.. How much muck comes up the exhaust valve guide depends on back pressure amongst other things. Generally oil will be sucked DOWN the inlet guide sometimes causing carbon build up on the underside of the valve head and other parts of the combustion chamber. Some of the build up in a combustion chamber is caused by dust cemented in with the carbon. Nev

 

 

[Bruce Robbins]

Just to clarify,

 

The new Jab engines use roller Lifters, not roller rockers.

 

 

[facthunter]

My response was to jetjr's post re roller rockers. They will relieve side loads on a valve stem, (if fitted) Nev

 

 

[jetjr]

Yep sorry Bruce your correct of course, not sure what I was thinking about. Old Aus V8 I think????

 

Again it seems Ian's overall approach has strong merit for sorting engines out

 

Breaking through bolts has rarely had so much debate, Ive always felt this kind of "big" bolt breakage had to be detonation related and with 6 channel data I get, on what I thought was nicely running 3300, I am not at all surprised. Some temps are scary. Lots of fiddling and they are pretty good and far more stable, EGT getting too cold/rich on some cyl in some parts of flight but fuel is cheap compared to rebuilds.

 

 

[turboplanner]

Another way to get thru bolt failure or bent/broken con rods is piston seizure

 

 

[AVOCET]

Dont you dare not post ,

 

Seems to be the "norm " these days as members get elected to board positions & then go silent ,

 

Post under nom deplume ?

 

Mike

 

 

[Oscar]

Nev - they'll reduce any 'wiping' load for sure, but if the contact geometry isn't correct, they can still impart a side load that may be as great (or worse!) than a properly-designed plain rocker tip.

 

My response was to jetjr's post re roller rockers. They will relieve side loads on a valve stem, (if fitted) Nev

Nev - roller rockers will reduce the 'sweep' load as the contact patch moves across the valve stem, but unless their geometry is correct, they may not reduce the side loads very much (and could increase them if badly designed).

 

 

[Dafydd Llewellyn]

And may remove the principal means of valve rotation. Swings and roundabouts again.

 

 

[Guest Maj Millard]

Dont you dare not post ,Seems to be the "norm " these days as members get elected to board positions & then go silent ,

Post under nom deplume ?

 

Mike

Who are you referring to Mike......?..

 

 

[Guest Andys@coffs]

Me...I simply said I would take a step back to prevent being misrepresented but then I just deleted it and intended to say nothing at all, and this is the last "all" WRT this thread

 

 

[fly_tornado]

Andy, remember why you wanted to be on the board in the first place.

 

 

[AVOCET]

Hi Maj , i was refering to Andy ,

 

I was just about to post some thourghts on this matter ;

 

You Maj , & Andy are the only two board members that ive got to know through this site , i have found your contributions to be at times most helpfull , in regards to grass roots involvment , timely and relevant info .

 

This one on one communication is the way of the future and if Andy & yourself hold back because of fools and the such , then we just go back to sitting in the dark ,

 

To me , what constitutes good leadership is the ability to take hold of this format and work a way around the idiots who end up taking us all down .

 

Time to get the thinking caps on and get around these posting issues ,

 

There must be a way of moderating negative feed back with all this technology .

 

Nobody with half a brain suffers Fools Gladly ,

 

I beleive this forums on the Up , and to loose valued opinion ( no matter who argues what ) would be a tragedy .

 

Mike

 

 

[turboplanner]

POST DOES NOT ADD VALUE - MOD

 

 

[dazza 38]

Andy and Ross, I dunno about loose but we don't want to lose you two guys from posting here .

 

 

[Guest Maj Millard]

I won 't be posting any more on this subject.....I wish Jab owners the best in solving their problems. I have highlighted what I feel are the concerns, so its over to other interested parties now. My job in highlighting concerns where most were ignoring them is done. I have better areas to put my time into anyway..I have always enjoyed the verbal jousting when it was done intelegently.....which is with most of you.

 

 

[Guest Maj Millard]

Andy and Ross, I dunno about loose but we don't want to lose you two guys from posting here .

Dazza ......I will be posting on ths forum of course ....but I'm done in respect to Jabs.....but like pushing jelly up a tree I'm afraid.

 

 

[Guest Maj Millard]

I must have posted in invisible ink

POST DOES NOT ADD VALUE - MOD

 

 

[turboplanner]

POST DOES NOT ADD VALUE - MOD

 

 

[Dafydd Llewellyn]

One of the less voluble followers of this thread has sent me a photo of a valve spring retainer from a hydraulic-lifter Jab 3300, at around 700 Hrs TIS. See attachment. As you can see, it shows that the ground-off end of the spring coil has dug into the seat face to some extent. If this is representative of the condition of these components after 700 hours TIS, then I do not see this as a life-threatening situation. The retainer has clearly NOT failed and allowed the valve to drop - and is not likely to for a good time yet.

 

As far as I can ascertain, this is the original form of Jabiru valve spring retainer, made from C1020 steel (i.e. mild steel, not free-machining) as per the original Jabiru drawing. These retainers do not exhibit this sort of damage in solid-lifter engines, to my knowledge; however the hydraulic lifter engines have much stronger springs, to help prevent lifter pump-up (though they do not seem to be a complete cure for it).

 

More recently, in the light of experience, I am informed that Jabiru has switched to a bought-in spring retainer, which is hardened. The subject engine had these in one cylinder, and they had not been marked by the spring. The example in the photo might not show any significant marking had the end of the spring been de-burred.

 

That's as much as I am prepared to say on this forum at this stage; and if this were all there is to it, I do not see any justification for the emotive garbage on this thread on this subject. I don't think I have the full story as yet, but at least here is some factual information.

 

 

 

[Oscar]

That image appears to be of the early-type retainer, as used on the solid-lifter engines, which would not be a good match I would have thought to the stronger springs for the hydraulic-lifter engines, surely?

 

Also, there is what appears to be a ragged line around the inner edge of the hole, that isn't consistent with the finished chamfer on these as new (see the examples in post #304) Is this just a small build-up of baked oil that has broken away when the valve was removed, or has the retainer worn to the point where it is coming into contact with the end of the Valve guide, which has left some deposit of guide material? What appears to me to be galling on the spring base surface is entirely different from the scraping damage of the failed example in the Jab. Service Bulletin.

 

 

[Dafydd Llewellyn]

Can't tell more until I get the thing in my hands.

 

The SB clearly shows a quite different condition. The valve was evidently not stuck in the collets in this instance; however some torque would still be applied to the spring retainer, and the digging in of the end of the spring that resulted has evidently prevented the retainer from turning in the spring, so the thing has just settled down and continued to run.

 

The end of the spring obviously makes an effective cutting tool; it's obvious why Jabiru switched to a hardened retainer.

 

 

[Dafydd Llewellyn]

It's not obvious to me whether the failure shown in the SB was a "cutting" effect or a "rubbing" effect; however what IS evident is that the turning effect driving the valve rotation is sufficiently powerful, in the hydraulic lifter engine, to overcome the friction between the spring retainer and the spring, whereas it would seem to be insufficient to do that in a solid-lifter engine, with its lighter valve springs.

 

Whatever, all this has come about because of the issue of hydraulic lifter pump-up; and that may be traceable back to excessive oil pressure - which would bring us back to the oil pressure relief valve. This would maybe explain why so many engines DON'T show this problem.

 

Hmmm. Too many "maybes". Needs research. Think I'll stick to solid lifters and the original valve springs. For what it may be worth, the CAE engine uses 4140 steel for its spring retainers; in the "as received" condition it's about 2.5 times the strength of the original Jab spring retainers.

 

 

[facthunter]

Controlled valve rotation is usually done by design of the washer at the BASE of the spring. Each time the valve opens it increments a small amount and rotates very slowly. Considered a good idea by some. It's more recommended in sidevalves (Flatheads) where the heating is very uneven..

 

Engines running Avgas (containing lead) usually run much stronger valve springs and narrower seats to maintain contact through lead deposits. (I've always thought narrow seats make valve temps rise). Mogas doesn't have this problem.

 

The Rotex 912 engines run mogas as they run too cool for the tetra ethyl lead formulation to work well. They sometime lose compression when they have been using avgas due lead build up unevenly on valve seats. This sometimes recovers after return to mogas but you can't be sure some seat damage hasn't been done in the meantime. Most times you get away with it.

 

The common message seems to be run solid lifters and keep the engines temps down. Have you valve geometry right. Solid lifters need a camshaft change at the same time. Also putting those heat reading washes under the plugs could affect their heat range. Perhaps go one colder on affected plugs to be safe. . Nev

 

 

[pmccarthy]

There is a deluge of Jabs for sale in this month's Sport Pilot.

 

 

[fly_tornado]

Ross

 

have a look @ LAA's safety newsletters about Jabiru distributors

 

http://www.lightaircraftassociation.co.uk/2014/Mag/June/safety%20spot%20June.pdf

 

http://www.lightaircraftassociation.co.uk/2014/Mag/July/safety%20spot.pdf

 

http://www.lightaircraftassociation.co.uk/2014/Mag/Aug/Safety%20Spot.pdf