Have you ever broken a barrel base stud?

[Yenn]

jetboy.

 

Are you adjusting head bolt tension at the same time that you have to adjust valves.

 

If no adjustment to tension is needed then why do the valves need adjustment.

 

If the valves are getting tight that could be because they are getting longer, which could be caused by them heading towards "tulip" shape.

 

Talk to someone who knows the engine well, maybe even talk to Rod Stiff at Jabiru. I am sure he would not want you to have an engine failure and he would know more about the engine than anyone else I know. In short, if in doubt go to the top!

 

 

[Bruce Robbins]

The valve clearances tightening up usually indicates that the valve seats are recessing into the heads. The valves face and/or seats could also be wearing away. Either would warrant further investigation if the trend continues.

 

Bruce.

 

 

[Guest brentc]

Sorry to say it guys, but join the club. Now you know how I felt when I did my leakdown (with the exception of the whack in the eye) arrrrgggghhhh!!!!!!

 

I finished assembly of mine yesterday. Put it all back together, ran it up, all looked good. Engine failed at 10 ft on takeoff. Put it back down again (lucky it failed when it did - 5 seconds later could have been fatal). Turns out when I replaced some fuel hose, the firewall steel bracket was a little sharp and caused some of the fuel line inner to slice off and restrict fuel flow which caused the fuel to stop feeding at certain power settings. Needless to say that I was not impressed as the engine almost stopped instantly and I've never had an engine failure on take-off in over 1,000 hours flying.

 

Did around .5 after that problem was fixed. Seems to possibly be down a little on power at present, however it's all new gear including pistons and a re-bore so I'm not surprised on that. Should loosen up a bit over time. Will fly again on Monday.

 

 

[Guest brentc]

Ralph, I do mine religiously at 25 hours. No point waiting for 50. Doesn't take long to do and if it makes it run better then why not. I also change oil & filter at 25.

 

 

[vk3auu]

Rod Stiff

 

Sorry to hear about your mishap Brent, the Gods must have been smiling to give you a successful outcome.

 

Perhaps some of you Jabiru owners should encourage Rod Stiff to join the Forum.

 

David

 

 

[jetboy]

minor valve recession

 

Thanks guys,

 

I only mentioned the occasional readjustment to to highlight the problem with the new manual showing head bolts, valvegear checks @ 100 hrs.

 

Yes I do check the head bolts @ 50 hrs and they have rarely moved.

 

As the engine is at 195 hrs there has only been 3 50 hr checks and 2 of those are post carby tuning kit install. So forgive me for not knowing what the trend is. I have recorded which things needed adjustment, to compare at next check.

 

I will be doing leakdowns and borescope checks @ 200 hrs and depending on that outcome may rejet the carb in line with the most recent documentation. EGT / CHT are in limits and it runs OK in colder weather. If I tested with a Lambda probe I might be OK to leave alone, but in the light of the recent data I will probably err on the conservative side.

 

Ralph

 

 

[Guest brentc]

Ralph, one of the most important indicator would be the colour of your exhaust. Whilst it won't tell you head / cylinder bore condition, it will tell you if you're running too lean.

 

 

[jetboy]

Thanks Brent,

 

My notes from the last 50 hr for the plugs reads:

 

"No.2 darkish, others light brown."

 

The exhaust usually is a light gey/tan similar to the Cessna 150 that also ran 100 Avgas. Cruise EGT is 695 and full pwr 680 which is OK for the original carb tuning but on the high end for the currently published 2nd revision.

 

For peace of mind I'd still like to know if the current spate of valve troubles is occurring to Welltite seats or a different seat material. If valves are tuliping into the heads I suppose that is a case of overlean. At last 50hr all my exh. valves were found at .008 and were reset. Inlets were good.

 

Ralph

 

 

[Yenn]

brentc.

 

How many thou were cut out in your "rebore".

 

I didn't think there was enough meat in the cylinders to bore them out.

 

 

[Guest brentc]

Sorry, my mistake. (again) They were honed.

 

oops!

 

 

[Guest J430]

Just a note for those with a J400/430/200/230.........

 

The needle jet 285 or 2.85mm seems to still be the go, talk to the factory to verify.

 

History, when Jabiru and Ian Bent at CAMIT did the trials they settled on a 2.78mm jet, which they ran in BNP and then (as I was there with Rod at the time) we tried one in our plane. It ran fine from about 25 hours to 475 hours with no valve damage at all. Colours were all good. We always ran it around 20-21 LPH in the cruise and did not try getting below 20 just to save a buck! This would have leaned it too much.

 

Recently we went to the 2.85 which was the jet size they settled on for the production version economy kit, and the one most will have. Seems the 6 cylinder will not run well on a 290 or 295 jet, mine did not! So its a 285 for me.

 

I think Jabiru will be just increasing the 4 cyl jets from 2.75 or whatever it was 2.7# up to 2.85 and that will be the only change. They may say something bigger for the 6 cyl in very cold regions.

 

Again if in doubt ask them.

 

J

 

 

[jetboy]

Just done a similar exercise to Brent at 475hrs, all valves and seats were fine, very good indeed. Valve guids on Inlet were out to or exceeding max bore.How is that? The Exhaust wre fine. Two sets of rings carboned up, hence poor leak down and we did the work.

 

Total cost approx $2000-$2200.

 

Now it goes like a rocket! Has been machined and refurbed by very precise and tight tolerences so may be better than new!

 

J

 

PS And I had a economy jet that was leaner than all yours! I had the first experimental one, which was 0.07 smaller .....now running the 285 jet which is the standard economy for the 6 cyl and I understand the 290 or 295 makes them idle rough!

Reply to J430 posting:

I'm getting worried about the valves / guides issue, having come across an example on Matronics which I'll copy here.

 

The factory must know something about material changes that us field testers are not privvy to. I can smell another CAA AD if this trend continues without some proper explanation. Is it possible that valve leakage is occurring regardless of lean mixtures, but due to abnormal guide wear?

 

Ralph

 

Posted: Fri May 11, 2007 3:22 pm Post subject: New rocker arm bushings in Well, the old bushings were a teflon-coated bronze over a steel shell

 

(TPFE, I believe they are known as) and for whatever reason, they

 

failed at...or at least I discovered them failed at...273 hours. I

 

decided not to replace them with the original style bushings, because

 

I don't know the history of how these bushings hold up under the

 

splash-lubricated, high-pressure (the valve spring), environment they

 

operate in. Now to be perfectly honest, maybe nobody else has had a

 

problem with these bushings, but I did, so I elected to try my own

 

"shade-tree engineering" and put in oilite bronze bushings. In doing

 

so, I decided to supplement the oil that ordinarily makes its way

 

into the side of the standard bushings. The standard bushings are

 

allowed (according to my owners manual) .004"-.010" side clearance. I

 

did not change this, but I did drill a .093" hole vertically into the

 

rocker arm, at exactly the 12 o'clock position of the rocker arm.

 

This will allow the oil a chance to run into the hole and help lube

 

the bushing.

 

 

 

If anybody cares, I'll continue to report how I installed the

 

bushings. They came 16mm wide and the rocker arm is 15mm, so I

 

shortened them on my lathe. I had pressed the old bushings out, and

 

after drilling the rocker arms for the oiling holes, I drilled the

 

bushing oil holes a little larger, then pressed them into place,

 

keeping the alignment of the holes in mind. They all came out aligned

 

as hoped, and then I had to ream the bushings to the size suggested

 

in the owners manual... .474"-.475". This provides for 2-3

 

thousandths oil clearance for the .472" shaft. I then swapped the

 

rocker shafts side-for-side, to enable the new bushings to ride on

 

the un-used part of the shaft. I also chamfered the sides of the new

 

bushings to further allow oil to make its way into the oil space

 

provided between the shaft and arm.

 

 

 

I've got to further say that I don't know squat about teflon in

 

engine bearings...my only use of teflon (that I know of) is frying

 

eggs in a pan....low (relative) heat, no pressure, and the eggs taste

 

fine. I wouldn't have eaten eggs cooked on the teflon that was

 

visible inside the removed bushings...they looked like the frypan had

 

been attacked with a steel spatula, if you'll permit me the kitchen

 

analogy. : )

 

 

 

Again, I'm not saying that Jabiru made a mistake, maybe I just got a

 

lemon, and if my "fix" doesn't work out, I will have no apologies to

 

make. My engine is in a Kitfox Model IV *experimental* airplane, and

 

that's JUST what I'm doing...experimenting.

 

 

 

Lynn Matteson

 

Grass Lake, Michigan

 

Kitfox IV Speedster w/Jabiru 2200

 

flying w/275+ hrs

 

do not archive

 

 

 

 

 

[Guest J430]

I found the rocker bushes a little worn but did not replace them, my worn parts were the Inlet Valve Guides. Not worn out severely but to the end of their life tolerence. Which was rather early.

 

Will see what another 500 hours brings I guess, but at present its going great!

 

J

 

 

[facthunter]

Worn Inlet guides.

 

Just a comment on the effect of worn inlet guides on mixture. It would have more effect on the mixture when the throttle is closed or partially open, when the vaccuum is higher and the mass airflow is lower, and would be less of a problem at full throttle, however it will tend to lean the mixture, from what it would have been otherwise. Another concern is that the metal from the guide, ends up going through the motor( not desireable) and the worn guide allows the valve to become misaligned with the valve seat, which was always considered to cause valve heads to tend to breakoff due to the tendency to bend as a result of the misalignment.

 

Is the geometry of the valve in correct relationship with the rocker arm? The point of contact of the valve and the centre of the rocker pivot should be a right angle from the axis of the valve ,when the valve is half open, otherwise excessive side load will be imparted to the valve.This would wear the guide oval at the top (rocker) end..... N.....

 

 

[Guest J430]

facthunter

 

I have no idea.....they all came from the factory as a brand new engine!

 

I assume they are all much the same........the exhaust valves and inlet valves and seats were all in very good condition. The exhaust guides were too.

 

Has a lot of very experienced folk baffled. I can assure you that the refit is very very exact (apart from new rocker bushes which we should have done, but not critical), and the resulting performance is amazing.

 

I am yet to see another with a similar problem so I will wait and see what time brings.

 

J

 

 

[facthunter]

Inlet guides.

 

Yeah ,Good luck J430,( I'm not being facetious)

 

This sort of problem is not unknown in auto engine production where a supplier changes the specifications of a material slightly ,with sometimes expensive consequences. Rectification! It is really beyond what we should be doing here, with a proprietary engine, which is in some instances, certified, because we don't have all the facts, and the manufacturer should be involved, primarily.

 

I can understand the users concerns, but be a bit sympathetic towards the manufacturer who has limited resources and puts out several different engines in relatively small numbers .

 

Bear in mind that Lycoming have had a long history of necessary rectification of engine faults, with its piston engines, and that the development of the Rolls-Royce RB 211 stalled and nearly sent the company broke in a big way, before becoming the excellent Jumbo Jet engine that it did eventually.

 

By pointing out the above, I'm not trying to stifle comment, and these forums are an excellent place to indicate the existence of a problem, but as a general comment, may I say that without expert examination of these individual failures ,( I will call them that ) we won't get past a sort of feeling that SOMETHING is wrong.

 

If I can end with a single comment re. valve life, I would advise against doing anything that might cause the engine to run lean. It's false economy. Nev..

 

 

[Guest Andys@coffs]

Is the geometry of the valve in correct relationship with the rocker arm? The point of contact of the valve and the centre of the rocker pivot should be a right angle from the axis of the valve ,when the valve is half open, otherwise excessive side load will be imparted to the valve.This would wear the guide oval at the top (rocker) end..... N.....

Reasonable Question to ask, though the problem as I see it is that the geometry is not adjustable, other than the tappet clearance, which should only be set to specification (10 thou). Therefore the only way the geometry can be out is if the valveseat has lost all its meat and the valve is recessed into the head, or the pushrod ends / rocker are worn. Bottom line is that if the major components meet the new spec, or are better than the min worn tolerance described in the engine manual then the geometry shoulf be Ok? Or have I missed something?

 

Andy

 

 

[Guest brentc]

Heard about a valve breaking off recently. Engine had around 1,000 hours. 2200, first life.

 

 

[facthunter]

Reply Andy's

 

IF the settings (geometry)are OK. ex factory the ONLY changes would be the result of seat (valve) wear, insert wear,( or impact into head.) or valve stretch. Pushrod end, cam follower etc. are taken up by adjustment. Most causes of valve guide wear are caused by unsuitable metals. Generally the inlet wears more than the exhaust, which is a little surprising. the valve stems are usually treated with a phosphate coating, ( black & cheapest) or hard chrome (industrial. Shiny & expensive as it has to be ground to size). The guide material is usually Grey iron (cast) Hardened iron, hardened steel (Rare) or various bronzes. The trick is to match the metals so the valve stem does not "Gall". this is where the surface of the valve stem "picks-up" portions of the guide material, and becomes rough and wears rapidly. Visual inspection of the metal surface with a magnifying glass will detect whether this is happening. ..Nev...

 

 

[Guest J430]

Nev, agree with what you say. I have reasonable confidence the guides and seats are now true. Once ne guides were shrunk to fit they were then reamed to size and then the valve seats done to the guides. Valves should be in perfect alignment now, if they were not from the factory.

 

Will see in time I guess......3 or so years!

 

J

 

 

[Guest pelorus32]

Here is an interesting article by a well respected columnist:

 

http://www.avweb.com/news/pelican/182155-1.html

 

If you are not registered you will need to to read it. It's worth it and there's other good stuff there.

 

The article deals explicitly with valve problems and makes a number of assertions:

 

1. Valve problems are NEVER associated with running Lean of Peak (LOP);
    
    
   
2. Valve temperatures are the critical issue;
    
    
   
3. Valve cooling is absolutely related to the quality of the valve-seat and valve-guide fit. Any failure of this geometry will lead to the kind of valve problems discussed in this thread;
    
    
   
4. Valve temperature is NOT related to EGT but to CHT;
    
    
   
5. Valve failures are almost always the fault of the manufacturer not the pilot;
    
    
   
6. Repeat lean mixtures are not the problem. Running rich of peak might be;
    
   

 

As I said I think it's very worthwhile to read this article. But then again I'm a luddite:). I also like his other columns on engines at the same site. He has done quite a lot of bench running to support his assertions. He also takes a two part swipe at ATSB over their Whyalla findings.

 

Regards

 

Mike

 

 

[Captain]

Mike

 

One of the problems with threads such as this is that the main noise comes from those with issues and in some (but not all) cases there are other contributing causes or histories that are often not discussed. EG there was recently a problem attributable to J but on further investigation the engine had experienced a prop strike which would probably have caused problems for any engine at some time down the track.

 

Sure there have been some issues and I for one am trying to gain a better understanding of those, and how they can be or have been cured.

 

Having said all that, thanks for the link in your last post and another factor is that valve material might also be an issue & I am in the middle of investigating whether titanium exhaust valves (or some suitable alloy) might be a worthwhile upgrade for my 3300 at 250 hrs.

 

Regards Geoff

 

 

[facthunter]

Valve problems.

 

Mike ,I have read the article & I personally would not like to see those assertions acted on without qualification. Some of his statements are dead wrong. Ie Retarding the ignition will make the engine run cooler. Running lean of peak, never associated with valve problems, & more. He doesn't mention that valves warp and unseat, sometimes and that cylinder heads are liable to distort when hot. He didn't mention the need to preserve tappet clearances at all times.

 

I could destroy an exhaust valve on a dyno- coupled engine on high load, by retarding it and leaning it out ,in less than 5 minutes, without exceeding the head temp that would be normal for the engine. Nev....

 

 

[Guest pelorus32]

G'day Nev,

 

I think there would be many people much more able to comment on this than me :;)3:.

 

But as your signature says, never stop learning. It's always worth reading and thinking about even if you decide you don't agree with it.

 

Kind regards

 

Mike

 

 

[Yenn]

I havn't read that article today but I have read most of what he has written. He is talking from a GA point of view and especially high powered engines. His flying has included radials and high performance warbirds and I believe he has a lot of experience with GAMI the injector people to give him plenty of practical and theoretical knowledge.