Valves

[Guest Fred Bear]

Anyone in the Jabiru 'know how' have inside info as to what is being done about valves breaking off and kissing pistons? I'm not having a dig at Jabiru, I love flying their a/c but our lives are hanging on the other end of that lovely Jabiru sweet purr (when it's running). Our flying school has just rebuilt some and I have been told that the new valves are of much better quality.Does anyone know the real deal?Have Jabiru managed to get rid of the nasty valves that have been causing these catastrophic failures of late?It seems to happen (with the old materials) at around the 500hr mark and bang they go :;)6::censored:Interesting to see the time frames between the a/c involved but that obviously depends on what sort of life the a/c has had and how many students have hammered the out of them Any more info would be appreciated.

 

 

[Guest brentc]

Interesting question and scenario Darren, however I have never heard of a valve breaking off during my association with Jabiru's and Jabiru enignes which spans over around 8 years.

 

Are you sure it was the actual valves breaking off, or something else that could have caused that eventually?

 

I have heard of many other issues, of which most are fairly standard for engines overall.

 

I've seen the following major's as an example on Jabiru's:

 

- Overheating, causing a number of other issues

 

- Poor valve seating / sealing

 

- Cracked valve seats / heads

 

- Hammered valve seats

 

- Broken stud bolts

 

- Faulty fuel pumps

 

- Faulty crank shafts

 

- Broken flywheel bolts

 

What CAN happen, is if the engine overheats and or suffers from a lack of oil, the valve(s) can seize in the valve guide(s), stop the valve from moving and the piston can hit it and I guess potentially break it.

 

Perhaps this is what you speak of? If a valve actually 'broke' off, it would do more than kiss a piston, it would be floating around in the head doing crap-loads of damage.

 

I would suggest that at the 500 hour mark the valves would be seating poorly, the heads may have cracked if the engine has been running hot and it would be down on power but unlikely to break valves.

 

Of course I'm not an expert and I don't know every engine, but I have seen a lot of things happen.

 

 

[Guest Fred Bear]

Perhaps this is what you speak of? If a valve actually 'broke' off, it would do more than kiss a piston, it would be floating around in the head doing crap-loads of damage.

Brent, the one I personally know of did just this. Stuffed the whole engine, bent the crank shaft and the lot. The other incidents of late not too sure what the go was 100% with the valve.I will do some more questioning over the weekend and see what else I can learn and see if you can offer any sort of help/advice/comments.I know oil is never a problem with our Jabs.They always have plenty.

 

 

[Guest Fred Bear]

Brent. Spoke to someone today re this issue. Valves running to hot, mixture and other things could lead to this sort of failure (which I am sure you are aware of). At The Oaks we were supplied with new valves from Jabiru after some consideration. These seem to be ok and we have played around by ceramic coating them. Looking at new valves from the US of A within the next few months though. Now, we had three sets of valves from Jabiru. First were giving no trouble for thousands of hrs and were decided to be replaced at one stage. Second set put in. Second set seems a common thing of breaking off at 500 odd hrs. Third set (which are in there now) we are the guinea pigs for. Today I flew the machine that just had a rebuild with the new valves. Oil temp just below 150 p's and t's spot-on and purring like a kitten. Time will tell.

 

Further note: Oil was never an issue in this case. Valve seat??

 

 

[Guest grantisaac]

hi,was wondering if the failure you are having is with the hydraulic tappet motor or the old one,we had a valve break off on one of our club jabirus and lodged itself in the piston,we have since brought a new hydraulic tappet motor

 

 

[Captain]

What did you discover Brent?

 

How did things go over the weekend BC?

 

Did you get it all done?

 

And what did you find?

 

Regards Geoff

 

 

[jetboy]

My 2200 #1680 has engraving on each head "welltite" or "wellite" which i assume relates to the valveseat material and / or valves alloy used.

 

So at some stage they must have changed the materials, for better or worse?

 

I need to recheck the carb jetting as I have the first iteration of the economy tuning and its been revised twice since

 

Ralph