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VFR Pilot

Liquid cooled heads

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Has anyone else besides Kent Karge in the states had problems with the Jabiru thin finned head rockers not lining up with the valve stems in the liquid cooled heads.

 

 

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VRF Pilot

 

I believe the Liquid Cooled Heads were designed to replace the original Thick Finned Heads and as such the casting for the head replicates the dimensions of the original Thick Finned Heads.

 

If you replace these old heads with new Thin Finned Heads you also need to replace the rockers and the tappet covers as the old one don't fit the new style heads. The rocker offset is different and the 4 mounting holes for the rocker covers are slighly wider apart on the new heads.

 

With this in mind it is no wonder you will encounter problems trying to fit rockers from the thin finned heads to the Liquid Cooled Heads as they would not line up very well with the valve stems.

 

Safe Flying

 

Andrew (JabSP6)

 

 

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Thanks Andrew

 

That pretty much seals it for me then, even if I got a set of old rockers i'm still in trouble. I think the rockers would have to be drilled for the top end oil feed?

 

I will have to make do with my standard heads, maybe make a better cooling fence than the supplied fiberglass ones.

 

Cheers

 

Jeff

 

 

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Thanks AndrewThat pretty much seals it for me then, even if I got a set of old rockers i'm still in trouble. I think the rockers would have to be drilled for the top end oil feed?

 

I will have to make do with my standard heads, maybe make a better cooling fence than the supplied fiberglass ones.

 

Cheers

 

Jeff

What sort of aircraft have you got it in jeff?

 

 

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Jeff, can a run a poll by you?

 

If you could buy air cooled heads that ran cooler yet gave more power is that a viable option for you and how popular do you think a product like that would be?

 

What would you expect the cost to be?

 

 

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Jab engines are quite well made and stout down low and I give them credit for that but the heads are a truly bloody awful design, every aspect of them - hmm, reminds me of a few old girlfriends actually.

 

After having a good look at the heads last yearI figure there might be a small market for something a lot better. The water cooling is an option but I can see why some wouldn't want to go that route and would simply prefer a better air cooled version.

 

A run down;

 

Change the shape of the exhaust port to a much more efficient shape allowing better flow not only decreasing temps but increasing horsepower at the same time.

 

Change the shape of the inlet port to a more efficient shape allowing better flow increasing horsepower.

 

Maybe increase valve size although flow numbers need to be determined first.

 

Add more squish in the chamber around the exhaust valve area while opening up around the inlet valve to equalise chamber temps better.

 

(The above will allow less throttle to be used for the same horsepower at cruise also reducing temps along with more take-off power at the same throttle as before).

 

But most of all a total redesign of the finning arrangement now on it's 4th iteration is needed. While it would seem logical to do the large fine finning as they have done, it actually isn't, there is a much better and well proven way to do it. I guess having grown up and done my apprenticeship on air cooled engines and performance modifications on them during the 70's and 80's gives me a bit more insight and I'm not Robinson Crusoe there, plenty of others around with the same knowledge that Jab could have asked but obviously didn't.

 

If you want I can set you up for the first 3 and optionally 4 items on the list locally, results 100% assured but not the finning of course. Very little outlay compared to the WC heads too.

 

Otherwise at this time I just want opinions if I made a batch of 100 heads would they sell? How much is a new Jab head out of interest?

 

By the way, for your cooling shrouds, I suggest you might try decreasing the mouth opening size and test which way the temps go, sometimes if the opening is too big you can actually get flow stagnation or even reversal - just something to try, it may be worse.

 

 

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Hi ozbearThe motor is going into a Zodiac XLB

You have probably heard this before but the exit for the airflow is also very important you may need to try lips on the cowl to create a low pressure on the exit side.

 

 

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You have probably heard this before but the exit for the airflow is also very important you may need to try lips on the cowl to create a low pressure on the exit side.

When working with my Sonerai.. the formula we worked on was ( at least) 2 to 1 ie Twice the area on the air outlet to the in.. When I changed to the watercooled Terrier.. I used the same principal and never had a problem with cooling

 

There is already a low pressure under the plane, artificially inducing more low pressure with lips etc only 'assists' at best.. but if there is not enough through flow.. doesn't alleviate the problem

 

 

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i thought the low pressure was on top of the fuselage

Actually on top of the wing .Hi tornado what we are talking about is creating a localised low pressure by using a lip on the bottom of the cowl .But you make a good point you would think the top of the fuse would be a lower pressure.

 

 

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Tornado not as funny as it sounds maybe it would all work better exiting the top and sides entering the front and lower front of the cowl food for thought.

 

 

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i thought the low pressure was on top of the fuselage

Look at the dust and grease that collects under the fuselage ...

 

 

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Look at the dust and grease that collects under the fuselage ...

Jabirus are always going to leak oil.

 

 

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OK if you can get out and clean your windscreen. It would be better to reverse the flow as heat goes upward but you don't want the oil and fire etc. You will get a low pressure area anywhere the airflow curves, but you get nothing for nothing. Nev

 

 

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How many Jabirus have had engine fires? Not talking about a 70 litre radial engine burning 2 gallons of oil per hour with a 18 gallon sump. 4Ltrs oil max.

 

Let me remind the nanny staters that the merlin engined planes all had side exhausts...

 

 

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You just told us the jabs leak oil. Are you now saying they don't? How much oil on the windscreen is too much? Answer ANY. .Nev

 

 

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The oil leaks when the engines cool 004_oh_yeah.gif.82b3078adb230b2d9519fd79c5873d7f.gif and the metal contract (shrink) and allow clearances to increase.

 

 

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The oil leaks when the engines cool 004_oh_yeah.gif.82b3078adb230b2d9519fd79c5873d7f.gif and the metal contract (shrink) and allow clearances to increase.

What a load of horse sh#t FT, please qualify that statement with facts not just theories.

 

 

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Put your thinking caps on guys. A restriction constitutes a depression not a curvature. Wind blows around my arm but it wont lift it up for me.

 

Every action has an equal and opposite reaction. Down wash off the trailing edge creates an upward force combined with pressure under the wing and thrust.

 

That should get things firing.

 

 

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