Cylinder heads on 3300 engines

[Paul davenport]

Is there a difference between the early 3300 hydraulic exterior lubed heads and the later hollow push rod heads and the roller cam heads. On inspection of a mates later hollow push rod motor his heads seem to have more finning around the inlet exhaust manifold area, and his CHT. temps seem quite reasonable without any of the mods suggested by jab

[Bruce Tuncks]

There have been lots of changes to Jabiru cylinder heads. My original heads ( 1998 2.2 ) were the second iteration. Within 2 years there was a third and they kept coming. Each iteration had more fin area.

Also, have a good look at Lycoming cylinder heads... very complex finning.

I have been operating with 1998 heads on the front 2 cylinders and the next iteration on the rear 2. This gives quite even ( finally!) cht's.

I agree that each change helped with the cht's, so your guess that there was a change in the 3300 heads is probably correct.

[Paul davenport]

Thanks for your reply. Your motor is a real mixture isn’t it, as long as it works and is reliable what else matters. My mates 230 is a later model with more hours on it but the engine has been overhauled by jab and is standard with hollow push rods and as such has more fin area than mine which I have modified to hollow push rods. His CHTs are lower with only a few simple mods, whereas mine has been a work in progress. My temps are now very even and mainly around 138 or lower on all but the hottest days and I choose to stay ground bound on those

[Bruce Tuncks]

Yes I was concerned at the assymetry of different heads front and rear. But the engine is already assymetric in that the cooling air runs front to rear.

If there was a prize for the oldest cylinder heads still in use I reckon I would win it.

Your temps are similar to mine and if anything they are a bit too cool. There are some who say that 150 C is a better figure. I don't like to see the hottest cht go over 160 C on climbout and so far this has been held to even on a 33 degree day.

 

My plane has an arduino-based system measuring each CHT and EGT , thanks to an expert clubmate ( Jab 7252 ) and so I see each cylinder to the nearest degree.

 

Remember that the factory says 170 C is ok and Lycoming say higher still. A Lycoming I know operates at 190C and this is actually cool. The max redline is 260C but Lycoming says that a max of 223C is better for a long life engine. Mind you, the alloy heads on the Lycoming appear to be much harder than the softer Jabiru heads they used before the new gen 4 engine.

[Thruster88]

Lycoming have the CHT probes on the bottom of the head near the exhaust port, this is perhaps why their numbers are higher.

[Paul davenport]

I went for a fly yesterday and temperatures were 138 and lower. I think for longevity on the 6 this is about right as in my opinion a lot of problems are caused by temperatures as hot as what the factory calls normal, but I am happy to be wrong. Rotax temperatures are significantly lower and they do not seem to have any valve issues, now before I start WW3 it’s just an observation and I love my Jab warts and all

[Bruce Tuncks]

The Rotax has a water-cooled head. You can buy Rotec water cooled heads for Jabirus, but most of us have chosen to stick with the old air-cooled heads.

This has saved us lots of dollars and kilograms.

[Bruce Tuncks]

But I agree about cooler being better. There was a Jabiru engine guy who answered their phone. Once I asked him how hot was ok... " as cool as possible" was his answer.

[Paul davenport]

It’s nice to have a cooling margin up your sleeve. Bit like temp guage on a car every one feels ok with the guage reading in the middle. Yes I saw a Rotec head set up I too like the jab simplicity

[jetjr]

"Cool as possible" was typically a safe statement as that wasn't very cool, there are some getting very cool running engines however care needs to be taken comparing numbers as theres several cht measuring points and methods too

Metallurgical limits (ie where alloy changes irrecoverably) are not too far from max cht published. Not much info on these limits and how they were measured

[Bruce Tuncks]

In the early days, the cylinder heads actually distorted. Straight lines of cooling fins became curved . The factory red-line was 200 C, subsequently lowered to 175 C.

I moved the measuring point from the tag-washer under a sparkplug to the fin-base near an exhaust port. Checking by running the 2 points at the same time showed no difference, which I reckon showed that the highly-conductive head didn't have greatly different temperatures from spot to spot.

[facthunter]

What happens to the Alloy (IF it's been heat treated) is that above about 260 C it can lose it's heat treatment properties and become softer and weaker. This is a PERMANENT change as the treatment is done just after the casting is produced and usually cannot be redone to an old fully machined case. it's the same if a case is welded. It's weaker than original and may also warp. Another result is an insert may come out at the time or later or the overheat may cause detonation and /or ring groove carboning, or head warping. Generally the only bolts that (took up) were the ones nearest the exhaust ports . Nev

[Old Koreelah]

Those temps should be regarded as vague approximations (unless your CHT system is carefully calibrated).

I've set my alarms at 150C and anything above that worries me.

[Guest Machtuk]

I never see above 110C CHT' in flight, maybe a little higher taxing in after landing.

[Paul davenport]

Love those temps, 6 or 4 what have you done to get them

[jetjr]

Cht probes on a screw between plugs was 20 deg cooler than down the hole, with CAE blast shields fitted the screw placement was pretty much the same as deep in the head

Air passing probe cooled a lot

[Guest Machtuk]

Love those temps, 6 or 4 what have you done to get them

 

4 banger. Well cowled and very close fitting plenum chambers on either bank with a lot of attention to detail. I also have a cowl flap but rarely use it.

[Bruce Tuncks]

I'd love to see a pic of your cowl-flap Machtuk. I thought about these but chickened out and just did a skirt.