Jabiru Design Fault Oil Leak?

[derekliston]

I have a 2200 Jabiru on my CH701. For a while I couldn't find an engine oil leak, it was and still is, nuisance value more than anything, using probably less than a teaspoonful of oil per hour, barely noticeable on the dipstick but spread nicely on the lower cowl. I eventually discovered that, inside the rocker boxes there is a small hole drilled through the back at the top, which exits between the fins above the cylinder. This I discovered was factory designed to prevent carbon build-up on the valve stems (I think) Anyway, a very small amount of oil or oil vapour blows out of these holes. The only suggestion from the factory is to lower the oil pressure, which I don't want to do. I am sure that somewhere on this site I read about that problem but I cannot find the post. Their solution had been to fill the little holes with high temperature RTV and to drill small holes in the rocker covers. I am hoping that whoever that was will read this and give me details of the size and positioning of the hole in the rocker cover.

 

 

[jetboy]

It was a design feature they put in with the hydraulic lifters to stop oil filling up the rocker cavity by some siphon action or lack of free draining down the pushrod tubes

 

but later they changed the lifter and the issue went away

 

someone on the Yahoo group did the mod to the covers

 

so it depends what rebuild spec your engine is up to because I think new engines didnt need the holes after all

 

sorry not much help as my engine is the solid lifter and blows about 50ml / hr out anyway

 

I dont get much corrosion down the belly of the 701!

 

 

[derekliston]

It was a design feature they put in with the hydraulic lifters to stop oil filling up the rocker cavity by some siphon action or lack of free draining down the pushrod tubesbut later they changed the lifter and the issue went away

someone on the Yahoo group did the mod to the covers

 

so it depends what rebuild spec your engine is up to because I think new engines didnt need the holes after all

 

sorry not much help as my engine is the solid lifter and blows about 50ml / hr out anyway

 

I dont get much corrosion down the belly of the 701!

My engine is also solid lifter. I bought a rebuild rather than a new one. Don't you have a collector bottle on the firewall to catch the blow by?

 

 

[planesmaker]

The hole in the head ( don't start me on the engineer who thought it up) was to allow air in to help drain the rockers of oil. It was a jabiru 'fix'

 

 

[derekliston]

The hole in the head ( don't start me on the engineer who thought it up) was to allow air in to help drain the rockers of oil. It was a jabiru 'fix'

Thanks for the input, but I was aware why the holes are there, what I need to know is how to fix the problem.

 

 

[bexrbetter]

Don't you have a collector bottle on the firewall to catch the blow by?

Blow By? Twightlight Zone, I seem to have been sent back to the 1950's.

 

If it was mine I would be setting up a PCV system. The lowered crankcase pressure would help draw the oil down the pushrod tubes, help prevent detonation from blow by, and, as a bonus, the heads should run cooler.

 

 

[derekliston]

Blow By? Twightlight Zone, I seem to have been sent back to the 1950's.If it was mine I would be setting up a PCV system. The lowered crankcase pressure would help draw the oil down the pushrod tubes, help prevent detonation from blow by, and, as a bonus, the heads should run cooler.

I am a retired LAME but I confess I have no idea what a PCV system is, would you mind elucidating? By the way, I have the large plenum chambers fitted, my EGTs and CHTs are good, only problem in Qld Summer is oil temp!

 

 

[geoffreywh]

Positive Crankcase Ventilation, a one way valve, (think ball in a tube) a means of ensuring that the crankcase is subject to negative pressure. Some cars had a tube (engine breather) connected to the air cleaner lid.

 

 

[jetboy]

Derek, I'm sure if your engine has been rebuilt with solid lifters you should just block the holes as I think the heads were holed for the hydraulic lifter problem which you dont have?

 

yes I have the oil catch bottle but really need a vapor trap upstream of it to separate that and return it to sump

 

dont like the idea of a PCV system wouldnt that decrease the detonation threshold of the engine by ingestion of oil mist the only good thing might be corrosion protection of the cylinders - something my engine might benefit from but I havent tackled that issue yet (Camit oil injection etc.)

 

 

[horsefeathers]

I am a retired LAME but I confess I have no idea what a PCV system is, would you mind elucidating? By the way, I have the large plenum chambers fitted, my EGTs and CHTs are good, only problem in Qld Summer is oil temp!

Hi Derek.

Best thing I ever did for temps was to put a thin aluminium plate between the oil cooler and the silencer. It lowered oil temps (approx 90 degrees ATM), and as a bonus, lowered my CHT temps consistently by 25degrees

 

 

[onetrack]

Here's a pretty good explanation of the PCV system for Derek ...

 

Positive Crankcase Ventilation (PCV)

 

 

[derekliston]

Thanks to everyone for all the info. I don't think I will be changing over to PCV though. To horsefeathers, thanks for that but I don't think it would work on my engine with the oil cooler - muffler positioning but I will have a look.

 

 

[horsefeathers]

Hi Derek.

 

Forgot to post the link to the fotos on this forum showing the plate - The idea is that is directs air down under the engine, and stops it mixing as much with the air exiting after cooling the heads, allowing a better airflow past them.

 

Works well for me, but YMMV.

 

Oil Cooler plate fotos

 

 

[bexrbetter]

Here's a pretty good explanation of the PCV system for Derek ...Positive Crankcase Ventilation (PCV)

That is merely emissions based and not explaining the real advantages of lowered crankcase pressures increasing compression ring and oil ring control helping to keep oil out of the combustion process and not, as jetboy wonders, "sucking more in".

 

Meh, too hard, that's 5 minutes I could have spent on my own engine.

 

 

[bexrbetter]

Now that you mention that..

I just popped this in the XPB thread Aaron, doesn't belong here.

 

 

[seb7701]

Hi Derek.Best thing I ever did for temps was to put a thin aluminium plate between the oil cooler and the silencer. It lowered oil temps (approx 90 degrees ATM), and as a bonus, lowered my CHT temps consistently by 25degrees

HF - so glad you posted the photo as I am looking at ducting my oil cooler at present. Considering you scored what I would call a terrific reduction is CHT's, do you reckon it's a case of directing oil cooler exhaust somewhere a little better, (probably downwards?) rather than randomly in the lower cowl where it can bugger up the downwards flow from the heads etc?

 

 

[horsefeathers]

Hi Seb .

 

Yes, I think the plate pushes the air under the engine, limiting the mixing with air from the exhaust from the ram air ducts.

 

I'd like to claim it was all my own work, but really I was just following ideas in Jabiru's cowl airflow diagrams.

 

In the winter just finished,I had to restrict the oil cooler air intake,as the oil wouldn't get hot enough. However, the restriction didn't seem to affect CHTs, so it seems like the plate is doing its job, keeping the flows from the cooler and the heads somewhat separated.

 

When I get around to it, I'd like to completely separate oil cooler airflow by ducting, but this plate worked so easily, I don't think i'll be doing any further changes any time soon.