Engine test run – part two

Having completed the initial test runs in some baking hot weather .. 34’ no less, I’ve now conducted further ground tests with better conditions and cowls on.

This means the ducting starts to work better and the smaller cylinder head cowls can do their bit .. ducting the air, which has been slightly rammed over the rear cylinder heads and also, through a specially added pipe, directly onto the mags.N

NOTE – Paul HS spotted that my mag brass pipe jets ended about 1” away from the body of the mag. He quite rightly said that would make them less effective as the stream of air around the engine would tend to break that flow … will extend these with sleeved outer .. rather than break he fibreglassed fitting

Once the engine got right up to normal ish running temps .. normal as you can get on the ground … I removed the cowls and found the interior and bulkhead were covered in fresh clean oil.

There was so much that you simply couldn’t see where it was coming from … a lot of cleaning down with de grease spray and rags and try again … and again …

Eventually .. turned out to be next day, I located that it needed to be topping 2400 RPM and pretty warm engine oil … about 60 … both quite tricky on the ground as the cable brakes aren’t too happy holding her at that power for long

Then jumping out and torch in hand to look everywhere … spotted the rear left cylinder … cylinder 4 I think .. most rearward on a Jabiru with its offset crank… had clear oil running down the outside of the rocker tube .. with evidence that possibly both tubes we’re seeping

Looking at the engineering diagrams these alloy tubes run between the engine sump and the rocker head ..the T bar rubber unit takes a pressure central feed he rocker and these tubes run – unpressured – to drain back into the sump having done their stuff and lubricated the rockers.

Hence .. the grunt needed to get it to show .. at anything cool and around fast tickover … it simply doesn’t show

Update … further checks .. located a small drilled hole in each rocker box head … pointing upwards .

. These very small shafts allow any excess oil that overfills the rocker to vent and exit over the cylinder head fins.

This now moves us down the path of … why are the rocker boxes overfilling … further discussion reveals that a larger bore sump feed tube may have been added in place of the normal smaller bore.These w

These will now be replaced with the normal smaller bore and a glass topped rocker cover used to see exactly what is happening under power conditions.