Having had the much improved refurb of the engine it looks like we have too much oil getting into the rocker boxes … it’s good to have them lubed …but not over lubed
The pipes from the sump route oil up to the rocker boxes and it then drains back down the alloy pushrod tubes …
If the feed is too great then 5e exit back down into the sump can’t keep up … so the rockers fill and, eventually, it reaches the old vent drilled hole that allows venting to the head fins
To confirm all this I’ve now got use of a converted rocker box head … that has had the centre cut out and a glass inspection panel sealed in place. This will allow us to run up to speed and eyeball exactly what is happening
If we find the oil supply is too great … then it’s probably a simple switchover of the oil feed pipes … it seems the ones in place now are high capacity feed
Update .. late September … looks like it might have been user error. I replaced the oil cooler matrix with a new slightly larger one … and, on refilling with oil, I was over generous allowing for the new EMPTY matrix … by about 750ml ! This had nowhere to go .. except out through the breathers …lesson learned 😊
As well as the flight in the Sherwood demo aircraft recently .. I managed to get a session in a Cessna 152 Aerobat courtesy of my son Will .. as a birthday present
This had a few advantages
1 – It kept me current , 2 – Refresh on type .. (flown a C150 exactly 1 hour in the last 12 years !) 3 – Familiarisation of Beccles area and 4 – Spinning refresh !
The spinning was awesome … doesn’t take a lot to push her up and over with 2 large ish gentlemen in there 😊
When we got to loops ..my first one just didn’t quite make it over the top … entry speed was 120 but maybe I didn’t pull back hard enough in the first sector … over we went .. on our back and she ran out of ooomph
Flicked over and straight into a spin ….
The well rehearsed spin recovery (I’d refreshed 15 mins earlier) came straight in and we were out in a couple of turns without much G
Great great fun … thanks Will and thanks Stuart 😊👍
Months sitting in the hanger waiting for the engine … then leaving it with no covers on .. needs a good hoover out .. other vacuum cleaners are available ! And deeper surface clean and then polish
All this focus on engine and bits for the annual ….and then, when the engine did a classic ‘dog fight’ on me yesterday … covering the screen with oil spatters as the cowls were off … I picked up a can of de greaser and a rag
In the heat of the moment … I didn’t check the tin …
As soon as I pressed the spray the screen section went completely opaque !
Brake cleaner and Perspex DO NOT mix well 😔
New screen from stores … not bad at under £40 … will take about 40 mins to fit with those very very small Allen bolts and washers but be like glass once in
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.