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
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 that’s 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.
My first aviation engineer was Bob Wright from Jersey Channel Island Aero Services .. I used to love his easy going solid support and guidance ..not making me feel like some oik … muscling in on his profession but embracing, supportive and inclusive
Bob sadly passed away a couple of weeks ago … thank you Bob for all that you freely gave both in skills, friendship and support … I couldn’t have started OR finished without you.
Next was Mike Fleming, who also freely gave huge amounts of time to ‘watch at a distance’ a great skill … to not dive in and show me how it’s done (when all I would have learned was how good HE was at doing it !) but instead, nudge, ask (timely) questions … see if I understood what I was doing and what would then logically follow …. Mike did (and still does) provide context and oversight that meant you felt supported .. and learned from mistakes rather than bury your head in your hands !
Now, in the U.K., I have the pleasure of working with someone like James Milne. A wonderful easy going mine of knowledge and niceness
I could learn something every minute from this guy …. His focused ‘no nonsense’ approach to each and every step and then setting up and driving action to rectify anything is just great to be around.
At the Ranger annual today he spotted that a bevel was not quite as free as it should be .. he followed this through and suspected that he undercarriage had been stressed at some point.
To validate this we needed to get the weight off the undercarriage so, within minutes he was up a ladder, we had moved the aircraft to position it under a main hanger beam. A strop was erected and we had the aircraft floating just above ground level.
We slackened the main u/c pins and then strapped the Left and Right wheel .. so it wouldn’t splay on release, then removed the centre V brace.
Now, with the weight off … you could see and feel the saddle clamps had started to dislodge. I don’t recall any particularly heavy landings .. apart from the first grass one crossing the channel to Sandown …maybe it could have been just 5 years on concrete landings …
Whatever .. it’s been spotted … it’s a relatively easy reconstruct and replace with new parts … 2 brace arms, 2 cross plates, 4 mounting arms .. 4 saddle clamps and a set of nickel rivets
After a good few years of ONLY a tarmac landings .. and around 250 of those … plus, over time, I’ve had the port undercarriage leg off and changed and the starboard one off and new end roses …not forgetting I’ve had both legs fitted with new rubbers post the Smoke (Baby) oil getting on the, and expanding the rubber … it sort of feels about time to recheck all the symmetry
Getting out the original plan sheet for measurements and remembering the technique to strop both legs together to prevent Bambie impressions … it was a good exercise today if not a tad sweltering at 32’ outside the hanger 😔
So, start with central plumb line to give me a checkpoint … found I was a few mm out each side …
Now add the strop to hold the wheels … the knack being to leave sufficient slack in the strip so that you can pull the wheels outwards to accommodate the increased leg length as you wind the rose outwards
Bit of IN and OUT a few times little more gentle slackening …. Then done .. never like leaving her on a trolley Jack for longer than necessary
As quite a lot was changed and updated the engine needs a careful planned set of ground run tests.
The first involves a short 1 min run and then removal of each rocker cover to check oil is indeed being pumped around each bore
It’s now been converted from Hydraulic lifter valves to solid lifter valves, the old way (hydraulic) meant that I didn’t have to do any valve checking as they self adjusted. Now I need to include regular movement and gap checking.
The checklist calls for around 10-15 timed and controlled runs .. starting with low revs ..up to 1200 and short runs just to get all oil distributed evenly.
It’s always a pain when you have emptied the oil cooler matrix – this is a new one so starts empty ! .. you need to allow for sufficient oil in the sump to fill that and perhaps any new filter that may have been added.
The dipstick on the Jabiru isn’t the greatest piece of metal known to man as, in the taildragger configuration, you don’t get an accurate reading, the dipstick being calibrated to read when the engine is in a flat orientation. The standard dipstick doesn’t reach the bottom of the sump !
Over and above the standard dip test every flight….I’ve got used to checking every so often by trestling the aircraft up to flying angle .. ie Straight and Level (you need to do this when occasionally checking the rigging and wing dihedral). Anyway, the standard dipstick mark is ignored and it’s ‘about’ 1/8” (in old money) covering the bottom tip of the stick.
At the last annual James, my engineer, grabbed the prop ..pulled the engine into its S&L position and put a stick down to check… the simplicity of this was quite obvious … vs ‘it should be about 1/8 on the bottom of the stick’ .. so I’ve created a new dipstick that goes directly to the bottom of the sump.
The remaining tests slowly take the revs up through 1800 block tests as they call them .. successive run ups and cool downs … giving you chance to check all is working.
Once you get to the 1800 tests the idea is to take it to 50’C oil temperature and THAT should open my TOCA – Thermostatic Oil Cooler Adaptor .. a neat slim block that fits between the engine and the oil filter effectively blocking (COLD) oil circulation until the engine reaches 50.
The subsequent runs take the revs up to 2400 which is where it will be difficult holding her on the brakes so the chocks will come in handy … pays to keep the elevator back in these power checks !
Forgotten I had missed writing this post … long awaited update to engine and all put back in place
Took the opportunity to replace old hardened engine mount rubbers that had started to craze… also freshen up odd little scrape on the engine mount with hammerite … wish I’d still been around Jersey and my friend Mike Flemings powder coating skills !
Refit was a breeze … slight jiggle whilst the whole thing is safely suspended on a car hoist makes it a bit like a lunar docking … getting all 4 lugs neatly aligned and NO pressure on them until nuts done up
Then set about removing the awful (my word) wiring block and replacing with much nicer quality unit and a chance to really check each end point and put new crimped ring ends in position
Also make sure that L and R CHT and EGT are indeed LEFT and RIGHT !