Peter wrote:
given that the middle of the crank is full of oil
Hmmm…
I have to correct my statement above. The middle of the crank will be full of oil with a variable pitch propeller. With a fixed pitch prop there is no oil flowing into the prop hub.
What is all that debris?? Especially this
You mean that discarded piston ring? I’ve no idea! And I was flying with this. Indeed the last flight, when I had serious trouble clearing the plugs, was a departure over the sea from Walney Is.! We just packed it onto a pallet and sent it off to Lycoming’s concentration point in Holland. I was careful to share these images with them re core charges, etc., prior to ordering the replacement and never heard any more about it. I wonder whose flying that crankshaft now there’s no machining tolerance in the nose so it must have been scrapped.
The grey sludge is a mixture of all sorts of stuff, microscopic bits of bearing shell, aluminium and lead that has blown by the piston rings from the fuel , fortunately mineral oils hold most of the lead blow by in suspension otherwise this would build up quickly in the oil galleries in the crankshaft.
This is why it is essential that multi grade semi synthetic oil must be changed at 50 hours as shortly after 50 hours the mineral part of the semi synthetic can’t hold any more lead and it will start to block the oil galleries .
Thanks A and C! At last, a reason for 50Hr oil changes!
Are blocked galleries an issue in Lycomings and does that have any relevance to the camshaft failures?
The problem with lead build up in the engine only reared it’s head when Mobil introduced Mobil 1 fully synthetic oil to the aircraft market, after much success in the automotive market ( that is using unleaded fuel ) it must have seemed the logical move but the problem is that lead can’t be held in suspension in a fully synthetic oil and so the lead that got into the oil as a result of blowing by the piston rings was simply centrifuged out of the oil inside the fast spinning parts of the engine .
The brain of a rocket scientist is not required to understand that it did not take long for this lead sludge to start reducing the diameter of the internal oilways inthe crankshaft………. very soon a few large top of the market twins that got a lot of use for business started throwing connecting rods out of the side of the engines and Mobil withdrew the product from the market after having to pay a lot of compensation.
Moving back to the Lycoming issues as long as the oil changes are done at 50 hours even a semi synthetic oil ( like Aeroshell multigrade ) will clear the lead from the system and the oilways will not get blocked.
Cam failure is usualy a function of corrosion and this is generally a result of under use or the engine not getting above 180F for an hour or so . The UK’s biggest fleet of Lycoming 360’s has very few engines that don’t make TBO with cam failure being almost unheard of but the engines are flying well over 500 hours a year and are reaching and maintaining an oil temp in excess of 180F for three or four hours a day.
This is interesting because Mobil 1 0W20 is very useful for removing sludge from piston rings which have been bunged up by burnt oil (engine running at too low power for too long) but then you add it as only about 10%, and only in the last 5hrs before a service. Obviously this is unauthorised…
Thanks @A_and_C for explaining about Mobil fully synthetic oil and keeping lead in suspension. I knew there were issues with some oils but never understood why.
It’s a great forum – thank you.
It’s also why you shouldn’t put fully synthetic into an old engine previously run on mineral oil thinking you’re doing good; quite the opposite!
(cars)
Interesting thread, I wonder if we can reach the front bank using a preformed gooseneck tube through the sump aiming hit the case split on an angle then feeding the scope tube through that? Would need a specific crankshaft position to slide past and maybe a gentle rotation to take it up the last bit to the front bank? Is 6mm small enough to do this?
Anyone tried these 古安泰 Coantec ME+ borescopes?
https://www.coantec.com/product/Details/17
http://braydentechs.com/borescope/automotive-borescope/
