Oil drain down from cam carriers

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Plentywahalla
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Oil drain down from cam carriers

Post by Plentywahalla »

Some may remember my earlier post about the problem I had with some errant vapour blasting media causing a momentary loss of oil to the exhaust cam. It made the cam belt jump a few teeth and bent the exhaust valves. It is all back together now and I was spinning the oil pump up prior to fitting the cam belt to check oil feed to the cams.

I got nothing flowing at all unless I spun it up to about 2000 rpm. This was obviously not right so I stripped all the auxiliary housing again and checked this excellent forum for ideas. That is when I discovered the secrets of the pressure relief valve. It was stuck wide open with, you guessed it..... more blasting media. The workshop manual does mention a pressure relief valve but it doesn't show where it is or how to access it. I had all the parts cleaned but not knowing it was there meant it was left with media in it.

About a mile before where the engine trashed itself I had floored the throttle to avoid a chav in a tricked up Corsa. I think the overpressure opened the valve and it stuck that way depriving the exhaust cam of oil. I have now replaced the valve and the oil pump and have good oil flow. But it is now giving me another thing to worry about. I have the cam covers off to view oil feed to the cams which is fine. But the oil appears to be taking far too long to drain back into the sump. I put in five litres of 20W/50 but by the time it has filled the filter and the cooler, the amount held in the cam carriers means the sump level is alarmingly low.

Is that right?? I know that 20W/50 is thick old stuff on a cold day but the drain holes down into the head are quite small and the slant of the engine means that on the exhaust side they are well above the bottom of the cam carrier. I am pumping oil without the engine running so I don't know if the cam gear actually assists it pumping oil down via the buckets. They are such a close fit I can't see much oil getting past them. I have only been pumping oil slowly and am worried that I have got something wrong somewhere. If the engine is running at high revs the oil delivery to the cams will be even higher but the drain down rate will be the same, so I can see another oil starvation problem looming.
1988 Lotus Excel SE - newly on road
2004 MG TF - my sunny day driver
1991 Mercedes SL - owned 28 years
1968 Triumph Vitesse - Griffon Kit Car
1971 Europa type 54 - Type 47 restomod
2010 Volvo XC90 mobile dog kennel and tool box

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bash
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Re: Oil drain down from cam carriers

Post by bash »

Speak to lotusbits, they do a jet that restricts the amount of oil that goes into the carriers, they developed it for thier rally cars because at higher revs too much oil was held in the cam area.
Bash
Ps, put restrictor into the search section it will turn loads of info up.
Two things are infinite: the universe and human stupidity; and I'm not sure about the universe.

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Re: Oil drain down from cam carriers

Post by Pete Boole »

bash wrote:
Mon Feb 06, 2023 17:09
Speak to lotusbits, they do a jet that restricts the amount of oil that goes into the carriers, they developed it for thier rally cars because at higher revs too much oil was held in the cam area.
Bash
Ps, put restrictor into the search section it will turn loads of info up.
Yep - it fits to the top of the block/bottom of the head - not what you want to hear when you've just rebuilt the engine!!

Pete

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Plentywahalla
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Re: Oil drain down from cam carriers

Post by Plentywahalla »

No, exactly, I'm not keen on stripping the head down again. It's annoying as I've had many conversations with Mike over this engine and he has never mentioned it. Thanks for all the advice and I have read the past posts so I know exactly where it is meant to go.

I did wonder whether the attitude of the car makes a difference. My drive slopes downhill and the way the car is parked means its nose down. As all is spannered back together I can't see where the head drains into the sump. I can't move the car to level ground until it is running again.

Also, is 20W50 the best oil. i've seen other grades being discussed.
1988 Lotus Excel SE - newly on road
2004 MG TF - my sunny day driver
1991 Mercedes SL - owned 28 years
1968 Triumph Vitesse - Griffon Kit Car
1971 Europa type 54 - Type 47 restomod
2010 Volvo XC90 mobile dog kennel and tool box

Pete Boole
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Re: Oil drain down from cam carriers

Post by Pete Boole »

Oil drains back to the sump from both the front and rear of the cam housings.

Pete

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Lotus-e-Clan
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Re: Oil drain down from cam carriers

Post by Lotus-e-Clan »

In a healthy engine with a vacuum-tight breather system, there should be slight negative pressure in the crank case at higher revs , especially at part throttle. This should help drain oil back to the sump.
Peter K

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