Lotus Elan

Poor compression - cause? Updated

PostPost by: rgh0 » Fri Jul 17, 2020 12:36 am

The modified McCoy Stromberg to Weber conversion heads do not have the standard breather oil knock
out chamber, as this machined off as part of the conversion and for some reason yours is similar. Do you know the source of your head? QED many years ago developed a similar head conversion that may also have removed the breather box . I have never seen details of their conversion but i understand it had welded in inlets. They sold it for a short while in the late 80's early 90's before they started casting their own new heads

Putting a breather on the front of the cam cover is the normal way to deal with not having the standard breather chamber arrangement. The standard breather chamber does not really contribute to head oil drainage and removing it does not affect it.

If wanting to use the engine block breather rather than add one to the cam cover then you need to set up something like Ford used so the oil is knocked out of the breather gas flow and drains back into the engine

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PostPost by: pharriso » Fri Jul 17, 2020 12:51 am

rgh0 wrote:Do you know the source of your head? .....
cheers
Rohan


Hi Rohan, we discussed these heads here - https://lotuselan.net/forums/viewtopic.php?f=39&t=43120&start=&uid=4893

These heads are similar to a Lotus development head that Simon has in the QED showroom, I photo'd it when I visited in 2013:
IMG_1612.JPG and

IMG_1615sm.JPG and


These heads are unique in that:
1. They do not have breather boxes with the drian to the block
2. they do not have half moon castings on the inside of the plug wells
3. The rear cam bearing either isn;t there, or appears to be a later addition, on the QED head the boss is in the head, but no caps.

At the moment I think I am going to try fitting my spare UK BV head. This will give me a chance to see if the engine has been rebored / rehoned & an opportunity to get a look at the head.
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PostPost by: rgh0 » Fri Jul 17, 2020 1:36 am

pharriso wrote:
rgh0 wrote:Do you know the source of your head? .....
cheers
Rohan


Hi Rohan, we discussed these heads here - https://lotuselan.net/forums/viewtopic.php?f=39&t=43120&start=&uid=4893

.


Thanks I had forgotten about that discussion.

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PostPost by: Andy8421 » Fri Jul 17, 2020 5:35 am

pharriso wrote:
Andy8421 wrote:
pharriso wrote:
Back to why I am testing: What would cause a lot of crankcase pressure & oil being flung out the breather hole in the block to the tune of 1/4 pint every 20 miles or so.


The breather hole is in the head?


No, this is with my very strange head without a breather box. There is no oil drain to the block & no breather hole to the airbox. There are several of these heads knocking about with shortened runners, was discussed by another poster in a seperate thread. Let me see if I can find it.

The only "breather" available is the hole above the fuel pump, used with a oil/air seperator on Ford Kent engines.

Apologies if this is a stupid question, but you are using some form of separator / velocity drop chamber and not just venting out of the hole in the block?
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PostPost by: pharriso » Fri Jul 17, 2020 12:37 pm

Andy8421 wrote:Apologies if this is a stupid question, but you are using some form of separator / velocity drop chamber and not just venting out of the hole in the block?


Andy, Not a stupid question at all, hopefully this is the issue since otherwise the engine appears well!

When I purchased the car in 2013 It has this Ford Kent air / oil seperator with the hose going below the engine:
IMG_E7178.JPG and
Elbow installed


I thought this was anti-social, so for the last 2-3 years I have been experimenting with a Burton elbow & a catch tank:
BurtonBreatherElbow_23.5mm.JPG and
Burton Elbow
]
IMG_0472.JPG and

IMG_8047sm.jpg and
Catch Can attached to Radiator support


Problem is the catch can fills up in 20-30 miles & then overflows oil either through the return (air) hose (routed to the air box) or through the filter on top, resulting in oil slicks and/or clouds of smoke.
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PostPost by: TBG » Fri Jul 17, 2020 12:44 pm

Gosh - all I have is a bit of copper pipe with rubber ends from the block to the air intake. Am I missing something here?:?
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PostPost by: Andy8421 » Fri Jul 17, 2020 1:50 pm

Phil,

I think I see the problem. The engine's 'breath' contains a mix of blow-by, oil spray and oil mist. The box cast in the later heads allows the spray and mist to drop out of the flow of blow-by and drain back into the sump, with just the blow-by exiting the breather.

Unless I misunderstand, your setup has no mechanism for the oil spray / mist to separate and drain back into the sump - it just collects in your catch tank. I think you need to reinstate the Ford/kent separator which looks to allow the oil to drain back into the sump. Given your picture, it might be worth buying a new one if you go down this route.

Good luck.
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PostPost by: SENC » Fri Jul 17, 2020 1:54 pm

I'd be curious if your antisocial version routed to the catchcan would do any better at separating and returning oil. I would expect it to with baffles and wire mesh scourer inside.

Are you using the mechanical fuel pump or converted to electric? If the latter, is the mechanical still in place or does the cap you replaced it with have a baffle?
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PostPost by: pharriso » Fri Jul 17, 2020 3:25 pm

Thanks for all the replies guys :-) I think we're getting somewhere...

TBG wrote:Gosh - all I have is a bit of copper pipe with rubber ends from the block to the air intake. Am I missing something here?:?


A tube from the hole in the block above the fuel pump directly to the airbox? You also don't have a breather tube from the cylinder head airbox to that hole?

Andy8421 wrote:Phil,

I think I see the problem. The engine's 'breath' contains a mix of blow-by, oil spray and oil mist. The box cast in the later heads allows the spray and mist to drop out of the flow of blow-by and drain back into the sump, with just the blow-by exiting the breather.

Unless I misunderstand, your setup has no mechanism for the oil spray / mist to separate and drain back into the sump - it just collects in your catch tank. I think you need to reinstate the Ford/kent separator which looks to allow the oil to drain back into the sump. Given your picture, it might be worth buying a new one if you go down this route.

Good luck.


SENC wrote:I'd be curious if your antisocial version routed to the catchcan would do any better at separating and returning oil. I would expect it to with baffles and wire mesh scourer inside.


Andy/SENC, that makes sense. My Kent seperator is just a hollow "box", nothing inside it; my recollection form the 80's is that they contained wire wool? Maybe I need to replace the wirewool in the seperator & then run it to a catchcan?

SENC wrote:Are you using the mechanical fuel pump or converted to electric? If the latter, is the mechanical still in place or does the cap you replaced it with have a baffle?


Standard mechanical fuel pump.
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PostPost by: SENC » Fri Jul 17, 2020 5:16 pm

pharriso wrote:Andy/SENC, that makes sense. My Kent seperator is just a hollow "box", nothing inside it; my recollection form the 80's is that they contained wire wool? Maybe I need to replace the wirewool in the seperator & then run it to a catchcan?

Just the Kent separator design should help, but the one I have has a couple baffles close to the inlet and I do believe would have had some very rough/loose wire wool, yes. That should allow the gases to pass but most of the oil to drip back in. I was asking about the fuel pump because I've been told without it the jackshaft can sling oil upwards towards that opening.
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PostPost by: mbell » Fri Jul 17, 2020 5:20 pm

You could also try a more modern separator like:
https://www.bimmerworld.com/Engine/Cran ... 7-E53.html

It might be difficult to pump in due to limited space.
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PostPost by: sprintsoft » Fri Jul 17, 2020 6:48 pm

Phil,

sorry if you already said, but are you getting oil blowing out of the dipstick tube?

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PostPost by: pharriso » Fri Jul 17, 2020 7:04 pm

sprintsoft wrote:Phil,

sorry if you already said, but are you getting oil blowing out of the dipstick tube?

Iain


None at all.
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PostPost by: sprintsoft » Fri Jul 17, 2020 7:18 pm

OK, that would support the evidence from your compression and leak-down tests that the engine is in good shape.

So from that we know the crankcase pressure is low, it is amazing that oil can still be constantly pushed all the way over to the catch tank so fast.

The block hole must be under constant oil splash pressure which does not allow the oil a chance to drain back.

no solution - just thinking out loud...
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PostPost by: Andy8421 » Fri Jul 17, 2020 9:02 pm

pharriso wrote:
Andy/SENC, that makes sense. My Kent seperator is just a hollow "box", nothing inside it; my recollection form the 80's is that they contained wire wool? Maybe I need to replace the wirewool in the seperator & then run it to a catchcan?


The cast box on later heads has no wire wool - technically it is a 'velocity drop chamber' - the speed of the blow-by / oil spray slows right down as it enters the box which is much larger than the breather pipe from the block. The slower gas flow can't support the oil spray which drops out of the flow and drips back down into the sump. There is coarse wire wool in the breather pipe from the box into the air intake - I assume to catch any oil mist still in the flow.

Your Kent separator does the same job. It doesn't need to be any more than an empty box to work.

Looked at in the same way, your catch tank is a velocity drop chamber, it just is missing the drain back into the sump for the collected oil. If you replace the Kent separator, you shouldn't need a catch tank.
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