crankcase ventilation/oil filler

[jk952]

There was a related thread but couldn't find again, and don't recall an answer to this, so:
Re Elan S2: Oil tends to leak out of the oil filler cap, this then runs down the back of the engine and drips onto the exhaust pipe - unpleasant burning oil smell! Replaced the seal on the cap, better but still leaks. Changed the breather tube from a "road drain", to being connected to the std. air box (twin weber set up). Had tried a pcv valve in this line prior - made no difference -but removed it. A couple of local Lotus owners (also forum members) have the same condition to some extent. One added a cover over the rear cam to reduce direct spashing to the bottom of the filler cap. I haven't done this yet.
I recently purchased a Caterham 7 - Kent crossflow - this has a noticeable slight neg. pressure if you remove the filler cap and place the palm of your hand over it. It of course has the std oval can thing beside the block, pcv valve, and about a 3/8 i/d line to the manifold. The filler cap is vented with a wire mesh inside, likely to serve as an oil mist catch.
My Elan has seemingly less neg. pressure when you do the same thing ( highly accurate palm measurement- before burning it Engine is a fresh rebuild so shouldn't have excessive blow-by, and actually runs great otherwise.
Is it possible they just didn't allow a large enough passage for air pressure by the time the rubber connector reduced the inside dia going into the crankcase?
Any modern daily driver has a significant neg. pressure if you remove the filler cap to the point of almost or actual stalling. ( different air fuel management sys of course)
Comments anyone, do you have the problem, how was it solved?

Thanks, Jack

[andyhodg]

Jack

I had a problem with leaks from the oil filler cap. I fitted a deflector under the filler cap, fitted a new seal and the leak remained. I then fitted a thin plastic shim approx 0.7 mm thick between the seal rubber and the cap. It is now a bit stiffer to fit and remove but no more leaks.

Regards

Andy

[peterako]

Nice post Jack, thank you!

My engine can occassionally 'blow' oil out the filler cap...down to exhaust manifold....sniff sniff

It's probably down to two things:

1. Worn filler cap rubber (it happens only when the cap closed in a certain position + some other unknown conditions)
2. Blow-by or (?) badly worn valve stems...

I have bypassed the oil-to-airbox connection and instead route to a catch tank. Though there is still mist out of the catch tank breather

Having said all this, when it's not leaking out the filler cap...my car consumes the manual spec. amount of oil...Hmm...

So, no solution from me....

And worryingly I had hoped that a rebore or similar would cure it.....

Engine behaves wonderfully al the same

Take care,
Peter

[neilsjuke]

Do check that you have the correct amount of oil in the sump as the dip stick may be wrong type or the front cover tube is to far out .
Cam cover may not be true/flat on cap edge
Neil

[types26/36]

I've also battled with oil cap leaks at various times, I normally make and fit a deflector plate which does help, I have also fitted new rubbers of various thickness's, added gasket material under the rubber and eventually get it to seal but it can be a time consuming process.
Also to save time and effort I take off the cam cover, do whatever is necessary but before refitting turn it upside down and fill the cap with a mixture of paraffin(kerosene) and oil and leave it for a while to see if it leaks, if it leaks start again.
Once the cap seals refit the cam cover.
I have had the pins that are worn, sometimes the cap's two prongs do not locate in the pins nicely, all of this can be seen from the underside before refitting the cam cover.
I have even had a cap that simply would not seal no matter what I did and the only option was a new (different cap)

[jk952]

A thank you to all of you for the responses, all good input. I will try some of them.
Hate to think that there may be too much blowby coming up exhaust valve stems, after having paid $ to an "expert" for putting in new guides, valves etc.! I tried draw filing slightly the top lightly to make sure it was flat( didn't remove much material though) , but there is a small contact area really. Also I wonder if the spring on the caps gets a bit "sproinged" - have two - both have the same result. With the new seal it is much better than before, so maybe if I add shims it will be tight enough. Have to remove anyway to paint so will try the kerosene idea also.
Still somehow wonder why it isn't vented as the kent stock set up....
As usual a great forum for bouncing ideas around.

Jack