engine oil leaks/crankcase pressure

[ricarbo]

I'm intending to get my 1973 Sprint back on the road and should be grateful for a bit of advice.
it's been off the road for the last 15 years. i rebuilt the engine with new standard size pistons about 6,000 miles ago. when i put the new pistons in, i measured the ring gaps and if i remember correctly, found them to be about 3 or 4 thou over the recommended maximum (the engine had done about 60,000 miles). i had it glaze busted, but i didn't have it rebored at the time, because i felt that if you can only rebore it three times, then each rebore brings the ultimate end of the engine nearer - perhaps a somewhat misguided notion.
Anyway, the problem is this; i find the cork seals at the cam cover and the top of the timing chain cover always fail in the same way, that is to say they move outwards until they start to leak, which makes me think there is too much pressure inside the engine. I also used to notice the dip stick would rise up out of it's tube and i'd have a leak there. Does any one have any ideas how i can check what the pressure in the crankcase is and any information as to what it should be?
I installed the cam cover gasket using Wellseal on the top surface only and used Lotus supplied gaskets only. After the first failure of the gasket between head and timing cover, i tried leaving out that gasket, as i felt the gap between the cover and the head wasn't big enough for the thick cork gasket. what i did instead was to form a silicone gasket using Hermetite instant gasket, but that leaked almost from the start, so was a clear mistake!
all the best.
R

[oldelanman]

Have you checked that your cam cover is not distorted ? If the hardware has been overtightened at some time it may be warped and will be difficult to seal effectively. Recommended torque for the hardware is very low (7lb ft I think) and it is very easy to overdo it especially if you are trying to cure a leak ! There are many different opinions on what sealer to use on the cam cover but whichever you use it's vital to clean the surfaces thoroughly first. I would also check that your breather tube from the back of the head is not blocked or kinked (if it's a rubber tube).

As far as your ring gap is concerned, I'm no expert but I think 3 thou extra gap equates to around 1 thou on bore diameter (if my maths is correct) which I wouldn't think is excessive but I'm sure one of the engine experts will have a more informed view on that. Do a compression test, that will show up any major problem.

Dip sticks do tend to rattle about and leak oil and the standard fixes are a spring to hold it in and/or a rubber spark plug cap which fits nicely over the dip stick and tube.

Regards,

[m750rider]

As stated, it sounds like your crankcase breather is plugged. I would check it before messing with the gasket any more.

[ricarbo]

Thanks for the replies. I don't think the cam cover is distorted, although it's not so easy to check as the cam bearing cap nuts prevent the cover from touching the head if the gasket is left out. I used a metal breather pipe between head and block at my first attempt and the Lotus rubber pipe at the second. i also carefully checked the steel tube between head and air box (Dellortos). On the first attempt i used 3M EC776 as recommended in the Autobooks manual, which is a very strong industrial adhesive. Torque setting as you say, with new nyloc nuts and correct rubber washers and plain washers. I like the idea of a spark plug rubber for the dip stick and will certainly try that. If it was a distortion problem, then that doesn't explain why the cork gasket on the timing case went the same way. So, i think i'm still left pondering if the crankcase pressure is excessive and how can i check it?
Regards
Richard

[oldelanman]

I don't think the cam cover is distorted, although it's not so easy to check as the cam bearing cap nuts prevent the cover from touching the head if the gasket is left out.

Richard,
There's your problem - you must have clearance between the cam cover and the bearing cap nuts otherwise you cannot compress the gasket. Maybe the cam bearing cap nuts are incorrect or possibly the cam cover has been skimmed to correct a previous distortion.

I'm not aware of a limit for acceptable crankcase pressure nor how or under what conditions you could measure it. If you think it's excessive a compression test will quickly indicate if you have a broken ring or excessive bore wear which could be causing it.

Regards,

[paddy]

If it was mine I'd try to measure the pressure by attaching a pressure gauge somewhere - eg by attaching it to the dipstick tube.

Paddy

[ricarbo]

Thanks oldelanman & Paddy. I did check there was enough gap between head and cam cover to squash the thick cork gasket to half it's thickness, so that should be ok, i think. the cam cover nuts aren't bottoming. I had a plan to use a thin paper gasket or even just silicone instant gasket but the gap was too large for that. i suppose a thin aluminium spacer could be made, but that wouldn't be a cheap solution for a problem that shouldn't exist.
I remember seing something in the Burton tuning catalogue about crankcase pressure limits, but can't remember the details and seem to have lost the catalogue. I just had a look on the internet and there was a tech tips section with a page on engine breathing systems suggesting a dry sump arrangement would get the crank case pressure below 2" on a water gauge, or even negative. My engine is standard, not dry sump, but perhaps i should rig up some flexible pipe to the dip stick tube as Paddy suggests and connect it to a gas plumbers manometer. Wish i knew what i am doing!! I've no idea what an acceptable value would be, other than that clue from Burton.
richard

[rgh0]

I doubt its crank case pressure causing the cam cover gasket to push out. If it was I think you would be spraying oil out all the crank seals. If you remove the vent pipe to the carbs and hold your finger over the hole should feel a very small flow of gas. Reconnect the carb vent pipe and then take off the cam cover oil filler and hold your hand over the opening and feel the flow of gas - it also should be very very small.

Normally the problem is just the gasket getting squeezed out through to slippery or distorted faces or overtightening. You should stick the gasket to the head or cam cover with a good gasket adhesive before tightening it down. You should only compress the gasket about 30% of its thickness any more and it will probably squeeze out. Tighten it down gently over a few days paying attention to how much compression and the torqued used

If it still squeezes out try sticking it both sides with a good gasket adhesive or a different brand of cork gasket.

cheers
Rohan

[Greg Foster]

Remove your cam cover and lay a straight edge over its gasket mating surfaces to see if the cover is warped. Make sure the surface is clean and free of gasket/sealant materials before checking. A good machine shop will be able to mill the surface flat if there is a warp in the cover. I also belt sand the flat of the "D" seals(Not on the engine) to just above the head surface so as not to compress the cork cam cover gasket too much in this area. Add a little silicone sealant to the "D" seals where they mate to the head and drop into place and let dry before tightening the flat new camcover and gasket . Hope this helps!

Greg

[ricarbo]

Thanks folks, i'll try all the suggestions and see how we go.
all the best
Richard