Crankcase pressure and related oil leakage

[The Veg]

As some of you may recall, I've had some issues with oil coming out of the engine after some driving recently. Here's a recap of relevant details:

-Engine rebuilt by previous owner at 79950 miles
-Rebuild included bore-over and Stromberg head modified to DBE Stage II specs
-Purchased by me at 80270 miles, now showing 80400

The last two drives were about 30 and 60 miles. I noticed a lot of oil leaking from the fill cap despite a nice tight fit even after I shimmed the gasket, some oil coming through the disptick tube (did the heat-shrink trick for that...was OK for the last two drives but today the stuff stayed in the tube when I withdrew the dipstick!),and a lot coming through the breather, which I have plumbed to a catch-can before connecting to the airbox. After the 60-mile drive enough oil had come through to fill the can and run all the way down the intake trunking, out the filter housing, and puddle in the nose.

Today I did a leak-down test and got a solid 2% dry at each cylinder. With numbers like that I didn't bother with a wet test. Even at 2% it's still enough air to be audible coming out whichever other cylinder also has its piston at TDC (can mute the sounds with a finger in the plug-hole) and hear the air glugging through some oil that settled in a downward bend in the breather-tubing. Since the air has to go somewhere I'm not worried about either of those. No bubbles in the coolant at the filler on the thermostat housing (Coolex housing). No sign of water in the oil, at least from what I can see in the oil that has left the crankcase- in fact after 130 miles it still hasn't darkened very much, so with that and the low leak-down numbers I'm not certain that blow-by is the problem. So why does it want to blow oil out? Or are these engines of the type that will puke the stuff out until they're happy with the level?

[2cams70]

Did you check the dipstick tube to ensure it's been pressed in the correct amount? If pressed in not far enough the engine will be over filled with oil when the oil level reaches the "full" mark. Try draining the sump and filling with a correct measured amount of oil

[The Veg]

I think the tube is close enough. Interesting to note that the WSM page posted in the thread about the tube is more detailed than the page in my 1974-dated WSM, which only gives the lower dimension of the earlier engines. Anyway, it's not easy to measure with everything assembled in there, and the instruction is bit vague about whether to measure from the upper or lower edge of the flange, but the difference isn't much. As near as I can tell, my tube is at the lower/earlier height, which would have the opposite effect of over-filling...assuming that the dipstick itself is correct. The point where stick becomes 'doubled' is what stops at the top of the tube, the stick is showing just past halfway between the FILL and FULL lines, and the oil still wants to blow out. Will double-check with a refill before too long.

[h20hamelan]

Which oil pump?

[rgh0]

I think the tube is close enough. Interesting to note that the WSM page posted in the thread about the tube is more detailed than the page in my 1974-dated WSM, which only gives the lower dimension of the earlier engines. Anyway, it's not easy to measure with everything assembled in there, and the instruction is bit vague about whether to measure from the upper or lower edge of the flange, but the difference isn't much. As near as I can tell, my tube is at the lower/earlier height, which would have the opposite effect of over-filling...assuming that the dipstick itself is correct. The point where stick becomes 'doubled' is what stops at the top of the tube, the stick is showing just past halfway between the FILL and FULL lines, and the oil still wants to blow out. Will double-check with a refill before too long.

The "doubled" section should fit into the tube until the curved bump in the double half section. if its not going in then your oil level will be substantially to high

cheers
Rohan

[Lotusian]

Yes, Rohan is right.
When inserted correctly, the dipstick will look like first photo.
If it looks like second photo, then you have several pints too much oil.
Ian

[HCA]

I can certainly see photo 2 would cause problems!

To negate the dipstick issue, why not drain out all the oil and refill with the correct amount, see if it marks the stick differently, and if lower, drive the car to see if any better. If it is not, then you can move on to the next...

[promotor]

As near as I can tell, my tube is at the lower/earlier height, which would have the opposite effect of over-filling...assuming that the dipstick itself is correct.

Is the dipstick correct?

[oldelanman]

a lot coming through the breather, which I have plumbed to a catch-can before connecting to the airbox. After the 60-mile drive enough oil had come through to fill the can and run all the way down the intake trunking, out the filter housing, and puddle in the nose.

Check that the head to block drain tube is not blocked - perhaps by the remains a breather tube grommet - if it is then oil from the back of the head will drain into the breather tube rather than down into the sump.

[The Veg]

Oil pump- I installed a NOS Ford unit that takes a spin-on filter. I'm not an expert on the intricacies of the lubrication system of the Twin Cam, but would the pump really have that big an effect on the amount of oil that gets atomised in the case-atmosphere or the amount of pressure in the case? It doesn't put anything into the engine that wasn't already there.

Drain tube- all good; I had the head off recently and installed a new tube when it went back together and took pains to make sure the tube went in straight and true and that everything was clean at both ends.

Dipstick- will investigate further and report back. I've already had to bend it creatively to clear the fan on the big bulky old-style alternator installed by a PO. It appears to be the correct TYPE and has a good bit of patina, but that doesn't mean it's original to the car.

Oil quantity- will investigate later and report.

[The Veg]

Dipstick- will investigate further and report back. I've already had to bend it creatively to clear the fan on the big bulky old-style alternator installed by a PO. It appears to be the correct TYPE and has a good bit of patina, but that doesn't mean it's original to the car.

Oil quantity- will investigate later and report.

Some progress to report:

The dipstick had a problem. As discussed earlier, it wouldn't insert fully to the 'hump' and the reason is due to a repair somebody made. It appears that the stick broke in the middle of the hump and somebody welded it back together there...and also put a bead of weld where the doubled section ends a little farther down, and the bead protruded enough to keep the stick getting past. So not only did I not know that this was incorrect, but with all the oil coming out of the engine I kept adding it trying to keep up to the mark- and doing that makes it quite easy to lose track of how much is in there!

So I filed-down the weld-bead until the stick could insert properly, and then it became apparent that the stick should clear everything, even that big alternator, without being bent, so I straightened it.

I drained the oil, using gallon jugs with one side cut open to see how much came out. Filled one and about half of the second, so I had about six quarts in the sump! Assuming about a pint in the filter, I refilled with four quarts and the dipstick reads very close to FULL.

I did a short mile or so after that just to see if all was copacetic. The hose from the catch can to the airbox was open, as I had the airbox removed, but I saw no evidence of a large blow from it, and hardly anything in the catch-can, perhaps just what had already been in the wad of metal wool inside the can. The new fill cap gasket allowed no leaks, however the dipstick tube blew enough droplets to hit almost everything in the left side of the compartment. I've since put some heat-shrink on it but haven't had a chance for another drive due to weather. Perhaps this weekend.

[The Veg]

More results:

I recently installed a new rubber seal in the oil-filler cap. Went for a drive and afterward found a sheen of oil all over an area within an 8-inch radius of the cap...and found that I had failed to screw the cap on properly! Shame on me for that one. Clean it up and beat myself up a little.

Then today, after installing a new ignition coil (see my recent post in What Did You Do To Your Lotus Today?) I went for another drive; did about 18 miles near home and everything seemed to work the best yet, at least as perceived from the driver seat, until around 16 miles when oil-smoke started to become a bother.

Got home and found that pretty much the whole left side of the engine compartment had been coated with oil!

None around the cap, so the new rubber seal did its job- MUCH improved over the POS cork seal that preceded it!
No noticeable increase in the catch-bottle or the plastic bottle downstream of that since the airbox is still removed.

I did put some heat-shrink on the disptick, enough that it gets fairly tight before the 'hump' reaches the tube, so how much could possibly still be coming out here???

Level in the crankcase SHOULD have been correct (right at FULL mark) before the drive, per the correction recently made to the dipstick (see my previous post in this thread). After the drive the dispstick showed it down by about 40% of the distance between the FULL mark and the ADD mark.

As much rotten luck as I'm having keeping oil inside this engine, the temptation to remove the Twink and chuck it off a cliff and do an 'Elon' conversion is starting to feel powerful!

I'm traveling for work again this week so that gives some time for the oil to drip-off a little and my temper to cool a bit (a BIT...!) before I can get my hands dirty on it again.

[Craven]

If you fit a suitable size flexible pipe to the breather that normally connects to the airbox, you can by simply blowing into the engine readily pressurise the whole of the crankcase any leaks can be found by ear.
A de-luxe version would be to arrange an air source from a compressor but only a couple of psi needed.
May have your own idea but you get the general idea.

[oldelanman]

Not related to your oil leak but it looks like your vacuum connection may have come adrift from the front crossmember.

IMG_20210110_152607.jpg (99.09 KiB) Viewed 687 times

[nmauduit]

Not related to your oil leak but it looks like your vacuum connection may have come adrift from the front crossmember.

good catch...

on the oil leak issue, have you identified precisely where it comes from ? e.g. starting from a clean engine, running it a bit at a time to see where it starts to shine? if the oil falls onto a pulley, it can spread quite a bit... or if there is a small leak on a pressurized circuit, it can spray like paint... You've seemed to have considered several potential sources at atmospheric pressure (from where blow-by would play a role), even if that does not go with a well rebuilt and well running engine, so maybe the pressurized circuit should be investigated as well (including the pump as it was changed : would it produce too much pressure by any chance ? )

good luck !