Crankcase Pressurization and Oil Leaks

[RJS]

Hey,

Gotta a TR4A with at motor rebuilt 10 years and 7K miles ago. Started suffering crankcase pressurization and oil leaks this past year. The leaks are pretty bad, most seals and a 3-6" puddle under the rear main seal after a 45 minute cruise. Here are the vitals:

Dry compression: 180/180/180/180 psi
Wet compression: 208/200/200/200 psi
Spark Plugs: look perfect, light tan powdery look
Intake Vacuum: a nice 20" Hg at idle
PCV: completely serviced, even replaced with new from Moss
Oil: Castrol GTX 10W-40

Other than the oil leaks, the motor starts, idles and cruises perfectly. Returns ~22mpg. If I remove the PCV and run a breather on the crankcase, it barely leaks a drop. (I know, I know, I know...I could leave it there but, I am dying to figure this out).

Any ideas what's going on? I have narrowed it down to a few theories.
1. given the compression numbers above, is the blow-by excessive? If so, would moving up to 20W-50 oil fix this?
2. alternatively, does it appear this motor is running a higher than stock compression ratio which is OK but creates extra blow-by volume which the stock PCV cannot process?
3. If all the engine gaskets are shot, could it be pulling in too much outside air, overwhelming the PCV which then shuts down (to avoid a massive intake vacuum leak) thus, pressurizing the crankcase?

Whew! To many variables and dynamics at work here!

Would appreciate any and all thoughts on this one.

Cheers

Bob

 

[Deleted member 8987]

How do you know it's high crankcase pressure?
Like, pull the dipstick and see if there is pressure whilst running?

If there is no pressure, you may just have failing gaskets/seals........but....and here I go with the memory bit again.....

I recall an LBC at one point, long ago and far away.....that the design of the tube for vacuum was such that it carboned up badly, doing a self-sealing act second to none.

Do you really have vacuum at the PCV valve?
Only way to actually know is pull the main vaccuum line whilst running and check.
It needs to be sufficient to kill the motor at idle.


Dave

 

[RJS]

Hey Dave,

Thanks. The vacuum on the intake manifold where the PCV plumbs-in is where I took the vacuum measurement and got the 20". The PCV is perfectly clean and functional (plus I installed a new one from Moss with same result). The reason I suspect it is pressurization is two-fold:
1. I get oil leaks pushing out my oil filler cap and out my dipstick tube
2. when I remove the PCV and attach a crankcase breather, the leaks go away/stop

Tomorrow, I plan on running a series of tests with a pressure/vacuum gauge on the dipstick hole while I test out various PCV and oil filler cap configs

How about my compression test results? Does that tell you anything?

Bob

 

[Deleted member 8987]

I wish my compression was that high.
That said, a leakdown may be in order to see what is happening.
20" at the PCV manifold port is good.
Still you should not have enough pressure to lift the cap.

Compressions are equal, so a major failure like a hole in a piston is unlikely, but excessive carbon buildup on top of the pistons, and in the combustion chamber.....

Do a leakdown, rings have to be leaking past to get that kind of pressure.

This is that pancake jobbie PCV valve, right?
Idling, you have actual suction on the other side?

 

[Deleted member 8987]

One more thing.....

Vacuum does not equate to flow.
If the port is restricted, you can still have vacuum, but no flow.

Start it up.
Pull the vacuum line off the port and see if the car dies.

It should make a horrible noise like the flushing of all the commodes in Alaska simultaneously, then die.

If it keeps running just the same, the port is resticted.

Just to check.

 

[Don Elliott]

Any good engine re-build shop can run a quick "leak-down" test. When my neighbour rebuilt the engine in my 1958 TR3A (a normally vented crankcase) in 1990, I gave him a new set of pistons/rings and liners plus everything else needed to keep it running like "new" for a long time. I never noticed if the bores in the cylinder liners had been honed or not before he assembled it all.

I didn't burn oil, but it leaked about a quart every 600 miles (Castrol 20W50) and this leaking started right after the re-build. I drove it that way for 94,000 miles and, in 2007, decided to do something about it. I took it out and took it all apart, took it to an engine shop and the specialist said I had been running too rich and the rings had worn smooth and were allowing blow-by. There was no dimensional wear anywhere. I had him hone the bores and I rebuilt the engine myself this time putting in new Hastings rings, a new rear seal and all new bottom end bearing shells again.

I made sure that the carbs were no longer running rich and in the 8,000 miles since 2007, I have been running Castrol 10W30 + 4oz. ZDDP Plus and have not had to add any oil between oil changes.

 

[RJS]

Hi Guys

Thanks. Yes, I have the pancake PCV valve. I pulled the vacuum hose off the port on the intake manifold and it definitely sputtered hard and died. Just what you would expect with a massive vacuum leak.

So, I plugged the intake port, hooked up a 1/2" hose to the valve cover vent and ran it down low by the chassis with a 45 degree cut on it. Went for a 45 minute ride and it didn't leak a single, tiny drop! None, nothing, nade.

Don, interesting you mention the rich mixture issue. After 2,500 miles, I traced a "hot start" issue back to an overly rich mixture (thanks to an under-qualified mechanic). It was just after I fixed this that my oil leaks started. Coincidence? So, naturally, I was concerned about bore wash but, most knowledgeable people (TRF, University Motors) I spoke to said that was very unlikely.

I was hoping the wet/dry compression test would confirm if this was an issue (again, 180psi dry, 200psi wet, ~11%). Can anyone tell me if these are acceptable results?

But, perhaps I really need a leak down test from a qualified shop to confirm once and for all.

Cheers

Bob
PS: Don, nice looking motor by the way!

 

[martx-5]

There's a ton of information at this site concerning crankcase ventilation and oil leaks. It's on a GT6, but the principles apply. Also, the link is for the last design, the one that truly worked. You can link to the earlier trials to see how this guy went through the whole procedure to rid his car of all the oil leaks by proper crankcase ventilation.

 

[Geo Hahn]

FWIW - my late (64) TR4 oozed oil from every conceivable location. I added a road draft tube as would have been found on the TR3 & early TR4s and this resolved the leaks. Oh I still get some drops but to the extent that crankcase pressure was making it much worse it is now fine.

 

[TR3driver]

It's always seemed to me that the way to go would be a true <span style="font-weight: bold">ventilation </span>system; like those used on American cars. The key point is that you don't try to seal up the crankcase, or hold a slight vacuum on it; but rather have a great, whopping fresh air intake (with a filter). This should be arranged such that, if blowby should exceed what gets sucked into the intake manifold; then the excess will flow backwards through the intake, and get sucked into the carb intakes.

This neatly side-steps what I feel is the fundamental problem : at full throttle (where blowby is maximum), there is NO vacuum. It also means that the blowby fumes are actually sucked out immediately, instead of only being removed once they are replaced with fresh fumes, which should help keep the engine cleaner inside.

I've not found time to implement this on my TR3 motors; but I plan to. 'Back when', they told us that the majority of unburned hydrocarbon emissions (a primary component of smog) come from the crankcase breather, so I'd like to clean up my act at least a little.

 

[AltaKnight]

I don't think it matters to your blow-by issue, but those compression readings seem to be very high, I suspect that the head may have been shaved at some point to raise the CR.

 

[RJS]

Hi All,

Thanks for all the input. Interestingly, two of you have hit on possible issues causing my pressurization and oil leaks (rich carbs and shaved cylinder head - well done, I'm impressed!). Again, it never leaked a drop for 6 years and 5K miles...so what changed?

Well, here are three possibilities:
1. I discovered I was running an overly rich carb mixture for about 2500 miles which may have led to bore-wash and compromised the piston rings
2. About a year (~1000 miles) before my leaks started my mechanic (at the time) removed and "re-planed" my cylinder head. Unfortunately, I have no idea how much he took off and if this resulted in those really high compression readings I am getting (and perhaps extra blow-by).
3. I have systematically moved down in engine oil weight from 20W-50 to 15W-40 to 10W-40. I highly doubt this is the cause but, for the price of 6 quarts of oil, it's worth a try.

I spoke to the original engine builder and we're going to perform a leak down test but, he's off to the SCCA National Championship races Road America so we won't be able to do this for a few weeks. He agrees the results of the compression test look quite high. In the meantime, I will perform various crankcase pressure tests from the dipstick tube running various PCV valves, oil filler caps (vented vs. non-vented) and 10W-40 vs 20W-50 oil. I'll let you know my results. The goal is to get 8" Hg vacuum on an otherwise tight crankcase. Honestly, I'd be happy to get 0"-4".

The motor runs perfect in every other way. So, unless the leakdown test comes back at 20% or more, I am reluctant to dig into the motor (i.e. ring job) simply to remedy this oil leak issue. I am much more inclined to try and modify the existing Smith's pancake PCV unit to process the additional volume of blow-by (the original design appears to be very sensitive and easily upset). I welcome any/all suggestions to modify an existing PCV set-up. If that's unsuccessful, then I'd consider some form of alternative PCV arrangement (Art, I plan to study the link you sent).

Thoughts, comments? Otherwise, stay tuned, I'll get back to you as I learn more from these tests.

Thanks

Bob
PS: for the 20W-50 I plan on trying the Castrol Syntech 20W-50 for classic cars.