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TR4/4A Crankcase vacuum-TR4A

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DanB

Jedi Warrior
Offline
The rear main scrolling seal on my 4A has been leaking since the EFI upgrade. I am pretty sure it is because of the amount of vacuum the new PCV valve is allowing (not enough). Does anybody know how much vacuum it takes to keep the oil inside the engine?

Thanks!

Dan Blackwood
South Charleston, WV
66 TR4AIRS EFI
80 TR7 DHC
 
I can't answer your question about vacuum, but the rear main seals on these engines are notorious for leaking. Have you converted to the upgraded seal yet?
 
No, Ian, I still have the original aluminum scrolling seal in it. Did you put a new seal in yours?
I assume you have to get the screw turned off the crank?

I am hoping I am not going to have to pull the engine. I will put up with a little leak for a while.
 
I still have the old seal style, but have the upgraded seal sitting on the shelf. Since the upgraded seal requires machining the crankshaft, I haven't done it either.

I don't remember if I replaced the old-style seal or not. I had the engine and transmission seperated about 10 years ago. If you can replace the seal without removing the crankshaft, then I replaced it about 10 years ago. If the crankshaft has to come out, then I didn't replace it.

I am really too young to have such a poor memory.
 
I know what you mean about...

what was it we were talking about?



They tell me memory is the second thing to go..

what was the first thing again?
 
DanB said:
The rear main scrolling seal on my 4A has been leaking since the EFI upgrade. I am pretty sure it is because of the amount of vacuum the new PCV valve is allowing (not enough). Does anybody know how much vacuum it takes to keep the oil inside the engine?
Click to expand...

The PCV valve probably won't be able to keep the crank case under vacuum. It's mostly used to normalize the pressure within the crank case. Exhaust gas that escapes by the piston rings ends up in the case, which presurizes it, which pushes up on the valve, which then vents (or is sucked) back into the intake. Once the pressure normalizes, then the valve closes.

The original engine vented exhaust through a breather tube. While the car is moving, a small amount of vacuum is generated by the venturi effect upon this tube, thus creating a small amount of vacuum within the case. That probably does help keep some of the oil in...

I decided to use the one piece seal and get the crank turned. It cost $30 for the turning and $100 for the polishing (two different people were involved).
 
rlandrum said:
...The original engine vented exhaust through a breather tube...
Click to expand...

And the TR4s vented using a tube (w/o a PCV valve) between the valve cover and carbs.

The little tube on the TR4 possibly didn't do much to relieve crankcase pressure but the road draft tube was effective and can be retrofitted (depending on how you feel about such things).
 
So, if the american PCV valve orifice is too small, I could be building up a little pressure, thereby causing the oil to push out of the rear seal past the scrolls. By removing the PVC all togther, and using tube, I can test to see if that is the case.

Thanks guys!
 
I know this info won't help this particular situation, but there is nothing wrong with the original scroll type "seal" <span style="font-size: 12pt">if it is set up properly.</span> Two problems exist. The first is that the seal setting tool offered by Moss (and maybe others) is made larger then the dimensions given in Factory Workshop Manual. The second is that the dimensions given in the manual are also too large.

My TR3 leaked virtually no oil from that seal before I started the restoration. I measured the dimension BEFORE I took the aluminium pieces off and the dimension was smaller then what the factory manual said. It also jived with the dimensions <span style="font-weight: bold">Randall</span> has given on several occasions. I made a tool to that dimension and after getting the engine fired up after the resto, I have virtually <span style="font-weight: bold">no oil leaks </span>from that seal...at least none that have dripped on my garage floor after about three hours running. And that's without any forward motion on the road draft tube to provide vacuum to the crankcase.

If anyone wants the exact dimension, I can dig it out.
 
Just in case you're wondering, as this discussion is apple and oranges: Up until the TR4A model, the TR3-TR4 motor used an open system as Rob described, Starting with the TR4A did not have the road draft tube (the block has a 1" freeze-style plug in its place) and also did not have an open valve cover breather. Instead it used a closed oil fill cap and diaphram style PCV valve that gets manifold vacuum off the intake.

But to answer Dan's question, I have no idea not even a wag. But I am interested in your EFI on the TR4A.
 
martx-5 said:
I know this info won't help this particular situation, but there is nothing wrong with the original scroll type "seal" <span style="font-size: 12pt">if it is set up properly.</span>
Click to expand...
:iagree:
However, it still won't tolerate much in the way of positive pressure. The TR3 crankcase vent system ensures there is never positive pressure on the seal, while the later systems almost guarantee that there is sometimes positive pressure on the seal.

When doing a PCV setup, it is important to remember that when blowby is greatest, there is NO MANIFOLD VACUUM. You must provide an alternate means for the blowby gases to escape, so they cannot pressurize the crankcase and blow oil out the rear seal. On American engines, this is normally done by using a fairly large diameter tube and filter, that is normally an intake to the crankcase. But at wide-open throttle, when flow essentially stops through the PCV valve, any blowby gases can flow backwards through the intake tube and out the filter (which is normally arranged so the gases coming out are sucked back into the engine intake).
 
PeterK said:
Just in case you're wondering, as this dicussion is apple and oranges: Up until the TR4A model, the TR3-TR4 motor used an open system as Rob described, Starting with the TR4A did not have the road draft tube (the block has a 1" freeze-style plug in its place) and also did not have an open valve cover breather. Instead it used a closed oil fill cap and diaphram style PCV valve that gets manifold vacuum off the intake.

But to answer Dan's question, I have no idea not even a wag. But I am interested in your EFI on the TR4A.
Click to expand...

Yeah... I always forget that the TR4s and the TR4As are quite different, and that I have a TR4 engine...
 
PeterK said:
Just in case you're wondering, as this dicussion is apple and oranges: Up until the TR4A model, the TR3-TR4 motor used an open system as Rob described, Starting with the TR4A did not have the road draft tube (the block has a 1" freeze-style plug in its place) and also did not have an open valve cover breather. Instead it used a closed oil fill cap and diaphram style PCV valve that gets manifold vacuum off the intake.
Click to expand...
There was also an "interim" version on later TR4, as seen in this page from the Moss online catalog.
 
As far as the EFI goes,
There are a couple of pictures on this thread: British V8 https://forum.britishv8.org/read.php?3,4507,5980

I found a manifold for some unknown GM engine on ebay and the outer runners matched perfectly to the TR4A head, so I bought it for 50 bucks, brand new, with injectors and all. We modified the center two runners and welded on the mounting flanges from an old intake. We also removed various things we didn't need and welded those holes up. I got an efi fuel pump from a Ford F150 and mounted it inside the rear wheel well. We had to run new fuel lines to create a return loop, and a bell crank setup was fabricated to hook to the throttle linkage.
All this is controlled by the Megasquirt controller, through the Megatune software on a laptop. I am still working on the fine tuning. When I am done, it will all be saved on the computer as well as burned into the controller.
I am also using an optical pickup on the distributor from the Crane cams/Allison ignition. It is now powered and controlled through the MS controller.
Now, back to the topic...
 
Andrew Mace said:
...was also an "interim" version on later TR4, as seen in this page from the Moss online catalog...
Click to expand...

Yes, that tube/flametrap/hoses is what my '64 has and it seemed to do a poor job of relieving the crankcase pressure. Also sucked a messy amount of oil into the carbs.

I fitted a breather tube as used on the TR3s and early 4s and vastly reduced the amount of oil that was oozing from every pore.
 
Yup, the port on the side of the rocker cover was much too small IMO for an engine with even slightly tired rings.
 
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