• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR4/4A Crankcase Breathing

Share this page

T

TR Tom

Member
Country flag
Offline
I have a late production TR4, long tube intake manifold with Stromberg carbs. (I’ve actually had two identical ones, the first in the 70’s, and my current one I’ve had since the 80’s). Something that always bugged me about both was the crankcase venting system. The late 4’s had the early version of a closed system, with the road draft tube plugged, a non vented screw on filler cap and a hose run from the valve cover, through a flame-trap/Y to the air cleaners. There is no breather regulator valve as fitted to the 4A’s.

While there are lots of reasons I’m sure for my many oil leaks, this particular system doesn’t appear to be very efficient at relieving crankcase pressure and can’t be helping the situation. Most closed systems on cars of this era use engine vacuum to suck out the fumes, then have a source of clean makeup air.

I’m thinking a good upgrade might be to leave the tube from the valve cover to air cleaners and then install a modified road draft tube ala Kas in his original Competition Prep Manual. I would then add some kind of air cleaner to the top of the tube. I have also already added a screw on cap with the small vent on top that I found at a swap meet. I think it’s a GT6 item and don’t really think it does much good

So I have two questions,

Does this sound like a good plan, or am I just wasting my time.

The other thing I always wondered was how the Kas modified vent tube stayed put. It’s a friction fit into the block, but the tab for bolting the original part to the block to keep it secure gets cut off in the modification.

Would be very interested to hear what all you out there think, and am very much open to other ideas.

Thanks
Tom
 
The factory never seemed to get PVC valves or use them. It would be a good reto IMHO.
Your intake may have a bung where the fitting should have gone.Worth a try.
Mad dog
 
Waste of time, IMO. The purpose of PCV was emissions. Period. For the amount of effort you are considering, you’ll end up with a hybrid that is non emission compliant. If you are not at all worried about emissions, just go back to the road draft system…less work!
 
As long as the rings are not letting a bunch of pressure build in the crankcase, a PCV valve can work.
I never saw the OE system on a 4a work well , so the factory guys were guessing.
If the intake vacuum is properly restricted for the PCV valve to evac the volume of gasses generated
IMHO it could be a good way to go.
Mad dog
 
Sounds to me, go backwards and set it up like a tr3. I remember when the positive crankcase ventilation came into my world in auto shop in the sixties at high school. We had to check the PCV to make sure the air only went one way so the gases would not go backwards.

Like MD suggest I believe in 1966 or so they were in some kind of planning stage, and who knows what they did with some of the venting hardware. I would go back to the open crack case system like John suggested because it is simpler and works fine.
steve
 
Thanks all for the replies.

While I have always strongly believed in the philosophy of simpler is better, I’ve never been a big fan of open breather systems. Aside from the fact they always seem to drip (the original reason Kas developed his modified vent) I am the kind of guy who can never resist a dirt road, so I like the fact that a closed system of some kind keeps as much dusty air out of the crankcase as possible.

I’m not opposed to a PCV type system as the ones on my other mid 60’s American cars are simple and effective. Unfortunately the later 4A style is neither. My late 4 intake also doesn’t have any tapped ports, so devising some other type of system would be a pain.

I keep coming back then to a modified draft tube system that in theory would solve any inherent problems. In addition to the mounting issue mentioned earlier, I’m also curious about adequate fresh air intake at the valve cover. Cars originally equipped with draft tubes had the large vented fill cap, while mine has the sealed cap and a very small vent on the side of the cover. Will this be adequate?

FWIW, even here in the People’s Republic of California, emissions laws don’t apply to a car this old, so that’s not an issue. My main concerns are reliving internal pressure efficiently and keeping the inside of the crankcase clean.

Thanks,
Tom
 
Last edited:
Back
Top