• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

TR4/4A pcv valve plus breather tube?

Share this page

KVH

KVH

Obi Wan
Silver
Country flag
Offline
The prior owner added a breather tube on the drivers side of the engine--of course. Can I put the pcv valve back on, too? I ask because it doesn't seem right for that hot air to be piling into the carbs all the time. Would it hurt to have both a pcv valve and a breather tube? No big deal?
 
I would expect you would be pulling too much air through the PCV valve with the breather tube in place. Do you have a 4 or 4A? It may not matter if your PCV is going into the air filters, but if it goes into the intake manifold you may have problems getting the right mixture.
 
Also seems like a bad idea to be pulling air up from the road into the engine. Especially in a dusty area like Az. That dust is seriously abrasive.
 
Are you saying I should put a plug into that breather tube hole? Once I do that--it will sort of be permanent. And I should ask: Will I be able to tap that in without a giant hassle--the fuel pump is apparently in the way. And I don't see much tapping room. The body of the car is 3 inches away. Just wondering.
 
Last edited:
KVH said:
Are you saying I should put a plug into that breather tube hole? Once I do that--it will sort of be permanent. And I should ask: Will I be able to tap that in without a giant hassle--the fuel pump is apparently in the way. And I don't see much tapping room. The body of the car is 3 inches away. Just wondering.
Click to expand...

You should either remove the draft tube and plug the hole, or remove the PCV system (there are little air filters you can put over the tube on the valve cover).

Yes, it is going to be difficult to put a freeze plug with the engine in the car, at least with the standard metal core plugs. You could try something like this:
 

Attachments

  • plug.jpg
    plug.jpg
    122.5 KB · Views: 168
I don't know if many TR4a have had the PCV valves removed and replaced with a road draft tube from an earlier model, but I did it to a 66 brg 4a that I owned in the 70s. Maybe you have my old car.
Berry
 
My '63 TR4 had a road draft tube but was spilling oil out onto the frame and the road. So I installed an electric fuel pump, removed the road draft tube and carefully tapped in a plug, obtained a fuel pump blanking plate and drilled it to accept a hose end, routed a hose to an oil catch can, routed a hose from the catch can to the air cleaners, obtained a TR4A valve cover and vented its tube through a small filter. The car now does not leak oil because the crankcase pressure is being relieved.DSCF8163.jpg
 
My first TR4A had the PCV removed and a TR4 valve cover and oil fill cap installed so I completed the process and installed the road draft tube (and replaced the intake manifold with a late TR4 one without the tap for the PCV just for looks).

Do you have a picture of what you have in the area of the valve cover and carbs?

Scott
 
KVH said:
How did you do that? I have a concave plug from Moss. Haven't tried fitting it yet. Did you have to raise the engine?
Click to expand...

The plug from Moss was slightly too large, so I used a grinding wheel to carefully and slowly reduce the plug. I raised the car and lay under it then used a small hammer - it's actually a tack hammer - to tap, tap, tap it into place. I put a thin coat of old style aviation Permatex on the plug before tapping it in.
 
HerronScott said:
My first TR4A had the PCV removed and a TR4 valve cover and oil fill cap installed so I completed the process and installed the road draft tube (and replaced the intake manifold with a late TR4 one without the tap for the PCV just for looks).

Do you have a picture of what you have in the area of the valve cover and carbs?

Scott
Click to expand...

Yes, there's a picture in a previous post in this thread.
 
My TR4 was oozing oil from various spots -- a condition I relieved by adding the road draft tube. I left the valve cover to carb connection in place (no valve) but that is a pretty small orifice (which is part of the reason why the ventilation was inadequate).

The 'plug' that was used when the road draft tube was eliminated is a little cup style - not the concave type 'freeze plug' that you hammer in. Depending on the fit of replacements, it may go in fairly easily -- I know the factory one came out without much trouble.
 
That's what I was hoping about that "cup" style plug. I may tap it in, but, then again, maybe I should try adding the PCV valve, leave the draft tube in, and see if that improves performance. I know I'm probably grasping at some faint hope here, but I'm trying to get the engine to run more smoothly, quit the pre-ignition, and stop all the unpredictable swings of idle speed as it gets hot, hotter and cooler. I'm thinking Randall may have had a point that my distributor bearing might be wearing out, allowing too much play. I'm yet not ready to worry about valve lash and other exotics.
 
The PCV valve is, in effect, a variable vacuum leak. At best, it doesn't make the engine run any worse; but it sure isn't going to help it run better.

Distributor bearings are easy to check: Hook up a timing light then watch what the timing mark does as you gently rev the engine up a bit and back down. If the bearings are shot, you'll see the mark jumping all over the place as the shaft wobbles back and forth.

Not sure why valve lash is "exotic" ... checking it is a standard part of every tune-up. A few thousandths won't make a lot of difference, but much more than that will. When I was having trouble with valve seat recession (which causes the lash to close up over time), rough idle was the first indication that it needed attention.
 
On my 4A I added the road draft tube, plugged the intake manifold and added this K&N filter. It's 1/2" rubber nipple slips over the valve cover vent.


engine_zps949c0491.jpg
 
Richard, what's the purpose of the filter on the Valve Cover vent ?
 
4A's valve cover cap isn't vented like a 4's. I was trying to follow Geo's plan to relieve pressure but it still tinkles everywhere it goes. Excited I guess.

bty had the Lightning out yesterday. No leaks!
 
sail said:
4A's valve cover cap isn't vented like a 4's. I was trying to follow Geo's plan to relieve pressure but it still tinkles everywhere it goes. Excited I guess.

bty had the Lightning out yesterday. No leaks!
Click to expand...

That filter should server a similar function to the wire mesh in the oil filler cap on a TR4 right?

Scott
 
Back
Top