TR4/4A Oil Mist on Bonnet Underside

[bammons]

I wonder if I could get some advice about the oil misting that I get on the underside of my bonnet (hood). The PO had removed the PCV assembly and installed the earlier TR4 road tube. So I know that I have to have the rocker cover vented and it is (see picture) via a small filter element installed on the tube where the PCV hose would be. My oil fill cap is not vented at all (the TR4 of course was) but it seems that what I have done should allow plenty of venting. My vent filter is stained blackish so I think this is where the mist is coming from but I might be getting a spray from the timing cover as it may be leaking a little (this does not seem likely). I do get a some dripping from the road tube that would be nice to correct. Does that mean somehow I have too much pressure and if so how can I fix it? Bruce

 

[RichB4493]

Double check that leak around the timing belt cover. A leak there will get misted/spread by the fan and belt. I had a small hole in my dining belt cover from a broken tensioner. The fan spread that consistently on the engine and hood. Does your 4 also have the engine block vent by the fuel pump?

If you think it’s pushing out that valve cover filter, tie a paper towel or rag around it to see if it’s really coming through there.

Rich

 

[bobhustead]

It has to be coming from the former PCV hose port on the valve cover. The top of the head connects directly to the sump via the non-pressure oil galleries that let the top end lube return to the pan. You don't need the vent or filter. Just put a rubber blanking cover on it. As for the drip from the draft tube, I would ignore it. It could be something as unserious yet PITA to fix as excessive blow-by in one or more cylinders.
Bob

 

[CJD]

If you look at the earlier road draft tube cars, you will note that the oil fill cover is baffled and is only open at the front. There is method to this madness, in that the airflow from the fan creates a high pressure at the oil filler vent. The draft tube generates a slight depression...on the TR2/3. This was designed to vent the crankcase by taking air in the filler cover and venting it out the draft tube. There is no telling if the modified TR4 will have a depression at the draft tube or not.

So...what I see is that your vent is not in a high pressure area, so it will vent blowby, just like the road draft tube. In addition, the early filler cap would retain any vented blowby that overwhelmed the draft tube at full throttle, and allow it to be sucked back in the engine once blowby was reduced at partial throttle. Your vent is open 360 degrees and has no way of retaining any oil that blows out.

The PCV system was one emissions modification that was a win-win improvement to cars. It reduces emissions by burning them, and does not in any way hurt performance or economy. Even when I built 750+ horsepower cars, I still included a PCV system on them. I guess I am hinting that I would keep the PCV system if my car came with one.

 

[poolboy]

The problem is the 'filter' you stuck on the valve cover vent..It's creating back pressure, forcing the crankcase pressure to escape elsewhere.

 

[bammons]

OK I see the consensus is the added vent. I got the car this way (except the vent I added) as the TR4A would have had the PCV. (Interesting is the PO also went backwards with the carbs. He put on H6's and took off the Stromberg's. I have changed again to HS6's). So the solution is for me to cap/block the vent tube? For now as I have other work on the car a simple solution would be best but I might start thinking about putting the PCV back on. What I don't understand is if Triumph put a well vented oil fil cap on to relief pressure then surely it seems I need something up there as my vent cap is the TR4A unvented cap. But right now I will do as you guys say. As far as the timing belt cover I am taking the car to a mechanic soon to fix something and I will get him to look while on the lift to see if it needs attention. Thanks for the help that was fast and clear! Bruce

 

[poolboy]

This is how it was intended with ZS carbs and the stock air cleaners....you just need to find a way to get a little suction on the valve cover to relieve the crankcase pressure with your SU carbs....Maybe the 2nd picture will give you an idea...whatever you do don't plug or seal the nipple on the valve cover,,That'll be even worse than that 'filter' you put on it...and what were you wanting to filter ?

 

[bammons]

I am not trying to filter anything and I don't like the filter/vent I added. It was just put there to aid in relieving pressure in lieu of not having a vented cap as the road tube cars had. I recently added new air filters and they came with holes and plastic nipples to allow for the hoses to fit. i have them blocked off but I could do as Poolboy and simply run hoses to them as in your picture. I had forgotten that the TR4's actually had hoses but no PCV. So my TR4A intake manifold has been blocked off by the PO at the point the TR4A PCV attached. Assuming I can remove the bolt that is blocking it should I just make one connection at that point or at the air filters? In looking at the MOSS catalog there is a note saying the TR4A oil fil cap has a small hole but my cap does not seem to have that. Bruce

 

[poolboy]

If you have HS6 carbs are there evacuation port nipples on those carbs that were designed to connect to the valve cover vent just like the picture I posted...big brass nipples jutting up at a 45 degree angle ?

See the location of the "CRANKCASE VENT" about half way down in this link

https://mossmotors.com/media/instructions/370-847_848_849_INST.pdf

 

[CJD]

Whatever you do, ensure you have clean air entering the crankcase somehow, and old, blowby air leaving it. You cannot just have one opening, or your oil will contaminate with acidic blowby gases and hydrocarbons. So option 1 is correctly vented cap, remove the extra vent, and road draft tube. Option 2 is back to the factory PCV, which is the way I would go.

 

[charleyf]

Bruce, My story is that I took a TR4A block to use in my TR4. I removed the block in the hole for the draft tube and inserted a draft tube. Built the engine and put a regular TR4 valve cover on it. Of course with the fully vented filler cap. That was at least 20,000 miles ago.
My suggestion is that either you find a filler cap that is open/ vented. ( I recall some conversations about such caps a few years ago.) Or change the valve cover to the standard TR4 and then use the regular filler cap.
Charley

 

[Sarastro]

We have been all through this problem in the early Porsche community. Porsche 912 owners have often replaced their original Solex carbs with Webers, in the process losing the vent to the carbs. The original design was the same as in Ken/poolboy's first picture. Many people just replaced the vent with the same filter you are using, and found that, in a few weeks or months, the engine compartment had oil all over the place.

The simplest solution is probably to set things up as in Ken's picture. It should work and keep things clean. I see that you have the fittings for the latest version of the vent system, the one with the PCV valve. You could also do that.