The V8 Owners Forum -

Hey Guys,

Go easy on me as I'm a total engine biff so please keep any responses simple and technical free! I have a P6 engine in my Stag running a Holley 390, 360 low profile manifold, electronic pump and low profile filter. The non-P6 rocker covers vent via silicone hoses into the base of the filter (no flame trap or gauze fitted).



I've recently got the car all sorted and have started driving it a tad more aggresively at higher revs. I recently noticed a little oil in the V, assuming it was the rear rope seal, I then noticed a spray of oil (clearly high pressure) on the bonnet. This spray seems to line up with that I think is a crankcase breather (poor photos attached). Oil pressure is fine, running Halfords Classic.




Why is this happening - Is it my venting sent up wrong?
How do I stop it? Can I fit a catch tank (the nozzle appears to be 8mm)?
Should I have a flame trap fitted? If so what do people suggest?

Thanks!

Flame traps ( ore more to the point, oil/air separators ) would be wise.

If that pipe you photo is a breather you could either direct it to the air filter area too, via suitable oil/air separator...or if it's only 8mm, just plug it up and let teh rocker covers do the breathing

stevieturbo wrote:Flame traps ( ore more to the point, oil/air separators ) would be wise.

If that pipe you photo is a breather you could either direct it to the air filter area too, via suitable oil/air separator...or if it's only 8mm, just plug it up and let teh rocker covers do the breathing

Stevie,

Thanks. I'm going to make certain the oil is coming from that pipe by connecting a small length of silicone hose and giving the car a good blast round the block. If the inside of the hose is oily then clearly it's the source of the leak.

I'm pretty clueless, so is an oil/air seperator the same thing as a catch tank? So, are you saying that I need to plumb both rocker box covers and potentially this crank case breather into it, and then plumb the a single feed into the air-filter?

That is a breather pipe, and on the standard set up which used it (P5B/P6B) it would run from there, through a (petrol) filter, and into the airfilter housing.

harvey wrote:

That is a breather pipe, and on the standard set up which used it (P5B/P6B) it would run from there, through a (petrol) filter, and into the airfilter housing.

Thanks Harvey. Is it normal for it to be squirting out small amounts of oil at high-revs? I'll check to make sure that the other breather hoses aren't blocked.

So looks like I'm going to arrange the breather pipes into some complex-t-piece arrangement into a single hose to a catch-tank, then another hose to the air-filter. Can anyone recommend a cheap catch-tank (£20 ones on Ebay?)? I assume it's best to minimise hose-length to prevent condensation in the hose?

ziptie_engineer wrote: Is it normal for it to be squirting out small amounts of oil at high-revs? I'll check to make sure that the other breather hoses aren't blocked.

All I would say in answer to that is that when that particular system (including the rocker cover pipes, hoses and flame traps) gets blocked, the air cleaner housing can fill with oil, and when it's all nice and clear, it doesn't.

With the breather system you have that pipe is not required. Block it off and clean the area to make sure its not seeping oil from where it enters the valley area through the block as they can seep oil form that joint.

I just spent an hour doing a big explanation about this thing and the forum logged me off so I lost it.

So I will briefley say that with the open breather system you have into the air filter.... If that pipe is still spitting vapours hard enough to spray oil out that your engine is breathing heavily possibly due to wear of the rings / pistons / bores? OR that your pipes from the rocker covers are choked or too small.

Having said that!! The breather pipes from the rocker covers MUST run uphill from the rocker covers into the air filter and prefereably have some metal gauze filters / flame traps fitted. Other wise oil vapours will condense in the pipes and form a blockage at the Tee piece. What you have fitted is basically a large oil trap at that Tee piece. The idea is for oil to be allowed to naturally drain back down those pipes into the rocker covers. Even with vapours travelling at X veloctiy up those pipes into the air filter, oil droplets will seep backwards to drain back into the rocker covers as soon as they become too heavy for the escaping vapour velocity to hold them in the pipes. So if you have oil logged the Tee piece this could be creating a restriction that is holding blow by gasses back and forcing them to exit via the old valley breather and spit oil vapour out which will gather on and surface it meets to form droplets.
We are talking fractions of a PSI for this to happen !!

One way to resolve this issue is to do what I did back in the day. Fit elbows to the rocker breather pipes. Fit the Tee into the air filter pan as close as possible making sure that you go up to the 3/4" connection into the air filer with a 3/4" tee. Fit 3/4" pipes which run downhill to the 1/2" connections in the rocker covers and make them fit with what ever fittings you need to use. The larger bore 3/4" lines from the 1/2" rocker coneections will reduce vapour velocity and reduce the risk of oil making it up into the air filter.

You may have a perfectly good working engine that is suffering form an incorrectly installed rocker breather system. Or an old smoker that is blowing so much chuff past the pistons that all or your breather pipes cant cope.?

If you want to do some sort of test with the system as it it then clean all that crap up and then remove the pipes from each rocker cover and route these pipes into a catch can or bottle of some sort instead of the air fiulter so you can catch whatever comes out.

Right update:

I pulled apart the breather hose and found a plug of black plastic-ee-gunk (looks and feels like instant gasket) at the top of the t-piece, so you were both spot on!

Perry; thanks for such a detailed post; how detailed was the one you lost! I've tinkered this morning and tried to implement a temporary fix. I've cut down the inlet to the air-filter and cut down all of the breather hoses. The problem is that due to bonnet clearance issues (low profile filter and manifold) I doubt I can ever get the hoses to run straight down to the rocker covers (even with a complex arrangement of bend sections).



So, do I just upgrade to larger bore pipe to limit the effecting of a blockage and try to maximise the angle? Or would a catch tank setup help? Should I fit the old style in-line P5/P6 flame tramps as well?

ziptie_engineer wrote:Right update:

I pulled apart the breather hose and found a plug of black plastic-ee-gunk (looks and feels like instant gasket) at the top of the t-piece, so you were both spot on!

Perry; thanks for such a detailed post; how detailed was the one you lost! I've tinkered this morning and tried to implement a temporary fix. I've cut down the inlet to the air-filter and cut down all of the breather hoses. The problem is that due to bonnet clearance issues (low profile filter and manifold) I doubt I can ever get the hoses to run straight down to the rocker covers (even with a complex arrangement of bend sections).



So, do I just upgrade to larger bore pipe to limit the effecting of a blockage and try to maximise the angle? Or would a catch tank setup help? Should I fit the old style in-line P5/P6 flame tramps as well?

If you cant get the hoses into the right orientation Zip! Then run both of them into a catch tank / breather tank so any oil droplets can settle in the tank while still allowing the gasses to pass freely to the air filter. If you can find somewhere to fit a tank then it does not matter if the hoses from the rocker loop like they do now. Any oil that condenses in the hoses will either drop back to the rockers or run down into the tank to collect there. And if the two rocker hoses breath into the top of the tank and the tank has a 3rd outlet at the top so gasses can flow into the air filter you should be good to go mate

In one of my previous engines I actually drilled the rocker covers and fitted hose connections on the side of the rocker covers that faced into the valley area so they would be below the Tee on the air filter. This worked a treat to be honest as the hoses then ran uphill to the tee piece I may have a pic to show if I can find it. ? I drilled each rocker cover and tapped each hole 1/2" bsp then screwed and glued a couple of 1/2" bsp hose tails into each rocker cover. The hose connectors were roughly in line with cylinders 1 and 2.
These side connections into the rocker covers can be wherever you cna squeeze them in to be honset. As long as they run uphill to the Tee connection they will work. And possibly be a lot cheaper than plumbing in a catch tank.


Perry

Question here

Would it not be another route to solve this by

Putting those small air filters on the rocker covers and routing that rear pipe to the bottom of air filter

It would sort of reverse the air flow currently happening bit do the same thing?

Ian

Ian Anderson wrote:Question here

Would it not be another route to solve this by

Putting those small air filters on the rocker covers and routing that rear pipe to the bottom of air filter

It would sort of reverse the air flow currently happening bit do the same thing?

Ian

That is a common mod Ian. But the small K&N filters on the rocker covers do tend to get oil logged and then become blocked as such. If the rear valley breather pipe is not leaking from where it enters the block it can indeed be routed to the main air filter. But the small outlet pipe is not really worth bothering with on any engine which breathes a little heavy. I converted my rocker cover oil filler pipe to a large breather which was much better than the K&N option.

Cheers Guys.

Perry- I like the concept of drilling the sides of the rockers. So.... I drill/tap/glue some 1/2" hose tails into the side of the rockers. Then run them up to a 1/2" t-piece fitted as close as possible to filter. Cheap, sounds effective, and less buggering-about trying to make space for a catch-tank!

Only questions are:

1) One of the REME Artificers (geeks) at work warned me against this solution He said that the rocker cover could easily crack (as it's cast aluminium) and that those outlet needs to be in the top as that's where the maximum pressure is...... Sounds like rubbish to me. Plenty of engines have their breathers in the side, pressure is relatively uniform and surely the suction provided by the air filter makes it irrelevant?

2) Is it also worth fitting small air filters to the original outlet holes on the rocker? They are pretty inexpensive, will look better than just plugs and surely the more breathing the better?

3) Surely, for almost nil-cost, it wouldn’t hurt to stick an inline T-piece with a 8mm convertor to also feed the small breather into the hopefully newly upsloping 1/2” pipe?

Thanks for all your support guys; super-useful.

Sorry being stupid, meant 3/4" not 1/2".

Just another thought, with this solution is there a danger of sucking oil into air-filter/carb?

I would certainly use the existing outlets
Quite often there are splash protectors inside to stop sucking oil out the rocker cover

It will also save the possibility of wrecking the rocker covers
Ian