302 Breathing !

[Richard Ibrahim]

I'm having trouble breathing! When I first put my car on the road in 1999,I fitted a PCV(the right way round!)between the Holly 600 and the RH rocker cover, with an open filtered breather cap on the LH side. I always felt this was unsatisfactory - lumpy tickover/slight oil leakage from the cap.A couple of years back I changed over to an open breather to a catch tank on the RH cover.
Last weekend I did a high mileage trip and as I got home, I found that the engine stalled at hot tickover. I discovered that the end of the breather pipe was just below the fluid level in the catch tank(whoops - who's a dozy git then?). Interestingly, the accumulated fluid(about a third of a litre)in the tank was largely water, plus a little oil, but there is no sign of water in the oil system (condensation?).
However,even before this silly event, the breathing still appears poor as I still get slight oil blowout/leakage from the filter cap.
All ideas would be welcomed.

[John Lind]

Hi Richard

You are making a link between poor idle and crankcase ventilation problems. Are you sure these two events are related so directly?

Does it normally idle well when very hot?

You should be able to check if crancase ventilation is an issue by removing the filler cap. Doing that will just open everything up. If the idle does not change then I doubt if crankcase ventilation is the culprit.

In general terms it is a known issue that water builds up in engine oil when an engine is used for short trips only for a while. When you go for a long drive and the oil gets hot and stays hot for a while, all the water evaporates out. It could be that your catch tank may have proven this, although a water - oil system leak is possible. Do you use your car for shopping trips?? Seriously, if the car has done a lot of short runs this situation is possible, particularly if the English weather has been living up to its reputation [img]/ubbthreads/images/graemlins/grin.gif[/img]

Regards

John

[Richard Ibrahim]

Thanks John for your response. You're right in your assumption that the car had been used for a lot of short trips(particularly in the winter here).I've taken the car for a spin most weekends to get the papers and milk- Sunday papers just fit behind the seats!Your diagnosis appears spot-on, as the oil system shows no sign of water contamination.
The car will normally idle OK, both hot and cold(no choke fitted, of course)at quite low RPM (700), but has always seemed a bit lumpy until about 1500 revs.I've checked everything from ignition function/timing etc, compression check, cam lift,etc.- so perhaps it's just me being a bit fussy(but I'd still like to improve it!)
My comments on the engine breathing were more concerned with the slight oil seepage that I get from the filter breather cap - and just wondered what the optimum breather solution is.

[John Lind]

Richard

The optimum solution is usually whatever your happy with, but my car has its PCV connected. I think even if your not an environmentalist, a PCV does a good job and does not hurt performance too much. If you had a race car it would be different, but on the road its worth it IMHO. On my car I dont have a vented cap (they are illegal here) but a hose from the other rocker cover to the air filter. The result is more or less the same as what you had before but a bit more sealed.

One thing to remember, presuming I've got PCV action correct is that the PCV valve is (should be) closed at idle. If that's not the case then the PCV would leak air into the inlet under the carb and make the engine run lean at idle. Presuming your PCV was working correctly its closed at idle and crankcase pressure will try to build up from gas leaking past the piston rings. This will result in gas and oil mist coming out of your vented filler cap until the PCV is opened when you open the throttle. I don't know if that is what is causing the oil around your filler but it is possible.

I haven't had much to do with carbies lately (EFI is good), but I remember that they don't like getting too hot. You sometimes get vapour locks in fuel lines and strange events when the fuel in the float bowl overheats. This is a guess, but I've seen engines with plates under the carb which protect the carb from engine heat. I would try to monitor the fuel line and float bowl temps and see if there is a link between the idle and the temperatures. I could easily be wrong here however.

Good Luck.

Regards

John

[Richard Ibrahim]

John,
Thanks for the input.
I've just been on a US Ford Motorsport site :http://www.americanspeedcenter.net/fordMS.asp.(a good site with a tempting new GT40 h.p.engine for minimal money).In place of the open breather cap,I think I'll have a go, at fitting one of their sealed caps that has a stub intended for a PCV connection -but lead the pipe straight to the catch tank.At least I'll know it can't be wrong - and it should cure the oil seepage.
Now, I must get back to finding the loot to build a matching 917!
Regards,
Richard