Engine Breathing

[v8bloke]

Hello Guys
I have a slight problem that I would like to resolve and would be grateful for some advice.
My car is an MGB GT V8 with a 4.6 motor, fitted with Merlin heads and a few other go faster goodies.
Car is making 277bhp at wheels. It is used on the road but mainly at Trackdays so is driven very hard and with the chosen camshaft likes to rev to over 6000rpm although max bhp is around 5850rpm.
The problem I have is that at high rpm oil is ejected out of the breather system into the catch tank.
I am using an open  breather setup with a pipe from each rocker cover via Moroso seperator/breathers to a catch tank which has a single outlet fitted with a filter. When on track and using max rpm the catch tank slowly fills with oil that is grey in colour at a rate of about 1/2 pint every 20mins or so.
I have only had this problem since fitting Yella Terra roller rockers. In an effort to cure this I have fitted 1.5mm restrictors to the oil supply holes to the rockershaft which helped a bit.
Using 20w/50 oil.
When driven normally and up to about 5500rpm the catch tank stays empty.
What can I try?

Thanks

Mark

[perrymgbv8]

Have you tried letting the oil in the tank settle for a day to see if it is still grey ?

sounds like it may be air in the oil or moisture?

[v8bloke]

Hello Perry

It stays grey. Oil in the sump is perfect. This is a long standing problem that I have had.

Mark

[perrymgbv8]

That sounds odd Mark??

But if the oil in the sump looks fine it could still be moisture or air I think.? Perhaps the air or water is sufficiently entrained to stop it precipitating out at ambient temperature??

I dont use a catch tank on my 4.6. I have a big open breather on each rocker cover to atmosphere. Both of these steam like chimney's while the motor is cold. and I see a little vapour at idle when the engine is hot.

[v8bloke]

 -- moved topic --

[roverman]

Mark, we could all stop guessing, if you had a sample of that "muddy" oil tested in a lab. Maybe $20. to see what's really going on . Diesel trucks use this service a lot. Had a leakdown or blowby gage, on this engine ? Might be revealing. Good Luck, roverman.

[tr8todd]

I just got done battling the same over oiling roller rocker problem.  2 engines, same problem, 2 different solutions.  For the more sedate street engine, I went with the same .055 oil restrictor under the rocker stantions.  For the more aggressive engine, we blocked off the oiling holes from the head all together and used hollow Chevy pushrods to oil up thru the pushrods.  Haven't run the second engine yet, so I don't know how well this will work.  Conversations with some other people that have come across this issue, leed me to believe that the best solution is to restrict the oil flow and to also install a vacuum pump on the engine.

[BlownMGB-V8]

I'm not sure that a .060" orifice is enough of a restriction. A roller bearing needs nowhere near as much oil as a plain bearing of the same size, but more importantly the plain bearing itself acts as a restriction, where the roller bearing does not.

Proper manufacture of the roller setup would have accounted for this difference by reducing the size of the oil feed holes at each rocker bearing. This is much preferred to restricting the supply to the hollow shaft as it insures even oil distribution, where a single restriction would tend to starve the front of the shaft and over-oil the rear. Testing with the oil being used at the expected pressure and temperature would indicate adequate hole size, possibly something in the range of about .010" would give enough flow. It doesn't take much to lubricate the roller bearings and just a little getting to the pushrods and valve tips would be adequate. It means new rocker shafts but your roller rocker manufacturer really should be the one to fix this.

Undoubtedly the gray color of the collected oil is due to water and combustion byproducts. Put it in the oven for an hour or two and it'll probably go back to normal. All of the volatile elements collect in the rocker covers on start-up and are eventually boiled off... unless you collect them. Might try running the inlet to the bottom of the catch can.

JB

[v8bloke]

Thanks for the advice guys.
The Yella Terra's use a bronze type bush on the shaft but they have a small oil outlet on the top of the rocker presumably to flick oil to the roller tip. I might try a smaller reducer in the oilway. Yella Terra are pretty poor at answering emails.
 Mark

[DiDueColpi]

Hey Mark,

If you have bushed rockers is there a chance that the shafts are in upside down with the oil holes pointing up?
Be carefull with restrictors and bushed rockers. It's easy to starve them.
I think that we all assumed that these were full rollers.
Jim's theory on the condensate in the oil makes sense.
Otherwise anything that colour would have you picking your engine out of your tires by now.
It's a little concerning that you have that much though.
Are you running a thermostat or a restrictor? Over cooling could cause large accumulations of moisture in the valve covers.
On an aluminum engine its very common for the valve covers to run cold enough to cause a problem.
Insulating them might help the grey matter.

Hope that helps

Cheers
Fred

[v8bloke]

Fred
Rockershafts are deffinateley the right way up.
 Did a trackday yesterday at my local circuit (Castle Combe) and the catch tank stayed empty all day apart from a very small amount of water!
I would think that the grey colour is condensate.
Because of the improved handling I can take some corners in a higher gear than before so this must help by reducing long periods of high rpm.
And yes a thermostat is fitted and engine runs at normal temp.
Thanks
mark

[roverman]

Perhaps a non-waterbased coolant ? Non or low hygroscopic ? roverman.