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Why is my new engine (a "lively" 1300) pushing out a pint of oil after, say, 30 minutes of spirited driving? An unrestricted and generously sized breather pipe runs from flywheel bell housing to the rocker cover which, in turn, has another similarly generously sized pipe leading to a catch tank (manadatory for some track days)

check the rocker cover isnt filling with oil and overflowing, if the timing chain end cam bearing is fitted wrong it wont limit oil flow to the rockers and they get a constant flow rather than a pulsed flow.

OK thanks

Excess clearance on the rocker bushes or blocked drain holes to sump. Most likely the former.

I had the same problem with mine which was caused by the breather design of the rocker cover. I'll post a pic at some stage.
Posting a pic of your engine bay might help

ivor badger wrote: or blocked drain holes to sump.

What all eight of 'em.........

Smiffy wrote:

ivor badger wrote: or blocked drain holes to sump.

What all eight of 'em.........

The less likely cause, but there is not 8 drain holes out the tappet chest is there?

".....but there is not 8 drain holes out the tappet chest is there..."

Uuumm how do you think the push rods get from the crank case to the top of the head

And why would you run a breather hose from one end of the crank case (flywheel bell housing?? - actually I think you mean the drop/transfer gear case) to the other end of the same volume (tappet case)??? Run all hoses to the catch tank - and use an oil separator at each outlet.

New engine??? The wrong running-in procedure (too gentle) can cause glazed bores and hence excessive blowby. BTDT

Cheers, Ian

1071 S wrote:".....but there is not 8 drain holes out the tappet chest is there..."

Uuumm how do you think the push rods get from the crank case to the top of the head

And why would you run a breather hose from one end of the crank case (flywheel bell housing?? - actually I think you mean the drop/transfer gear case) to the other end of the same volume (tappet case)??? Run all hoses to the catch tank - and use an oil separator at each outlet.

New engine??? The wrong running-in procedure (too gentle) can cause glazed bores and hence excessive blowby. BTDT

Cheers, Ian

there are obviously 8 pushrod holes out the head. By the same logic, these holes do not run into the crankcase, because there are 8 tappets directly underneath them. So the oil runs out other holes provided in the bottom of the tappet chest. There is the possiblity of pieces of old gasket getting in the tappet chest and not cleaned out, especially if using a 1300 block.

as for breathers, I did the 3 hoses to the catch tank bit. One from the end cover and 2 from the rocker cover. That matched the tubes as supplied with the engine. I was then in the supplier fitting the engine in the car and got asked what i was doing. It was then pointed out that the idea was a hose from the end cover to the rocker and the a hose from the rocker to the catch tank. Worked perfectly.

now the original problem appears after 1/2 hours running. So it is a gradual build up of oil to the breather system and the most likely cause is too much oil for the drain system to the carankcase to handle. Which equals too much oil flow from the rockers or blocked drain to crankcase.

You are right - I hadn't thought enough about how the followers work. So I thought I'd go and look at a block in the shed. Unfortunately I could only find one (a 1275) without a 'box but it still had the crank and cam installed - which made the view of the relevant area somewhat restricted...

Now oil from the rocker case must drain down the pushrod holes - there aint any other way.

From what I could see there are two drain holes leading into the crank case (well there are 10 but 8 are filled with cam followers). Each of the drain hole is about 1/2" diameter (much the same as the holes that carry the cam followers). One is above the dizzie drive and the other above the fuel pump cam lobe. It can only be that the push rod holes must be connected by a gallery to the two drain holes into the crank case.

As these "drain" holes are the only exit for crank case fumes into the rocker case I would assume that excessive blowby may impede the return flow of oil. One could check by removing the oil filler cap with teh engine idling. Excess crank case pressure will be obvious...

I still can't see sense in connecting one part of the crankcase to another. In Oz, where a transfer case breather is fitted, fume pass into an oil separator and then through a PCV valve into the inlet tract. Its pretty common the retrofit such a vent but connect it to a catch tank adn then atmosphere...

From personal experience I can confirm that excess crank case pressure will carry with it a lot of oil - a litre in 20 km in fact!!

However, cure (the primary) problem and you solve the other.

Cheers, Ian