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MG Midget and Sprite Technical - Tweaked 948 Advice: venting

Hi guys,

Background on the situation:
Ex race/rally car from 1970's that was done originally by some BMC garage guys up north and the engine tuned to practically formula junior spec.

Set up as stands:
948 +60 with flat top hepolite pistons
12g295 head, compression around 10.5-1
Camshaft: completely unmarked spider drive cam but appears to be around the profile of a 649 cam (300/300).
Carbs: Twin early HS2s with K&N cone air filters

Now the advice I need is how to go about setting up the venting on this engine. There is lots of discussions about 1275's, PCV set ups etc, but the 948 seems to originally have just vented via the tappet covers to atmosphere and via the rocker cover to the back of the air filters.

The tappet cover vent is in place still, although the metal end of the tube is partially crushed, looks almost deliberate to reangle the set up straight down...

The rocker cover vent is leaving me a bit mystified as what to do as can't easily run into the back of the air filters..

I have absolutely no experience with this kind of thing and could really do with a bit of a dummies guide discussion to help me understand what need to achieve with these early type engines.

Thanks in advance for anything!
D Paul

First try venting them both to atmosphere with just a hose on it through one of the holes in the splash panels.
If this leads to exesive oil leakage through the rear scroll the try some form of suction with a pvc valve to the manifold.

Remember that it will never and does not have to be bone dry at the rear main seal.

And trust me FJ spec is (nowadays) a little wilder ;)
Onno K

I run a 948 with same carbs and std KN filters. I run the rocker breather into the backplate of the forward KN filter.
The downpipe from the tappet chest cover may have been flattened to give clearance on the back of a LCB manifold as is mine.
Alan
Alan Anstead

unproven but I was told years back that the original style plastic, vented oil cap is better for engine breathing that the chrome caps with hole (was refering to standard engines at the time)

the original style plastic, vented oil cap are only £4 from MGOC Spares (but can be £10 from other suppliers)

the ones I got from MGOC Spares can be opened for filter cleaning too


Nigel Atkins

Thanks for the replys,

Good to know can just try venting them to atmosphere to start with....

Ah yes you are right, its got an LCB on it and without the 'kink' it wouldn't clear, close enough as it is!

Hehe, yes fully aware FJ spec these days is a fair bit heavier, just going on the specs in a 1st edition vizard and having spoken to a guy that co owned the garage with the guys that owned the car (unfortunately now passed on).

As long as the oil consumption is less than the 3000miles limped a 1098 mini back from Hungary with totaled piston rings (1L oil per 500miles or so...) I'll be happy :P
D Paul

The 'easy clean gauze' was an unwelcome feature after I found the plastic retaining disc sitting on top of the rocket!!
Doug Plumb

Like Alan I run a pipe into the back of one of my K & N's, this pipe runs into a catch tank bottle and then has two pipes running from the catch tank bottle to the rocker box and the other to the tappet chest. Oil filler cap is the steel one.
It doesn't leak when running but as usual I get drips when stationary from the rear main.
Engine is similar spec to 'D Paul's' but I'm running K & N pancakes.
Ed H

>>The 'easy clean gauze' was an unwelcome feature after I found the plastic retaining disc sitting on top of the rocket!!<<
interesting as the original design was possibly totally sealed as we learn from the good book 'An air filter is incorporated in the oil filler cap. The cap and filter are renewed only as a complete assembly.'
Nigel Atkins

They always came apart, but you have to be certain to push the disc in past the retaining ridge. It will seem to stay in place outside the ridge, but falls out when it gets warm.

FRM
FR Millmore

This thread was discussed between 17/10/2012 and 19/10/2012

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