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MG Midget and Sprite Technical - 1500 Midget Crankcase Breather

My engine has a extra pipe fitted to feed extra oil to the rocker shaft.
When I removed the intake yesterday, I noticed oil puddling in the bottom of the manifold?
Is it possible that the extra oil fed to the rocker shaft is being pushed out of the rocker cover breather and into the carburettors?
The engine has good compression and appears not to be burning oil.
I can't imagine that this is doing much for the octane rating of the fuel, so is it acceptable to seal off the vent tube on the carburettors and fit a small filter to the breather on the rocker cover?
steve

Have you noticed excessive smoking from the exhaust? If not, I wonder if that's oil in there. I've seen a bit of fuel puddled in my manifold, are you sure it's oil?

-:G:-
Gryf Ketcherside

It's definately oil - no doubt about it.
There's also no noticable smoking from the exhaust.
I'm not sure if it's some kind of crank case pressure from worn piston rings, or caused by the extra oil in the rocker box from the additional oil feed.
Is this a feature of this type of engine?
Steve

Is your car fitted with a PCV valve?
Stefan

No,just the standard breather pipe from the rocker cover split between each carburettor.
Steve

Hi Steve,

I've just posted about a very similar - if not identical - problem:

1500 rocker cover vent + excessive oil consumption.

I'd be very interested to know if you've found a solution.

Cheers

Michael
M Davies

<< Is it possible that the extra oil fed to the rocker shaft is being pushed out of the rocker cover breather and into the carburettors? >>

On my 1500 the rocker cover pipe was, until recently, plumbed directly to the air filter intake (Weber DGV) rather than the manifold. This setup made easy to see that the crankcase oil was being pushed beyond the steel gauze under the cover and into the induction, as the air filter housing and carb top would both be covered in engine oil after a decent run. I also had the excessive smoking that Gryf mentions. Removing the rocker oil feed eliminated both problems.

Some recent threads have cast doubt on the wisdom of installing the rocker oil feed at all. Mine stays off for now. I'm thinking an inline needle valve to reduce the volume of flow might be a solution?

Richard
R J Reeves

Hey steve,

Im assumming you have duel HS4s over on that side of the pond....Id be tempted to look to see if its dash pot oil from the carbs...as in perhaps worn carb pistons...perticularly if the oil is miniumle...are you having to top off the carbs on a regular basis...remember a little oil makes a huge mess.

Agian Im just guessig

Prop
Prop

This whole rocker feed issue is interesting. I removed mine (it made no difference to the high oil consumption) and have now bought a 'restricted' screw for the banjo that connects to the head (from Moss - I think you have to ask for it as they don't advertise the problems associated with the auxiliary oil feed) - but I haven't fitted this yet...
M Davies

EVERY rocker feed kit I have seen uses a –3 hose with a banjo fitting to go into the oil gallery plug at the back of the head, and a 3/8" UNF female fitting that attaches to an adapter block that has a 1/8 NPTF male thread that screws into the main oil gallery beneath the distributor (the adapter block is there so that the oil pressure gauge line / pressure transmitter can be retained). This is a BAD idea. By connecting the rocker feed in this way you will INEVITABLY rob oil from the centre main, hence you will actually make your motor more likely to go pop!

Additionally, with no restrictor, you will over-feed oil to the rockers causing problems with inlet valve stem oiling at low rpm (meaning your motor will both burn oil and be closer to causing detonation from the reduction in octane of the fuel/air charge!). Finally, merely fitting an external oil feed while the internal oilway to the cylinder head is active will cause cavitation in the oil galleries and all sorts of flow problems.

By far the best way to fit an external rocker feed is to firstly block off the vertical oilways in the block and head (use a tap and an 8mm grub screw in both block and head) and to take the feed from the main gallery at the rear of the block (opposite number 3 main) via the 5/16” UNF oilway plug tapping. To do this you will need a –2 to –3 male-male adapter to screw into the side of the block (the fact that this tapping is -2 means that you do not need a further restrictor).

This photo' shows the WRONG way to fit a rocker feed:


Deborah Evans

The RIGHT way to do it:




Deborah Evans

Steve, it is very likely that your 'puddle' is actually seepage through a poorly sealing rocker cover gasket (the Triumph 4-pots are NOTORIOUS for this - you need to seal the rocker gasket with something like 'Welseal'), exacerbated by oil pooling at the top of the head as a result of an unrestricted rocker feed. I modify the upper face of the cylinder head opposite the valve gear to give a better 'channel' for oil return to the sump via the tappet chest.

With regards to the rocker box breather, I would suggest running a tube to a catch tank (or even into the chassis web by the inner wing) and blocking off the feeds to the carburetors. This will also benefit by stopping the octane reduction caused by the oil fumes feeding into the inlet tract.
Deborah Evans

Hi Deborah,

Thank you very much for your extremely interesting and authoritative posting. It all makes a lot of sense. May I ask some supplementary questions?

Q1. Is an auxiliary oil feed - correctly installed in the manner you suggest - worth it for a car that is almost exclusively used on the road?

My engine's only done about 3000 since a full rebuild (including the balancing you recommend elsewhere), and I'm therefore a bit reluctant to whip it out again in order to tap and block up the oil ways. I assume one can't do this with the engine in situ?

I have the oil cooler you suggest, and oil pressure is good (for example 60+ psi driving at 70 mph for the 100 miles to London). It's just that I have a pint less oil when I arrive there...

Q2. Is it worth fitting valve seals?

I bought some feeble looking o-rings (from Moss - who I am now going right off - following the auxiliary oil feed debacle) which I have hesitated to fit.

Q3. Would you suggest re-fitting an original rocker cover in place of the (Moss!) alloy fashion item?

The original has the baffle and mesh which reduces the oil pushed or drawn into the breather pipe (but is a bit tinny)

I like your idea removing the breather pipes and venting into the chassis web - with the additional benefit of rust control - but don't really want oil all over my nice drive... (see photo below)

Thanks again

Michael

M Davies

Re. Deborah's words>>"With regards to the rocker box breather, I would suggest running a tube to a catch tank (or even into the chassis web by the inner wing) and blocking off the feeds to the carburetors."<<

---------------------------------


I offer myself willingly for sacrifice at the altar of the High Priestess (what a way to go) . . . but didn't I read (somewhere) that one of the purposes of the 1500 rocker cover 'breath pipe' conected to the induction manifold was to maintain a slight negative pressure in the engine's crankcase?

Having said that, I did also read (somewhere) that Gordon Brown is a financial genius. So what do I know about anything.

I am ready to be taken to the altar . . . .

AH (London)



Andy Hock

This thread was discussed between 22/03/2008 and 04/02/2010

MG Midget and Sprite Technical index

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