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MG Midget and Sprite Technical - On the scrounge

Does anyone here have access to a lathe who may be able to make me an oil metering pin for my shorrock supercharger?
This is a simple job as the pin simply needs to be 1.265" long by 0.3105" in diameter. The material isn't that important. I'd guess that it could be turned down from the shank of a bolt.
I'm more than happy to pay someone for their time and of course to cover cost of postage, or if you prefer I could make a donation to your favourite charity.

Grateful for anyone's help.

Simon
Simon Wood

Yes, can do - what surface finish do you need?
Chris at Octarine Services

With dimensions of 1.265" x 0.3105" the first question I would be asking before taking on the job is what are the tolerances.
David Billington

Lol - as an ex aircraft engineer I am used to working to within a tenth of a thou if needed.

I don't know what this pin does but if it needs a hardened & ground surface, that is one thing, if it is just a push pin then surface finish is probably OK as it is turned.

Just threw out a test pin made from high tensile steel - see pic.

Chris at Octarine Services

Having done a bit of research it seems that these pins have a reduced diameter at one end to take the spring and originals are ground.

It appears you can buy the "B" pin - listed at £16 but whether they have stock is probably another matter!

More info needed I think! Why do you need the pin?
Chris at Octarine Services

Thanks everyone for your replies.
Firstly I got the diameter wrong in my original post. I think that I am looking for a pin with 0.3115" rather than the 0.3105" that I originally quoted.

A bit more info: The pin that I currently have is 1.265" x 0.3110" diameter as measured on my ancient micrometers. This seems to stack up with what would have probably originally have been fitted to the supercharger. I'd describe the finish as shiny but not quite mirrored. Bear in mind that its probably 50+ years old and my enegineering terminology is limited by my ignorance.

The pin acts as a restriction to the oil supply. It doesn't move and so I'd guess that to all intents and purposes, could be considered to be "non-wearing". All the oil that is supplied to the supercharger is blown into the inlet manifold and every time that I diamantle thinks I see what looks like a lot of oil in the intake system. I have always had oily plugs.

So the mission here is to reduce the oil flowing into the supercharger a little. The shorrock literature that I have suggests that if over-oiling is suspected, a 0.5 thou increase in metering pin diameter is worth a try.

For what it's worth, the pin sits in a hole that has a bore of 0.3125" (5/16) according to the shorrock specifications.

Am I making sense here and does my plan sound sensible?

Simon
Simon Wood

I just had a look and found some more details also, this was interesting http://www.rjh-heritage.ch/index_htm_files/Shorrock%20Supercharger%20B.pdf may need copy and pasting due to the spaces (%20). 1 pint for every 850 miles, people used to complain about the Lancia Beta Volumex oil consumption being high IIRC lower than that.
David Billington

David,

Yes indeed, I have all of these documents and acknowledge the 850 miles per pint bit.

I'm on a bit of a mission here to reduce my oil consumption and oil leaks. It's a bit of an ocd thing at the moment.

Having sold my Lotus recently I'm looking for stuff to do.

Lol

Simon
Simon Wood

I will take a picture of the pin tomorrow and post it here.

Simon
Simon Wood

.3110 is the "A" pin and max size - has it got "A" stamped on one end?

Have you tried heavier oil?

I suggest maybe a .3113 & .3115 and see which one reduces oil flow to an acceptable level.

I'll have a play tomorrow - need to set up the grinder on the cross slide first ....
Chris at Octarine Services

Will have to think about how it's possible to measure the oil consumption accurately with a leaking engine. Initial thoughts would be a cylinder containing oil with a separator plate pressurised by the engine oil pressure, plate travel would indicate consumption.

What engine is it, I remember there used to be a lovely frogeye with original Shorrock supercharger installation out of Bovey Tracey in Devon IIRC, been a few years since I've seen it though.
David Billington

The 850 miles per pint is irrelevant with other leaks - I would measure the hydrocarbons in the exhaust - even significant blue smoke would indicate oil burning - obviously there will be some extra oil burnt over a normally aspirated engine but I would think you would want no more than a very light blue haze.
Chris at Octarine Services

Am I missing something(?), 850 miles per pint is teetotal to BL/BMC and IIRC others, I don't know if this is the fiendish US quart/gal/pint system but -

"2, 400 miles or more per gallon (600 per qt.) is an acceptable consumption rate after the vehicle has completed at least 5,000 miles, and is widely accepted."

BL Technical Service Bulletin - 72-A-4 OIL CONSUMPTION
http://www.spridgetguru.com/TSBs/TSB_no72a4.pdf

Nigel Atkins

Engine is a 10CG. Rebuilt about 40k miles ago. No discernable bore wear, head rebuilt maybe 20k miles ago.

Original draft-tube type crankcase ventilation, though I have now redirected this to a catch tank.

I'm down to just a few oil drips on the garage floor when left overnight after a run - under the bellhousing jiggle pin and under the front crank pulley. Have changed sump, timing cover, tappet chest, rocker box, oil filter gaskets and the front crank seal. I suspect that the engine front plate to block gasket may benefit from replacing. Anyone know whether this can be done with the engine in-situ?

I'd be delighted with 850 miles per pint and no Nigel you are not missing anything here. Shorrock has a total loss oil system. Oil is fed into the rear bearing via the oil pressure gauge capillary pipe, this enters the compressor and is ultimately swept into the engine with the fuel mixture.

I'm not trying to be overly scientific about all of this just interested to see whether a larger diameter metering pin will make any difference to my oily plugs and slight blue haze in the rear-view mirror, the latter only really being noticible immediately after start-up.

Simon


Simon Wood

Simon,

Email me your details to chris@octarine-services.uk

and I'll send you a 0.3115 pin.
Chris at Octarine Services

0.3115

Chris at Octarine Services

An update here on oil consumption.
I have done about 300 miles since fitting a new pin, kindly supplied by Chris. In that time I estimate that I have used less than half a pint of oil. Along with fixing my leaks this is a vast improvement.

Many thanks to Chris for coming up with a new metering pin

Simon
Simon Wood

I had a Shorrocks on my Frogeye when I bought it fifty years ago.
Having blown the first one I picked up a second hand one, for £25, from Adlards of Putney.
After a long run oil would collect in the bottom of the cylinder. One day two ladies walked past the rear of the car just as I fired up. They suddenly disappeared in a cloud of smoke that would have made a destroyer Captain proud!
Alan Anstead

This thread was discussed between 25/08/2019 and 22/11/2019

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