Oil metering hole size

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REW
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Oil metering hole size

Post by REW »

Many questions and some answers in other threads with respect to single rocker box oiling. I have one question left: size of the oil hole feeding the exhaust valve stem.

If you look at the photo the hole is just a drilling approx 2.3 mm diameter. You can see where a drill has caught the inside of the rocker box. It looks like the metering jet may have been drilled out. What size do you suppose that orifice should be?

Ron

1951 Matchless G3L thumping round the Durham Dales.
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REW
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Oil metering hole size

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I feel the oil flow to the exhaust guide will be excessive if left as above and may well be why there was so much carbon on the valve, guide and head when I started this clean up. Had another search for info and this time came up with similar situation identified by Peter LeCompte. He fitted a metering jet in the hole (as above) and one in each blanking plug over the push rods. Now, how do you get and fit these plugs and what size?

Don't mind doing some experimenting if I have a clue on jet size, so, any one got any measurements please?
Ron

1951 Matchless G3L thumping round the Durham Dales.
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tr7dan
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Oil metering hole size

Post by tr7dan »



Ron. I had the same problem myself with suspected over oiling of the exhaust valve stem. I found this in the maintenance book if it's relevant to your query








Dan
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REW
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Oil metering hole size

Post by REW »

Thank you Dan, that really does give a workable solution. Can I ask, did you manage this ok and what appprox internal hole did you end up with in the supply jet?

If I may also ask, what metering is there in the supply over the push rods? Many have plugs with flats (as in your extract above) I seem to have plugs with no way through!
Ron

1951 Matchless G3L thumping round the Durham Dales.
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john
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Oil metering hole size

Post by john »

Ron,

I will measure up a few rocker boxes I have in the garage tomorrow.

But what I have seen from your photos looks completely normal, so don’t have nightmares. Hopefully I can get some hard figures to put your mind to rest.
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REW
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Oil metering hole size

Post by REW »

Thanks John - you know this has exercised me for a while!

Could you measure the front oil metering jets too if you have them in a rocker box, as distinct from the the plugs with flats I know from a previous post you have too?

Ron
Ron

1951 Matchless G3L thumping round the Durham Dales.
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john
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Oil metering hole size

Post by john »

Ron

I have had a chance to get into the chilly garage. The first thing I measured was the push rod oiling jet.


1946, rocker box 2mm dia hole

Pre 1954 2mm dia hole
Post 1954 (I think) are oiling plugs which are 4.75mm plug with a 0.3 flat.

Secondly I measured the exhaust valve oiling jet

1946, does not have them
Pre 1954, the two rocker boxes I have are on my two bikes unfortunately.


Post 1954, I measured 3 boxes and they all have 2.3mm dia holes.

So I would say your rocher box is standard.

JohnT

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REW
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Oil metering hole size

Post by REW »

Thank you very much for that info John. Yes, as you say, mine are very much "normal" which should stop me going on about this and get it put back together.

Again, thanks for your work on this, braving the cold too.What a marvellous club and membership we have!
Ron

1951 Matchless G3L thumping round the Durham Dales.
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john
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Oil metering hole size

Post by john »

Further previous posting I have taken the rocker box of my 1953 bike and measure the rocker feed oiling hole. 1.85mm

If we convert that to area,
Early box (non plug), Push rod feed, 2.67mm2 Rocker feed, 3.14mm2
Later box, Push rod feed, 1.53mm2 Rocker feed, 4.15mm2

The total area stays the same but the proportion going to the valve rocker arm has been increased.

Why? I don’t know but it would be interesting to debate.
But I don’t think you should drill out the plugs to make it look like the early head as you would increase the amount of oil going the metering holes and reduce the amount of oil going to the rocker bearings.
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REW
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Oil metering hole size

Post by REW »

John, thanks for the updated info re earlier rocker box oiling.

My post 54 rocker box oil gallery results in 5 feeds I think:

one at each end feeding the rocker axles though I can't measure these obviouslytwo facing push rods; flats in plugsone feeding exhaust valve reservoir. This feed is separate from the rocker axle feed

The two flats are tiny at .3mm which, using an internet site to calculate the area came to .5mm2 each! The exhaust valve feed is the big one and I calculated as you did about 4mm2. However feed to the exhaust valve seems generous and other forum members have even done without this feed! So I reduced it to 2mm2 with a short piece of brass pipe as described in earlier workshop manuals. The idea is to force more oil to the rocker axles and hence to the ends of the rocker arms.

This may well be nonsense but it has been great fun in its forensic intensity and like you, I would love to know the deep thought (or not) that went into it originally.

If I have now buggered up my rocker box I shall shortly find out!
Ron

1951 Matchless G3L thumping round the Durham Dales.
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