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1930 rocker arms

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I was wondering if anyone could possibly help with the supply or source of supply for a pair of rockers to suit a 1930 Norton 500cc (Model20) Unfortunately I do not have any dimensions but I believe the Norton part numbers are 5732 (Inlet) and 5733 (exhaust)

The ones currently fitted to my engine are incorrect in that the tappet is not in line with the valve stem. (see photo) I believe they could be 350cc rather than 500cc.

If anyone could help with a drawing or photo with accurate dimensions that would also be very much appreciated.

Thanks and regards Ian

 

 

 

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Hi Ian,

Thanks for taking the trouble to post the pictures. At first glance they look the same as the ones on my engine ? I'll take one off sometime this week and measure it to see how it compares.

Thanks again Ian

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Hi Ian,

Thanks again for taking the photographs in your earlier post.

I have taken one of my rocker arms off the bike and measured it up. It does look the same as yours but I wondered if you wouldn't mind just confirming a couple of dimensions. In particular the overall length and also the centre distance between the tappet centre and the rocker spindle centre. On my rocker arm this is 1.43 inches. (see attachment)

Many thanks Ian  

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Hi Ian,

Will look at mine and do some measurements as requested.

Might take me a day or two though.

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The original picture shows the adjuster on a disc...but that disc (whatever it is) is well to the right of the valve stem. So isn't there a bit of an optical illusion making it look more offset than it is? ( And what is the disc? An oversize valve stem cap?)

Also...might the geometry be further improved if the adjuster were a bit less far out. That is..with a longer valve stem? It would best be checked at half lift.

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Thanks everyone for your observations so far. Here's a few more pictures. As David comments there is a valve stem cap on the top of the valve. I've removed this and taken a picture of the valve open and one of the valve closed, there is clearly a misalignment issue between the tappet and the valve stem.  

I've also attached a picture of the valve stem cap showing the sizes. It adds 5/64" (0.080") to the length of the valve stem. Many thanks  Ian

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I wonder if the valve guide is not on its original axis? Has it been made in Plumstead that would be perfectly possible!

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Hi Ian,

Finally had the chance to do some measurements, apologies for the tardiness.

I agree with most of your measurements. The only two I get a significant difference are:

i) Front taper o.d. was 0.527" against your 0.5"

ii) Distance between centres of cam and adjuster tulip is 1.50" against your 1.43"

Whether this is significant, I don't really know.

I checked this measurement two ways including averaging the value measured from both edges of the taper to the centre of the adjuster tulip. (1/2(1.273 + 1.798)= 1.503").

Any questions please let me know.

regards Ian

 

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Hi Ian,

Thanks again for taking the time to measure your rockers. I think you've answered my question regarding the length. If the centres on yours are 1.5" that's a 1/16" of an inch longer than mine. If mine were 1.5" the tappets would be in line with the valves. I've clearly got the wrong parts fitted, so now the hunt starts for the correct parts.

Thanks again for all your help - much appreciated. Cheers  Ian

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Hi, Just a quick update on the misalignment problem with the rockers on my 1930 Model 20.  

On the VMCC Goostrey run earlier this month there was a lovely 1930 Model 22 twin port Norton. When looking at the rocker geometry everything looked good and in alignment. I took some photos and later realised that the pillar bolts supporting the rocker box were shorter than on my engine. I contacted the owner who kindly measured them for me and they are 1.74" (44mm) between the cylinder head and the rocker box, mine are 2.062" (52mm). A friend has measured his 1930 Model 18 and they are the same as mine at just over 2"

Whilst the Model 22 is a different bottom end to the Model 20, I think the top end is the same so I'm thinking that if I make some new shorter bolts then the rocker arms may come into line. What I am wondering is why there would be different length bolts between the single port and the twin port heads?? Cheers  Ian

 

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Ian, Just out of curiosity I measured my pillar bolts on my 31 model 20, they measured 1.8"

That's pretty close to yours

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Hi Ian, Just removed rocker box off my 1930 Model 20.

Pillar bolts measure 1.812" (or 1 13/16")

Photo attached.

regards,

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Thanks very much to Ian & Ian above for measuring your pillar bolts. This confirms that the ones on my engine are too long. In the next few weeks i'll strip the top end, measure up and report back. Cheers  Ian

 

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Now the riding season is over my friend Derek called around and we removed the rocker box and head from my 1930 Model 20 with the misaligned tappets & valves. We made up some adjustable temporary pillar bolts and once these were set at 1.8" (1 13/16) as per the two gents above the tappets were concentric with the valve stems - see photo.

Quite why the twin port would be different from the single port I really don't know. So the next job is to machine up some new shorter pillar bolts from EN24T and then shorten the pushrods and tubes by an equal amount and hopefully that will solve the problem.  

Thanks again for all the help and advice - much appreciated.

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Hello Ian

An interesting topic, I have a model 1933 model 50 that uses the same type of rocker box as yours but no oil feed pipes. The bike was registered Sept 32 so not far of yours. Looking at the parts book for that year it appears that my head has recessed pockets for the head holding down bolts to sit in. This is shown in the parts book for 1933 and the cylinder head is the same.

Your head for your year shows the casting being flat with no pockets for the bolts to sit in. I think maybe it has been fitted with later holding down bolts as the rocker box also appears to be the later type with oil feeds to the valves 1934 onwards I think. Your rocker arms are correct after 1933 the exhaust rocker arm had a horn cast onto it to help the valve lifter cam to rotate, further more the tappet adjusters increased in diameter from 1/4 to 5/16.

I am glad you found where your problems lay. Some new sleeve head bolts and your there, by the way my bolts are 1.850 long 74mm. Hope you do not mind me adding to your post with a little snippet, kind regards.

Charles Gough

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Hello Charles,

Thank very much for the information above regarding the difference in the heads and the rocker boxes. It’s interesting to know the differences and the years they relate to. At first I was convinced I had incorrect rocker arms but it turns out they are correct and it’s the pillar bolts that are wrong. Your measurement of 1.85” ties in with the two gents above who also have bolts of 1.8” and 1.812” it just confirms my 2.062” long bolts were the cause of the problem.

Best regards  Ian

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Final update - looks like the problem is finally solved. The new pillar bolts have been fitted and everything is aligned. I took the bike out for a test ride and it's running great.  The attached pictures show a before and after with the new bolts. Getting to the bottom of this problem was a real challenge. Thanks again to everyone for your help and advice, it really has been appreciated.

All the best.  Ian

 

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