VCH or VHA

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Bruce Saunders
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VCH or VHA

Post by Bruce Saunders »

Recently acquired a replacement for my 1954 NH350 which had steel 500 flywheels, 500 barrel and alloy head, the basket case I bought is around 55 VH500 and has steel flywheels and a VHC or VHS head, woth plug facing forward, exhausf guide hole is two diameter larger at the top, has
dropped a valve, sests ok combustion chamber has valve dents and broken small fin to rear of plug thread, My question, is there a way to tell VCh head from VHA head or are they the same?
Bike is missing frony wheel and clutch/chain wheel mud gaurds. It came with a very tidy Burges? air filter
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nevhunter
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Re: VCH or VHA

Post by nevhunter »

I've only worked on the earlier round based cylinder version which I've owned for ages, but I'd think that one may also be a VCH because of the inclined spark plug and it's not like a 54 alloy head 500 I also have from a VH. Nev
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Roger Gwynn
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Re: VCH or VHA

Post by Roger Gwynn »

That is a VHA/VCH head with a very awkward angle of spark plug that makes using a TDC gauge impossible. 35-52 or A7/928, sometimes casting numbers are found on parts but not usually on this head. Used 1952-52, drawing is available from the club. The ally heads have a tendency for the ex guide to come loose and it sounds like someone has effected a repair, the hole should be 5/8 all the way.
Roger Gwynn, Membership Secretary, curator of the Machine Register and the works drawings. Director of Draganfly Motorcycles, Craven Equipment and Supreme Motorcycles mostly retired.
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paul.jameson
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Re: VCH or VHA

Post by paul.jameson »

As well as the issues Roger relates, some of which apply to other alloy 500cc heads, there are a couple of other points to note on this VHA/VCH head. One is that the combustion space is larger than that on the later heads, leading to a lower compression ratio. The other is that the rocker box bolts are cycle thread instead of the stronger whitworth thread used on the later alloy heads. This leads to stripped rocker box bolt holes all too often.
Paul Jameson
35 LG (project), 37 RH500, 52 ex ISDT KHA, 54 KH(A), 75 Healey 1000/4.
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Bruce Saunders
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Re: VCH or VHA

Post by Bruce Saunders »

Thanks for info, the threads are cycle thread and
I have a Alloy VH500 and NH350 head and thought
the combustion chamber looked deeper the the VH500 head , previous
owners have fitted inserts to the inside rocker bolt threads, but they are very small diameter.
Hadn't thought about the timing issue, quess need to use a degree wheel to set timing. Lot of parts to find before that happens. I have two cams ones ex my old 54 VH500 simgle lobe,and the others a twin lobe. I only have worn cam followers for the single lobe cam and pretty sure Franklin Cams still repair them here in New Zealand, just wondering how hard it would be to find cam followers for the twin lobe cam?
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paul.jameson
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Re: VCH or VHA

Post by paul.jameson »

Time the ignition before you put the head on !
Paul Jameson
35 LG (project), 37 RH500, 52 ex ISDT KHA, 54 KH(A), 75 Healey 1000/4.
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
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Re: VCH or VHA

Post by Brian_Walker »

20180605_231132.jpg
Here is my 1951/52 VCH head.
1951-52 VCH under restoration
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