350 Heavyweight cylinder barrel changes 1956 to 1958-61

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350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby LynP » Fri Jan 11, 2019 12:16 pm

Hi, please can anyone help by telling me if there are any differences between the 1956 and 1958 350cc heavyweight cylinder barrels? from the spares lists. The 1956 is part no. 022647 and in 1958/61 it is no.024000. In relation to this question, I believe that at some point the size of the fins on 350s were increased slightly and a small rounded cut out was made in the top fin under the exhaust port in the head, I would like to know what year that increase first happened.
Last edited by LynP on Fri Jan 11, 2019 6:39 pm, edited 2 times in total.

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Re: 350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby Rob Harknett » Fri Jan 11, 2019 12:25 pm

Also at some point the L hand side bottom flange changed from square profile to bevelled. On the square profile type you may find pt. no. cast.

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Re: 350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby Mick D » Fri Jan 11, 2019 2:04 pm

Hi

My 61 cylinder has '024073' cast into the bottom flange LH side and has the top fin dressed back below the exhaust port.

Regards Mick

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Re: 350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby LynP » Sat Jan 12, 2019 4:29 pm

Hi again, thank to those who posted with their thoughts. I think I may have found the answer I was looking for. In 1956 the shorter push rod chrome tunnels were fitted and the cut outs in the cylinder head were no longer present, so by my reasoning the little cut out in the barrel probably came at the same time as the heads were changed, I hope so anyway, as I have just bought a barrel that had been fitted to a 1956 16m which does have the little curved cutout in the top fin under the exhaust port, of course it could have been fitted later.

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Re: 350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby 56G80S » Sat Jan 12, 2019 5:33 pm

IKBA about the 350s so let's get the straight first.

But I did find a difficulty setting the new chain tension on the SR1 on my 56G80S 500 because, unbeknowest to me, it had a later barrel fitted when I got it. This after 40 years of riding it with the "original" chain! I had made a change to the mounting plate though.

I had to trim the fins so that the mag could go far enough back to set the chain tension. But there were already the small cut outs under the exhaust port.

Hope you have the barrel that you need.

Johnny B

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Re: 350 Heavyweight cylinder barrel changes 1956 to 1958-61

Postby LynP » Tue Jan 15, 2019 7:40 pm

Hi again. Just an update on my progress. First of all thank you Johnny B for your input and yes it seems that I have got what I needed.
I received the barrel that was fitted to the 1956 16M and it has the rounded base and the small curved cut out under the exhaust port on the cylinder head and it looks the same as the one I have with the missing fin. In conclusion, unless it was a later fitting by a previous owner to that particular 16M then 1956 to 1961 350cc cylinder barrels are the same. If I am correct perhaps this will be of interest to others.

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