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BrizzoBrit
BrizzoBrit
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Joined: Aug 2016
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I have a 1954 MSS with a 350 top end. Was this a common practice for racing? The bike has been totally restored and is stunning, I'm just a little puzzled by the change. Any information will be appreciated.

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Sounds like you have a squish head Velo. Common mod for racing engines is to use a 350 head (reshaped internally) on a 500 barrel.
Having a smaller bore, the 350 head internal dome diameter is smaller, so at TDC the piston has a close clearance to the head around the periphery, as the piston approaches TDC it squeezes the mixture into a really concentrated area, in the middle of the dome giving better combustion.
How does it go?
BTW If ever you work on the motor you'll need to be very careful to reassemble it to the same height with regards to piston and gaskets. The clearance between piston and head at TDC can be quite small, like 0.030"- 0.040 (ish)
-Jools

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Thanks for the reply , I traded for the bike last fall and it would not hold oil, need a check valve and some generator repair. Just got it completed and hope to take it down the road tomorrow. I was told when I got it that the cylinder and head were 350 but the bottom was MSS. The serial number is that of a MSS, but other than that I just have the information that was given to me. Is there a way to determine the displacement without taking it apart? Is there a visual difference in the cylinders? The bike also has a different timing side cover than I see on pics of MSS or MACs, it is flatter in appearance? I will post a pic if I can figure out how to do that.

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Yes you can check the displacement and compression ratio without taking it apart, but you'd need to have the motor out of the frame. OR...
It might be possible to do it 'in-situ' but rather difficult... you have to orient the motor so that the spark plug hole is dead level, and is right at the highest point.
You'll be pouring in fluid which will need to come right at to the base of the spark plug hole. Picture it. There will be YouTube videos of the process - quicker than me trying to explain it.

Last edited by Joolstacho; 06/06/17 8:20 am.
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[Linked Image]

Not sure if the pic is available for you to see, please let me know .

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Ok Joel, that is my bike, any idea thoughts would be great. I sent a PM with the engine number.

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Sorry Jool , auto correct strikes again!

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Sorry Jool , auto correct strikes again!


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