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Plunger 350cc Manx flywheels - Help!

Submitted by ian_allen on Tue, 02/12/2014
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Hi.

Is there anybody out there with an original 48-50 plunger 350cc Manx who can tell me what diameter the flywheels should be? I've asked around the experts and have had differing opinions. The crank assembly changed for 1948 (the flywheels, rod and piston) - presumably to fit the 'new' 500 size crankcases. Any info much appreciated.

Regards,

Ian.

Submitted by andy_marks on Tue, 02/12/2014

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I know a guy with a Manx spec Inter of that era (not sure of exact year, I know its plunger). Would that be any help? The bike is complete and I doudt its the sort of thing he'd have made a note off, but I can ask next time I see him if it would be of any help?

Andy

Submitted by ian_allen on Wed, 03/12/2014

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Thanks Andy.

I'm afraid it's got to be pukka Manx, the post warInter bottom end hardly changed at all whereas the Manx did. I think I may have nearly cracked it by working out the maximum permissible flywheel diameter from the barrel spigot depth and the crank centre to crankcase mouth distance but it would be nice to get it confirmed.

Thanks again.

Ian.

Submitted by jonathan_newton on Wed, 07/01/2015

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Previously ian_allen wrote:

Thanks Andy.

I'm afraid it's got to be pukka Manx, the post warInter bottom end hardly changed at all whereas the Manx did. I think I may have nearly cracked it by working out the maximum permissible flywheel diameter from the barrel spigot depth and the crank centre to crankcase mouth distance but it would be nice to get it confirmed.

Thanks again.

Ian.

Stu Rogers, srs norton....... A walking cammy encyclopaedia....

Submitted by ian_allen on Wed, 07/01/2015

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Thanks Jonathan. Things have moved on a little since I placed this post. I've been onto Stu throughout this restoration and even he is unsure, trouble is there seems to be some disagreement even among the experts. I've been told 7.5", 7 & 5/8" and 8". 8" seems too big and would not clear the crankcase oil scraper. Added to this the con-rod length and piston changed was well for 48. If anyone has an unmolested 48-50 350 Manx it would be nice to know and to confirm the con-rod length (6.5"?). I'm having to go for a special 7" conrod so I can use a pre-48 piston as both the 48 rod and piston are as rare as hens' teeth. It's a bit of a minefield but it does look like I'm finally getting there thanks to Stu, Ken McIntosh and Ian Bennett.

Thanks again.

Ian.

 


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