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Question re 196cc villers

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Question re 196cc villers

Post  Fun on Mon Mar 06, 2017 6:43 pm

Hi all

After dismantling my engine which is stamped as a TT engine ( 172cc) to sort out the spark plug problem, I have measured the diameter of the piston and measured the stroke and is actually 196cc. The piston has no oversize markings wondered if it may have been adapted at some point, I'm pretty sure it's not an original 196cc but would welcome advice on identification. Wonder if it has just been rebored to take the larger piston but many years ago?

Fun

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Join date : 2017-02-06

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Bore and stroke

Post  piston 197 on Mon Mar 06, 2017 8:41 pm

The 172cc engine has the following dimensions

57.15mm (STD) bore to 58.65mm ( +060) x 67mm Stroke

The 196cc engine has the following dimensions

61mm (STD) bore to 62.5mm(+060) x 67 mm stroke

as both pistons have a similar compression height ( approx. 1 7/8") then to bore the 172cc barrel out to fit the bigger piston is quite feasible if the port walls on the transfer ports are thick enough, so if yours has been done then it looks to be possible assuming you have the 61mm piston fitted ?

JH
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piston 197
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Re: Question re 196cc villers

Post  Fun on Mon Mar 06, 2017 8:51 pm

That Could make sense I measured it at 61mm, does not leave much of a sleeve at the bottom of the barrel ( not sure that is the right definition!, but the round part that protrudes at the bottom tis very thin) there is not much meat left, it also has a 1.2mm copper base gasket plus .5 mil fibre one and from what I can see rather the know it would seem the ports gave been ground down by a similar amount ( different scoring) and very little clearance on the head so assume skimmed or ground down within an inch of its life !

Fun

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Compression

Post  piston 197 on Mon Mar 06, 2017 8:56 pm

The 172cc has a compression height ( pin to top of piston) of 1 7/8"
and the 196cc has a compression height of 1 15/16"

This would be a difference of approx. 1.5mm so would be the reason for the spacer under the barrel, the piston length below the pin is also different between the 2 pistons, so will alter port timing, so may explain the grinding down of ports to compensate for the different port timing as well ?

JH
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Re: Question re 196cc villers

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