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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Squish Clearance / Deck Height
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<blockquote data-quote="timetraveller" data-source="post: 43125" data-attributes="member: 456"><p>Just to go back over some of this; a normal Vincent engine does not have squish bands and the only place one normally has to be careful is the clearance between the valve heads and the cut outs in the tops of the pistons. I have found a lot of pistons where the radius of the cut out is marginal and cutting the curves back on their upper edges by about an eigth of an inch ensures that there is plenty of clearance. If using Big Sid type two inch valve heads then even more clearance would be needed. If one increases the bore size to 90 mm from the original 84 mm then it might be thought that there would be a squish band produced but if one measures the diameter of the cut out in the cylinder head this is 86 mm, presumably to allow for oversized pistons after a rebore. So going up to 90 mm only gives a 2 mm wide band and unless the piston crown is machined to match this it is not really a squish band. The Terry Prince head design is much superior in this respect and it sound as though BS has had his heads welded up to do something similar to the TP design. John Emanuel also designed his own modifications to his cylinder heads having had the use of an expert and a gas flow rig. To the eye, John's final design and Terry Prince's look very similar. The difference in engine behaviour is quite remarkable. Several years ago I was in the paddock at Brands helping Roy Robertson. I offered to move his bike from the lower part of the paddock to the upper part for him and made a total prat of myself by stalling the engine, three times, while trying to pull away with 2,000 revs on the clock. There was essentially no torque on that engine at 2,000 rpm. When Roy converted to TP heads the engine became more like a traction engine with regards to its ability at low revs. John Emanuel also found this.</p></blockquote><p></p>
[QUOTE="timetraveller, post: 43125, member: 456"] Just to go back over some of this; a normal Vincent engine does not have squish bands and the only place one normally has to be careful is the clearance between the valve heads and the cut outs in the tops of the pistons. I have found a lot of pistons where the radius of the cut out is marginal and cutting the curves back on their upper edges by about an eigth of an inch ensures that there is plenty of clearance. If using Big Sid type two inch valve heads then even more clearance would be needed. If one increases the bore size to 90 mm from the original 84 mm then it might be thought that there would be a squish band produced but if one measures the diameter of the cut out in the cylinder head this is 86 mm, presumably to allow for oversized pistons after a rebore. So going up to 90 mm only gives a 2 mm wide band and unless the piston crown is machined to match this it is not really a squish band. The Terry Prince head design is much superior in this respect and it sound as though BS has had his heads welded up to do something similar to the TP design. John Emanuel also designed his own modifications to his cylinder heads having had the use of an expert and a gas flow rig. To the eye, John's final design and Terry Prince's look very similar. The difference in engine behaviour is quite remarkable. Several years ago I was in the paddock at Brands helping Roy Robertson. I offered to move his bike from the lower part of the paddock to the upper part for him and made a total prat of myself by stalling the engine, three times, while trying to pull away with 2,000 revs on the clock. There was essentially no torque on that engine at 2,000 rpm. When Roy converted to TP heads the engine became more like a traction engine with regards to its ability at low revs. John Emanuel also found this. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Squish Clearance / Deck Height
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