E: Engine Squish

[oexing]

Well, yes, staking, the lock ring is about the only place on a Vincent I do a light staking. Not for loose valve guides but just to secure the lockring. Loctite at this place would not be desirable, too much heat possibly. Or later, when undoing the lockring, the low strength type may be a bit tough for the fragile tool. But basically the shrink fit of the new guide has to be perfect for safe operation. As the length of fit is a bit short compared to "normal" engines I kept the lockring.
For checking parallel faces and preload of liner to head you can get a feeler gauge of 1-2 thou - allright, metric gauges are finer selection, from 0.02 in 0.01 steps to 0.10 mm . Or can you get feeler gauges in half thou steps ? Anyway, check gap with feeler gauge going round the head for correcting any flaws when lapping, if this is what you do.

Vic

 

[Cyborg]

Well, yes, staking, the lock ring is about the only place on a Vincent I do a light staking.

Vic

I’m assuming that caused you a few sleepless nights?

just for the record… I hate staking too.

 

[timetraveller]

So, for the record, my measurement of 103.5ccs was not too far off. Note that on the big port heads the radius of curvature inside the combustion chamber was less than on the normal heads resulting in less volume in the head itself. If we take 103 cc as the volume in the head and 500 ccs as the swept volme then a completely flat piston which did not protrude above the liner would give a CR of 5.8 : 1. It only needs three mm of extra piston top to give the 6.8 : 1 CR of early Rapides without a compression plate.

 

[Cyborg]

So, for the record, my measurement of 103.5ccs was not too far off. Note that on the big port heads the radius of curvature inside the combustion chamber was less than on the normal heads resulting in less volume in the head itself. If we take 103 cc as the volume in the head and 500 ccs as the swept volme then a completely flat piston which did not protrude above the liner would give a CR of 5.8 : 1. It only needs three mm of extra piston top to give the 6.8 : 1 CR of early Rapides without a compression plate.

Well your measurement of 103.5 could have been right on the money. I’m the last person to be deciding what the best method is, but what you stick in the plug hole would make a difference. Type of plug and heat range would make a slight difference. Doesn’t really matter if the object is to make sure everything is equal between cylinders so every cylinder is pulling their weight. Also where one reads the pipette (bottom of the meniscus) could make a difference. Even on that I stand to be corrected. As I’ve mentioned before my knowledge of the sciences is pretty much limited to turning beer into urine.
Speaking of science perhaps you can explain to me why the James Webb takes about a 6 month tuneup before it runs properly.

 

[timetraveller]

First of all the JWT has to cool down. It and its detectors are designed to work only a few degrees above absolute zero, -273 deg C. You might think that in space that is easy however there is a lot of thermal energy in the solar system, even Sunlight reflected off the Earth or Moon and as there is no air, there cannot be any heat removed by convection. It has to be radiated away. Next the mirror is made up of 18 separate hexagonal mirrors. Each of these can be distorted and tilted to allow them to individually aim at a common focus point. We are talking here about controlling the surfaces to about one millionth of an inch, both in shape and tilt. This all has to be done after the cooling process or thermal expansion of either mirrors or their supporting structures. Patience is the order of the day with all this.

 

[Cyborg]

Apologies to the OP for the highjack.

Thanks for the explanation. Hopefully the mirrors behave, Story Musgrave and his crew are probably too old for that sort of sort of adventure.

 

[timetraveller]

And it is all done remotely. Currently we do not have the technology to send and recover people from where the JWST is.

 

[chark_mandler]

Hi TIm, I ran the racing Ariel 350cc and Model 50 Norton engines at 40 thou squish. Both had new flywheels, mainsheets and 35mm pins, the weak area of the Ariel being the cases. Both revved to 8500 rpm and did not display any contact when stripped. I would imagine 40 thou on a relatively low revving Vin would be fine.

 

[Mike 40M]

My new 350 Manx engine was set up by Molnar to .030" squish. Had to fit double spark plug washers to keep plug gap. Tries to keep it under 8000 rpm, but in the heat sometimes some 500 more.

 

[vibrac]

I have gone for .040" and the CR is 8:1 at least it was but I checked over my 2 plug hole head and there are a number of problems I need to sort so as I want this Comet to be the backbone of my Classic Riding starting early this year I grabbed a black shadow head I rescued a year or so ago (someone had put the exhaust valve right through the head and fins!) that only has one plug hole and with the extra 12 thou of base to make .040 I guess I am about 7.8 so no worry about going into the twenties BTDC on the BTH and if I have to kick her over (never had to last year) I guess the lack of a valve lifter wont bother me. a bit more work to loose a few more pounds of the cycle parts and I should be on the road by March. If I get time to sort the twin plug head it is not a big hassle to swap