E: Engine Squish

[Marcus Bowden]

That is why on my Grosset trigger unit which has a mechanical Ad/Rd from a Citroen I also fitted a manual Ad/Rd as it's firing twin double-ended coils that need to be retarded after starting.

 

[Bill Thomas]

Or a "D" distributor with a bit of plastic tube over the shaft to make less movement,
Of the bob weights and just turn the body to retard.
Just my thoughts .

 

[Marcus Bowden]

I've just done that on my latest "D" Comet acquisition but haven't done any thing to the advance and retard gadget but haven't been on the road yet as waiting for new battery same shape & size as the old 6V version, but starting is very instant even on the kickstart.

 

[vibrac]

Tim, Hate to sound negative, but the twin spark BTH will probably cause you more grief than you might know........The issue is that the advance curve is the same as per the single spark version, only the output wires are simply doubled up to drive 2 output coils. What this means is that if you run say 26 to 28 degrees full advance, the fully retarded possition will fire way after TDC. If your engine has electric start you might get away with it, but on the kickstart it will be difficult to start......Good luck with it all.

I think you may be right Greg I did consider that but when all is said and done its just a couple of connectors to unclip then I am back to single spark and I get a ready in situe backup for my coil and my decompressor back. I will let you know how I fare. There is no way I am venturing out with a coil ignition system on the road lighting and ignition are safer if kept apart

 

[Monkeypants]

Terry's instructions suggest for 50 thou as a safe squish clearance. His instructions are meant for fitting his top ends to a standard Vincent bottom end, which is not without a good deal of flex (see Picador engine dyno testing, MPH)

I ended up with a bit less, just over 40 thou. Given the very skookum cases, crank and rods present, I thought it would be ok at that. On disassembling the engine for crank dynamic balance at 1500 miles, the squish areas were completely free of carbon. Also, there were no signs of piston contact with the heads.
The engine is 92x102, 11 to 1 Cr.
Maybe it would work at an even tighter squish clearance, however getting it wrong could cause a very bad day!

One of my concerns with this engine was that the big cams, carbs , high compression and funny heads would make it useless at low and mid rpm. We've probably all ridden a bike like that at one time or another, where you must rev the piss out of it just to pull away from a traffic light. They are quite horrid for road use.
I'm happy to report that this engine works quite well at low speed. As TT posted about Roy's bike, the Prince heads seem to work efficiently right from just off idle on up.
There is a definite extra surge between 4000 and 6500 rpm, but that might be due to the MK5 cams kicking in. Below that it's very manageable.
BTW, Roy gave me advice on ignition timing, which I followed (Pazon). It worked out spot on.

Glen

 

[greg brillus]

Well my last performance road bike was a KTM RC8 and with several upgrades and powercommander on the fuel system it was a monster of a V twin engine (150 HP) The later ones had 175 hp........So by comparison our Vincent engines are very primitive and docile, even when we try to hot them up.........Your 11:1 pistons probably give about less than 7:1 with the late timing of those cams, and this drops the dynamic compression very much..........The old school cams/followers and valve train in these engines is what limits the available horse power, the bottom end is capable of much more.......like most all engines really.

 

[royrobertson]

Hi Greg not sure what dynamic compression is? are those hp figs real or just ones taken of the crank with no generator etc. as most of them are. How quick is it and what does it do a quarter in?
My old bike did a timed 150 mph with just a top fairing and 166 mph the following year with a Super Nero copy fairing at the Classic Bike Speed trials on petrol and in race trim nearly 20 years ago. Not exactly Docile!
Cheers Roy

 

[Bill Thomas]

I like the idea of something a bit more powerful, But !,
It often means more rev's,
Some of the modern stuff , Short stroke lots of rev's,
Which I don't like.
When I hear the road tests , I am always on the look out for rev's at 70 mph,
Don't think any off them better a Vincent Twin ?.
Although I have had a Twin for 56 years !!,, HOW LONG ?, That can't be right ?,
I think I am a bit of a single cylinder bloke ?, Like a Goldstar ?.

 

[Vincent Brake]

Dynamic comp is,
The ratio: when inlet valve closes,
So cc from that exact piston hight.
to the combustion camber cc.

Hotter cam with steep curves closes sooner, giving more final compression.


All learned from Mr. Ing David D.

And yes indeed, girls are lining up now. As I will be fast!!!

Thnx David

 

[greg brillus]

Just to answer Roy's question.......My bike is a single Norvin, slimline frame.......TTI box.......Not a sprinter, a road racer.........It put out 48.2 HP and 45 Ft lb's of torque at the rear wheel.......I have no idea of 1/4 mile times as I've never done it........It does go well, but not enough to beat other decent 500 classic racers, even though It has good torque pulling out of corners........This is against others running Manx's, JAP speedway engined Nortons and similar........We are starting off carrying out some mods to the valves, rockers, and the ports........definitely going to play around with roller followers and better cam profiles.......An engine this size should be putting out more like 60 plus HP in my opinion.