Misc: Everything Else Starting Problem - Series 'C' BIG Single

[Jez Nemeth]

Contacted 3 companies this am -

1st : Can do a Liner to fit,
2nd : Can do the boring/finishing but can't supply liner.
3rd : Well that was in my wonderings one - ceramic coating people who have yet to get back to me, but from everything I've read, to confirm they do/do not coat Iron liners.

For my purposes there doesn't seem to be a real need for the difference a coated liner/cylinder surface might make, diamond hone be fine...

Wanted to know info to evaluate and make balanced choices you understand.

Piston pin is 22mm, and considering a Piston size less tight all round would certainly play to longevity in the future, performance can take a knock here for practicality -be happy about that.

What do these things rev to as standard by the way? Might be way out in assuming that 5,6,7000 rpm is normally achievable...I don't have a rev counter and not sure what a Comet does, Big Bore Comet, Twin, Tuned Twin either...sorry to say it, but working off Japanese/German motorcycle experience here...

 

[Bill Thomas]

I know nothing about liners etc.

But 5,800 revs should be tops Standard,
Anything over that , It's down to you if you want to risk it,
Even 5,800 you should not hold for long.

I have pulled 6, 500, I really wanted to !, On standard gearing with a Twin, L/ning Spec'.
I think Comet , Most I ever did was 6000 Standard Gearing, Grey Flash Spec'.

Most of us would be lucky to pull 6000 because these bikes are over geared , To live long .

The other thing is Piston Speed , When you get to 102 stroke you are pushing your luck,
At 6000, I think that is in Tuning for Speed ?.
Maybe Nikasil makes things better ?, But I don't know .

 

[Bill Thomas]

I like Greg's idea,
Even with a 95 mm piston you would still be 750 cc ?.

 

[timetraveller]

When young and hairy I used to sprint a Vincent with standard bore and stroke. I normally revved to 6,000 rpm but over quarter mile sprints I did try revving to 7,000 rpm with only one gear change, rather than two. My times were longer with the higher revs and my conclusion was that I was so far over the top of the power band that the time saved by one less gear change was offset by the reduced power and acceleration at the higher revs. That was with Mk II cams. I did go to a half mile sprint, rode the bike to the meeting, and crossed the finishing line at 7,000 rpm which on the gearing equated to 140 mph. That was with Picador cams. Bill's warning about piston speed at high revs with a long stroke is good advice. Although Bill is not a fan of squish bands I like them but they do require the ignition to be retarded. Twin plugs also require less advance. The figures you were using seem like a good choice to me.

If it is not practical to go to a rolling road when the engine is rebuilt then I like a thing called a Gunsons Colour Tune. It is essentially a glass sparking plug and one can see the mixture strength from the colour of the flame. I have had one for many years and although one would not want to do the final tuning with one, they will certainly get you into about the right ranges. Alternatively Vic's advice about using an exhaust sensor is a way to go that is not too difficult or expensive.

 

[Bill Thomas]

At least most people think the timing is about right.
Maybe back it off 2 degrees,
It did feel Fierce on start up ?.

 

[oexing]

Studying the picture of the wrecked piston I would not think there was a problem of too tight running clearance in the Nikasil cylinder. Big question is what came first, seizure or softened piston from too much heat on piston top. Typical seizures don´t melt the ring zone like here. The design of the piston , not a full barrel type, does not help preventing overheat in places. Seems to me the piston top got excessive heat from too retarded ignition , plus very weak mixture . So when the piston collapsed at the softened top it did the deposits on the cylinder in upper place - not a typical seizure from tight fit. In other engines oil can help cooling the piston but not on a Vincent. So my choice of pistons would be the old style with solid skirt top to bottom. For ignition, don´t know if dual sparks was active here. So if so, I´d think around 25 degrees should do. With single spark I´d keep minimum 30 degrees, rather more like 32-34 degrees. Simple check is accelerate from medium revs and listen for knocking and set accordingly. Jaguars had Lucas distributors with knurled finger nut on outside for quick adjustment on roadside for advancing or retarding ignition after fillup with 3 star, 4 star 5 star fuel, whatever you had. And these had 630 to 700 cc cylinder bores - with 2 " SU carbs !!
Before replacing the Nikasil cylinder I´d first try to save it after cleaning it up and do a measurement for shapes. A liner would certainly not help with heat distribution or keeping size in operating temperatures, would not be much better at dissipating heat at through holes for studs, can´t beat all alu cylinders with Nikasil.
Colortunes can be helpful for setting starting mixture but cannot stand road use for long. Looking at the piston top and spark plug for soot or not should give an idea about mixture for the basic setting.
But then, I am not an active Vincenteer yet, just thinking . . .

Vic

 

[Monkeypants]

I wonder if the engine is just too big for the cooling fin area?
The Prince Top ends have about 30% more cooling fin area than stock.
So far that has worked with my 1360, but I only have about 6,000 miles on the engine to date.
So the 1360 is 36% oversized from stock with a roughly matching increase in cooling fin area. It also has a 2 start pump, not just for the extra lubrication, it's also to help with cooling.
Your 833 engine is 66% larger than stock. The cylinder head is TP but the cylinder must be something else? I suspect it would have less fin area than a TP cylinder as the 833 bore is so big at 100 mm vs 92 for the TP setup.
So you might have 25% greater than stock cooling but need to cool 66% more motor.
That's just the extra capacity. Hot tuning adds heat as well. I guess that's why tuned motors are called "hot motors" or "hotted up motors" The things we do to them adds power and that has to add heat.
That was why Terry was adamant about the 2 start oil pump for extra cooling, it makes sense.
Does the 833 have any kind of increased oiling?

Glen

 

[Jez Nemeth]

You know Glen -It's one of the biggies with this unit, how to cool it down? -I'm tempted to re-write the rule book here and add a modern pump system, with a long thin oil cooler hidden underneath the sump...and even thought about adding watercooling -which, could be done with only two short unobtrusive pipes being visible, same system as many use with a 4mm water jacket liner - pump off the primary crank sprocket...doable certainly. The muff is bigger than standard and has more fin area, but a bit more cooling wouldn't go amiss certainly, got to remember that this unit popped after about 6 miles . . .so not long to get to critical heating levels once started...

 

[timetraveller]

I suspect that even with a twin start pump the flow rate of oil in a Vincent is too low to make much difference to the cooling, and I am a fan of twin start pumps. If you do go for a high pressure, high flow rate oil pump then a trick that was used many years ago on a friend's Norton twin racer might be of interest. The big ends were plain bearings and the tuner drilled a small hole in the big end of the con rod, inserted a pipe and then took that pipe up along the conrod and then through another hole in the small end. This resulted in a jet of oil being fed continuously to the inside of the piston crown to cool it. The pipe was held into the holes with what looked like epoxy resin and never came loose or caused any other trouble.

 

[vibrac]

Twin starts are OK but even with internal baffles at sustained high revs we were getting an oil weep out of the cap (R of course)
Another hidden benefit of the JE front end is the head stock holds enough oil weep for a days racing
see second picture