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

[Jez Nemeth]

A twin with big cams sounds lumpy at idle. It's very different from a Rapide with MK1s or Mk2s. The idle is consistently inconsistent.

What happens with a single?

Your engine in the video sounds quite similar to a regular 500 at idle, maybe louder but also very even.
Was the engine built for road or race?
I don't know how you manage to kick it over. I have quite a time with the 1360 which is 680cc s per pot. It has big cams which ease the kickover a bit.

Any idea of the CR on this engine?
Glen

Hi Glen -engine was never built for intended use as a bike -Renwick had it on a bench linked up to his dyno and thrashed the hell out of it testing his homemade cams, carb settings and basically how to wring as much power out of an engine without blowing it up...don't care to think what this thing has been through -80+ bhp was mentioned, but can't confirm that -set up is for sprint, running dope, so i suppose 'road'...and testing for Epimetheus. Not been to his workshop -those who have may know much more than I do -love to talk to Eddie again to gleam what I can from this back story...
Yes does sound like a standard Comet, slightly deeper ,but not as much as you'd think for the xtra 300 cc... forgive me mate -might be missing the obvious -what's CR...?

 

[Monkeypants]

Sorry, Compression ratio

 

[Jez Nemeth]

of course...thank you, sometimes I can be a complete muppet and miss the obvious...

High, 10:1 + ?? Not a clue, once the piston's up there's not much space in that head, but the central combustion space around the valves makes it difficult say, had to ensure what i was doing with the valves I was fitting was ok -didn't know if stuff had been altered from standard variation at all, all been gone over in that head, machined here and there beyond TP's original big-bore head unit -so had to check, measure everythang...and then there's that squish-band which adds to the whole compression picnic -so difficult to guesstimate -it's high, and that's why Bill's thoughts on raising revs on tick-over sounds about where it wants to be naturally.

Had no idea how it would behave on first start, pleasantly surprised that it is usable, trying to tame it further by lowering the tick rate is not the direction it clearly wants to go, to use a metaphor -the thing will never be a puppy, but an obedient sheepdog/bulldog be a good result to my thinking

 

[Jez Nemeth]

Just a thought...could possibly get some of those BT breathers made if there was demand for them as a discrete alternative to the Elephant's trunk -can find out if there's interest? Don't want to pee on anybody's campfire, but nice to have choice...

 

[Bill Thomas]

Didn't you say you are using Mk2 cams Jez ?,
Sounds to me, Nice slow running, Not too wild ?.

 

[Jez Nemeth]

Using 105's -but there seems to be little difference to my eye, it seems that they're just set at slightly different opening closing times to the MK2's -The Chapman MK's 2 I'll now put on the 500 with the BTH seem to have slightly sharper exit ramps, but we are talking a thou or so...so pretty much same profile, just gentler on the 105's because of position, come into the show a bit later than the MK2's (or is it earlier? -think later).

Cams sound in right place, as long as they're too far out shouldn't impede starting would they?

 

[Jez Nemeth]

Compared to what I suspect Renwick had in there, think MK2s/105's will be a much gentler proposition and better all round. Will just adjust carb back -then off T3 van fixing body panels today and be back later -still have paperwork and External Examiner reports for other Universities to complete before away all next week, those reports won't write themselves & can't wait for creative AI to catch up with menial tasks...be after my time that one...grandpa did people really spend their lives tapping away on keyboards an' staring at little screens for work? Yup can't wait.

 

[Bill Thomas]

It will give your leg a rest, So maybe best,
I know you can get so involved in a job, It's not good.

 

[Jez Nemeth]

Aiming to get street performance on this bike to be somewhat like a DR750/800 then be pleased with that result. It's the second thought to have all the elements in place to be able adjust the set up for sprinting with it easily enough. Those things can be put in place now while working out starting, and smoothing out all the teething issues to make that easier I reckkon!

 

[greg brillus]

The engine would definately run better and idle stronger with twin plugs.........a large diameter piston like that works well with the fire lighting from either side of the chamber........That might be something to look at at some stage.