Why.......?

[PaulC]

....does a single need a valve lifter when a twin doesn't and why can you sometimes kick a single several times without using the lifter, but then suddenly come up against compression? My right knee would like to know the answer!

Many thanks.
Paul

[Klaus]

....does a single need a valve lifter when a twin doesn't and why can you sometimes kick a single several times without using the lifter, but then suddenly come up against compression? My right knee would like to know the answer!

Many thanks.
Paul

Hi Paul,

I gues your Norton is kicking you back.
Singels are most long strocke engines, and you need the push to pull the piston over TDC. So it is recommended touse the valvelifter to bring the piston in a position just after TDC. A powerfull kick is the right way to start without kicking back.

At a twin engine is always one piston in a firing position. But with the ignition in an advanced postion they also can give a painfull remembering.

For an easy start a big singel without swolen knee, have a look at here:


cheers Klaus
https://www.youtube.com/watch?v=S_cEjvlX4Y4

[muskrat]

Yum Yum very nice Klaus. I could start my A7SS 14:1 racer like that two.
G'day Paul. It might take a few revolutions for the single's rings to wake up or valves to seat properly. My XT500 can be like that after a rest for a few days.
Cheers

[KiwiGF]

I've always assumed that on a single it does not fire on the first tdc but on the second, so the momentum in the crank has to carry the piston up to the second tdc and first firing, and not the push from the kickstart, on a twin one can kick/push the piston through tdc and the firing.

So on my b31 I use the lifter to get the piston just past the first tdc so all my foot energy then goes into getting max crank speed on the second tdc.

On the single i Use the manual retard it has to the max, to limit the chances of a kickback, I suspect on full retard the firing on my b31 is so close to tdc a nasty kick back is not likely.

I could be wrong in what is actually going on but thinking like this gets my b31 started!

[duTch]

 Wouldn't the only resistance on 'second tdc' only be pushing exaust gas out and no spark ?

[PaulC]

Thanks for all the replies.
It's not kick back that causes my knee to suffer when starting the single, it's when I'm half way through a kick and suddenly come up against compression. The only way I seem to be able to avoid this with confidence is to use the lifter to get over compression for each kick.

Paul

[Joolstacho]

With a single, you (ideally) need to get it up to compression on the firing stroke (listen for the carb sucking as the piston goes down, slowly bring it back up) then ease it a little over compression, then give it the berries wiv yer leg. That should give you best chance to start the *astard.
Some singles, notably Velocette have such a low kickstart ratio that they are really easy to kick over even though they might have a high compression ratio, which is okay, BUT because of the low ratio a good kick doesn't turn it over much, that's why it takes about 3 decades to learn how to start a Velo!!! (It should much easier with 'cooking' porridge singles like B31/3 though).
 
Paul, do this. You've already sussed it yourself, (use the lifter) If you've bought it up to and eased it over compression you'll get a good full swing at it without de-kneeing yourself.