How much compression?

[IanHood]

I have a '74 450 yellow desmo that I have put an R/T head on and have blocked the hole for the decompressor. I had assumed that it would have quite high compression, and would potentially be an ankle breaker, but I have to literally stand on the kick start with my full 14 stone to get it over the compression stoke. Is that what I should expect?

Ian

[blethermaskite]

I am not sure about the 450 but my 350 mk3 will hold my 10 stone nearly for as long as I stand on it.......its 10 to 1 ratio. If Bill in Scotland sees this he will know. Cheers, George

[IanHood]

Hmmm, no wonder they put a decompressor on it

That at least gives me confidence I don't have a shaved head or decked barrel anyway.

[Eldert]

what i do with my 500 is put in first gear , pull backwards up against compression put in neutral again and give it a good kick

works better then trying to get past compression with the kickstarter .

Eldert

[themoudie]

Aye Ian,

I would expect nothing less from one of those old birds!

With 13,000 + miles on my motor (450MKIII), since the last rebuild (road piston ~9.0:1+rings+liner etc) at 85Kg (13.3 stone after a good curry) I can still stand on the kickstart, with little movement for a minute or two. However, I've kept the de-compressor! So, can prime the cylinder, with air/fuel, afore setting up for the starting kick.

I would use Eldert' solution as an interim solution, but refit the decompressor.

Make sure that you are wearing good solid soled boots, NO TRAINERS, and give the kickstart lever a good long swinging descent. NO MINCING ABOUT, WITH YOUR TOES AND PRODDING AT IT, HOPING IT WON'T BITE YOU.

IF YOU HAVE THE STATIC IGNITION SET AT 0° TDC, all should be well and even better if you have a good electronic ignition fitted and a clean spark plug.

Even from cold, with a touch of choke, mine will start first kick, if primed and tick over like a LISTER stationary engine, albeit at 1,100rpm.

All the best, good health, Bill

[Dodge]

You just have to give it a lot of wellie! Don’t be timid. Eldert’s and Bill’s advice is good. I got it wrong a couple of times. First time the kickstart rubber flew off and broke a window on a house on the opposite side of the road; second time it sheared the kickstart shaft - That required a complete engine stripdown! That is why a lot of singles (even the 250’s) have a bent centre stand.

[IanHood]

Thanks all. I do have the Electrex ignition and it does start reliably but was just curious and wanted to make sure I didn’t have something wrong with it.

Ian