Options to Convert G80 to Head Mounted Decompressor

[dave16mct]

18 CS Alloy short stroke, not sure of year but about 1960. One plug is normally situated , the other is central (I'll have a look tomorrow to make sure). I've had look at Enfield heads and the hole for the decompression valve looks bigger than I thought, so may not be possible. As you say 'where would it go?' Seemed an easy option when I wrote though!
Dave.

[clive]

Those heads sound like gold dust Dave but they would not fit on a 48/early 50s iron barrel, even if Andy could find/afford one!

[GOLDSTAR]

thats interesting, the short stroke head had a central plug and a strange flame path in the head, modern l/reach plugs foul this and the gap closes, I believe there was a special plug for these engines at the time but now a second compression washer has to be fitted, anyway my head has a blind casting on the side as per the earlier and road singles, perhaps a small 10 mm decompressor valve could be fitted here. even more interesting, a second plug fitted here would it improve combustion, BMW retrofit a second at times, how would you fire it, can a mag fire two plugs? dunno kind regards

[dave16mct]

Yes Goldie, I was wrong and mine are like that. Centre plug with a boss where the 'normal' positioned plug would be. Sorry, its an age thing (again!). One is on a complete engine ready for an future project '57 in a 58 comp frame.
Cheers Dave

[Andy Whitaker]

Not finished yet but here is where I have got to with my valve lifter. The shaft will need case hardening and I think I am going to need to bush the inner end of the shaft and where it rotates in the cover. Will fit a bracket to a rocker bolt and a spring loaded cable to ensure the lifter 'parks' out of the way OK once engine has (hopefully) started. The biggest challenge was aligning and referencing everything - made some templates and referenced off the inner drilling back on to the inside of the cover to drill through that.

Andy

[Iron Head]

Just a quick additional note about 9 months on (needed to make one good magneto out of two) to say that the decompressor works likes like a champ and bike starts first or second kick!

[JOSEGALLO]

Hello Andy. I have the exact configuration you describe in my model 18 1948. No decompressor in the cranckcase or the rocker box. Is the modification working ok? Thanks

[Iron Head]

Hello Jose, apart from a small oil weep it is still working perfectly and has a really light ‘action’ versus my G80CS. You do need to bush where the actuating arm locates in the rocker box but it was pretty easy using a Japanese motorcycle style clutch actuating arm with a bit of grinding. Out of interest how have you been starting the bike so far?

Iron Head