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.
Options to Convert G80 to Head Mounted Decompressor
- dave16mct
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- clive
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Re: Options to Convert G80 to Head Mounted Decompressor
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!
clive
if it ain't broke don't fix
if it ain't broke don't fix
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Re: Options to Convert G80 to Head Mounted Decompressor
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
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Re: Options to Convert G80 to Head Mounted Decompressor
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
Cheers Dave
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Re: Options to Convert G80 to Head Mounted Decompressor
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
Andy
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- Iron Head
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Re: Options to Convert G80 to Head Mounted Decompressor
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!
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Re: Options to Convert G80 to Head Mounted Decompressor
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
Last edited by JOSEGALLO on Tue Nov 16, 2021 1:13 pm, edited 1 time in total.
- Iron Head
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Re: Options to Convert G80 to Head Mounted Decompressor
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
Iron Head