Wet Sumping of AMC Singles

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Iron Head
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Wet Sumping of AMC Singles

Post by Iron Head »

Apologies if this has been covered ad nauseam over the years but I got thinking last night about the following as I drained my '48 G80 of about 2/3rds of a pint after 2-3 months standing.

Do all AMC singles wet sump and, if so, what year spans are worst.

(Ambiguous question I know) what is a typical amount of oil to drain after (say) 3 months of standing?

Do bikes wet sump worse on the side stand or main stand?

Does wet-sumped oil always also fill the primary chaincase?

Just interested!

Iron Head
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dave16mct
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Re: Wet Sumping of AMC Singles

Post by dave16mct »

In general the singles don't wet sump. However the oilpump bore may get worn after 60 years or more of use or through bad maintenance, dirty oil or swarf scouring. You can minimise it by bringing it onto compression before leaving it, also leave on the mainstand and use straight 50 oil. If it wetsumps badly you could fit a tap in the feedpipe. (aaaaah!) Or you could modify the sump plug by drilling and fitting an allen screw which can easily be removed or left out to collect oil until you ride it next. By the way some twin owners would love to only sump 2/3rds of a pint in 3 months! Best way of all to combat wetsumping is simply ride it, often!
Cheers Dave.
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1608
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Re: Wet Sumping of AMC Singles

Post by 1608 »

And yes, if enough oil sumps it will reach the main crank bearing and enter the primary chain case, nowhere else for it to go. You may then experience clutch slip.
Obviously, leaving it on the side-stand will allow ingress to the primary side sooner.
StephenG80
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Re: Wet Sumping of AMC Singles

Post by StephenG80 »

My 54 sumps and I fitted a valve but I am not confident in it and it has only marginally improved things. I am thinking of fitting a tap BUT with an electrical switch which would earth out the HT lead if I try to start her with the tap closed (so she won't start). Still toying with the idea. :roll:
Mick D
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Re: Wet Sumping of AMC Singles

Post by Mick D »

Hi Dave

What's the theory behind leaving it on the compression stroke?

Regards Mick
Brad
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Re: Wet Sumping of AMC Singles

Post by Brad »

Leaving the engine on compression ie TDC will at least ensure that the valves are closed making it easier on the springs and maybe keeping moisture etc out. When I got my g80, it came with an anti wet sumping tap on the flow oil pipe. I didn't like it so I took it off. It may well be a coincidence and I am not bright enough to understand fully all the science surrounding the position of the oil pump at rest, but I always leave the engine at TDC and I don't suffer from wet sumping.....so far.
If it ain't broke, fix it till it is. ;)
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dave16mct
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Re: Wet Sumping of AMC Singles

Post by dave16mct »

It was thought to leave the oilpump in the best position to prevent wetsumping. Those who have studied this have found the theory a bit hit and miss, but it does seem to work. Not a bad idea anyway as it relaxes the valve springs in this position. Many old sages of the club swear by this method and it does seem to work so that's good enough for me.
Cheers Dave.
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Re: Wet Sumping of AMC Singles

Post by 1608 »

It also ensures the big-end being just a bit higher and so in theory may have a slightly less tendency to have a syphon effect, but it can't hurt.
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Re: Wet Sumping of AMC Singles

Post by Mick D »

Thanks Dave and others

Food for thought there :)

Regards Mick
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Iron Head
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Re: Wet Sumping of AMC Singles

Post by Iron Head »

Many thanks for some great feedback and tips guys, much appreciated.

Iron Head
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