wet sumping again

Information relating to the Matchless G12 or AJS Model 31 650cc twin
Locked
Mollbhan
Posts: 109
Joined: Sat Apr 06, 2019 11:52 pm
Location: Perthshire UK

wet sumping again

Post by Mollbhan »

I apologise for bringing up what must be one of the most widely discussed subjects on the forum but I am a new boy here and don't know my way around yet. I have just bought a 1961 G12, for which wet sumping seems to be a fairly common problem with bikes that sit unused for periods of time as mines will probably be. I am aware of the dangers of shut off taps in the oil feed line but there are valves available on flea bay, about £20.00, which appear to be fit and forget and do not need turned off and on. Must be plenty riders used them, any comments?
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: wet sumping again

Post by SPRIDDLER »

Welcome, Colin.
Ask away; we were all new boys once.
I've never had a twin nor fitted a pressure valve so can't help much on that score but here's the 'Search' icon with which you will find answers to almost every question about our AMC bikes. If you put 'Wet sumping' as search words you'll get 90 pages of wisdom, waffle and a bit of irrelevant wit. You could try 'Wet sumping valve' but I'll leave you to find your way around the search facility. ;)
Search icon.JPG
You do not have the required permissions to view the files attached to this post.
'There is a tide in the affairs of men
Which taken at the flood............'
User avatar
Duncan
Member
Posts: 2118
Joined: Thu Jul 10, 2003 1:00 am
Location: HAMPSHIRE UK

Re: wet sumping again

Post by Duncan »

Hi Colin

Unfortunately I have no experience of the "auto" ball and spring type of valve, I have the body of one fitted on a pre war bike but the previous owner removed the internals, I believe these were normally fitted to Velocette's. I don't really know anyone else who has fitted one but there again I have not heard any first hand tales of disaster directly because of one.

If you check out the adverts list you will see that Andrew Dove makes a switch that will either make or break a circuit to prevent sparks appearing at the engine: http://www.jampot.com/Ads_G_TradeList.asp

If you strip your pump and face off the end plates you can normally cure the worst of the symptoms.
MalcW
Member
Posts: 626
Joined: Tue Oct 24, 2017 12:05 pm
Location: DEVON UK

Re: wet sumping again

Post by MalcW »

Personally I'm not sure I would trust one. It's one more thing to go wrong, with disastrous consequences. My Model 31 wet sumps, gradually, but as long as I ride it at least once a week it isn't an issue. Anyway, that extra oil splashing up the bores on start up can't be all bad. Can it?

Malc
mjf65
Member
Posts: 113
Joined: Wed Oct 03, 2018 2:07 pm
Location: United Kingdom

Re: wet sumping again

Post by mjf65 »

What's the risk of starting up a twin that has wet sumped? When I got my model 31 all the oil was in the primary chaincase & sump with nothing left in the tank so what would have beeen the consequences of trying to run it up?
User avatar
Duncan
Member
Posts: 2118
Joined: Thu Jul 10, 2003 1:00 am
Location: HAMPSHIRE UK

Re: wet sumping again

Post by Duncan »

mjf65 wrote:What's the risk of starting up a twin that has wet sumped? When I got my model 31 all the oil was in the primary chaincase & sump with nothing left in the tank so what would have beeen the consequences of trying to run it up?
If it would start, no oil feed to the big ends until the oil tank fills, over pressurising the crankcase forcing oil out of any available joints (air will compress oil wont) these will not self heal afterwards, oil forced up past the pistons oiling the plug, lots of smoke and oil on the outside of the engine and across the drive, clutch slip if the primary is full. Mild wet sumping is not normally a problem but you had best drain the crankcase if you have a tank full in there.
Mollbhan
Posts: 109
Joined: Sat Apr 06, 2019 11:52 pm
Location: Perthshire UK

Re: wet sumping again

Post by Mollbhan »

Thanks for the replies boys, I don't think I have a serious problem with wet sumping if a problem at all and tend to agree with Malk, a valve in the oil feed line is just something else to go wrong, I would probably worry about a lump of crud getting stuck in the valve, I think anything like this in the oil line has to cause some restriction to the oil flow.
pwaltham
Member
Posts: 48
Joined: Sat Jan 01, 2000 12:00 am
Location: County Durham UK

Re: wet sumping again

Post by pwaltham »

I fitted one of Mr A W Doves anti-sumping taps to my model 31. Just make sure it is the correct one for either magneto or coil ignition and wire it in so that it prevents starting until switched on. If you have a mag ignition you will need the bakelite mag cover.
After 5 or so prods on the kickstart you will remember that you fitted it and don't forget to turn it to off when parking.
I've never had any problem with it and it works a treat.
Locked