Rate of oil return to the oil tank on twins

Information relating to the Matchless G12 or AJS Model 31 650cc twin
g5wqian
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Re: Rate of oil return to the oil tank on twins

Post by g5wqian »

i have a 600 twin 1956 , the oil can come back in a steady thick stream from when its started cold and then can be a much less of a flow when its hot and the oil has thinned out .
usually there is some oil in the sump that will be pumped back up into the tank so i tend to find for first couple minutes if sat at idle it will have a fair amount of flow showing which will lean out later .
the pressure relief valve is in the top of crankcase along with oil filter , you have a straight slot chrome screw and fibre washer with a hexagon behind it , this is where you check oil pressure from but when you take out the relief valve in order to check oil pressure you do not rev engine up much as the oil pressure is very high , i had 75psi without much more than taking it off idle revs .

i remember having to make an adapter up to allow me to screw the pressure gauge in.

not sure if early engines and later ones have different relief valves but mine was simply a ball bearing ,spring , and the valve end along with oil filter and union .

if i remember rightly i had to use something magnetic to get ball bearing out with .
all i know is that whatever it is , it works very well and the ajs/matchless have a very good oiling system .

on other hand my ariel single just spits oil out the return and sometimes you have to look hard to see if any is coming out , but it does the job fine .

hopefully you have no problem and things are all good .

ian
Groily
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Re: Rate of oil return to the oil tank on twins

Post by Groily »

g5wqian wrote: Fri Oct 28, 2022 6:31 am the pressure relief valve is in the top of crankcase along with oil filter , you have a straight slot chrome screw and fibre washer with a hexagon behind it , this is where you check oil pressure from but when you take out the relief valve in order to check oil pressure you do not rev engine up much as the oil pressure is very high , i had 75psi without much more than taking it off idle revs .
i remember having to make an adapter up to allow me to screw the pressure gauge in.
ian
I wonder if we're confusing the anti-drain valve that lurks in the bits at the drive side of the filter chamber, with the pressure relief valve? Which, where fitted, is either a spring-loaded cylindrical device on the timing side (free to pull out on early engines when the timing cover is removed, or captive, later ones), or is integral with the oil pump mounting plate on late engines.

Some engines, some years, didn't have a prv at all as is implicit in comment from ajscomboman earlier on, but I think they all had the anti-drain item. Detachable ball and spring under separate slot-head screw on earlier engines with a floating felt filter, captive ball and spring in a one piece drive side plug (with a mesh and/or felt filter also integral) on later ones.

http://archives.jampot.dk/book/Workshop ... .NEILL.pdf explains quite a bit about the various differences on page 9.

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With ref to return flow, I've always found revs produce a near-steady stream, tickover regular spurts, when the engine's hot. Cold, a steady flow as the sump empties, from tickover upwards until the crankcase is empty. Even with an oil tap on the feed, some oil will have collected down below and will be scavenged from the get-go, but less than on an engine with no tap that has wet-sumped, obviously! Neill says somewhere that there's always going to be about 8 fl oz in the motor.
(This is why a quick check for return flow on start up is no test of whether you've remembered to switch the oil on, for those who don't have an ignition cut-out incorporated with a tap . . . There will be a return - to start with!)
neil cairns
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Re: Rate of oil return to the oil tank on twins

Post by neil cairns »

As long as the scavenge pump is keeping the sump empty, all should be OK? My '59 G12 returns its oil to the tank in a 'dribble' on start up then a 'pulse' once hot, not unlike my two 18S (even though the G12 has a gear-type pump and the singles a reciprocating one).
MalcW
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Re: Rate of oil return to the oil tank on twins

Post by MalcW »

neil cairns wrote: Sun Apr 09, 2023 8:46 am As long as the scavenge pump is keeping the sump empty, all should be OK? My '59 G12 returns its oil to the tank in a 'dribble' on start up then a 'pulse' once hot, not unlike my two 18S (even though the G12 has a gear-type pump and the singles a reciprocating one).
Sounds perfect to me. On startup it's clearing a bit of wet sumping; after that, you get a pulse of oil once there's enough in the sump to grab hold of.

Malc
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