Oil sumping

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
Locked
exdysonman
Posts: 6
Joined: Mon Jul 25, 2016 3:57 pm
Location: LINCOLNSHIRE UK

Oil sumping

Post by exdysonman »

Hello
I have just rebuilt my 56 g3ls after a broken piston
It runs well and after a 20 mile run perfect and no leak but on return trip it was chucking oil out of case vent
What is happening is oil in not being scavenged as fast as it is pumped in
I have replaced gaskets and sealed all screws and still same problem
No wear in pump or its pin.Any ideas
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Oil sumping

Post by SPRIDDLER »

Welcome to the Forums, Steve.
exdysonman wrote:I have just rebuilt my 56 g3ls after a broken piston
It runs well and after a 20 mile run perfect and no leak but on return trip it was chucking oil out of case vent
By 'case vent' do you mean the short open-ended pipe from the crankcase breather behind the inner chaincase at the main bearing housing ?
What is happening is oil in not being scavenged as fast as it is pumped in
Can you see the oil returning to the oil tank? The return capacity of the pump is greater than the feed so after th'engine has run for a minute or two the oil will only return in spurts and bubbles.

I have replaced gaskets and sealed all screws and still same problem
Did this include the thin paper gaskets at each end of the oil pump plunger housing end plates?

No wear in pump or its pin.
Have you replaced the pin the correct way around? I.e with the reduced diameter end of the pin in the holder/pin guide?

Other possibilities (among many others) that immediately come to mind are......
Piston ring(s) fitted upside down or excessive ring gap.
Piston or other swarf in the crankcase blocking the oil return drilling.
Oil feed and return pipes inadvertently swapped.
Chaincase over-filled. (Oil should only just reach the bottom run of the primary chain).

Did you discover the cause of the piston breaking up?
'There is a tide in the affairs of men
Which taken at the flood............'
exdysonman
Posts: 6
Joined: Mon Jul 25, 2016 3:57 pm
Location: LINCOLNSHIRE UK

Re: Oil sumping

Post by exdysonman »

Hello
This piston snapped just above gudgeon pin ,quite common I'm told
Yes I did mean that vent
Oil return takes three or more minutes but is very slow,my brother has a G80 and return is a lot faster
Pin is right way and I fitted both new gaskets and sealant and fibre washers on screws
Crankases were dishwashed and and blown through and then had wire through each gallery
Return to tank comes from top of pump
Oil return pipe has clear piece and you can see lots of air bubbles coming up it
raffles
Member
Posts: 609
Joined: Mon Jan 01, 1990 12:00 am
Location: NORTHAMPTONSHIRE UK

Re: Oil sumping

Post by raffles »

check the oil feed pipe at the tank I have known the in line (in the pipe) filter to be blocked or crushed
Tony
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Oil sumping

Post by SPRIDDLER »

I *think* the problem lies in the Return line rather than the Feed.........

It's not my experience that a broken piston, especially in an unstressed 350 is 'common'. Could it have some connection with your oiling problem? Perhaps excess oil in the combustion chamber causing some sort of hydraulic stress?

Was the cylinder wall scored by the broken piston?
Did you rebore or hone the cylinder?
Presumably the new piston came with new rings......
Did/does th'engine smoke or the plug become shiny wet/fouled (with oil)?

When the engine is stopped (and de facto the pump isn't operating) oil will drain down from the rockers and cam chest into the bottom of the c/case and above the level of the return pick-up gallery. Once th'engine is started the pump will reduce the drained down oil in the c/case to the level of the pick-up gallery and you will get air bubbles rather than a continuous flow since the return capacity of the pump is always greater than the feed side (regardless of engine speed).

How much oil was exiting via the c/case breather; a slight mist......occasional drips......a puddle with th'engine running when stationery.....all over your boot/rear tyre?
'There is a tide in the affairs of men
Which taken at the flood............'
exdysonman
Posts: 6
Joined: Mon Jul 25, 2016 3:57 pm
Location: LINCOLNSHIRE UK

Re: Oil sumping

Post by exdysonman »

Hello
Engine was running beautifully loud bang and stopped prior to this almost constant oil with extra spurts
Bore damaged and resleeved fitted nos wire wound piston complete with rings
When run good oil flow and after 20 mile run was OK nearing home I pulled up and oil spraying from vent and out cylinder base gasket and into chaincase
I drained about 1/2 pint of oil from sump and checked all screws etc then restarted
Very slow return and tank level dropped 1 inch in a couple of mins and started coming out vent again when I drained it 1/2 pint again slight smoke when running stationary for a while
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Oil sumping

Post by SPRIDDLER »

exdysonman wrote:.. nearing home I pulled up and oil spraying from vent and out cylinder base gasket and into chaincase
It sounds to me that either the pump isn't doing its job or there may be excessive crankcase pressure, possibly from piston blow-by. I've not had the pleasure of a wire wound but I believe the wire wound pistons need only a minimal clearance in the bore - around 1.0 to 1.5 thou (?) from fading memory* , whereas for a pattern piston I work on a rule of thumb of 1.5 thou per inch of bore - around 4.5 thou for my 350. I'd rather have a bit of slap from cold than a seizure ?(who wouldn't? ;) ). Perhaps you have allowed excessive clearance for the NOS wire wound?

At risk of stating the b.....ng obvious, the 'loud bang' doesn't sound good......... :? Was it from the zorst or th'engine?

*Edit: F W Neill's book for a wire wound '53 350 gives the nominal clearance as a miniscule 0.0007" (0.7 thou) at the top and 0.0011" (1.1 thou) at the bottom of the piston. You'd need some pretty accurate kit to measure that.
Last edited by SPRIDDLER on Sat Jun 03, 2017 3:13 pm, edited 2 times in total.
'There is a tide in the affairs of men
Which taken at the flood............'
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Oil sumping

Post by Mick D »

Hi

The presence of air bubbles in the return flow would normally indicate the sump was empty but this is obviously not the case here. The only explanation I can think of is that the gallery from the sump to the pump is obstructed and causing the pump to cavitate.

Regards Mick
exdysonman
Posts: 6
Joined: Mon Jul 25, 2016 3:57 pm
Location: LINCOLNSHIRE UK

Re: Oil sumping

Post by exdysonman »

Thank you all
Turns out rear plate on pump is slightly distorted and letting air in
After grinding on a flat plate and a new gasket and sealant we are pumping away merrily
The bang was the piston jamming in barrel
Thanks again
Steve
Locked