G5 CRANKCASE BREATHER OIL LOSS

Information relating to the Matchless G5 or AJS Model 8 350cc Lightweight
chesp
Member
Posts: 5
Joined: Wed Nov 04, 2015 9:47 am
Location: WREXHAM CB UK

G5 CRANKCASE BREATHER OIL LOSS

Post by chesp »

Hi Everyone,
This is my first time on the forum with a problem of oil leakage from the crankcase breather. I have owned the G5 for 44 years but it has been in bits for 40 of those years.I have recently completed the rebuild over the past year and it is complete and running. On the first road test I noticed on my return, oil had been discharged from the crankcase breather, approx 1.5 pints lost over 20 miles.
I have checked externally the tightness of lock bolt for the breather stator ring and that was still in place (the later type of breather is on this engine, separate lock bolt and breather hole in crankcase). I have also changed the felt oil filter for the wire mesh type in case oil flow was restricted back into the integral oil tank. Unfortunately this has not solved the problem. I know that a small amount of oil escapes through the breather oil but not to the extent I am experiencing.
If any one has experienced this problem, I will look forward and appreciate any suggestion to what is the cause and remedy is to this problem.
User avatar
clanger9
Member
Posts: 1163
Joined: Sat Jun 20, 2015 9:38 am
Location: Chester, UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by clanger9 »

Daft question, but is the oil level in the tank too high?
1989 Moto Morini Dart 350
1993 Ducati 750SS
chesp
Member
Posts: 5
Joined: Wed Nov 04, 2015 9:47 am
Location: WREXHAM CB UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by chesp »

No. Oil was measured in at 2 1/2 pints and top level sits roughly 1/2" below the oil return hole in crankcase.
I have also ensured that the small breather hole between the crankcase and the oil tank is clear.
User avatar
clanger9
Member
Posts: 1163
Joined: Sat Jun 20, 2015 9:38 am
Location: Chester, UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by clanger9 »

Hmm, there are a few things you can look for if it's not scavenging properly:
- Is the "plug" end of the oil pump properly sealed? The big screw plug can be tricky to get all the way home. Needs the gearbox out to check this.
- Is there a blockage at the scavenge pickup? This is just above the rear sump plug, so you can remove the plug and have a look inside.
- Is the return oilway clear at the bottom of the filter housing. There's a cup washer down there for the felt filter that isn't needed with the mesh filter.
- Is the horizontal oilway from the top of the filter housing clear at the crankcase joint? If you used the dreaded silicone to seal the flange then it's possible for a blob of sealer to get lodged here. Maybe give it a poke through the return hole with a pipe cleaner.

Finally (again, apologies if it's a daft question, but after a rebuild anything's possible): you did put the oil pump guide pin in the right way round?
1989 Moto Morini Dart 350
1993 Ducati 750SS
chesp
Member
Posts: 5
Joined: Wed Nov 04, 2015 9:47 am
Location: WREXHAM CB UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by chesp »

Thanks for those suggestions. It seems that I am not going to get away without a partial strip down.
I will check those first two items. I have checked the remaining three and the are satisfactory.
Again, thanks for your help I will let you know how i get on.
User avatar
Ozmadman
Posts: 2651
Joined: Wed Dec 14, 2011 1:02 am
Location: ESSEX UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by Ozmadman »

You mentioned checking the breather stator bolt but is there definitely a breather rota on the crank. It fits on the crank and runs within the stator ( called a timed breather) I only mention this as mine was completely missing when I rebuilt my engine. If it is missing then the engine is constantly breathing
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
chesp
Member
Posts: 5
Joined: Wed Nov 04, 2015 9:47 am
Location: WREXHAM CB UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by chesp »

I am quite certain i fitted the rotor but if all else fails I will be splitting the crankcase for examination. At this moment I am trying to avoid doing that. Thanks for you input
User avatar
clanger9
Member
Posts: 1163
Joined: Sat Jun 20, 2015 9:38 am
Location: Chester, UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by clanger9 »

Before you take it to bits, it'd be worth taking a close look at the return feed. Is it a healthy "pulse" or is it bubbly/frothy?
Paul posted a good video a while back showing what a healthy return feed should look like.
1989 Moto Morini Dart 350
1993 Ducati 750SS
User avatar
clanger9
Member
Posts: 1163
Joined: Sat Jun 20, 2015 9:38 am
Location: Chester, UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by clanger9 »

Ah, I just had another thought: you mentioned you've changed the felt oil filter to the earlier mesh type.
However, the later engines have a longer filter to cope with the higher oil pump output. I'm not sure if you can/should mix the early mesh filter with the later crankcase. I guess the early filter it could limit the return flow. Just a thought...
IMG_0215.jpg
Before you dismantle it, I'd double-check it has the correct filter for your crankcases.
You do not have the required permissions to view the files attached to this post.
1989 Moto Morini Dart 350
1993 Ducati 750SS
chesp
Member
Posts: 5
Joined: Wed Nov 04, 2015 9:47 am
Location: WREXHAM CB UK

Re: G5 CRANKCASE BREATHER OIL LOSS

Post by chesp »

The return is 'pulsing' but not as strong as the one shown in Paul's video. Possibly hinting to an oil flow problem/lack of scavenging in my engine. The wire mesh filter I have fitted is bigger than the felt filters, it is the filter that was in the engine when I dismantled it. The filter occupies the full filter housing in length and diameter. There is no metal cup washer at the bottom but there is a holed rubber sealing washer. The opposite end is attached to the chromed screw plug.
Post Reply