Oil scavenge problem

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: Oil scavenge problem

Postby Kneedy » Tue Jul 03, 2018 12:30 pm

Good point, Mick. I'm just about to start pulling it apart again, when I built the bottom end, over a year ago now, I thought I'd been so careful, but obviously missed something. When it does scavenge its only a frothy dribble, even with increased revs. My Triumph has a healthy spurt under similar conditions.
Thanks for your input, watch this space!

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Re: Oil scavenge problem

Postby Kneedy » Tue Jul 03, 2018 7:38 pm

Engine out and stripped, correct 2 start axle fitted but I have sussed the problem. The replacement case had been modified as if for competition, grub screws to retain cam followers, etc. When I got the case it was completely bare, apart from said grub screws, which I used.

However, the plain main bearing bush had been similarly modified, with a drilling made half in the bush and half in the case, to take a 3/16 grub screw to prevent the bush turning under extreme conditions. The modified bush was not present when I got the case. When I fitted the new bush it was a good interference fit in the hot case and I decided not to use this method, I only intend plodding not racing. The grub screw hole appeared to be blind and I thought no more about it.
Knowing more about the oil circuit now, thanks to this forum, with the cases split when I tested the long diagonal scavenge oilway using the WD40 squirt method it was apparent that the grub screw drilling had just broken through into the oil way, so the pump was trying to suck air, and wouldn't have drawn oil until the crankcase was half full.

So now all I have to do is block the half (D shaped) hole in the case. I was advised against welding the same area on the original damaged case due to distortion, don't like the idea of chemical metal in case it breaks up and blocks the oilways, so am thinking of fitting a solid bung, interference fit with bearing fit Loctite, had good results with that in the past. Any suggestions gratefully accepted.

Many thanks for all your help, I had not reckoned with the blessed 'tuner' and my own lack of attention, and will post when she's a runner again.

Jeff

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Re: Oil scavenge problem

Postby SPRIDDLER » Tue Jul 03, 2018 9:17 pm

Kneedy wrote:the plain main bearing bush had been similarly modified, with a drilling made half in the bush and half in the case, to take a 3/16 grub screw to prevent the bush turning under extreme conditions. ........ so am thinking of fitting a solid bung, interference fit with bearing fit Loctite, had good results with that in the past. Any suggestions gratefully accepted.

It should be a solid peg. Pt. No. 012233.
See your bike's spares list. Page 8
http://archives.jampot.dk/book/Spares_l ... _G80CS.pdf

Crankcase bearings.JPG
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I poke badgers with spoons.

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Re: Oil scavenge problem

Postby Kneedy » Tue Jul 03, 2018 10:06 pm

Ok thanks for that, so that is standard then. no sign of it on the damaged original case, or the remains of the destroyed bush that came out of it. Maybe the replacement case had been 'uprated' to a 3/16 threaded peg/grub screw. Can't imagine factory machining would have broken through into the oil way. My first Matchless, its seen some action in the last 62 years, as they probably all have, interesting learning curve!
all the best

Jeff

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Re: Oil scavenge problem

Postby Mick D » Wed Jul 04, 2018 7:20 am

Hi

I'd have no reservations about using a good epoxy structural adhesive, I've used Double Bond and Metalset for years and have never seen it fail or degrade.

https://www.smooth-on.com/tb/files/METALSET_A4_TB.pdf

The only other option I can think of is an aluminium taper pin cut lengthways.

Regards Mick

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Re: Oil scavenge problem

Postby Kneedy » Wed Jul 04, 2018 9:15 am

That's worth knowing, Mick, thanks. The aluminium pin was the route I was considering, I've never used an epoxy inside an engine, though I know the 2 stroke tuners use it for stuffing crankcases so obviously works ok. The thread in the hole would provide a good key. I'll try to find out more about the proper peg, though I'm sure the hole in my case has been opened up, the bush would need machining to accommodate half a 3/16 peg/screw.
Grandad duties taking precedence for the next few days but that will give me time to consider my options, plenty to think about!

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Re: Oil scavenge problem

Postby Kneedy » Thu Jul 12, 2018 7:59 pm

following Mick D's recommendation and having researched it I bought some Metalset A4 and have used it to plug the offending hole, taking care not to block the oilways. With it cured and checked I rebuilt and refitted the engine and ran it up this afternoon. After a 2 - 3 minutes there was a healthy flow of oil back to the tank, pulsing at idle but a good jet with the engine speed increased.

I ran it for 8 minutes at a fast idle, high ambient temperatures in the garage (30+ DegC) meant it got very hot and I didn't want to overheat the new bore and piston, but there was no repeat of the problem, ie chain case filling up, and the oil tank level stayed stable.
There is oil spitting from the crankcase breather, but that could be blow by as the new rings and bore are not bedded in yet. I did check the breather disc and housing while it was apart.

So a lot closer to giving my late friends' widow a pillion ride, which was a condition of the sale to me! It was always his intention to restore the bike when he retired, but sadly he never got there.

Many thanks for all the help and advice, a great result!! :beer:

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