Oil pump rear cover threads

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Oil pump rear cover threads

Postby Spanielsam » Mon Dec 28, 2020 7:55 am

Hello
The threads in the crankcase that are used to hold the rear oil pump cover are shot and I wondered if anybody had explored the possibility of using slightly larger threads / screws , is there enough meat in the case to drill and re thread ? I have looked and I think a M5 might work but no idea if I would be damaging anything internal
I know it's a bodge and when I take the engine out for a full rebuild in the future I will go for the holes being welded and drilled / tapped correctly
I have tried several sorts of sealant and it always seem to leak
Any advice is appreciated

It's a 1956 G80S
......

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Re: Oil pump rear cover threads

Postby clive » Mon Dec 28, 2020 8:34 am

Cannot help as its not a bodge I have ever done. I was just wondering though how you intend to drill and tap with the engine in place. If you are taking the engine out I would go for a helicoil insert of the correct size rather than going metric especially now the Brexit deal has been agreed. :roll:
clive
if it ain't broke don't fix

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Re: Oil pump rear cover threads

Postby Greybeard » Mon Dec 28, 2020 9:26 am

3BA helicoils are available - at a price :shock:
https://www.sdtsengineering.co.uk/produ ... r-kit-3ba/
but you would still have to drill/tap for a wider threaded insert which would probably be getting nearer to 5mm anyway (worth checking though if thats the route you decide to go). You might get away with a 2BA which needs an 4mm tapping drill.

Steve

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Re: Oil pump rear cover threads

Postby alanengineer » Mon Dec 28, 2020 10:42 am

helicoil kits are available from tracy tools at very reasonable prices

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Re: Oil pump rear cover threads

Postby Reynard24 » Mon Dec 28, 2020 11:28 am

With the engine in the bike there won’t be room for drilling to allow the use of larger screws but if you want to keep the engine in situ and bodging is therefore on the cards why not use something like JB Weld to secure slightly longer BA studs into the damaged holes and then use nuts to hold the plate?
I’ll get my coat.

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Re: Oil pump rear cover threads

Postby Mick D » Mon Dec 28, 2020 1:37 pm

alanengineer wrote:helicoil kits are available from tracy tools at very reasonable prices


But not BA sizes unfortunately - I use these: https://uni-thread.com/tr_ba_kits.php

I'd leave well alone until I could get the engine out and do it properly.

Regards Mick

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Re: Oil pump rear cover threads

Postby Spanielsam » Mon Dec 28, 2020 2:35 pm

Thanks for your replies, I guess if there is enough meat for a helicoil there will be enough for a M5 stud. The stripped 3BA thread measures around 4.1mm and so I would only be opening it up to around 5mm, my plan is to use M5 socket head setscrews as studs and then locking nuts to fix the blanking plate in place, if that doesnt work the engine will be pulled apart and crank case sent an engineering firm. The leak is too big to ignore and I am worried about the pump sucking in air
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Re: Oil pump rear cover threads

Postby Mick D » Mon Dec 28, 2020 3:03 pm

Spanielsam wrote:my plan is to use M5 socket head setscrews as studs and then locking nuts to fix the blanking plate in place


Lost me there! - do you intend to cut the heads off of the set screws or use over long ones with nuts wound down to secure the plate - either way it will be a blast to do in situ, please take photos ;)

Regards Mick

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Re: Oil pump rear cover threads

Postby Pharisee » Mon Dec 28, 2020 4:41 pm

Mick D wrote:
alanengineer wrote:helicoil kits are available from tracy tools at very reasonable prices


But not BA sizes unfortunately - I use these: https://uni-thread.com/tr_ba_kits.php

I'd leave well alone until I could get the engine out and do it properly.

Regards Mick


No. 3BA Helicoils (and I use that term generically, like "Hoover") are available as one of the oil pump rear cover screw holes on my '55 M18S has been repaired in that way. The repair was carried out by a guy in Maidenhead who specialised in repairing vintage machinery. He advertised on the internet but his name I can't now remember. I took the engine bottom end to him and he did the work while I waited. The oil pump was not returning oil to the tank. Of the four screws securing the rear cover, one was tight, two were loose and one was stripped. The pump has behaved perfectly since the repair.

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Re: Oil pump rear cover threads

Postby 56G80S » Tue Dec 29, 2020 5:08 pm

Following this with interest as back when I was only 22, I over tightened and snapped one of the little bolts and a local (Marske) engineer got the stub out and recut to a larger bolt but the thread is "weak". Right up against the crankcase, he said doing the job was very awkward.

As I have the engine out it is something I'd wish to put right while I can.

Please post how you get on.

Johnny B

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