reparing sump plug thread in situ

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
StephenG80
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reparing sump plug thread in situ

Post by StephenG80 »

Whilst not ideal, is there enough clearance in the inside of the crank cases to fix the sump plug thread (helicoil) in situ. I am intending to drain the petrol tank and gently lay her on her side - but if there is not enough to for the tapping threads to go fully through to cut then that is a non starter (I know this is not ideal and the swarf will need to managed so no lectures please :D ).
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les ward
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Re: reparing sump plug thread in situ

Post by les ward »

I did something similar many years ago, when I was young and daft. I drilled out the hole and tapped to a BSP thread to fit a new sump plug, using a tap for a blind hole. My father in law, who was a toolmaker for the Electricity Board experimental dept, helped, but made me do all the work. We were very careful with the swarf, using grease inside to catch the swarf, and then flushing out many times with a fluid he got from work.
When bits of swarf turned up on the filter in the oil tank I decided to take it apart and clean it all out.

So in my experience you can do it in situ, but I wouldn't do it again myself.
StephenG80
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Re: reparing sump plug thread in situ

Post by StephenG80 »

re internal clearance - when you daft and young Les , was this on a G80s?
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Duncan
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Re: reparing sump plug thread in situ

Post by Duncan »

les ward wrote: when I was young and daft
Ah, those were the days, with youth gone that just leaves daft I suppose. :?

I believe there was part of a Jampot article covering this several years ago using a pipe cleaner and grease to cleam the sump.
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cfaber
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Re: reparing sump plug thread in situ

Post by cfaber »

With Helicoils you have to drill, tap, thread the coil in then snap off the coil driver barb, with all that you're introducing a lot of swarf (metal chips, etc.) into the crank case directly below the oil pick up. I wouldn't do this, but if you decide to, be sure to flush the case out as good as possible and be sure to retrieve the driver barb as this thing will literally destroy your motor if it ends up in the oil pump.

For reference, on my '54 S casting it's 15.40 mm from the face on the bottom of the crank case to the oil pick up
Image


with an 10ish... mm casting thickness (when you account for the facing on the plug hole) there's not a huge amount of meat there for the helicoil to grab onto and it may be hard to find one that is short enough.


Image

So you have about 14mm of clearance from the hole face to the bottom of the pick up hole without crashing into the casting.

Image

Good luck!

Oh and by the way, I have a similar issue and will be plugging the hole in the casting with a pin then machining it back flush, and then drilling and tapping a fresh correctly sized hole, but to do this, the engine has to be apart :D
Fix it until it's broken!

Otherwise how will
anything get done?
StephenG80
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Re: reparing sump plug thread in situ

Post by StephenG80 »

thank you everyone - those measurements were very useful cfaber! I am concluding I will just drill the plug head horizontally for safety wire and leave it be for for now with a new dowty washer and sort it properly with the engine out at some time. With the dodgy thread I can't nip it up tight to stop it weeping completely, but at least it wont go anywhere with safety wire on it. Rights that decision made 8-)
Mick D
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Re: reparing sump plug thread in situ

Post by Mick D »

Hi

There is another option, (bodge), you could consider if you have access to someone who knows how to use a screw cutting lathe.

Turn up a replacement plug with a slightly oversized thread, (same TPI) - the plug will then form a mating thread in the case as it's screwed in which will more than likely give you a seal in conjunction with a Dowty washer. No swarf will be produced and you will still have the option of Helicoiling or sleeving in the future.

Regards Mick
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REW
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Re: reparing sump plug thread in situ

Post by REW »

Lots of great advice there for a proper job. Fwiw I do not remove the sump plug on my machines at all and so I would probably use silicon sealant to both seal and fix the plug in place until the motor had to be opened. :shock:
Ron

1951 Matchless G3L thumping round the Durham Dales.
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Re: reparing sump plug thread in situ

Post by Triumph-Legend »

Stephen G80 wrote:thank you everyone - those measurements were very useful cfaber! I am concluding I will just drill the plug head horizontally for safety wire and leave it be for for now with a new dowty washer and sort it properly with the engine out at some time. With the dodgy thread I can't nip it up tight to stop it weeping completely, but at least it wont go anywhere with safety wire on it. Rights that decision made 8-)
Problem.
Thread either partially or completely stripped in the case.
Helicoil not really an option due to high risk of swarf contamination whilst drilling / tapping and fitting Helicoil. Same applies to using an over size plug.

Firstly is the thread on the drain plug in good order? If yes, drill and tap a thread through the drain plug, around 3/8 or 1/2 inch should work. The bigger is better as this will be your new drain hole. Have a check with your measuring stick to see what size works best without taking away all the strength from the plug. Then just use a suitable size short bolt and fibre washer screwed into the revised drain plug hole.
If you have a mate with a lathe, you can skim down the original drain plug head to give a flat surface and reduce the head thickness a bit.
Fit the new smaller size drain plug using a plain and fibre washer into the original drain plug.
Now this won't cure the leaking from the original drain plug / case thread, especially if the thread is knackered. So this needs to be sorted out.

Lay the bike on it's side, Do a really good job of cleaning out the drain plug hole. Also rough up the drain plug thread a bit the allow the epoxy to get a decent grip. Now fit the original or a new, (modified by drilling and tapping), drain plug using a small amount of epoxy resin around the base threads of the plug. Leave the top two or three thread free of resin. Don't put the resin into the drain hole as it will be pushed through as the plug is screwed in. JT Metal weld or similar on the threads will work fine. wipe of any surplus resin to make a tidy finish and also to allow a spanner to grip the original plug.

Hold the original bonded in plug with a spanner when loosening and tightening the new drain plug during oil changes.

Using this method you will cure the leaks without causing further damage to the case and the case can easily be Helicoiled during the next engine overhaul.

As another rather more risky option. If there is some decent thread remaining in the cast but the existing drain plug is a very loose fit. See if your local engineering shop will turn you up a new plug with a slightly over size or very slightly tapered thread. Don't over do this as it is possible to crack the case casting if excessive force is used.

I would go with option one as it is a simple home fix.
56G80S
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Re: reparing sump plug thread in situ

Post by 56G80S »

As a disciple of BodgeIt & LeggIt - I would do the "wire on" mod and use plumbers TPFE to seal up the thread. Not as secure as the epoxy approach but much more straightforward.

This isn't a criticism of others views, just what I would do as a stopgap.

Johnny B
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