Running in / did it seize ?

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: Running in / did it seize ?

Postby bjorn » Wed Jun 13, 2018 9:21 pm

Trevor,
The hairpin valve springs are quite noisy and could well be your "whirring" sound if the engine is rotating without firing, i.e. no exhaust noise.

A check to see/hear where the whirring comes from could be done as follows: Find a suitable long downhill road stretch with no or little traffic. Turn off petrol tap! Take off spark plug cap and put it onto a "loose" plug taped or wired to the engine - must have earth connection to the metal. Original plug to remain in head of course! Engage 3rd gear, pull in clutch and coast till you reach a reasonable speed. Release clutch and listen to the noise(s) !

Bjørn

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Re: Running in / did it seize ?

Postby Spanielsam » Tue Dec 04, 2018 2:48 pm

Hello, a follow up to my previous post

I finally decided to lift the head to see what had gone on as it was eating away at me
It looks like the piston has seized and has marks in one place , the bore looks ok with very light scoring , i think i will clean both up and see what happens bearing in mind the bike has done 300 miles since it happened

I think i might have found out what i might have done wrong but would appreciate some guidance / advice

When i rebuilt the engine i used gasket cement in addition to the base gasket and i think the sealant might have gotten into the groove that runs around the base of the barrel which i guess might have stopped oil getting into the holes that are in the barrel , i would appreciate your comments if you think this might have caused the issue and do more experianced owners use gasket cement of the base gasket ?
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Re: Running in / did it seize ?

Postby spookefoote1956 » Tue Dec 04, 2018 3:38 pm

Why did you use goo?
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Re: Running in / did it seize ?

Postby SPRIDDLER » Tue Dec 04, 2018 4:07 pm

Which face of the piston are you showing? Front or back? There seems to be a vertical line running through the score mark.
Later barrels were fitted with no other engine modification (edit: other than a blanked off feed hole) and therefore didn't need a groove in the bottom of the cylinder. I've blanked off the oil feed to the barrel in the crankcase face on my G3LS and used a non-grooved barrel on an engine that previously had a grooved barrel and not had any issues.
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Re: Running in / did it seize ?

Postby Spanielsam » Tue Dec 04, 2018 5:58 pm

The photo is of the back of the piston, and I was probably clutching at straws regarding the gasket cement blocking the groove ? I would like to understand why the seize occurred and then has done another 300 miles with no apparent problems
Do you think the long groove has been made by a foreign part , you have got me thinking now ?

I used gasket cement as the faces are ok but not brilliant and so it seemed like a belt and braces approach
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Re: Running in / did it seize ?

Postby SPRIDDLER » Tue Dec 04, 2018 6:25 pm

From earlier posts it seems you have only covered around 500 miles since a re-sleeve and new piston.
You mentioned that the rebore was by TL Engineering so the piston clearance should be fine.
As the scoring is on the piston thrust face it looks to me like a fairly mild nip-up, not particularly unusual after a rebore, and just a clean of the piston and cylinder (perhaps a light honing) would be sufficient.
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Re: Running in / did it seize ?

Postby Spanielsam » Tue Dec 04, 2018 6:38 pm

Thanks Spriddler, your comments are really appreciated

This is my first experience of an old single and its difficult to differentiate its engineering versus the likes of my Yamaha two stroke

All good experiance and i love riding the bike
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Re: Running in / did it seize ?

Postby clive » Tue Dec 04, 2018 6:54 pm

looks like a mild overheating nip up. So long as the rings are free I would just clean the piston up and if you have access to a hone, a light hone of the bore. If you feel the base gasket needs any help I would use nothing more than Wellseal. As suggested the oil groove was later phased out so even if it was blocked it is unlikely to have caused the problem. I would say it was just a little tight. As Sprids says you have now done 500 miles and risks should be reducing I would still take it easy for another 500 miles though.
clive
if it ain't broke don't fix

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Re: Running in / did it seize ?

Postby Spanielsam » Tue Dec 04, 2018 7:49 pm

Thanks for your reply Clive

The rings are all free in the grooves with no carbon build up and look as good as new
Its just under the rings where the problem appears to be

I expected a ring to be broken or something similar but the top end of the piston looks good

I will put it back together and treat it very gently for a while

Thanks for all the responses, without this forum i would be lost
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Re: Running in / did it seize ?

Postby Dixter » Wed Dec 05, 2018 10:20 am

Trevor, when pistons get nipped up, I’ve done it a few times myself, a small amount of aluminum is transferred into the pores of the ferrous metal cylinder. Running a bead hone or similar thru the bore does not remove the microscopic particles. Aluminum rubbing against aluminum will promptly gall one another. There is much value in chemically removing these particles to reduce the likelihood of future nip-ups.

The method passed on to me by an old time friend and professional motorcycle mechanic is to use a few crystals of Draino drain cleaner, a common form of caustic soda or lye. Note, this is nasty, nasty stuff. To do this safely, degrease the cylinder, lay it on its side, surface to be treated at the bottom, cut a rectangle of paper toweling two inches wide, 4 inches long, and lay this strip over the area where the galling most likely occurred. Liberally wet the paper with water. Sprinkle 1/4 teaspoon of caustic soda crystals on the paper, and allow to sit 15 - 20 minutes. There is no harm in doing this twice.

However, there is big harm to humans, breathing the fumes, or getting the crystals or wet solution on your body, or in your eyes. Skin will burn immediately. Wear rubber gloves and account for spills on your work surface.

Wash off the caustic soda, hone the surface, clean, oil, and reassemble.

Safety first,
Dick
Dick Casey
The RideNut

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