AJS & Matchless Owners Club

Thanks Rob

I see where you're coming from now.

Little end bush galling and mis-aligned oil way still factors in my head though

maybe related causes and effects

Regards Mick

Hello again folks. Pictures. Not for the faint-hearted. Also news on bore size etc.
In short, the bore is fooked, +010 thou piston clearance on +0.020 O/S piston. Need new piston, & rebore, & little end bush.

The wear on the left side of the bush was not caused by this piston. I think we may be looking at a previous seizure repair job.

Off to consult with Roger Crashby now.

Thanks for responses so far. Will attend to replies on bent rod very soon.

TTFN Jack

'I think we may be looking at a previous seizure repair job'

Criminal!!

Feel for you

Mick

Has anyone seen a G80CS piston like this before? Steve Surby tells me it is not an AMC piston. No markings other than "FRONT" stamped on the exhaust valve cutaway. This first photo shows the polished edge of the crown. The previous post's piston photo shows the wear at the bottom of the skirt on the opposite side. Tis' a monster crown. Weight is 514 grams bare, 614 grams with pin fitted.
Test reassembly shows that this piston was not in contact with the little end bush, nor does the piston show any signs of wear to the inner boss. The bush must therefore have been machined away in a previous disaster.

Thanks to Bjorn for your comments. The little end is in such a poor state, it may well now be crooked. The crankcase faces are perfect & the bore, apart from being O/S appears good & straight too.
One thought has occurred. With the bush being so short on one side, would the rod end now be unbalanced? This together with the excessive bore clearance may have allowed the piston to lean to one side?
Just an idea. I'm going to replace the bush, rebore to +040 & fit a new PML piston. It was running OK despite all the wear & damage prior to dismantling, just rattling a bit at low revs , so I'm going to see how it goes after fitting the new stuff. Can't be worse surely?
TTFN Jack

The piston is not AMC & fit to the head, which is very important, unknown. Send me a PM & I'll respond with photos of genuine AMC piston & PMLI replacements. PMLI is the only source I know of for good replacements of the 1960-up G80CS piston & are slightly lighter than original. Regards, Don.

Cheers Don. PM away to you.

One more thing I discovered yesterday: I extracted the old little end bush. It is made from aluminium. Not what I expected to find. Replacement is bronze & twice the weight. Never seen a little end bush made from alley before. Bit soft for that purpose?
TTFN Jack

jack clegg wrote:Cheers Don. PM away to you.

One more thing I discovered yesterday: I extracted the old little end bush. It is made from aluminium. Not what I expected to find. Replacement is bronze & twice the weight. Never seen a little end bush made from alley before. Bit soft for that purpose?
TTFN Jack

You're right; aluminium would much too soft. Could it be aluminium bronze which is significantly lighter but more expensive than phosphor bronze.
A very knowledgeable engineering pal made me a timing side bush from ali bronze which he assured me was far more hard wearing and generally better than the phosphor bronze original. I took his word for it and looking it up I find....(Wikipedia)

Aluminium bronzes are most valued for their higher strength and corrosion resistance as compared to other bronze alloys. These alloys are tarnish-resistant and show low rates of corrosion in atmospheric conditions, low oxidation rates at high temperatures, and low reactivity with sulfurous compounds and other exhaust products of combustion. Aluminium bronzes' resistance to corrosion results from the aluminium in the alloys, which reacts with atmospheric oxygen to form a thin, tough surface layer of alumina (aluminium oxide) which acts as a barrier to corrosion of the copper-rich alloy.

Aluminium bronzes are most commonly used in applications where their resistance to corrosion makes them preferable to other engineering materials. These applications include plain bearings and landing gear components on aircraft.........

Hi

The bush looks well manufactured, is there an annular groove around the outside so as the oil holes in the rod and bush do not need to be aligned?

Aluminium bronze will not be too much lighter - only around 10% is aluminium.

Regards Mick

Hi again,

No groove, oil hole was totally blocked off. Replacement bronze bush from Steve Surby weighs 45 grams. Old ally one weighs 13.5 grams. Soft as shite & was rather too easy to extract IMO.
Awaiting arrival of piston from US. I want to see the wrist pin size before fitting the new bush.
I had an idea that the bush would be pre-sized to fit nicely once fitted in the rod, but the new bush is too small for the old pin, which means nothing I suppose with a non-std piston. I hope PML pins are made to the original size?
TTFN Jack

jack clegg wrote: Replacement bronze bush from Steve Surby weighs 45 grams. Old ally one weighs 13.5 grams. Soft as shite & was rather too easy to extract IMO.

How bizarre that someone would use aluminium. You said it's a new acquisition; maybe it was just done to get it running to sell. I wonder if there's more to be discovered........At least the piston wasn't made of best oak. Might be worth checking the big end to see if it has a couple of nylon stockings wrapped around it.