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After its behaviour in France/Germany a couple of months ago, I've got the Sport's engine on the bench. Stripping everything down to get the engine out of the frame I realised that a 40-year old bike is probably feeling a bit weary: the fusebox had fractured completely into two halves; one airbox to carb rubber and one carb to manifold rubber tore in half when I started to remove them carefully etc. Anyway, heads and barrels off and pistons removed. The bores look tidy, with some slight vertical scoring and criss-cross honing marks still visible, although I didn't think that Gilardoni barrels would be honed...

And here are the pistons: the rear one (closest to the camera/telephone) is oily and carbony, the front one looks better. But the combustion depressions don't look like Morini pistons that I've seen before, they don't have vertical slits in the skirts and the diameter is 65.85mm. Both cylinders had 100psi compression when I checked before stripping. Any thoughts?

That's someone's home brew 400 conversion (a bit under 390cc) using an unknown piston.

Polo/Lupo pistons are 67mm (402cc) and have an off centre combustion chamber.

Are you sure they were Gilardoni barrels? It's not impossible to have them bored out and re-plated, but it's not cheap.

An update, but no answer to the piston question. The engine was played/experimented with by Alex at NLM, who's sadly no longer here to ask about it. Pistons and plated bores are all within tolerance and OK to use again. The unpleasant noises in the engine were the left hand main bearing cage, which had broken and distributed itself around the engine. Amazingly, the bits didn't do any damage. And now, thanks to George Lane, it's back together again, and a bit of Araldite will sort out the fuse box. Winter in the garage...

The gudgeon pins are off centre, so you cannot use any old piston that happens to have the same bore. People who have used Guzzi pistons to make 550's have come to grief in a very short distance because of that. A useless piece of information for you all is that, landrover petrol pistons from the Mk2 have de saxe bore (like the Morini) and it just so happens these pistons fit The Sunbeam Coupe de la Auto grand Prix car of 1913.

harrymuffin wrote:The gudgeon pins are off centre, so you cannot use any old piston that happens to have the same bore. People who have used Guzzi pistons to make 550's have come to grief in a very short distance because of that. A useless piece of information for you all is that, landrover petrol pistons from the Mk2 have de saxe bore (like the Morini) and it just so happens these pistons fit The Sunbeam Coupe de la Auto grand Prix car of 1913.

Ah - the sort of pearls of wisdom the chap at Piston Services, Cinder Bank, Netherton (gone now ) would probably have known about. He used to have an AJS *car* parked outside his premises (shed). In a similar vein, you can put a 350 Panther piston in a 1929 Raleigh 350, though you may have to saw a bit off the skirt.

I knew the place well. But, do you know the 'shop' in West Brom that had a small service hatch when having asked for some obscure part for a 1907 Triumph would disappear and come back in five minutes with the part wrapped up and brand new. It was a place of last resort if Vale Onslow did not have it, trouble is, thinking back to the 1960's has caused brain fade and I cannot remember the name of the place.

harrymuffin wrote:I knew the place well. But, do you know the 'shop' in West Brom that had a small service hatch when having asked for some obscure part for a 1907 Triumph would disappear and come back in five minutes with the part wrapped up and brand new. It was a place of last resort if Vale Onslow did not have it, trouble is, thinking back to the 1960's has caused brain fade and I cannot remember the name of the place.

Hmm. The small hatch sounds a bit like Perrys. Their workshop used to be on the first floor and all the bikes had to go up and down on a lift. Never knew they had such esoteric parts though. I bought an AJS 16C from them in (consults notes on flysheets of "Tuning for Speed") 1970. There was also Roy Peplow at Carters Green (trials Tiger Cub expert) but he had a counter as I remember it. Then there was a shop in Smethwick (The Globe?) that had loads of stuff for old British bikes including shelves of Hepolite piston's for obscure lightweights. I can remember when Vale Onslow still had a shop in Soho Road Handsworth. Then there is Chris Williams (of Aunty Alice Panther vintage racing outfit fame) at 'Autocycle'. I think he (or his brother?) are still in business in Netherton.

Sorry for the thread swerve Mark! Glad to hear the mechanical mayhem wasn't as bad as it could have been.

More hijacking - but I bought my first helmet (Silver Cromwell 'Pudding Basin') from Vale Onslow on the Soho Road, also drooled over the bikes in the window of Greys (I think) on Wellington Road down by Perry Barr.

Ming wrote:More hijacking - but I bought my first helmet (Silver Cromwell 'Pudding Basin') from Vale Onslow on the Soho Road, also drooled over the bikes in the window of Greys (I think) on Wellington Road down by Perry Barr.

Ah yes I remember it well. I did more than drool. I bought (on tick) a used T100SS from that branch of Greys and later traded it in (with slightly bent forks - a long story) for a Suzuki B100P.

Hi MarkB,

These look a lot like the pistons my dad has in his 400 (350 Sport). His are marked up as ASSO Werke, who seem to make pistons for all sorts of bikes. His crowns are perhaps a little shallower, but his CR is over 11:1.

P.S. His are definitely Gilardoni barrels too, 'Gilardoni' is cast into the aluminium.

Hi Donkey, thanks for that: I was going to hijack 72degrees's post in projects to get my revenge, but you've brought the topic back! Someone else mentioned Asso as well, but I've not been able to find any images with the same crown shape. My barrels also have Gilardoni cast into them, with the chrome bore in good condition, so the pistons have gone back in, as they have been for the last 20-odd years. As I've found at Cadwell (and not through my riding skills) my engine is wonderfully grunty coming out of corners compared with other 3 1/2s, and I'm glad I can keep it that way.

The Gilardoni process is essentially the same as Nikasil; Silicon Carbide particles suspended in a Nickle matrix.

Morini probably adopted Gilardoni barrels in order to make the engine quieter, which would have helped with overall noise limits. The barrel having a similar expansion ratio to the piston means you can run much tighter clearances without the likelihood of seizure. You also get better heat transfer and in high volume it's potentially cheaper than a separate liner.

Getting barrels re-plated is quite common for two-strokes.

How come my brand new Gilardoni barrels have got liners then?

You don'the have to plate the parent metal. It isn't unknown to have plated liners that are shrunk in. Although yours are new, it is a common repair method for engines that are too damaged to be replated. Bore out damaged cylinder, shrink in liner and job done.
George.

Hmm. But these are brand spanking new 71 bore barrels with steel liners and factory wrapped with cast iron compression and oil rings.