Hi all
I have a Model 20 dynamo crank that has just been reground to the 3rd regrind size as detailed in the AJS/Matchless workshop manual. As I read that, it means the journals are now 30 thou undersize, so I need +-.030 shells; have I read that right? Related to that, the manual shows three regrind dimensions, but the club sells big end shells up to +0.060, so it's presumably OK to go beyond the sizes shown in the manual? Not that I'm hoping that will be required any time soon...
Also, does anyone know where I can get a pair of +0.060 std compression pistons for the same bike? The club doesn't list that size.
Many thanks,
Malc
Big end shells and piston
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MalcW
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moley
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Re: Big end shells and piston
Cox and Turner will make you any size rings they are very knowledgable andy
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Groily
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Re: Big end shells and piston
Feked SAY they have JPs in +60, see
https://www.feked.com/jp-pistons-for-aj ... -1955.html
Whether they actually do, and the exact cr, would need a call.
Some people don't care for JPs all that much, but a pair have been very OK in my 650 twin. My 500 is on Hepolites (or AE) from memory, which are also in a spare engine that sits there ready to fit (- which means I won't need it with any luck as you only ever need what you haven't got!)
Usually, though, it is necessary to match the pistons to the bores so that the correct skirt clearances are achieved for the actual bits being used. You might be wise to look into that to avoid any risk of nipping up.
Lots of these cranks have been taken down below -30thou, yes. I have run at -80 in the past, when it was a 'thing' to use BMC A series shells with tweaks. Should be plenty of life left in yours with any luck and they do last very well between grinds anyway if the oil is changed regularly. Thirty to forty thousand miles should be no problem, some people have managed quite a bit more.
I am a completely one-eyed fan of these engines and think they are the bees' knees for 'reliable' and are good to work on.
https://www.feked.com/jp-pistons-for-aj ... -1955.html
Whether they actually do, and the exact cr, would need a call.
Some people don't care for JPs all that much, but a pair have been very OK in my 650 twin. My 500 is on Hepolites (or AE) from memory, which are also in a spare engine that sits there ready to fit (- which means I won't need it with any luck as you only ever need what you haven't got!)
Usually, though, it is necessary to match the pistons to the bores so that the correct skirt clearances are achieved for the actual bits being used. You might be wise to look into that to avoid any risk of nipping up.
Lots of these cranks have been taken down below -30thou, yes. I have run at -80 in the past, when it was a 'thing' to use BMC A series shells with tweaks. Should be plenty of life left in yours with any luck and they do last very well between grinds anyway if the oil is changed regularly. Thirty to forty thousand miles should be no problem, some people have managed quite a bit more.
I am a completely one-eyed fan of these engines and think they are the bees' knees for 'reliable' and are good to work on.