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Allan G
Allan G
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A10 crank into A65
#390949 08/22/11 11:47 am
Joined: Mar 2011
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wak Offline OP
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Hi,im just starting to build the engine for my metisse, iv got a alternator A10 crank to use in A65 cases iv made a sleeve for the bush and bored out some T140 rods, i plan to use T140 pistons,as anyone done this and any advise would be well recieved,cheers wak


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Re: A10 crank into A65
wak #390954 08/22/11 12:13 pm
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Ive done it with stock A65 rods. Your triumph rods may be longer dunno. My cases were 1969 modded to take 1970 barrels with the bigger studs, the later barrels have a bit more meat to them
You may need to remove material from the top of the cylinders to get a reasonable comp ratio, the stock A65 rods with T140 pistons and A10 crank do not come far enough up the bore because the T140 pistons have a lower gudgeon pin to crown height. Crown height is shorter than the gain in stroke from the A10 crank. From memory around 40 thou was removed to get 9.5 :1.

I wouldnt take as much of if doing it again aim for 8.5 to 9:1, this motor is more pinky than my other short stroke 750.
Doing this again I would use low comp flat top triumph pistons to get a better chamber shape at TDC and adjust barrel height to suit.


SRM did it for me and end fed the crank as well.

Also hours of fun ahead adjusting pushrod length, you need to pull the steel cups off one end and shorted by the same as the barrel, checking v/v opening at 1/2 lift gives 90 degree rocker geometry.
My dynamo A10 crank needed a thread cut for the rotor, but yours should be OK. This motor is very/ too loud through std goldie pipes from Unity Equipe.


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
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Re: A10 crank into A65
wak #390977 08/22/11 2:43 pm
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wak Offline OP
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Thanks for that Gavin, the T140 rod is the same forging as the A70 same centres but you have to take 0.040" off the width and take a few thou out of the big end bore or use triumph shells and grind crank to triumph size (ideal if you Have a worn crank)I got mine line bored as a pair for £20,i dont intend to go too high with the compression i dont think theres much gain now days.How does yours go ? what sort of revs do you take it to ?


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Re: A10 crank into A65
wak #391140 08/23/11 8:55 am
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Why not use A70 pistons then the valve cutaways in the crown will be in the right spot and at the right angle. Ed V who advertises on this site has them in a forging with good quality rings.
http://www.shopevengineering.com/pr...182&shopBy=-8415&catalogId=-2087
I use his B44 pistons but they are similar, they can be fitted much closer than cast, so don't rock about as much, and the rings are better, my experience has been good, far better than anything I have used before. I think any extra cost is more than worth it and better value. Plus as an alternative to T140 pistons don't need extra machining.
When I used an A10 crank I fitted an A65 flywheel, I don't think the A10 fitted in the case? They run very nice with the extra displacement.


mark
Re: A10 crank into A65
wak #391148 08/23/11 11:18 am
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wak Offline OP
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Thanks for the info Mark,iv never seen pistons like that before how ideas change ! All i want is 45 rwbhp at about 6000 rpm with a target weight of 290lb. I was hoping to get away with 7.5 -1 cr and 30mm single carb,i used to race a bored and stroked A65(norton crank ,B44 pistons)it was very fast but i cant imagine it as an every day ride!


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Re: A10 crank into A65
wak #391224 08/23/11 5:52 pm
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wak Offline OP
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a bit of green laneing ,but il probably fit k70 tyres and have it as a bit of a flat tracker,my pre 65 mx days are well over and anyway it'l be far too pretty to get mud on !!!


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