Its probably been asked several times already, but how much labor is involved with running an A10 crank in an A65 mill? I've been browsing around for info and some say to use the stock rods with Triumph T-140 pistons. It appears that this would be like running +.040 on the bore size, but I'm still curious about the wrist pin height. The T-140 had a stroke of 82mm (from the specs I've read anyway) and the A10 crank has an additional 2mm of stroke so won't the T-140 pistons poke through the top of the deck too much at TDC? I have to do a full overhaul on my A65 anyway so I thought that while (whilst) its apart this would be the time to stroke it. That is, if its a worthwhile mod. If its not worth the trouble then I won't bother with it. Are there any issues (tuning, etc.) to be concerned with? Cam choice? Any advice or info would be appreciated.
It's been a while since I looked at any of this , but as I recall , the triumph pistons were the same bore as std on A-65 , but I'd double check this . The compression height of the Triumph piston has the gudgeon pin set higher in the piston allowing for very close fit using the BSA rods and A-10 crank , the only issue with fitting these is you may be required to clearance the piston skirts to clear the flywheel.Also , you will want to use the later A-10 crank with the big journals . This should provide a stronger engine with more torque . A better source for pistons might be ED V., he stocks repro pistons for an A-70 BSA(the factory setup long stroke ) , but as far as I know these are only available in max bore .
Bill. As you are now going to turn your short stroke A65 into a long stroke (almost) A 70 it would be very prudent to get the crank carbo-nitrided. This will substantially increase the toughness ( resistance to cracking amongst others ) of your crank. Even better it is usually done by heating in a furnace with a controlled ammonia rich enviroment so there is absolutely no dimensional changes so it can be done after you have the journals machined. Commercial names for the process are things like Tuff Coat , Tuff Ride , Carbo Tuff. Almost every steel heat treater will do this process however it is much cheaper if you can schedule it to be done concurrently with lumps of steel of a similar size to be treated to a similar depth so you should ring around and then book it in to be done. Also check that the heat reater dose not pickle clean before treatment and what surface preperation they want to be done before it gets there.
Bike Beesa Trevor
Re: A65 Stroker (A10 crank) ???#19562 01/14/071:58 am01/14/071:58 am
Back when I was molding glass bonded mica we occasionally had mold cavities nitrided. There's a heat-treatment facility around the corner from where I work. I could inquire there. Would you recommend a different (lighter) flywheel or any lightening of the stock A10 flywheel?
The whole crank ( including pistons & rings) will need to be rebalanced both statically & dynamically. In general The heavier the crank the smoother the ride . The lighter the crank the more responsive the motor. You and only you have to make this decision. The flywheel will benifit from light machining aka the late A65. After that it all starts to get expensive. Regrinding the cam to suit the new stroke will be of benifit as will be flowing the head but will you be utilizing the increase in performance and are you willing to pay the price ?
Will I be utilizing the increase in performance? Well, I won't be taking it to the track and racing, but I do like to ride at a rather brisk pace. Will it cost too much? I've been into classic bikes and cars for years and its never been a cheap hobby so the short answer is I won't be selling everything and buying a scooter anytime soon. Now, with regard to lightening, balancing, etc. Of course I'll have to rebalance it, but I'm just curious about what would be a good compromise in terms of vibes, revs, etc. My stock 750 Norton (73mm bore x 89mm stroke) pulls decent revs. I don't see the A65/A10 combo being like a farm tractor in terms of the bore/stroke relationship. If I can just turn the OD down on the flywheel to lose a little weight that would pretty simple. Hope I'm not sounding too cynical now!
Thanks Panic. There's always a lot to consider when doing mods. If I screw up and make it too light I can add some tungsten to it later. Maybe not, I'll probably focus on keeping the recip components on the lighter side.
I used an A10 crank in my A65 some years ago, and I'm sure the A10 flywheel was too big a dia to fit the cases, I fitted an A65 flywheel, however to get it on past the crankpins etc I had to chanfer the flywheel a fair bit, if you try fitting one it becomes quite obvious where it needs doing. To retain the alternator etc I drilled and tapped the end of the crank for a bolt. Also it needs a roller conversion because of the differences in bush size on T/side end and reducing the drive end for the A65 rollerbearing I think. Std length rods and T140 pistons with modified valve cutaways if you are fitting bigger valves etc, which can give a real power gain. Naturally proper A70 pistons should already have valve cutaways at the correct angles, and should be better. Spitfire cam is fine in these, in my opinion its better to flow the head to get it breathing better.
Hi I am trying to do this mod at the moment! I have some full skirt bsa pistons @79mm,I also have a devimead big bore barrel,with the a10 crank. A n a10 big journal crank came my way a while ago,it had had the flywheel reduced,but i do not know how much by,when i assembled it all the full skirt pistons touch the flywheel at bdc or before,b44 pistons do not. Which are the best to use? Is it still possible to have the crank balanced after the flywheel has been reduced? Has this mod been documented anywhere,and if so is the specification available on the net? The crank came as a big journal,with end feed conversion,but it was past a65 shell sizes so it is on t140 shells and rods with steel end caps. Any info will be gratefully received!
Re: A65 Stroker (A10 crank) ???#19569 01/17/0712:18 am01/17/0712:18 am
Thanks Mark. I usually try to stay on the conservative side when it comes to selecting a camshaft. If head work will do the trick then I'll certainly opt for that over a different cam. Does the drive side journal of the A10 crank use a different bearing? I know the timing side journal is smaller than the A65. Whatever the case it doesn't appear to be too involved to get it set up for the A65 cases.