A65 crank in an A7

[Radlan2]

Hi folks
    Further to a flurry of postings back last Dec/Jan I have not posted anything but have read a lot of interesting stuff on this great forum.
     I have made progress building a big bore A7 using Triumph T110 71mm pistons in a thick flange Daytona barrel. I tapped the crankcases for through bolting and I have plugged,welded and 're-drilled the head to match, and made special studs out of EN24T.
      My question to the knowledgeable is, I found the information of the NJ 206 bearing very interesting. My plan is to use this bearing and turn/grind the drive side of the A65 crankshaft to fit. I am doing this to get the benefit of a large journal crank. The SJ  crank had a reputation for breaking according to Roland Pike. (And now they are 50 years older!)
       Has anyone else done this or thinks it is a bad idea? It seems a lot easier to me than boring out the cases to accept the larger A65 bearing.
          Interested in any thoughts
               Chris

[ironhead]

Hi, I think you will find the A65 crank is  1.125" ( 28.575 mm )  & the 206 bearing is 30mm  .  building up the shaft or fitting a sleeve is what will be needed. Ive been going to do this mod for a number of years now myself. hope it works for you.

[Radlan2]

Hi Ironhead
     Ahh yes that was a bit of a dumb mistake, but the same still applies easier to change the crank than the housing. In fact I can make a sliding fit sleeve to get everything right before making an interference fit sleeve for the final assembly. I will not go to building up the shaft with weld to do this.
     Also I would use the early type A65 crankshaft for this, good plan?
           Best Regs
                Chris

[edboy]

hi chris. a good idea to use the a65 crank in a a7. i think you need a pre 65 crank as the offset changed. also you could have the journal hard chromed to 30mm diameter. probably easier than machining. be careful with the nj bearing as the rollers can catch and turn when assembling crankcases.

[muskrat]

G'day Chris.
I had played with the idea of an A65 crank in my A7SS racer. I made a shrink fit sleeve for the DS main. Unfortunately that's as far as I got. After the last SJ crank snapped I hung up my race suit. The A7SS is now a A10RR+ and on the road as my Cafe.
Are you thinking of using the longer shaft for an alternator conversion?
Both my A7 plunger (with the SS racer top end) and Cafe are through bolted. A good mod for rev heads like me. I made cast iron studs to fill the barrel holes and re-drilled. Same with the twin carb heads, tapped the bolt holes and made alloy studs to suit. Lani at Coppergasketsunlimited has the template for the head gasket, extended ears for the four outside bolts. https://www.a7a10.net/forum/index.php?topic=1806.msg12343#msg12343
Cheers

[Radlan2]

Hi Edboy, Muskrat.
       Thanks for your replies, good suggestion about hard chroming to build-up the shaft I hadn't thought of that,don't know if they can build it that thick, Philpots the fork chroming people advertise a service for cranks.
          Musky, I will probably shorten the crank, I usually run total loss electronic ignition which lasts about 3 1/2 hours with 11AH battery. I have tapped the crankcase 3/8 WHIT x 1 1/4 deep to make certain the theads do not weaken from heat cycling.
          The barrel had already been through drilled when I got it so it was easier to convert the head and case than go back. Like you I tapped and plugged the head with 12mm alloy and welded and 're drilled. It's a twin carb big valve A10 head, I contacted Lani a while ago but then things went quiet, hope he's ok.
            Thanks for your encouragement
                 Chris

[edboy]

i will make the pushrod cover to frame mod as soon as i have time. good barrels are in short supply.

[Radlan2]

Predictive text? Non comprende

[Radlan2]

I am not a crossword puzzle person, a bit cryptic for me, took me all day to work out what you meant!! To stop your barrel breaking at the base you are going to make a lump of wood to wedge between the rocker box and the frame.

[muskrat]

G'day Chris.
I made a jack bolt from the frame tube to the rocker box as well. Welded a 5/8" nut under the frame tube and screwed a bolt onto it. Then bolted a 1/2" plate to the r/box and screwed the bolt down till it was firm. Sorry I can't find a decent photo.
Cheers

[edboy]

yes sorry about confusion, i was absorbed with muskrats link where a contributor had made a alloy spacer with adjusting lock nut at the pushrod to frame bracket. worth a look and a good precaution as i ve had the barrel base break years ago on the m25. that episode put me off the bsa for a few years.