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How To: 1913 Veloce motor bottom end build

August 2, 2012

While rebuilding the 1913 Veloce motor, I wanted to make sure that the heart of the motor was strong and would last for a long time.  The first step was to layout all the parts in Solidworks.  Then I could measure and modify things if needed quickly, and without cutting metal.  The only fundamental change was to eliminate the bronze bushing in the big end of the connecting rod, and to insert an INA needle roller bearing.  But of course, that wouldn’t fit into the rod, so a new one was designed then cut from 4140 chrome moly steel.  It mostly matches the size and shape of the old one, but the big end is larger and the section thickness is a bit more.  Also it is a bit more squared off as it is machined instead of being forged.  It should be plenty strong for the 5 horsepower motor, or 10 times that amount.  A new crankpin of 8620 steel was needed too, to match the INA inner roller bearing race.  It is oversized compared to the original and the crankpin OD now matches the OD of the(redundant) inner race, and the rollers ride directly on the pin surface.  This was done so that the crank pin could be as large of a diameter as possible to retain strength.  It was heat treated and hardened to Rockwell C 62 to .050” depth.  Edwards Heat Treating did the case hardening and I highly recommend them.

veloce crank assyveloce crank assy xsection

Section view of the crank assembly.   On the far right is a representation of the inner wall of the crankcase, to verify that the crank pin nuts wouldn’t foul the boss for the main bearing.  No crankshafts or main bearings are shown in this view.

Veloce connecting rod




 Veloce crankpin

By using CAD, I was able to compare the old and new crankpins on top of each other.  Things like the taper fit vs a .002 interference press fit, or the new vs old OD were easy to check.  I owe Greg Summerton for his advice on the best size of the pin OD, the root radii and the selection of the better INAs from their big catalogs.  He has used similar designs while rebuilding big JAP racing V twins in Australia.   When the layout was done, I created some fabrication drawings:

veloce crank pin


veloce con rod rev02


The crank pin after heat treat, but before grinding.



The crankpin after grinding at Harbur Grinding.  They kept the two outer surfaces round and concentric to .0001”.  Crank pin nuts are new items, made to fit a flathead HD.  They were bought aftermarket, for about $10-15 with keepers, and were already heat treated and ground perpendicular on the mating surface.  I set the threads on the crankpin to match the available nuts, instead of making nuts, or trying to buy a set from England.  So there is one American thread set on the bike, but it is buried very deep inside the machine.  Smile




Here is the rod with the INA bearing installed.  There is a grooved machined into the face of the big end of the rod.  This should allow oil mist to get into the needles.  There is also .028” of end float for the same purpose.  Early motors like this do not have positive oil flow to the crankpin,and rely on the mist that flies around inside the motor from a hand pump that puts a squirt through the crankcase wall every few miles.  Primitive, yes, but it works for 4-6hp.  Needle rollers don’t require a lot of oil if they aren’t heavily loaded, so this setup should last longer than the old plain bronze bushing.  A few guys have run these bearings on their early Triumphs, Premiers, etc. and report that the motor revs a bit more freely, and have lasted for several years thus far.  The INA rollers and outer race were used, but the inner was discarded.  The rod also has a new  bushing in the little end that I made from bearing bronze to fit the piston wrist pin.



Ready to assemble.




Here it is with the VW bug 1600cc piston in place.  This piston is a good fit for early Triumph and other motors.  It is just about .015” over the nominal size of the old cast iron piston, so you don’t need to remove too much material from the bore to fit it.  The early barrels are pretty thin down by the mounting flanges, and mine had already been broken and repaired at least once before I got it.   Fingers crossed that it will last for a while….


Here’s an old photo of the motor upon the first disassembly.  You can see the old rod, cast iron piston and crankpin at the bottom of the image.1913 veloce motor

19 Comments leave one →
  1. Jim Abbott permalink
    August 2, 2012 12:14 pm

    Pete: Maybe it’s the perspective but the new rod makes the piston look absolutely tiny!
    From one illustrator to another, nice drawings. Jim A., Tucson, AZ

  2. Anonymous permalink
    August 2, 2012 12:50 pm

    very nice pete ,did you do the machining of the rod? jon szalay

    • August 2, 2012 2:09 pm

      Hi Jon. I sent the STEP file to a local CNC shop for the rod. I probably could have machined most of it on my little mill/drill with the a ball end mill and a boring head, and some neat setups to get the tapered sides. But it would have taken me two days. The shop did it in a hour, and charged me a decent price. Let me know if you want a copy of the CAD file for your HD single! 😉

  3. Lindsay Brooke permalink
    August 2, 2012 12:58 pm

    Pete, this is one of your most interesting posts. Goodman’s boffins at Hall Green could not have imagined the CAD environment. Very nice work. Best wishes on running in the 100-year-old engine. Lindsay Brooke, SAE International, Troy, MI.

    • August 2, 2012 2:18 pm

      thanks Lindsay. It would be great to see what the Goodmans, Harold Willis, etc. would do with today’s tech. But is a different game now. I design and build in CAD for 40 hours a week in my day job, but play around with hand files, torches and hammers, etc after working hours while playing with the old bikes. The 9-5 work is a challenge, and the after hours work has different challenges, that’s for sure.

  4. Anonymous permalink
    August 2, 2012 2:41 pm

    cmon pete,, thats no fun,, i made a rod by hand in the back of a van in parking lots throughout the midwest ,, cad what ?ha ha!! really nice job i am envious of your technical skills
    jon szalay

  5. August 2, 2012 5:12 pm

    Looks good Pete. I am sure it should preform and last quite well. Sure, the lack of direct lubrication seems downright scary when looking at old stuff from the modern perspective where all engines have positive feed to big ends…. but then all you ahve to do is consider two strokes…and how their needle roller big ends survive on that TINY amount of oil mixed in with the fuel! Of course their rods have slits to allow easier access,, but I am reasonably confident that your arrangement with the slots and generous side clearance should suffice for aa low speed and low pwer machine. Good luck fella! I am envious of such an early machine.

  6. August 2, 2012 8:52 pm

    Waaaaaaaaaaa??? This a Lamborghini (sp) or something? Such beautiful work! I’m finally playing with assembling/building/improving my 1917 Henderson motor. Small cylinders make it look like a toy to me. Thanks again, Paul

  7. August 3, 2012 4:51 am

    Just curious Pete, the new pin has no tapers? Mike

    • August 3, 2012 9:22 am

      right. It is a .002″ press fit into the flywheels. Plus the nuts are there to be double sure that it can’t move.

  8. Kelvin permalink
    August 3, 2012 5:10 am

    Well done Pete. Good to see the homologation of new technology putting the old and intersting back on the road where they belong. I am envious of the workmanship involved at all levels!

  9. Doug Lyon permalink
    August 3, 2012 9:15 am

    Great article and marvellous work! On the Precision I just made another bush. The pin is very flimsy on that motor, about 0.75″ OD so the crank is easily flexed! Yours should be a lot stiffer. I used an INA bearing on my ’34 W7 BSA, but got the one with the oil hole in the outer race, which seemed to be standard. When I pressed the bearing in, a sliver of the rod liner I’d made broached through the oil hole and jammed the race – didn’t see that one coming. Luckily they are pretty cheap! Keep up the good work!

    • Brent Lenehan permalink
      October 27, 2012 6:48 am


      I notice your post above and that you have a 1934 W7 BSA. I have a 1936 Q7 BSA and live here in Alameda. I would be interested to share some experiences with you as I believe they are quite rare in the US.

      Brent Lenehan
      510 910 9954

  10. August 4, 2012 9:31 pm

    Had to google ‘Solidworks’ but other than that a nice clear and concise explanation of applied engineering logic.

  11. August 6, 2012 10:43 pm

    Damn, you’re a fancy pants.

  12. Bruce Farren permalink
    August 17, 2012 12:44 pm

    Hi Pete,

    Doing a similar job myself at the moment. I am making a new big end for my 1929 AJS. Same material as you for the pin (8620) and 52100 for the rod liner. Don’t need to make a rod luckily. Keeping the original design for the bearing, two rows of 1/4″ x 1/4″ crowded rollers. Once the crank is done, many more parts for the motor to make after that!

    • August 17, 2012 1:25 pm

      That’s fun work Bruce. Be sure to send me some photos. I saw one of the in the VOCNA newsletter I think.

  13. Brent Lenehan permalink
    October 27, 2012 6:43 am

    I notice that Doug Lyon makes a comment on this article in August and notes he has a W34-7 BSA. I have a similar bike – 1936 BSA Q7- here in the Bay Area and I would be interested in sharing experiences. Anyone know how I can contact Doug?

    Brent Lenehan
    Alameda CA

    • October 27, 2012 10:15 am

      Hi Brent. I’ve sent Doug your email address. He’s in the southern portion of England though, not the USA.

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