I've been sorting the cranks out after making a pair of bob weights. One crank checked out good at 85% BF and from some numbers etched in it (EB xxxx) I think it was electronically balanced. It also has additional weights welded inside the counter weights. The other crank checks out at 62.7% BF. I'm guessing the bike would had a pair of cranks balanced at the same time. I'd be interested what other Triumph drag racers may have done to their cranks.
Race engine = higher reciprocating balance factor
Street engine = lower reciprocating balance factor
Unit construction =higher reciprocating balance factor
Frame design = reciprocating balance factor TBA by use
Still, looking at your cranks, I can't help being frightened by imagining them turning at say 8000rpm with the sheer mass of the centre flywheel and the distance between the 2 main crank bearings... It's a far cry away from my Harley K/Sportster cranks where the main bearings are 3"1/2 apart and the flywheels directly around them.
Or the Vincent cranks as you know them!!!
Remind us what is the joint between your Triumph flywheels and the cranks themselves?
I also remember a very old discussion (where??? Getting old...) on the necessary timing between the 2 engines to get traction in an orderly fashion so to speak (... while burning nitro in a near uncontrolled way...)
All the best from Patrick
PS, story from my misspent youth... Friend of mine in Paris had a British bike shop... He decided to make publicity for it by buying a Triumph nitro dragster in Great Britain. Seller offered him for a small extra fee to assist him in his 1st outings... Declined...
1st metting in Le Mans if I remember right... 1st start up... Engine exploded breaking all else around the bike... Magneto, head, cylinder, gear box AND frame...
Help me out here, not sure what you are asking.
"Remind us what is the joint between your Triumph flywheels and the cranks themselves?"
Yes, billet cranks break and nitro can destroy even the best parts. Today you can purchase forged billet cranks for many vintage race motors.
As for timing the 2 motors, recently I had a conversation with Sonny Routt and was told to set both motors exactly the same otherwise the chain between motors will not last.
Anyone balancing these flywheels will agree there are many factors that make the least vibration. John Healy is a good source of information on the subject so will definitely pay attention to his writings.
Does anybody know what would be the best BF for two motors bolted between ridged plates revving to 8 or 10,000 rpm on nitro. Wish I had the time and $$ to experiment but alas, I just want to hear them run and smell that mix of nitro and castor oil.
Patrick, yes one piece flywheels. Actually 2 pieces as the counterweight ring is shrunk then bolted to the crank. The 3 piece crank has the rod/main bearing journals bolted to the center section. I don't know anyone who has used this type.
I will actually test run the motors on methanol and when everything checks out a nitro mix will then be used. The location of the injector inlets make it difficult to squirt a startup fuel so I'm thinking of a separate setup just for starting when the main fuel is nitro. May not be necessary but will consider it.
Since you like vintage and unusual machines can I send you some photos of a bike engine that has no name on it but the guy I got it from said he thought it was a French bike motor from the 1930s.
The project is coming along. It came with a set of Norris "D" grind cams and a set of cams in a Harman & Collins box. I'm not sure what they are except they are reground from Triumph cores. I'm going to use the Norris cams. The tappets are pretty rough so I'm trying to built a tool to hold them so they can be ground. It should work. It can be adjusted for the different radii required for different cams. Most of the build so far is on our club site.
Yes Patrick, the shaft is movable in an oscillating motion. Most of the tappets required only 1 or 2 thou to clean up. One tappet was a 3/4" radius and took more time to re-shape to the 1-1/8" radius called for in these cams.
The flat radius basically open and close more instantly as there is less ramp effect. The duration at the cam increases by about 10º. The important thing is that with two cams the LSA can be changed because of the extra keyways in the cam gears.
I'm having trouble dialing in these Norris 'D' cams since they don't match the specs shown in my Norris book.
I have the lift and duration, but the rest of the numbers will be trial and error. It comes close to a 'R' grind so
that will be the baseline. Now it's just finding the best combination. This is a copy of the 'R' stats.
I finally got to talk with Jim at Megacycle who was familiar with my Norris cams and the setting. So for now
they will be set straight up at 105º and mag timing around 42º.
I had an issue with my tappet re-surfacing fixture. My mistake. The rotating shaft in the fixture block wasn't
parallel to the surface that rests on the surface grinder magnetic chuck. It was off by .002". Luckily I checked 2
tappets on the cams before grinding the rest. The timing side is finished for now, until the Joe Hunt magnetos
return from being rebuilt.