Commando Crankshaft Porn

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Sounds good to me Jim. I read an interview with AMC designer Phil Walker who said the RR type alloy used in the Matchless/AJS twins should have a service life of fifty years plus. Next question is ....does anybody in the US make Commando 'rods in Titanium?
Martyn.
 
Matchless said:
Sounds good to me Jim. I read an interview with AMC designer Phil Walker who said the RR type alloy used in the Matchless/AJS twins should have a service life of fifty years plus. Next question is ....does anybody in the US make Commando 'rods in Titanium?
Martyn.
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I don't know of anyone who makes them as a stocking item. There are a few outfits that make Ti rods to order. Jim

http://www.spmtitaniumrods.com/
 
worntorn said:
Are the Molnar rods going back or headed for the futures shelf?

Glen
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I will wait till the Ti rods get here before I decide. I will likely keep a pair as spares or for the next build. A Bonneville bike is still on my bucket list.

Jim
 
There have been a fair number of high end production cars and bikes that come from the factory with titanium rods, so you might take that as evidence of their suitability for road use.

Ken
 
lcrken said:
There have been a fair number of high end production cars and bikes that come from the factory with titanium rods, so you might take that as evidence of their suitability for road use.

Ken
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Yes, Corvettes and Porsches to name a couple.
From the research I have done the two main problems with Ti rods for high mileage have been fretting between the rod shell and rod and galling on the thrust surfaces.
Porsche uses a rod bearing with thrust washers built in like a main bearing.
Chevy uses a coating on the id of the big end and on the sides of the rod to solve the problem. Jim
 
I've noticed that if a bracket gets loose on my Seeley, and rattles on a titanium bolt, there is a dramatic reduction in dimension on the bolt which occurs very rapidly.
 
For several years a friend kept a souvenir door stop from our days involved in IMSA road course racing. It was a segment of a Crower billet crankshaft with a Crower titanium connecting rod and piston attached. The engine had disintegrated during competition. The engines had a resonance issue that proved to be catastrophically destructive. The amazing part was that in spite of breaking a 4340 crank and the entire bottom end of a high nickel content cast iron engine block; the titanium rod held its place. It was bent but did not break.
We went on to solve the resonance problem with welded on counterweights and a higher balance factor.
The door stop proved to be the bomb. Anytime the front door needed to held opened, just grab the piston-handle and chock the door. A new delivery man or customer was always impressed.
Titanium rods have been a part of mainstream motorsports since the 1980s. An engineered product that addresses the galling issue will have a service life comparable with a steel rod. All it takes is more dead statesmen.
Still not as trick as the billet door stop from Ken Canaga's. It's now Cozmo's crank.

BTW, Happy Birthday Ken !
 
if ya make Al rods robust enough and engine not on hi boost over 15 PSI and nitrous not sprayed in near red line to exceed normal rev' limits by over a couple 1000 - then Al rods should last forever like Norton issued. I remind thee that TC ran his 150 hp 8500 rpm engines for seasons of maximum output record runs on the factory Al rods and cast iron flywheels w/o an issue. I still hold any the available rods are w/o fatigue-strength issues and only let go when something else does first, from crank flex, rod bolts, piston failure, valve clash or case fractures. A review of rod factoids to choose from and why.
http://www.rrconnectingrods.com/how-to- ... g-rod.html
https://www.google.com/#q=comparison%20 ... 20material
 
Another Nourish Crank. This one is a short stroke (80.4 mm) with Jim Schmidt's extra long Carrillo rods and light-weight, high compression pistons.

Commando Crankshaft Porn


Commando Crankshaft Porn
 
ggryder said:
Another Nourish Crank. This one is a short stroke (80.4 mm) with Jim Schmidt's extra long Carrillo rods and light-weight, high compression pistons.
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Lovely stuff !! thanks for the image ggryder
 
That is a beautiful crank etc. however why go short stroke ? Doesn't the motor then resemble a Triumph motor without the advantage of the separate cam shafts ? I've had a lot to do with Triumph 650 motors over the years. My 850 commando motor is much better. If I was going to go short stroke, I'd work towards a 75mm stroke Triumph motor with a Rickman Weslake head and much bigger bore than usual, for a 750. Or perhaps go the other way and make it a 500, depending on the available race classes.
 
acotrel said:
That is a beautiful crank etc. however why go short stroke ? Doesn't the motor then resemble a Triumph motor without the advantage of the separate cam shafts ? I've had a lot to do with Triumph 650 motors over the years. My 850 commando motor is much better. If I was going to go short stroke, I'd work towards a 75mm stroke Triumph motor with a Rickman Weslake head and much bigger bore than usual, for a 750. Or perhaps go the other way and make it a 500, depending on the available race classes.
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If you wanted to utilise standard, available, NRE / Omega pistons, the best configuration for a 750cc short stroke 8 valve would be 80.5mm x 72.75, which still leaves space for a rebore to 81.mm.

The 'standard' Nourish 500 is 73 x 58.75. The best version I have ridden was Dave Degens own bike, based on unit Bonnie cases. That thing would rev to 12,000rpm, however, we realised that was into the range of 'diminishing returns' so he 'de-tuned' it to a ceiling of 10,000! It was a flyer!

Interestingly, although Dave Nourish made cranks up to 93mm stroke for big motors, he told me that he preferred the 89mm crank as it gave a broader power range.
 
I think my 500 was 71 X 63, have you made an error with the 71.5 mm stroke (61.5) ? My Triumph was extremely quick however extremely difficult to ride well - almost impossible with 4 inch megaphones. I used a two into one pipe to make it ridable, however it was s till nasty. It definitely needed a 6 speed box, I only had the 4 speed CR box. In a way I liked it, it was a thrill a minute and almost indestructible.
Compared with that my Seeley 850 is chalk and cheese. The Seeley is lovely to ride, I can do almost anything with it. I've never ridden any other bike with so much torque. Even my mate's old 650 Triumph which was totally set up to pull hard and is a really good fast old jigger, did not have as much when I rode it years ago. I'm amazed that the 850 motor is so good with almost nothing done to it - I never believed in it so the bike stayed unraced for twenty years. I've got it to the stage where I can almost race it again - I have to find some cash before I am too old to do it justice. Might get there next May if I'm careful or lucky.
 
I really like the thought of the late 7os thunderbird crank with the 75mm stroke. It would be short enough to give heaps of revs, still with a bit of decent low end. I've never tried to buy one of those shafts - any clues ? With all of those things, getting high comp. light pistons and a decent head is a problem.
I saw a 500cc Rickman Weslake being raced a few years ago and asked the owner if it was nasty to ride - IT WAS.
My old 500cc short stroke triton is still in the next town. I will probably get a ride on it again - it is really thrilling/exciting to ride , however you cannot relax for a second or it will bite you. I don't really need that level of anxiety. Apparently the 500cc Paton is like a modern 250cc MotoGP bike to ride.
 
acotrel said:
I think my 500 was 71 X 63, have you made an error with the 71.5 mm stroke (61.5) ? My Triumph was extremely quick however extremely difficult to ride well - almost impossible with 4 inch megaphones. I used a two into one pipe to make it ridable, however it was s till nasty. It definitely needed a 6 speed box, I only had the 4 speed CR box. In a way I liked it, it was a thrill a minute and almost indestructible.
Compared with that my Seeley 850 is chalk and cheese. The Seeley is lovely to ride, I can do almost anything with it. I've never ridden any other bike with so much torque. Even my mate's old 650 Triumph which was totally set up to pull hard and is a really good fast old jigger, did not have as much when I rode it years ago. I'm amazed that the 850 motor is so good with almost nothing done to it - I never believed in it so the bike stayed unraced for twenty years. I've got it to the stage where I can almost race it again - I have to find some cash before I am too old to do it justice. Might get there next May if I'm careful or lucky.
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Yes I did make an error, sorry about that.

The Nourish 500 is 73 x 58.75 as 'standard'
 
acotrel said:
I really like the thought of the late 7os thunderbird crank with the 75mm stroke. It would be short enough to give heaps of revs, still with a bit of decent low end. I've never tried to buy one of those shafts - any clues ? With all of those things, getting high comp. light pistons and a decent head is a problem.
I saw a 500cc Rickman Weslake being raced a few years ago and asked the owner if it was nasty to ride - IT WAS.
My old 500cc short stroke triton is still in the next town. I will probably get a ride on it again - it is really thrilling/exciting to ride , however you cannot relax for a second or it will bite you. I don't really need that level of anxiety. Apparently the 500cc Paton is like a modern 250cc MotoGP bike to ride.
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I can see the temptation with the 75mm crank (if that's what it is) but, it is still a Triumph crank... and in an 8 valve motor, under race conditions, it will still break through the sludge trap sooner or later!
 
ggryder said:
Another Nourish Crank. This one is a short stroke (80.4 mm) with Jim Schmidt's extra long Carrillo rods and light-weight, high compression pistons.

Commando Crankshaft Porn


Commando Crankshaft Porn
Click to expand...

Gotta love Nourish cranks I say... bomb proof, no flex, just great!

Which of Jims cams are you running?
 
acotrel said:
That is a beautiful crank etc. however why go short stroke ? Doesn't the motor then resemble a Triumph motor without the advantage of the separate cam shafts ? I've had a lot to do with Triumph 650 motors over the years. My 850 commando motor is much better. If I was going to go short stroke, I'd work towards a 75mm stroke Triumph motor with a Rickman Weslake head and much bigger bore than usual, for a 750. Or perhaps go the other way and make it a 500, depending on the available race classes.
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Alan, I’m not exactly steeped in Commando lore, nor the lore of any other bike for that matter. I have to admit that my motivation in going the short-stroke route is to allow me to build a 750 cc (race class limit) engine using 850 cases and cylinder barrel, which I understand to be usefully stronger than the 750 equivalents.

I’m not aiming for the most powerful Commando on the track; I reckon it would involve too much expense and effort to get there and stay there.

Having said that, stuck on top of this engine will be the splendid RH10 head that Jim Comstock completed and reported on a couple of months ago. So, I’m hoping the bike will be a pleasure to ride and quick enough to deal with the local competition.
 
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