Commando Crankshaft Porn

slimslowslider said:

comnoz said:

From my notes taken 30 years ago. As explained by Joe Mondello. Jim

The balance factor of about 65% creates the lowest peak imbalance force if the engine were mounted in a infinitely rigid frame.

The balance factor of around 58% creates the lowest average imbalance forces in the infinitely rigid frame.

The Commando engine with isloastic mounts creates the least amount of stress on its bearings and cases at 53% as that is where the engine motion creates a circle on its mounts. This takes into account the different mass of the engine in the vertical plane in comparison to the horizontal plane.

Click to expand...

Jim, concerning the different mass of the engine: what is considered as part of the "engine"?

Click to expand...

I can't say I have tried to figure it out but I would presume it would be anything rigidly attached to the engine.
I would suspect the cradle and transmission would need to be pivoted from the rear iso to find it's applicable mass in the vertical plane. Jim

comnoz said:

slimslowslider said:

comnoz said:

From my notes taken 30 years ago. As explained by Joe Mondello. Jim

The balance factor of about 65% creates the lowest peak imbalance force if the engine were mounted in a infinitely rigid frame.

The balance factor of around 58% creates the lowest average imbalance forces in the infinitely rigid frame.

The Commando engine with isloastic mounts creates the least amount of stress on its bearings and cases at 53% as that is where the engine motion creates a circle on its mounts. This takes into account the different mass of the engine in the vertical plane in comparison to the horizontal plane.

Click to expand...

Jim, concerning the different mass of the engine: what is considered as part of the "engine"?

Click to expand...

I can't say I have tried to figure it out but I would presume it would be anything rigidly attached to the engine.
I would suspect the cradle and transmission would need to be pivoted from the rear iso to find it's applicable mass in the vertical plane. Jim

Click to expand...

I've suggested a few times that the ends of the swing arm spindle could be picked up by silentbloc bushes attachéd to the Z plates. It would mean that the engine/gearbox assembly would rotate about the swing arm spindle. If I ever buy a fairly standard commando, I will try it - would be an easily reversible modification.

acotrel said:

I've suggested a few times that the ends of the swing arm spindle could be picked up by silentbloc bushes attachéd to the Z plates. It would mean that the engine/gearbox assembly would rotate about the swing arm spindle. If I ever buy a fairly standard commando, I will try it - would be an easily reversible modification.

Click to expand...

Not possible. The spindle is located forward of the Z plates.

Not possible to run the chain sprocket on spindle axis d/t the basic Norton design but it is possible to extend spindle lenght and Z plate metal to pivot in cradle and Z plate supports but then would loose the C'do isolation and traction pulse control dampening. Peel has swing arm extra support of swash plates half way down the legs I can fine tune to let frame twist up enough w/o damaging bushes or adding too much swing arm rebound to control.

A lot has been said now about heat treatment, interesting but I`m not 100 percent sure about some english words.
But one thing is sure, Bradley pointed out how important it is with stress relieving before nitriting.
The stress relieving dont affect the normalising or tempering? that is done, not familiar with farenheit but the stress relieving temperature is close to the temperature when nitriting, in my case about 600 C.
When i had the crank rough milled the cheeks came 0,1mm closer together, a workmate thought it wise to stress relieve before i went on.
On a Friday morning we put it in the oven, heated it gently all day 600 c, left in the oven over weekend.
Monday morning i had to take my gloves on to handle it.
I now leaving 0,3mm and will do the same procedure again before finish and have it nitrited
As you said Bradley, better to be sure than sorry.

By the way, Thank you Jim for the useful and interesting info abot that camgrinding.
I have actually got help to make a master, PW3 made to suit BSA lifters.

Sten

billet said:

By the way, Thank you Jim for the useful and interesting info abot that camgrinding.
I have actually got help to make a master, PW3 made to suit BSA lifters.

Sten

Click to expand...

Really?, will you be telling us more?, and where you are getting A65 followers from? or do you lan to make those too?

Steve

After 10 hours at 1000F -[540 C] and a 36 hour cool down the crank was ready to come out of the furnace this morning.



Just what I wanted to see. .0035in. runout at the PTO shaft. Plenty of material to finish grinding it true. I can now feel assured that the crank will remain reasonably straight through the nitriding process.



A new fine grinding wheel is mounted up and radiused for the finish work.

All the theory, guess work, and variables (different frames) about balance factors can be swept away with the simple test at the thread below.

balance-factor-scratch-test-tool-t15134.html?hilit=BALANCE%20FACTOR%20SCRATCH%20TEST%20TOOL

And yes - with this test I also found the peak forces to average at a minimum at around 65% wet. Peak forces are what you want to get rid of.

SteveA said:

billet said:

By the way, Thank you Jim for the useful and interesting info abot that camgrinding.
I have actually got help to make a master, PW3 made to suit BSA lifters.

Sten

Click to expand...

Really?, will you be telling us more?, and where you are getting A65 followers from? or do you lan to make those too?

Steve

Click to expand...

Yes, of course
I borrowed a Mick Hemmings made PW3 camshaft and measured it with a flat lifter as original
Then i got help from an engineer to calculate a new profile from my measurements, he made a measure every single grade from the center to the lobe.
An awfully lot of numbers and not useful for the CNC machinist so i got help from a friend who translated it to a drawing that was approwed.
Then i had two masters made, one natural size so i could double check with a radiused lifter myself and one the double size to the camgrinders wish.
(maybe i should try myself?)
I gave the CNC machinist at my job a whiskey, well worth it i think.
The liftcurve is close enough, It`s hard not to get the edge of the lifter not scrape against the flank and get the correct liftcurve, i will use a slightly smaller radius on the lifter to be on the safe side, 25mm or 1 inch.
The lifters are good used ones from friends that i shall regrind the faces on.

comnoz said:

After 10 hours at 1000F -[540 C] and a 36 hour cool down the crank was ready to come out of the furnace this morning.

Just what I wanted to see. .0035in. runout at the PTO shaft. Plenty of material to finish grinding it true. I can now feel assured that the crank will remain reasonably straight through the nitriding process.

A new fine grinding wheel is mounted up and radiused for the finish work.

Click to expand...

Jim, It`s really entertaining to see your backyard oven and see how you progress with your project !
My full respect!

bwolfie said:

acotrel said:

I've suggested a few times that the ends of the swing arm spindle could be picked up by silentbloc bushes attachéd to the Z plates. It would mean that the engine/gearbox assembly would rotate about the swing arm spindle. If I ever buy a fairly standard commando, I will try it - would be an easily reversible modification.

Click to expand...

Not possible. The spindle is located forward of the Z plates.

Click to expand...

Not possible ? - All that needs to be done is to remake the Z plates out of chrome moly steel of a different shape and include two mounts for the ends of the spindle and paint them black for that classic look. There could be a problem on the drive side in getting behind the chain cases - however impossible ? - I think not. The result would be that the swing arm would be held more firmly, and flex forces transmitted to t he main frame as it was pre-commando. The engine-gearbox assembly would be forced to rotate around t he swing arm spindle when vibrating. A disadvantage would be that vibes from the rear chain would be felt, however I believe the 'hinge in the middle' possibility would be gone. 'X' plates instead of 'Z' plates ?

billet said:

SteveA said:

billet said:

By the way, Thank you Jim for the useful and interesting info abot that camgrinding.
I have actually got help to make a master, PW3 made to suit BSA lifters.

Sten

Click to expand...

Really?, will you be telling us more?, and where you are getting A65 followers from? or do you lan to make those too?

Steve

Click to expand...

Yes, of course
I borrowed a Mick Hemmings made PW3 camshaft and measured it with a flat lifter as original
Then i got help from an engineer to calculate a new profile from my measurements, he made a measure every single grade from the center to the lobe.
An awfully lot of numbers and not useful for the CNC machinist so i got help from a friend who translated it to a drawing that was approwed.
Then i had two masters made, one natural size so i could double check with a radiused lifter myself and one the double size to the camgrinders wish.
(maybe i should try myself?)
I gave the CNC machinist at my job a whiskey, well worth it i think.
The liftcurve is close enough, It`s hard not to get the edge of the lifter not scrape against the flank and get the correct liftcurve, i will use a slightly smaller radius on the lifter to be on the safe side, 25mm or 1 inch.
The lifters are good used ones from friends that i shall regrind the faces on.

Click to expand...

Many years ago Ed Iskenderian published a book on computerized cam design which mentioned polycyclic profile - might help you. My feeling is that the only disadvantage of a Norton twin compared with a Triumph is that the inlet and exhaust cams cannot easily be timed independently.

Thank you for the tips, Steve.
It might not be too easy to find it,though.
Camshaft design is really not the easiest thing, a lot of geometry and forces to dig into, especially if you not smart enough (me)
From time to time i have tried hard and learned something but i think i will stick to this proven profile and lobe separation.
Yes, as you say, Triumph has the advantage of two camshafts.

comnoz said:

slimslowslider said:

comnoz said:

From my notes taken 30 years ago. As explained by Joe Mondello. Jim

The balance factor of about 65% creates the lowest peak imbalance force if the engine were mounted in a infinitely rigid frame.

The balance factor of around 58% creates the lowest average imbalance forces in the infinitely rigid frame.

The Commando engine with isloastic mounts creates the least amount of stress on its bearings and cases at 53% as that is where the engine motion creates a circle on its mounts. This takes into account the different mass of the engine in the vertical plane in comparison to the horizontal plane.

Click to expand...

Jim, concerning the different mass of the engine: what is considered as part of the "engine"?

Click to expand...

I can't say I have tried to figure it out but I would presume it would be anything rigidly attached to the engine.
I would suspect the cradle and transmission would need to be pivoted from the rear iso to find it's applicable mass in the vertical plane. Jim

Click to expand...

Rigid, that's what I thought. So the whole power plant (and starter stuff on mk3).
And I could imagine, although not really rigid, even swingarm, rear wheel, brake, the lot comes into it.
All need to follow in some way the movements of the power plant.
Meaning that it is only the rear wheel axle center that is always moving purely horizontally.(?)

Rigid, that's what I thought. So the whole power plant (and starter stuff on mk3).
And I could imagine, although not really rigid, even swingarm, rear wheel, brake, the lot comes into it.
All need to follow in some way the movements of the power plant.
Meaning that it is only the rear wheel axle center that is always moving purely horizontally.(?)[/quote]

Yes the swing arm and wheel would sure figure into the horizontal plane. Jim

billet said:

SteveA said:

billet said:

By the way, Thank you Jim for the useful and interesting info abot that camgrinding.
I have actually got help to make a master, PW3 made to suit BSA lifters.

S
Steve

Click to expand...

Yes, of course
I borrowed a Mick Hemmings made PW3 camshaft and measured it with a flat lifter as original
Then i got help from an engineer to calculate a new profile from my measurements, he made a measure every single grade from the center to the lobe.
An awfully lot of numbers and not useful for the CNC machinist so i got help from a friend who translated it to a drawing that was approwed.
Then i had two masters made, one natural size so i could double check with a radiused lifter myself and one the double size to the camgrinders wish.
(maybe i should try myself?)
I gave the CNC machinist at my job a whiskey, well worth it i think.
The liftcurve is close enough, It`s hard not to get the edge of the lifter not scrape against the flank and get the correct liftcurve, i will use a slightly smaller radius on the lifter to be on the safe side, 25mm or 1 inch.
The lifters are good used ones from friends that i shall regrind the faces on.

Click to expand...

Click to expand...

Why go to all the trouble when I already have a cam with PW3 profile for BSA lifters - the JS stage 2. Plus it as two improvements - slightly more duration and closer lobe centers. The lobe centers are too wide on the PW3 at 107 degrees resulting in performance loss. The lobe centers on the JS2 are much better at 105 degrees. You want tho lobe centers to be close as possible without causing valve clash - to about 102 degrees but that would cause valve clash on any stock head unless the cam was very mild such as a stock cam (stock cams are at about 102 degrees).

I tend to rely on cam profiles and timings for which the power outcomes are known. In Tuning For Speed there is a list of cam timings for various 50s racing bikes. When I think of a commando, I think of the 1959 AJS 7R - the best 350 of the era. As a benchmark I think of t he E3134 Triumph cam. If you fit it to both the inlet and exhaust of a standard Tiger 110 which normally used E3275 cams, and use the factory specified timings, and lengths of inlet and exhaust you get a torque increase right across the rev range, a pronounced cam spot at 4,000 revs and much more top end. That cam is replicated in a lot of very fast bikes of other makes. For a commando with the long stroke, heavy pistons and suspect bottom end it is too much. So in effect I've relied on anecdotal evidence and my own common sense and experience as to how I've timed my 850, and set up it's inlet and exhaust systems. I've advanced the cam 12 degrees to compensate for the back pressure of the two into one exhaust, and open the inlet earlier. However the closing points are not optimal. It seems to work very well, however I believe that is just partially a fluke. As far as profile is concerned, a safe lift rate and closing rate are essential. Triumph GP racers had severe cams and were valve droppers, that is why the E3134 was developed. Ed Iskinderian's polycyclic cams were way beyond me, and I don't know if the theory actually worked in a motorcycle engine. I suggest that lightening the valve train in a commando engine is pretty pointless, it will probably cop 9,000 RPM with our most ferocious cam for a while without causing much trouble, and we never go near that without a bottom end failure first.

It all ground true. The rod journals had moved about .008 in. closer to the mainshaft during heat treat so they didn't clean up till the last .002 when grinding but they made it at the standard size of 2.0 in. The rod fits with .0013 bearing clearance. Jim

Beauty. Great looking truing stand, too.

Getting a billet crank right can be difficult. The one in my 500cc Triumph had the RHS big end too narrow, and the rod had been faced off to fit . When I replaced the rod , I faced it off equally from both sides and ended up with the piston bearing against one side of the RH cylinder. Pain in the butt !