Reverse weighted Norton crankshaft ?

Tintin said:

Dances with Shrapnel said:

As far as moving as much mass to the outside cheeks, this is a flawed approach and I would tell anybody not to do this to a Norton crankshaft unless you are looking to optimize it for use as a boat anchor.

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I would agree to a certain extent if it wasn't for the bunch of bolts in the middle of that particular crankshaft.

I don't know if I can explain in detail the concept of bending moment adequately on this forum; this is engineering statics and dynamics. Forces that induce moments are calculated as one goes down one end of the crankshaft ceneterline. Pick a particular RPM (say 7,500) and for TDC, BDC, 90 and 270 degrees one can calculate the forces due to the dynamics of the crankshaft connecting rod(s) and piston(s) system. The crankshaft is only constrained at two points which are the main bearings. As an example, at TDC you have the forces attributed to the pistons and connecting rods deaccelerating partially balanced by the centripetal forces generated from the imbalance (by design) in the bob weights. If all of your out of balance mass were concentrated outboard by the bearings you still have the two con rods (inboard) trying to bend the sh*t out of the crankshaft. By placing some of the bob weight between the two connecting rods you now have a centripetal force reducing the bending moment. So look at this as a snap shot and then do the same analysis for 90/270 degrees and at BDC which has a different rod/piston deacceleration profile. The crankshaft is in different bending conditions at TDC, BDC, and 90/270 degrees. When considering durability of materials, fatigue is a fuction of the the number of changes in stress and the magnitude of the changes in stress. So by minimizing the magnitude of the load reversals (changes) due to the dynamic forces of imbalance you extend the service life of the part.

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I would perfectly agree with that statement if there was a middle bearing and no bunch of bolts.

The reason why I would like to do said non-linear dynamic FEA is that I have done my share of hand calcs on this kind of stuff - and based on my experience from working with some really good FEA and MBS specialist on cranktrains all I can say is that a simple FBD is flawed to some extent that the necessary abstraction level is quite high in comparison. We have e.g. run cranktrains covered with strain gauges everywhere and the reality behind the models is so complex that IMHO too many details are dropped on the path to your FBD. For BDC I agree with you that the mass distribution with similar portions of the bob weight either side would help the crank - for TDC it heavily depends how the roughly 50kN of gas forces are fed into the system - and that occurs either side. For 90/270 degree 100% of the bob weights outboard and a Laval rotor in the middle would be the best solution in terms of bending moment.

In terms of just the bending moment the whole system is flawed due to the absence of the middle bearing and either way you shoot yourself in the foot IMHO - you just have to decide which foot. In terms of vibration the weak rotor might actually help but without a proper analysis this is just a gut feeling as I said.


Tim

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Any engine design is a matter of compromise (call it shooting yourself in one foot or the other but please spare me the drama). You refer to computer modeling yet the analysis of imbalance in rotating machinery (and resulting forces) is not rocket science and has been evolving and going on in depth for well over of century.

This from wikipedia: "The quality of predictions from a computer codes has more to do with the soundness of the basic model and the physical insight of the analyst. ... Superior algorithms or computer codes will not cure bad models or a lack of engineering judgment."

Oh, there it is, "physical insight" and "engineering judgement". Norton (as well as Triumph, BSA and probably a whole slew of period parallel twin manufactures) had the opportunity to try and implement engines with bob weights all outboard and having flywheel mass all outboard.............but they did not. That is my first clue. The FBD bending moment analysis I referred to is from "first principles" of engineering analysis. If one has difficulty with this then one must really pucker up when crossing a bridge or driving a vintage bike or flying in an older aircraft. Read about the development of the SR 71 (Blackbird) and when it was developed and how (that was a slide rule era, not a super computer FEA/FDA era.

To allude to a FBD analysis as bogus or fataly flawed because a FEA was not conducted is something like throwing the baby out with the bath water. Furthermore, as quoted above (and from my professinal experience in numerical modeling) the insight must be there through engineering understanding and judgement before one can get anything close to meaningful results from a model.

As for bolt together crankshafts, the Norton flange bolt is rather eloquent for the application and I have never heard of a properly assembled Norton twin crankshaft failing in or around the flanges. All the failures I have expereinced and others that I know have experienced are failed cast iron flywheel, failure starting at the drive side main bearing filet, failure starting on the drive side rod journal filet or failure starting at the drive side oil hole to the journal. There may be others but I have seen enough of these to see a pattern.

If you feel the FBD analysis is flawed, so be it but it is closer to a working analog (a real live Norton engine); I do not see a preponderance of evidence that a parrallel twin would be better off with an outboard flywheel and all or most outboard bob weights. Maybe the world has missed something over the last 100 years or more.

I have gone to several reputable crankshaft fabricators and none of them have come up with the suggestions of moving most of the flywheel and bob weight mass outboard; they easily could have but did not. Are they missing something?

Have a read of Fayette Taylor (2 volume set) on IC engines, he has excellent sections on crankshaft design, balance and vibration. Much was pulled from WWII efforts of Germany. Makes for neat and enlightening reading.

Cheers

What are you doing to get larger main bearing journals?

"As for bolt together crankshafts, the Norton flange bolt is rather eloquent for the application and I have never heard of a properly assembled Norton twin crankshaft failing in or around the flanges. All the failures I have expereinced and others that I know have experienced are failed cast iron flywheel, failure starting at the drive side main bearing filet, failure starting on the drive side rod journal filet or failure starting at the drive side oil hole to the journal. There may be others but I have seen enough of these to see a pattern."

Frequent failures of the bolt up cranks on the works race bikes was what led to them using far stronger one piece billet parts, which I would imagine were almost certainly initially modified Triumph items. The sole reason for continuing to use bolt up cranks was to reduce costs, but no real reliability problems on road going motors using these, but not that great on serious race motors.

Carbonfibre said:

Frequent failures of the bolt up cranks on the works race bikes was what led to them using far stronger one piece billet parts, which I would imagine were almost certainly initially modified Triumph items. The sole reason for continuing to use bolt up cranks was to reduce costs, but no real reliability problems on road going motors using these, but not that great on serious race motors.

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For clarification are there documented cases of failures of the bolted flanges or failures attributed to the bolted flanges. If so, I would like to know.

From what I have seen, the failures are due to inadequate materials for race service (cast iron flywheels and cast steel crank cheeks), inadequate main journal diameter, inadequate main journal filet, inadequate rod journal filet and maybe inadequate machining, filet and polishing of the small oil feed hole on the journals.

Agree about cost (of manufacture)

If the factory bikes 3 piece cranks hadnt been a weak point, there seems little reason for them to have changed to much more costly custom made one piece parts? On Norton engined drag race bikes here in the UK fitting one piece Triumph or Weslake cranks was a common modification back in the day, so the factory race people would have known all about possible problems with the bolt up cranks, and how to overcome them from day one.

Carbonfibre said:

If the factory bikes 3 piece cranks hadnt been a weak point, there seems little reason for them to have changed to much more costly custom made one piece parts? On Norton engined drag race bikes here in the UK fitting one piece Triumph or Weslake cranks was a common modification back in the day, so the factory race people would have known all about possible problems with the bolt up cranks, and how to overcome them from day one.

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Well it seems like Steve Maney has effectively overcome this predictable failure while using the "factory" design through the use of improved materials. Back to my question regarding the bolt connection - was this the problem or are you lumping the problem into the "class of crankshaft". The reason I persist in questioning this is to understand the history and short comings of the crankshaft design.

As for costs, Steve Maney is offering his crankshafts at a price comparable to a billet crankshaft. Back in the period, CNC equipment was not as readily available and the billet would likely have been a less costly way to go.

Also note that Steve also uses a central flywheel (albeit lighter) and counter balance mass distributed across the center and side bob weights ala factory design.

I would like to hear from any and all about whether there has been an instance where his unmodified crankshafts have broken.

His ultra shortstroke is above 80hp rear wheel (est 95hp at crankshaft) and his 1,007cc (with bolt together stroker crankshaft) when highly tuned is good for +100hp rear wheel (est 115hp at the crankshaft). Now we are talking about a race bike applications with what some here opine as a "horribly flawed" crankshaft design (some exageration added) with nearly twice the power ouput of the stock application.

Then there is John Gregory and TC Christianson and the hog slayer. Through personal discussions with John Gregory (wrench, design and engineering behind the hog slayer) he stated that they would run a season on nitro methane and stock crankshaft and bearings. The hog slayer was at around 300hp (150 hp per engine). Now we are approaching three times the power output of stock. Granted these are short durations but it is a good indicater of the design and construction of a stock Norton crankshaft.

splatt said:

What are you doing to get larger main bearing journals?

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I use a pair of NJ2207E bearings. Load ratings are close to those of the NJ306E and from recollection, one of the load ratings may be greater than the NJ306E. There are static and dynamic ratings. The allowable misalignment is comparable (superblend nonsense) between the two bearings.

The black magic is cutting down the width of the inner and outer race (it is something like 1mm off each side). Machine a nicer radius into the inside diameter of the inner race that butts up against the cranks cheek. This allows for a more liberal filet radius on the main journals.

The challnge is getting a special cutting tool that is up to the task of machining bearing surfaces. I think the fellow who did the first set for me used a ceramic cutter.

Naturally you need to clean the bearing and lubricate after all of this. The bearings may need to be deguassed before cleaning as they magnetized.

The only NJ2207E bearings I have been able to source started with steel bearing cages which eventually gave up the ghost in my application. Another machinist and master engine builder (Herb Becker) machined a set of brass or bronze cages and they have not been a problem.

I use a custom billet crankshaft to my specifications. It is installed in my 750 Norton Seeley ultra short stroke (around 75mm stroke). The bike currently pulls 83 hp at the rear wheel and under an earlier state of tune was pulling 87 hp rear wheel. The crankshaft has been in use with one regrind and renitirding by the manufacturer early in its life since 2005. There's more than a fair number of good races on that crankshaft and I consider crankshaft breakage a non issue as the engine is configured. We are now aggresively breaking other stuff. In all seriousness, the engine is quite reliable and happily revs to 8,500 - 9,000 rpm.

There is at least one reputable opinion out there that my use of the larger main journal, although maybe clever, is not necessary once the crankshaft material is billet steel as opposed to cast steel. I tend to agree but still get the warm and fuzzies knowing I have gone the extra mile while the 18 pound lump is spinning away at high rpms between my legs. The opinion is supported by the numerous successful race applications of the Steve Maney crankshafts with counter balance mass distributed across the bob weights and a central flywheel (ala factory design).

Dances with Shrapnel said:

Oh, there it is, "physical insight" and "engineering judgement".

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Okay, as your basic strategy apparently is the usual lame discrediting of FEA against that mythical being called an "engineer" - what a surprise that you still need a decent engineer to compile a decent FEA regardless of the computing power behind it - coupled with some word twisting - there is a humble difference between "flawed" and "flawed to some extent" e.g. - I don't care about the rest of this discussion anymore. Thanks for questioning my ability of doing a "first principle" analysis in that respect.

As a final statement let me put it this way: The crank webs of the engines I'm working on would not look like they do without decent engineers performing decent FEAs.

EOD4me.


Tim

Tintin said:

Dances with Shrapnel said:

Oh, there it is, "physical insight" and "engineering judgement".

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Okay, as your basic strategy apparently is the usual lame discrediting of FEA against that mythical being called an "engineer" - what a surprise that you still need a decent engineer to compile a decent FEA regardless of the computing power behind it - coupled with some word twisting - there is a humble difference between "flawed" and "flawed to some extent" e.g. - I don't care about the rest of this discussion anymore. Thanks for questioning my ability of doing a "first principle" analysis in that respect.

As a final statement let me put it this way: The crank webs of the engines I'm working on would not look like they do without decent engineers performing decent FEAs.

EOD4me.


Tim

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Wow!

Actually numerical modelling is the cats pajamas and provides much insight provided the correct insight is used to develop, calibrate and verify the model; this statement has nothing to do with you or me. I am reasonably sure we agree on this.

Apologies if you have taken this all to heart. Perhaps I did "shoot myself in the foot" on this one.

Dances with Shrapnel said:

Also note that Steve also uses a central flywheel (albeit lighter) and counter balance mass distributed across the center and side bob weights ala factory design.
<snip>
Then there is John Gregory and TC Christianson and the hog slayer. Through personal discussions with John Gregory (wrench, design and engineering behind the hog slayer) he stated that they would run a season on nitro methane and stock crankshaft and bearings. The hog slayer was at around 300hp (150 hp per engine). Now we are approaching three times the power output of stock. Granted these are short durations but it is a good indicater of the design and construction of a stock Norton crankshaft.

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The factory themselves experienced crank failures with the 'stock Norton crankshaft' - didn't someone get their rear tyre punctured at Daytona when the cast iron flywheel disintegrated, so they knew it was definitely time for an improvement....

The question that has to be asked again though - is the central flywheel part of the stock crank setup necessary to the design, or forced on it by virtue of not enough space to place enough counterweighting outside the crankpins... ?

Dances with Shrapnel said:

You can certainly argue away against the laws of physics as to what makes sense to you about where a flywheel mass would be most beneficial for a Norton twin.

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Which laws of physics would they be ?
Putting a heavy weight on a rotating high-speed shaft well away from the bearings that support it is hardly good engineering practice....
Velocettes went to extraordinary lengths to minimise overhang near bearings.
Guzzi went to external flywheels so as not to compromise internal crankshaft design.

Nortons crank design is essentially a single cylinder concept, complicated by having 2 crankpins in the mix. Which seriously compromises where the counterbalancing can be organised to.

Someone previously suggested an infinite weight flywheel, and smoother operation.
No-one commented on this, and yet flywheel counterweighting and engine balance has nothing to do with damping the torque pulses to give the rider a smoother ride...

Rohan said:

Dances with Shrapnel said:

Also note that Steve also uses a central flywheel (albeit lighter) and counter balance mass distributed across the center and side bob weights ala factory design.
<snip>
Then there is John Gregory and TC Christianson and the hog slayer. Through personal discussions with John Gregory (wrench, design and engineering behind the hog slayer) he stated that they would run a season on nitro methane and stock crankshaft and bearings. The hog slayer was at around 300hp (150 hp per engine). Now we are approaching three times the power output of stock. Granted these are short durations but it is a good indicater of the design and construction of a stock Norton crankshaft.

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The factory themselves experienced crank failures with the 'stock Norton crankshaft' - didn't someone get their rear tyre punctured at Daytona when the cast iron flywheel disintegrated, so they knew it was definitely time for an improvement....

The question that has to be asked again though - is the central flywheel part of the stock crank setup necessary to the design, or forced on it by virtue of not enough space to place enough counterweighting outside the crankpins... ?

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Agreed, replacing the cast iron flywheel (and bob weights) should be the minimum modification for any road racer if you are going to spin at high rpm for sustained periods. Once the crankshafts began giving up the ghost I speculate here that the factory was in no financial position to switch to more costly machined billet cheek or billet crankshaft.

I see three aspects of your question 1.) what drove the design, 2.) where best to place the added mass for pure rotational effects and 3.) where best to place the counterbalance mass? Each design comes with compromises.

Rohan said:

Dances with Shrapnel said:

You can certainly argue away against the laws of physics as to what makes sense to you about where a flywheel mass would be most beneficial for a Norton twin.

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Which laws of physics would they be ?
Putting a heavy weight on a rotating high-speed shaft well away from the bearings that support it is hardly good engineering practice....
Velocettes went to extraordinary lengths to minimise overhang near bearings.
Guzzi went to external flywheels so as not to compromise internal crankshaft design.

Nortons crank design is essentially a single cylinder concept, complicated by having 2 crankpins in the mix. Which seriously compromises where the counterbalancing can be organised to.

Someone previously suggested an infinite weight flywheel, and smoother operation.
No-one commented on this, and yet flywheel counterweighting and engine balance has nothing to do with damping the torque pulses to give the rider a smoother ride...

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Well lets start with a body at rest tends to want to stay at rest (theoretical argument for the benefits of a heavy mass between the Norton journals to damp vibration). Another crude analogy would be bar weights on the ends of handlebars or clip ons to damp the vibration. Agree about engineering practices but as stated throughout this thread; engine design is full of compromises. One could argue with a very general statement that a flywheel is best kept between two bearings if at all possible rather than cantelevered off the end of a shaft (as in the apparent case of a MotoGuzzi)

I am not up to speed on Velocette's: I thought they were all singles. As for MotoGuzzis' if you are referring to the V twins, this is no longer a parallel twin with a 360 crankshaft and if I recall correctly, there is a common journal with side by side rods. This is a bit of apples to elephants comparison but maybe I am missing something here.

Yes I mentioned an infinite mass flywheel as a bit of a silly hypothetical with total disregard to "damping the torque pulses to give the rider a smoother ride" as the focus of the discussion had nothing to do with torque pulses. This was to attempt to illustrate a case.

Holding together for a few seconds in a drag race is not a very good indicator of the durability of any particular crankshaft design. The stresses and strains on a crank are far greater in road race applications, and this is the reason cranks on the factory road race motors failed, while those used for drag racing worked perfectly well.

The fundamental problem with a twin cylinder engine using a crank with only 2 main bearings is that the crank is poorly supported, and when a 3 piece crank is being used the chances of failures are greatly increased, in high stress applications such as road racing.

Where the crankshaft weights are located is not likely to make an awful lot of difference to something that came about due to want to reduce production costs to a bare minimum, and to accommodate the continued use of antiquated machine tools, that meant production of horizontally split cases using a 3 bearing design, would have been quite impossible.

Holding together for a few seconds in a drag race is not a very good indicator of the durability of any particular crankshaft design. The stresses and strains on a crank are far greater in road race applications, and this is the reason cranks on the factory road race motors failed, while those used for drag racing worked perfectly well.

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How many times has it been said, "Running great until it quit"? Time is a factor in the failure equation.

Carbonfibre said:

Holding together for a few seconds in a drag race is not a very good indicator of the durability of any particular crankshaft design. The stresses and strains on a crank are far greater in road race applications, and this is the reason cranks on the factory road race motors failed, while those used for drag racing worked perfectly well.

The fundamental problem with a twin cylinder engine using a crank with only 2 main bearings is that the crank is poorly supported, and when a 3 piece crank is being used the chances of failures are greatly increased, in high stress applications such as road racing.

Where the crankshaft weights are located is not likely to make an awful lot of difference to something that came about due to want to reduce production costs to a bare minimum, and to accommodate the continued use of antiquated machine tools, that meant production of horizontally split cases using a 3 bearing design, would have been quite impossible.

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Agreed that road racing is a greater test of durability yet you cannot discount what John Gregory did with the Norton engines. It is quite a testament to what the Norton crankshaft can withstand; this is just to illustrate the other end of the service duty spectrum. Factors in durability are the number of load reversals and the magnitude of the load reversals. I don't know if the Hog Slayer even reved exceptionally high - probably not.

As far as lacking a central journal, with engine design there is compromise. A down side to a third journal is more friction and as you pointed out, the costs (at the time) to effectively achieve a third journal given the state of the British motorcycle industry at the time. An upside to a third journal would likely have been less crankshaft failures with cast steel (one piece) crankshaft.

Regarding the statement: "and when a 3 piece crank is being used the chances of failures are greatly increased"; in general I would expect that but I have not seen the causal evidence of that with the Norton crankshafts. I have yet to see or hear of a failed bolted connection. As mentioned earlier in this thread, the failures start at the drive main bearing shaft filet radius, the LH rod right filet radius, the oil hole on LH rod journal or the cast iron flywheel.

Based in part on the race proven durability of the Steve Maney three piece crankshafts (steel flywheel and billet CNC machined cheeks) my opinion is that the failures of factory components are directly attributed to the materials of construction. I have yet to hear of an unmolested Steve Maney crankshaft failure.

As for Triumph and BSA, someone told me that their crankshafts started out from forgings. Anybody care to chime in on this?

The original 1937 design Triumph twins used a 3 piece crank, and this was retained into the 1960s. However the later unit twins all had forged one piece cranks, which were pretty much trouble free.

NOT TRUE as I have seen several broken turnip crank's if the owner started making good HP numbers.

Carbonfibre said:

However the later unit twins all had forged one piece cranks, which were pretty much trouble free.

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bill said:

NOT TRUE as I have seen several broken turnip crank's if the owner started making good HP numbers.

Carbonfibre said:

However the later unit twins all had forged one piece cranks, which were pretty much trouble free.

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Interesting that someone posting on a Norton forum would suggest that.......................

I am just trying to set the record straight. I have NO use for the brand X turnip BUT I an not totally brand loyal blind and will admit that some of them can make good power.also it is NOT a one piece in the true sense, it has a central flywheel that fits over the shaft and has 3 bolts to hold it on.

Carbonfibre said:

Interesting that someone posting on a Norton forum would suggest that.......................

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