Cylinder axis in 750/850 Norton?

When Norton originally made the 750cc engine out of the 500-650cc Dominator, they did it by machining the Dominator crankcase and cylinder head castings a bit differently and adding a new cylinder casting.

They had no room to keep the cylinder bore axis where it was, so they moved it straight backwards, creating the squish area at the back of the 750 Norton combustion chamber. This trick looks to have been used again for the increase to 850cc.

Having the cylinder bore axis aimed behind the crankshaft axis is the exact opposite of what major manufacturers and engineers have done in the past and present. Honda and Yamaha for two currently have engines with the bore axis aimed forwards of the crank centerline for added torque and less side-thrust on the power stroke.

This not only has the potential to hurt power output, but to have an effect on piston longevity, running temperature and noise.

One more detail that Norton may have compromised on when stretching the design to meet marketing pressure.

Re: Cylinder axis wrong in 750/850 Norton?

So, what's your solution?
Or should we all just have a massive rally to meet at the crusher and end this torment once and for all?

Re: Cylinder axis wrong in 750/850 Norton?

Do Honda and Yamaha have the same crank rotation as a Commando? Do you have drawings?

Russ

Re: Cylinder axis wrong in 750/850 Norton?

The original 750cc crankcases did not have enough room to move the crankshaft backwards to compensate, but this would be an easy enough modification to incorporate into new reproduction parts, allowing a bit extra room to move the crank back about 5mm.

Personally I don't have to worry about it because I mess with pre-750cc bikes. Just something I noticed that the guys messing with repro engines might be interested in.

Re: Cylinder axis wrong in 750/850 Norton?

Yep the off centering bores forward is a means to restrain piston slap on power stroke and adds some extra rpm jerk down tolerance to racers. In our rpm allergic engines the squish band is more worth while I think so good backward move on Norton adapting for street use. Here's some more gearhead entertainment on this subject, which can be gotten in several ways.

https://www.google.com/#psj=1&q=offset+piston+bores

Re: Cylinder axis wrong in 750/850 Norton?

Hobot, that is a very interesting link. I quit my short stroke 500cc Triumph when development reached the need to manufacture shorter barrels to fit shorter rods, to get more angularity. I was using 650 barrels already shortened by 12mm with the stud holes tapped deeper to accommodate the 63mm stroke. The motor was extreme top end - very little torque, and the bike was too difficult t o ride well. I did not think of offsetting the pin bore in the pistons. My Seeley 850 is sheer bliss.

From that link :

The amount by which the cylinder axes need to be offset depends on many variables, but the main ones are the ratio of crank throw to con rod length and the angle after TDC at which maximum cylinder pressure occurs. The design engineer may have the simple aim to have the con rod parallel with the cylinder axis at maximum pressure, or he may resort to more complex simulation in order to reduce friction over a given range of engine speed.

Depending on the angle after TDC at which maximum cylinder pressure occurs, this may preclude being able to practically apply the desired pin bore offset within the piston. In this case, the engineer will have to settle for the pragmatic approach and be satisfied with whatever gain is observed. The practical limit to moving the pin bore off centre is often the excessive moment due to the large distance between the pin bore axis and the centre of gravity of the piston.

Another point to be aware of is the effect on the engine stroke due to offsetting the pin bore. For a given crankshaft stroke, offsetting the pin bore or cylinder axes increases the stroke, and this may be enough to put the engine beyond the capacity limits of the class in which it is being raced.

Re: Cylinder axis wrong in 750/850 Norton?

Just before my friend of 40 years died a few months back, I had a discussion with him about building a fast Commando motor. The first thing he mentioned was shortening the stroke and I admit that I always used to think that way, however I now believe it is nonsense. Short stroke manxes are certainly faster than long stroke ones on big circuits, however what does that prove ?

Re: Cylinder axis wrong in 750/850 Norton?

beng said:

When Norton originally made the 750cc engine out of the 500-650cc Dominator, they did it by machining the Dominator crankcase and cylinder head castings a bit differently and adding a new cylinder casting.

They had no room to keep the cylinder bore axis where it was, so they moved it straight backwards, creating the squish area at the back of the 750 Norton combustion chamber. This trick looks to have been used again for the increase to 850cc.

Having the cylinder bore axis aimed behind the crankshaft axis is the exact opposite of what major manufacturers and engineers have done in the past and present. Honda and Yamaha for two currently have engines with the bore axis aimed forwards of the crank centerline for added torque and less side-thrust on the power stroke.

This not only has the potential to hurt power output, but to have an effect on piston longevity, running temperature and noise.

One more detail that Norton may have compromised on when stretching the design to meet marketing pressure.

Click to expand...

This sounds like 'bloke down the pub said', ie complete bollocks. As rvich says, do you have drawings? Apologies if I'm wrong.

Re: Cylinder axis wrong in 750/850 Norton?

pete.v said:

So, what's your solution?
Or should we all just have a massive rally to meet at the crusher and end this torment once and for all?

Click to expand...

Not me, I'm selling mine to one of those idiots who will pay 5 figures for a runner.

Re: Cylinder axis wrong in 750/850 Norton?

pete.v said:

So, what's your solution?

Click to expand...

You just have to turn the cylinders 180' next time you have them off.

Re: Cylinder axis wrong in 750/850 Norton?

I have measured the cylinder centerline on one 600 Norton and several 750 and 850 Nortons.

The 650 had a cylinder centerline around .25 mm behind the crank centerline.

Most of the 750s and 850s seemed to be from .50 to 1.0 mm behind the crank centerline.

Having the cylinder centerline behind the crank makes the engine quieter.

Having the cylinder centerline ahead of the crank will make for noisy pistons with the clearances necessary in a Norton.

I suspect the power differences would be small but I can not say I have tried it. Jim

Re: Cylinder axis wrong in 750/850 Norton?

Alan, Thanks for picking out a juicey quote I'd either missed or forgotten as ain't looked at this in years, since trying to figure out solution to beating the socks off them buzzy balloon tire newbies. But as you've learned and so so many others Norton's go into anaphylactic shock/siezures operating in the red zone at full power. I have seen the light along with Tom Drouin and a bunch of bunch of water and methanol sprayers dudes so going THE Hi PSI Torque route with 4 wide spread ratio's so I feel about each piston strokes' jerk aheads on a settled tire patch from the last one, dampened even more by the fro-aft dual iso's rubbers so it lifts the front out of traction in eye ball spreading leaps. I'm basically following the V8 Engine Masters philosphy and principles which is build a dragster engine that only needs one or two gears to get to full speed, then boosting with hi octane for full spark BMEP. But Peel ain't no factory Norton power plant so 8000 is reasonable to seek as the boost definitely softens the power hits and crank and piston jerks accellerating into ring flutter crown busting rpm the rest are a bit limited on.

The AMAL needle metering was not wasted on bringing me up to speed on the Lake needle measure and configuring. Sort of like making your own cam, which I may do after seeing what I run into on the Norris D+. I am so used to loosing traction so easy, its scares the shit out of me routinely but its so routine even unintened i had to get TF over it and make the best of it. I still have worn out Trixie to keep a toe hold on same planet as most of you and don't even need a tach on her to stay fully rpm shy of much 2S cam action. I'm back on my SV650 now its getting to cold to enjoy, up to about 60-70 seems a bit more eager to go than Trixie but after that easy neck and neck till about 90 mph poor ole SuVee feels like a slug falling off torque just as the rpm/ratio are doing the best they can. That is as fast as I usually take Trixe or SuVee, Trixie to protect her from me and not worth the wait on SuVee. SV650's advertised as 365 lb 70 hp mid 40's tq, which confuses me no end on the Combat specs. I look at them together in garage and its hard to conceive the quaint Combat as the hot rod but by gosh I know they sure can be, if Hard Hearted Enough.

Re: Cylinder axis wrong in 750/850 Norton?

More ben having his monthly anti-Commando rant here. ?
As someone said before, he should go to the toilet more often, instead of taking a dump here.

The arguments for and against DeSaxe and reverse Desaxe cylinder centres (being foward or behind the centreline) have raged to-and-fro for more than a century or more now - and much much longer in steam engines - so this is not exactly anything new !!

The dommie 500 engines are the only Nortons that have none of this - does that make them better in any way ??
Not that I have heard any convincing arguements for...

As Jim Comstock mentions, the Norton 650 engines have a bit of it too.
I'll find my pic of a later gasket overlaid onto an iron dommie cylinder head.
Easy to see how Nortons just stretched the engines to get bigger anf bigger capacity, using almost the same cylinder head bolt pattern even...

Re: Cylinder axis wrong in 750/850 Norton?

Must crush everything. Start anew. Computer stuff like Porsch H-D V-ROD project.

Re: Cylinder axis wrong in 750/850 Norton?

Torontonian said:

Must crush everything. Start anew. Computer stuff like Porsch H-D V-ROD project.

Click to expand...

No need, in my agony as to how my 850 may be suffering, I will make new pistons with the gudgeon pin 1mm forward of the cylinder axis! Tremble in fear Honda Race Department!

Re: Cylinder axis wrong in 750/850 Norton?

What about an oval bore. Worked well for honda.

Re: Cylinder axis wrong in 750/850 Norton?

Oval pistons, triangular camshafts, square wheels - indeed, why stick with convential thinking.

Onda probably spent more getting those oval pistons to work than Nortons spent on their entire race program ??!!
Different era's of course, but still....

Re: Cylinder axis wrong in 750/850 Norton?

Maybe we should mention the reason Nortons pushed the cylinder axis back slightly.
An enlarged bore couldn't intrude into the camshaft and cam follower area, but was free to push it back a little.

Engines like the 1920s Henderson 4 ran with as much as 1/4" reverse desaxe design.
It was rumoured that someone hadn't allowed for the camshaft lobes in the initial design, and it was simpler to move the cylinders to make everything fit.... !

Re: Cylinder axis wrong in 750/850 Norton?

Rohan said:

Maybe we should mention the reason Nortons pushed the cylinder axis back slightly.
An enlarged bore couldn't intrude into the camshaft and cam follower area, but was free to push it back a little.

Engines like the 1920s Henderson 4 ran with as much as 1/4" reverse desaxe design.
It was rumoured that someone hadn't allowed for the camshaft lobes in the initial design, and it was simpler to move the cylinders to make everything fit.... !

Click to expand...

Maybe but I suspect it was moved back for noise control. Bigger pistons, bigger clearances, more need for offset. 1mm offset is pretty common for noise control. Plus there is plenty of room to go to to a larger bore on the 920 kits without camshaft interference.

Ever heard an old Chevy 250 straight six in which some hot rodder has reversed the pistons for more power. They make a little more power -and sound like a diesel.
Even the heavy duty 292 Chevy 6 which had zero offset rattled enough that customer complaints were common. Jim

Re: Cylinder axis wrong in 750/850 Norton?

Didn't Nortons change the rocker ratio somewhere there along the way.
I've not really looked at the were, when and what of this,
but this would give more room to move things around ??

The cylinders in an Atlas still (almost) use the original headbolt/stud pattern of the early iron dommie 500,
so moving things back was simpler with the existing stud patterns ?