long and short on pistons and rods

Seems pistons are similar to tires in the conflict of how long they are made to last vs how much maxim performance allowed. Long heavy skirts last a long time but don't win power races while short light skirts are race worthy they soon wear themselves and bores [and bores!!] out. So far found references of short skirts lasting 10-30 hrs in performance applications but not much in milder public use. Can just change tires w/o new wheels each time but new bores each time piston clapped out, ugh.
oh yeah long rods help the side loads wear less and some lessor hi rpm pistons jerk forces, especially in long strokes.


http://www.dotheton.com/forum/index.php ... 6.445;wap2
http://www.thumpertalk.com/topic/696938 ... ort-lived/
http://forum.dirtrider.com/discussion/6 ... acement/p1

Not sure where your going with this.

Long rods relates to stroke and typically longer gives more power and less rpm...engines designed for different purposes. Low to mid torque with longer stroke for work or short rods for high rpm and top end performance.

Skirts on pistons tend to add weight so unskirted pistons allow higher revs due to reduction in weight. Unskirted pistons likely wear faster due to higher rpm and less contact support along the cylinder wall.

Don't confuse short stroke with short rod You can have a short stroke motor with a long rod for instance. One way of comparing things is to look at the length of the rod compared to the stroke, i.e. 1.2 x the stroke, or whatever. A "long" rod reduces side loads on the piston/bore, a "short" rod increases side loads etc etc. A long piston skirt, provides better seal (important, especially in two strokes) but greater friction, whereas a short skirt will wear quicker due to the increased wobbling effect, but when its not wobbling will generate less friction.
At the end of the day it's horses for courses, as with all design, its a compromise.
cheers
wakeup

Besides altering the going on's at TDC and BDC the con rod length also also sets the position where the crank throw is at right angles to the con rod.
That in itself has a bearing on piston placement in the bore.
Pistons wearing out in 10 hours is a little hard to believe in this day and age (drag racing excluded),with British bikes I would be more intrigued as to why the liners seem to wear out so quickly.
Maybe a Norton cylinder could have a nicasil coated bore,ceramic coated chambers,piston domes and valve heads along with piston skirt treatment.
Maybe there is a ceramic 'superblend bearing.

http://www.mt-llc.com/#

http://www.stahlheaders.com/Lit_Rod%20Length.htm

A light piston won't make more power.It will reduce vibration at a given rpm.It will reduce stress on the conrod,and give a little less inertia stress on the crank.At other (less critical) times,a heavy piston will reduce the force on the rod and crank.

The energy it takes to speed the piston up is returned to the crank at TDC and BDC.

Is it equal on both the compression and exhaust cycle ?

My 500cc Triumph had 63mm stroke and the long 650 rods. It was definitely a top end motor with very little torque. When it got going pulling high gearing, at the ends of the straights it was extremely fast, however everywhere else it was useless. Combined with long duration cams and exhausts with 4 inch megaphones it was simply nasty. I suggest angularity has a lot to do with the way the motor performs. Pistons at the top of very long rods have very little purchase , and the wear rates are probably lower. The other good thing is that rockover times are longer, so the motor has better combustion characteristics and can rev higher.
I reached the end of developing my short stroke motor, when I felt I needed shorter rods which then required new 650 barrels to be cast, and the capacity classes in our racing did not suit a 500 anyway. The only way to race the bike on a short circuit was to drop the gearing extremely low and rev the tits off it, then you would get beaten at the ends of the straights.

I suggest a good engine would be a pre-unit 650 Triumph fitted with the later 75mm stroke Thunderbird crankshaft, 650 pistons and long rods, with the barrels and pushrods shortened to suit and extreme cams. I don't know what capacity that gives, however it should be very fast. My 500 used to rev to 10,500 regularly, and the motor I've suggested should do the same and be better to ride with a decent frame. You would still have the need for a head with a squish band.

wakeup said:

Don't confuse short stroke with short rod You can have a short stroke motor with a long rod for instance.

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That's why I said I wasn't sure where Hobot was going with this. Your right, the distance of travel "stroke" is controlled by the crank...interesting that the length of the rod can have an effect on the strength...didn't realize that and I guess that was what Hobot was trying to get to.

Norton cylinder could have a nicasil coated bore,ceramic coated chambers,piston domes and valve heads along with piston skirt treatment.

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Yep the main issue that has been 'revealed' to me is the time factor of short light weight pistons used as intended in racers or somewhat longer in street bikes, ugh. I expect to tear up tires but not the wheels too so pensive about short pistons on bore life and time. Jim Comstock made me aware of this factor with the bad gas hurting a piston and adding its also done in the bore so that's the end of his 880 cylinder for that engine. He's not got particularly light/short pistons in his 880 so that was not a factor, only that when the piston gets like his then its more than just piston renewal involved. He suggested bore hardening to extend that part of going faster smoother longer.

I once fitted 30 gram lighter pistons to a Triumph 650 motor, and there was a noticeable difference in performance even though what was replaced was not clapped out. When you think about it, the pistons reach the top of the bore and the bottom, and reverse direction 8,000 times per minute, - a change in inertia must have an effect. I found that the motor would spin up more easily through the gears. My next big motorcycle purchase will be Jim Scmidt's rods and pistons. I've looked at modifying pistons out of Japanese 4 cylinder bikes and modifying the barrels, however Jim's stuff is a good easy answer. I think they are very good value for money.

About the wear rate of barrels. I believe that many cast iron barrels are made out of Meehanite which is grey cast iron to which calcium has been added to form a calcium silicide precipitate (Qualcast ?). Over the years I've seen some barrels wear very quickly, however a friend and I bought a 30s Empire Star BSA single and the barrel was so hard that it was almost impossible to bore.
I wonder what the Chinese and Indian bikes are like for barrel wear ? My feeling is that bikes with close bore clearance are faster, however I suggest that Nikasil on aluminium is an expensive way to go, and as I'm using methanol fuel, getting the motor hot enough might be a problem. If the bore is made too loose for the piston, and if the Nikasil hammers out and gets picked up by the rings - what then ?
I have a question about Norton twin engines. With the long stroke of commando engines, the piston speeds probably get close to the theoretical limit where ring flutter occurs, I wonder how much better the top end motors which rev regularly to 8,000 actually perform compared with those which are simply tuned to develop more torque? With my own bike, using the CR gearbox, it revs up so quickly through the gears it is frightening. I always try to keep the revs below 7000, however I usually see 7,500 and I'd really hate to see what the 850 pistons are doing to the aluminium rods. Once plastic deformation has occurred, the damage is irreversible.

My other yellow bike has a 95mm bore and 72mm stroke with an essentially skirtless piston, almost non existent oil rings and a single compression ring. The piston and rod have a 100hr life under racing conditions, this would be much longer just trail riding instead of MX. As well as the whole piston weight, rod length variables the piston ring thickness can have a big influence on things, 1.2mm or thinner stainless rings can be a lot closer to the piston crown due to their lower mass.

I looked at the 73mm pistons out of the Honda Fireblade. They are 100 gram lighter than an 850 Norton pistons, have very thin rings and are Teflon coated. They are shaped like the pistons used in fifties Manx Nortons. A full piston with rings and gudgeon is about $100. The gudgeon pin hole has four circlip grooves so a shorter gudgeon pin can be used. The piston crown is thick enough that it could be machined to protrude out of the bore into a Norton 750 commando head if the piston did not rock too much in use.

Thanks for some partial relief cheezy with the racing life time of super duper light short flip floppy pistons. 100 hr of freeway 70-80 mph cruise implies 50K+ miles which is reasonable tolerable before power drops and noise rises. Generally me-we think of race upgrades as being tougher longer lasting but some race items like tires and oil are meant to trash and replace if ya really gonna race. Aco 8000 rpm seems about tops for worth while rpm before Norton 89 mm stroke friction drops torque curve pull. I'm pleased to know shooting to 7500 is routine in some race frenzy so Peel's components should be ok to 8000 for dozens of hours on JMS pistons. Peel performance band is a mystery made more pensive with recent pow wow with Comstock who's done a number of boosted babies - telling me there is a fairly narrow rpm range the dang compressors or blowers-turbos [a significant difference power/rpm twix them] make enough boost to matter up til they choke on themselves or over boost. About 1500 rpm spread of useable boost is his expectations now. Peel should make over 120 lb torque so likely not need/want to exceed 7000 much but for a few record attempts. I don't particularly like Norton engines but how they look and sound and work for pleasant sane thrills, only thing special about the Commando I'm really addicted to is smoothness and with some simple mods the handling - therefore the only thing i want to impress upon the world at large is what they all are so so missing out on in security and power planting tire grip turning wise w/o any athletics or super man skills required so only objects in the path are of any safety concern. What this all means to me is I've a time factor to learn next Peel capabilities on JMS pistons used in anger then get objective pecking order track times and seeing if the best school pilot per track on their paired down dialed in track bike can even keep up with a camera to demo phase 3 > 5 energy handling. Then when pistons and bores worn out replace and detune with Norton rods and longer skirt piston to daily ride for 20+ yrs to get some pay back on the investment. I hope someone creative might pick up the frame power unit mounts over lapping tied together with isolastics and rod links and swingarm support and put a modern power plant in there that don't even need isolastic but for the valve train buzz.

hobot said:

Thanks for some partial relief cheezy with the racing life time of super duper light short flip floppy pistons. 100 hr of freeway 70-80 mph cruise implies 50K+ miles which is reasonable tolerable before power drops and noise rises. Generally me-we think of race upgrades as being tougher longer lasting but some race items like tires and oil are meant to trash and replace if ya really gonna race. Aco 8000 rpm seems about tops for worth while rpm before Norton 89 mm stroke friction drops torque curve pull. I'm pleased to know shooting to 7500 is routine in some race frenzy so Peel's components should be ok to 8000 for dozens of hours on JMS pistons. Peel performance band is a mystery made more pensive with recent pow wow with Comstock who's done a number of boosted babies - telling me there is a fairly narrow rpm range the dang compressors or blowers-turbos [a significant difference power/rpm twix them] make enough boost to matter up til they choke on themselves or over boost. About 1500 rpm spread of useable boost is his expectations now. Peel should make over 120 lb torque so likely not need/want to exceed 7000 much but for a few record attempts. I don't particularly like Norton engines but how they look and sound and work for pleasant sane thrills, only thing special about the Commando I'm really addicted to is smoothness and with some simple mods the handling - therefore the only thing i want to impress upon the world at large is what they all are so so missing out on in security and power planting tire grip turning wise w/o any athletics or super man skills required so only objects in the path are of any safety concern. What this all means to me is I've a time factor to learn next Peel capabilities on JMS pistons used in anger then get objective pecking order track times and seeing if the best school pilot per track on their paired down dialed in track bike can even keep up with a camera to demo phase 3 > 5 energy handling. Then when pistons and bores worn out replace and detune with Norton rods and longer skirt piston to daily ride for 20+ yrs to get some pay back on the investment. I hope someone creative might pick up the frame power unit mounts over lapping tied together with isolastics and rod links and swingarm support and put a modern power plant in there that don't even need isolastic but for the valve train buzz.

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Also of some slight significance the other yellow bike (FC 501) puts out around the same 55hp and will do the ton, smokes the same and is rather loud

Ah I was thinking more like 150 hp engine in isolastic set up though not necessarily anything Norton produced - to get the internal suspension to take up tire conflict vectors at powered hi load leaned on fork angles. Ohhwwuuu I just realized the electric bikers may be open minded to this and not need to worry about engine vibes too. There is definitely something about the isolated power unit that helps engine pulse tire traction so maybe it could help them with their smooth power that don't give tires a hesitation to catch up. I'll bet smoothness will be the main reason electrics become popular rather than some short range city use economy - when fuel cells allow further distance than any liquid combustion rig w/o most of it gas tank. Biggest sales point of JMS pistons for street use is the smoothness they provide as how much can ya sustain race power in public. I animal trained enough to expect to break free routinely so looking forward to the extra response from JMS kit but will harden bores first so maybe can get to use up two JMS sets before aging out or becoming lame so detune to Norton endurance kit for a side car set up.

hobot said:

Ah I was thinking more like 150 hp engine in isolastic set up though not necessarily anything Norton produced - to get the internal suspension to take up tire conflict vectors at powered hi load leaned on fork angles. Ohhwwuuu I just realized the electric bikers may be open minded to this and not need to worry about engine vibes too. There is definitely something about the isolated power unit that helps engine pulse tire traction so maybe it could help them with their smooth power that don't give tires a hesitation to catch up. I'll bet smoothness will be the main reason electrics become popular rather than some short range city use economy - when fuel cells allow further distance than any liquid combustion rig w/o most of it gas tank. Biggest sales point of JMS pistons for street use is the smoothness they provide as how much can ya sustain race power in public. I animal trained enough to expect to break free routinely so looking forward to the extra response from JMS kit but will harden bores first so maybe can get to use up two JMS sets before aging out or becoming lame so detune to Norton endurance kit for a side car set up.

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Norton had the ultimate in a smooth engine that could put out some pretty impressive levels of power. I have never ridden an electric bike but I imagine the Commander is pretty close to one. Is it the big flywheels twins have for balance that helps with traction or the power pulses compared to a 4... reverse ABS in a way

Norton had the ultimate in a smooth engine that could put out some pretty impressive levels of power. I have never ridden an electric bike but I imagine the Commander is pretty close to one. Is it the big flywheels twins have for balance that helps with traction or the power pulses compared to a 4... reverse ABS in a way

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Yeah and for what I've put in Peel I could of had one by now but its still a corner cripple to me so why bother with its even more limited combustion sealing issues than piston engines. Look up rotary engines down fall to fill yourself in on them as short lived but superior power plants for a time. I've both steep loose off canter hill climbs and insane rough and sharp narrow turns to judge hook up and corner loads and nothing but nothing beats the secure grip of tri linked Ms Peel to point I have to over do stuff to break free while others catch me out by surprise at rather lessor loads even in great traction conditions. I am left totally uncannily flabbergasted by what Peel can pull off - except she couldn't keep the pull past 135 so much as I don't think I can live long term on JMS pistons they are what may allow Peel to pull so far ahead of the elites in any slightly leaned conditions 200 hp 200 mph won't be enough to catch up on tracks like Barbers. A few years ago I asked a bunch of folks there what the top speeds reached were and told by one and all barely 150 mph. IIRC fastest cycle average speed was like 115 mph and F1 cars 125 mph. To give a sense of my disdain for balloon tire elites, one day I raced myself to work 19.5 miles in 16 min, with 6 miles of THE Gravel, 6.5 miles of steeple chase slopes then 7 miles of river valley level-ish twisties as tight as Barbers and a lot narrower w/o banks for over 120 average. 50 mph marked turns are same as straights to Peel only slowed to upper 90's for the 45 marked turns and then mainly so my head was not in the way of way ward lane crossers we all routinely encounter in the Ozarks. I have never been able to really let all of Peels hair out in public and have not yet tasted real pavement only tires on her so best is yet to come and I mean that sexually as well as fastest gun around. Peel's road orgasms are multiple and deeper more intense reaching than mere biological induced kinds. Pavement handling has been totally solved by Ms Peel so even above thrills is kind of boring to me now so only want to do race track time trials to see if all my nay sayers will eat crow in public and to alert elite designers to jump tracks with Peel's Norton isolastic miracle but Peel real challenges that excite me no end are not paved or beaten paths at all but where no police or even game wardens around. I am still in constant high from my hi times on Peel 7 yr later and not even successful subside by LSD over doses gives me such flash back daily thrills - so thank you Jim Schimdt to help demo what the whole rest of the world is missing out on.

hobot said:

Long heavy skirts last a long time but don't win power races

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What races?

The Norton twin has been around for over 60 years, there is nothing that is not known about it. It is an old long-stroke engine of poor enough mechanical design that when dopes try to make it run like a Jap bike it either costs them a fortune or it breaks.

The solution is to run a production class where the rules prohibit the use of silly parts. If someone wants to do something impressive, then lets see who can build the most powerful Norton twin using all stock specification parts, cam, valve springs and all that will run on pump gas. That will take a lot more art and brains than buying a wheelbarrow full of new design racing parts and bolting them together.

The Norton is a classic motorcycle with lots of history. Try to recreate and live it's history and/or the history of famous riders or tuners, or try to have the experience of those who rode them in the 40s, 50s, 60s or 70s. Then you will have special insight into their history.

I have a lot of old Nortons that I want to ride as they were back in the day, I am not interested in seeing how many modern parts or technology I can stuff into their cases. I want to know what a person felt in the late 50s or early 60s when they took their Norton out for a ride. They will all go 100mph, if someone on a bike with more power, technology or money stuffed into it wants to pass me go ahead. That does not have anything to with real Nortons or history at all.

Lots of people hot rodded Nortons back when they were new bikes, most of them probably made the bike slower and less reliable. It would be interesting to recreate what they did with parts and modifications they used though. I know where there is an old modified 650ss that has a crazy cam and badly ported head etc.. It probably would not be much faster than a well put together stock bike, but it would be interesting to take it for a ride just to see what quality of power it has, and what it's builder/rider experienced back in the mid-60s.

As the years go by the experience of taking a lot of old Norton motorcycles for rides will be available to fewer and fewer people. It is still pretty easy to get a ride on an original 70s Commando and see what it was all about, but almost nobody is going to have the experience of riding a real production racer, Manx, 88, 99, 650 or Model 7 twin and being able to know what those who rode them back in the day felt. Those with lots of cash can buy and build new "Nortons", but those replicas with their new parts and technology offer no experience of the past at all.

If you want to know what an engine with modern technology feels like then get on a Honda CBR for 5 minutes. Trying to make a 60 year old engine run like one is pointless, misguided and meaningless.

With careful assembly Nortons put together with stock spec parts have tons to give in the way of enjoyment, power and history for a reasonable price.