Maximum Streetable Compression Ratio?

acotrel said:

When I was a kid, we used to hot up 650cc Triumphs. My bike was on 11 to 1 comp with E3134 race cams, and ran on avgas. There was only one service station for miles around which sold it, so if you had to fill up, the bike ran like crap until you refilled with the 135 octane, leaded fuel. The bike was extremely fast for those days, however I got tired with the near misses and when I was 27 went racing for twelve years. It is a sublime obsession and I still love it, however cannot afford to do enough of it these days.

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The whole purpose of this thread is for me to gain the input from experienced Norton engine builders to build & tune an 850 Norton for maximum (streetable) performance for the 93 octane E-10 that is available in my area.

I'm not looking for a "touring" bike or a “competition” bike, rather a snappy performing "sport" Commando that I can head into the mountains W/on a Sunday morning to crank off 150-200 miles climbing grades @ WOT while running through the gears & taking it into the corners @ speeds that will bring a grin to my face..

Nowhere have I said that I have settled on "race" cam. I have the real world knowledge & understanding of the working of the internal combustion engine to realize that valve size, porting, cam specs, CR, gearing, etc must all work as a balanced package. I am seeking 1st hand knowledge as that pertains to the 850 Norton.

Indeed there has been a lot of knowledgeable input in this thread & I am leaning to a 10:1 CR W/stage 1 Maney heads W/a Stage 1 J&S cam.

The fact that I have put combos together like my 86 in Panhead that ran high 7s in the 1/8 mile while getting 46 MPG on the hi-way & a 4200#, 5.7 powered 2006 Charger that ran 12.0s in the ¼ mile while getting 26 MPG on the hi-way, might be evidence that I might know what I’m trying to accomplish.

As far as “illegal street racing”? Yes I would like to embarrass the souped-up Sportsters & big inch Hogs, & surprise some of the rice jockeys around town & on the twisties. I think a lot of the contributors on this thread are guilty of the same “evil” pleasures. A little stop light jockeying & cranking through the curves doesn’t necessarily constitute “illegal street racing”. Isn’t that pretty much what the whole “Café racer” thing is about?

BTW I’m less than a month away from my 63rd birthday, so don’t assume that I’m some snot nosed kid that doesn’t have a clue. Except for you a a few other judgemental posters on this thread, I have gotten some very helpful input.

Another data point from the 70's when I hopped up my 850 Commando Mk2a. I ran Omega pistons which yielded 10.25:1 CR. Best as I can ascertain is the cam I put in it is comparable to a Megacycle 06-020 grind and it ran fine.
The only problem I had was light smoke and detonation on one of the cylinders - found out that one of the pistons was not drilled for the oil control ring drains and was stuffing oil up into the cylinder. Pulled the piston and carefully drilled out the passages myself and the thing ran like a champ. I ended up terrorizing the county and state with a pair of Dunstall exhuast mufflers (if you could call them that); I started with the pea shooters but recall it improved with the more open Dunstall.

Andirondak's; old stomping grounds. You don't owe anyone an explanation or justification here, go out, experiment and have fun!

BitchinBeezer said:

Nowhere have I said that I have settled on "race" cam. I have the real world knowledge & understanding of the working of the internal combustion engine to realize that valve size, porting, cam specs, CR, gearing, etc must all work as a balanced package. I am seeking 1st hand knowledge as that pertains to the 850 Norton.

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Well there's a lot of good sense in talking to Jim Schmidt and Jim Comstock on a strong road 850 motor. Next, you have to consider where the power is going to - the transmission. The stock box has some weakness. It was designed in 1956 for the current 500 and 600 motors, so has some stress issues when pumped by an 850. 1) the original layshaft bearing needs to be upgraded to a quality roller or ball. 2) the box shell is prone to fatigue between the inner bearing recesses. A replacement thicker shell will help that. 3) The mainshaft thru to the clutch hangs out a long way and is prone to flex. The Maney outrigger bearing solves that. 4) the original triplex chain wheel drive is damn heavy. Replace this with a belt drive and save 2.6Kg giving the trans a little easier life and no primary case oil leak either.

Another whole chapter could be dedicated to stiffening up the frame, improving forks and brakes but I guess you want to start on the propulsion first. Good luck and have fun.

ML said:

BitchinBeezer said:

Nowhere have I said that I have settled on "race" cam. I have the real world knowledge & understanding of the working of the internal combustion engine to realize that valve size, porting, cam specs, CR, gearing, etc must all work as a balanced package. I am seeking 1st hand knowledge as that pertains to the 850 Norton.

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Well there's a lot of good sense in talking to Jim Schmidt and Jim Comstock on a strong road 850 motor. Next, you have to consider where the power is going to - the transmission. The stock box has some weakness. It was designed in 1956 for the current 500 and 600 motors, so has some stress issues when pumped by an 850. 1) the original layshaft bearing needs to be upgraded to a quality roller or ball. 2) the box shell is prone to fatigue between the inner bearing recesses. A replacement thicker shell will help that. 3) The mainshaft thru to the clutch hangs out a long way and is prone to flex. The Maney outrigger bearing solves that. 4) the original triplex chain wheel drive is damn heavy. Replace this with a belt drive and save 2.6Kg giving the trans a little easier life and no primary case oil leak either.

Another whole chapter could be dedicated to stiffening up the frame, improving forks and brakes but I guess you want to start on the propulsion first. Good luck and have fun.

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Yep, already plan to upgrade the layshaft bearing & go W/a belt drive. I had a 12mm belt drive on my 86 in Panhead stroker. Best thing you can do for a tin primary Hog.

Good advice on the outrigger bearing also. I'll consider that. There was a similar modification for post '65 Hogs running a tin primary. The sectionn that contained the bearing from an electric start (post '65) aluminum primary was cut out & used to support the longer electric start mainshaft. Perhaps that would help alieviate the cracking of the mixer case between the layshaft & mainshaft bore?

Indeed there has been a lot of knowledgeable input in this thread & I am leaning to a 10:1 CR W/stage 1 Maney heads W/a Stage 1 J&S cam.

Oh yes that combo will make ya grin w/o an octane of worry. Dances and ML have some more good items to include. Lighten up the bike too and try out the Triple helms Joint Watt's like linkage that transformed my concept of handling power in way over turns on choppy pavement in gusty conditions, yum bring on them decreasing radius wonders or just make em all decreaser's for the shear thrill of it. Alloy cradle and aluminum guts in forks, replace big long low load spacers with alloy, put rear sets on and remove center stand > will definitely be felt on throttle, brakes and flings. Dunstalls are good way to go after the heavy restricted baffle replaced with just plate with a 2"hole in it. I interviewed a few Norton Commando drag racers before they died off to be told AMC's gearboxes held up till about 100 hp clutch dumps then spilled guts on tract, so likely out rigger will be enough to get low 12's or even break into 11 sec 1/4 miles. Gear up up some say 21T and can hold 2nd 30-90 mph which not many bikes can accelerate as hard in that zone w/o popping wheelie to back off of. Fastest factory magazine tested model was in '72 or '73 750 that did 12.26 s 1/4 as fastest in the shoot out too. That does takes some mean hearted throttle/rpm attitude of course, so not for the reasonable mature among us, just the devil may dare wisdom till ya dead mind set

Good advice on the outrigger bearing also. I'll consider that.

http://www.youtube.com/watch?v=a-SOXVVdIZ4

in here , Mrs williams boy , Pete ; has a few things to say on the insides of transmissions .

The ' production racer ' , which is the PRODUCTION based machine , was plauged by D.N.F.s ,
this is as the I.o.M. is a bit lumpy & bumpy , in the broader sense .
Also the primary gearing is unaltered ( the trans was speeded up in the 72 F - 750 .)

" The racing heritage led to quickly detachable wheels and hairpin type valve springs that could be changed rapidly when racing. In 1933, the forks and gearbox were redesigned[1] and in 1935, the Sturmey-Archer gearbox was replaced, as Sturmey-Archer had stopped making gearboxes, so Norton bought the rights to the design and commissioned Burman to produce them. These gearboxes proved so good they remained unchanged for the next 30 years,[2] although the external appearance was altered several times, and the gearchange mechanism fully enclosed and thus lubricated. "

our antiuque 500 trans shafts go bannana shaped , under load ( tourque ) WHEN the WHEEL is on the Ground . When its alternateing as to its adhesion , the mainshaft gets confused also .
The wee cogs closeing & opening theyre operating parameters , as in clearances & messhing ( probly aptly spelt ) .

Therefore if youre one of those people that think a Bump is a Jump , it may pay to take a close look at the security of the transmission .

Standard tune with mproved breathing gets a workable relaxing machine , the GO factor of a hot cam can require youre undived attention , as if you look at the speedometer , you find the speed advisory signs dont have the neccesary ' 1 '
in front of them for the extra 100 kilometers per hour the ting is inclined to adopt . Haveing around 9 : 1 C.R , could ( might / may ? possibly ) result in less of a guided missile , where its possable to look around , to see if youre being persued
by Aliens with Flashing lights .http://www.youtube.com/watch?v=r4_sUKRJahQ

The chassis also can have some intresting behavioral characteristics , if all is well , perhaps best left to do its thing , rather than muscled . The fork damper updateing may stop the flapping on uneven surfaces when the fronts light .
So the sucker really wants refinement rather than revision . Or youd start with a clean sheet of paper . Or a pile or tube and a welding set , lathe & foundry . Economics & realities ( unlike Real Estate Agents ).



norton-t15430-30.html


Following the line of development of the series , to the factory ㅡmachines is iluminateing .

This things about the equivilant of a 74 works machine , if theyd drank wine instead of beer , we may wellve been able to get one , or a twin cam four valve water cooled 100 Hp sucker , like these spaghetti cowboys LATER did .



at some stage , it cheaper to start with the cardboard boxes , THEN look at what to get to put in them . Just imagine if Norton had still been underway the last 30 years , no body would be able to agree on ANYTHING .
Best value was a MkV 750 on Ebay , 860 $ , basically sound , what was left after rotting in the open , but 5.000 miles ' core ' for a hot rod lincoln , er Norton .



Or to make a Long Story Short . In Plain ENGLISH .The bar hards can whip weave snake & shuck if theses things afoot on a uneven road , and sometimes at other times too . requires a eye on the road , a ( restrained ) hand on the wheel .

as someone said , whens a Commando Not A Commando . :? take it easy , or you need velcro trosers & matching seat . :twisted: not sure d take my hands of the bars at 110 on the unsealed roads , Bonneville you could .

Matt Spencer said:

:twisted: not sure d take my hands of the bars at 110 on the unsealed roads , Bonneville you could .

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Reminds me of I time I had my arsehole pucker up & bite a hole in my undershorts.

I was headed over to a friend’s house on my 86 in Panhead. It was one of those cool, dry, high (barometric) pressure days when the engine could take big gulps of dense, dry air & respond gleefully with vigorous torque.

I turned a corner at an intersection & proceeded to pin the ears back on the old Hog & crank it up the moderate grade at WOT. (Always loved crankin’ up hills as I could get off on the torque W/O gaining too much speed)

Anyway, I had shifted to low going around the corner & I laid the ears back on the old stripped down Hog & ran through the gears, shifting @ 5000 RPM. About a 1/4 mile from the intersection, I topped the hill cranking 4500 in 4th, about 110 MPH W/the long legged gearing that the 4.520" stroke thrived on. I was still in the FAT part of the power band. The crest had a rather abrupt crown & as I went over, the front end refused to follow the grade. :shock:

As I rolled over the crest W/my front wheel floating 3 feet above the tarmac, events shifted into slow motion in my brain as they seem to do when I'm in a high pressure situation. I was faced W/the decision on whether to back off the throttle or just maintain WOT & "ride it out". Since I was now on a downgrade that equaled my upward angle from horizontal, closing the throttle & slamming the Showa fork down on the pavement didn't seem like a wise choice.

As I hung onto the grip W/the throttle still twisted wide open, the front end started to slowly settle to earth, gently touching down & continuing onward W/O any increase in the already considerable drama. Shortly thereafter I had to clamp down on the (front disc/rear drum) binders to haul the 550# brawler W/my 180# arse perched atop down for a 90° corner another ¼ mile down the hill from the crest.

Say what you want about Harleys, when stripped down & set up for cranking it on they are a stable, if not nimble platform once the later model Japanese forks were employed. Not in the class of a nimble Limey bike, but that bike saved my bacon on more than one occasion when my exuberance exceeded my discretion.

Hopefully, my 30 years of maturity since those crazy days will prevent me from getting myself into such hair raising situations, (maybe not) :twisted: but I still want a bike that will give me an adrenaline rush when I romp on it.

OH My Yes BitchyB, you know what I call phase 3 handling is about! I also know how dam well them big ole Harely's can handle with mainly lean fouling limiting them, UNTIL ya get the dam front tire traction out of the equation. HD's like yours may even handle better than the race elites that walk all over their rear patch pulling wheelie just going straight as they can over a crest, the poor corner cripples.

I am pleased to learn there is still effective squish in the .060" zone but don't "think" squish has much help in Norton unless more squish area provided. With your cycle wisdom deeply engrained and hi octane available I'd build it 10.5 static with the set up described for mid 8 dynamic CR, as will idle nicer and come on cam sooner and just grab lower gear if it balks-pings on throttle snaps as will not take ya long on how to grasp best safe operation getting it on. I've followed a big dude camp loaded on his factory 850 in serious Mt. twisties on my spiffed up race tire shod SV650 but dang it I had to stay in lower gears and grit my teeth to keep up with just his touring rates. His main advantage was pulling out of turns so well on the torque. He'd even lowered air in rear for softer ride but even with it wallowing some he sure impressed me on a factory 850 capability.

What ya really would like even more than the power to weight is taming the isolastics so ya don't have to slow down for turns but power up to get the stupid front out of the way so all mass on rear patch while nailing it out of there... TOTALLY solves all handling issues and no hinge/tank slap onset possible. With links and that power plant in a Commando you will become famous and sought out to contest against. Just don't press close if coming up from behind as might press someone into over doing it on their corner cripples, wait just a bit as once around them can leave em so far behind its their own dam fault after that.

hobot said:

OH My Yes BitchyB, you know what I call phase 3 handling is about! I also know how dam well them big ole Harely's can handle with mainly lean fouling limiting them, UNTIL ya get the dam front tire traction out of the equation. HD's like yours may even handle better than the race elites that walk all over their rear patch pulling wheelie just going straight as they can over a crest, the poor corner cripples.

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I had a 2” over stock ’73 Sportie front end (4” longer than a stock “Wide Glide”) & a 2 into 1 collector angled up & tucked tight up against the swing arm. On the 3.25 X 19 Avon Speedmaster shoe up front, it sat about right. Grounding wasn’t a problem, but the shear mass of the machine was. I had a tin primary (no electric foot) & a belt drive W/a trimmed down & flared FLH front fender on the rear. The bike was stripped down to “fighting weight” but still tipped the scales @ the local slaughter house @ 550#. It had mountains of TQ that came on like a freight train @ 3000 revs & it pulled to 6000, but I shifted @ 5000 to get on the fat part of the TQ in the next gear.

hobot said:

I am pleased to learn there is still effective squish in the .060" zone but don't "think" squish has much help in Norton unless more squish area provided. With your cycle wisdom deeply engrained and hi octane available I'd build it 10.5 static with the set up described for mid 8 dynamic CR, as will idle nicer

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By “nicer idle” do you mean low & smooth or just a little bit lumpy & nasty? To me the latter is more desirable as long as the thumper doesn't choke & stall @ a red light.

hobot said:

and come on cam sooner and just grab lower gear if it balks-pings on throttle snaps as will not take ya long on how to grasp best safe operation getting it on. I've followed a big dude camp loaded on his factory 850 in serious Mt. twisties on my spiffed up race tire shod SV650 but dang it I had to stay in lower gears and grit my teeth to keep up with just his touring rates. His main advantage was pulling out of turns so well on the torque. He'd even lowered air in rear for softer ride but even with it wallowing some he sure impressed me on a factory 850 capability.

What ya really would like even more than the power to weight is taming the isolastics

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Can you elaborate on the “taming the isolastics”?

hobot said:

so ya don't have to slow down for turns but power up to get the stupid front out of the way so all mass on rear patch while nailing it out of there... TOTALLY solves all handling issues and no hinge/tank slap onset possible. With links

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Links?

hobot said:

and that power plant in a Commando you will become famous and sought out to contest against.

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The local Hog jockeys that told me my “obsolete” Panhead W/70# offset ground flathead flywheels was “all wrong” ended up building 96” Shovelheads just to (barely) get around me. Even then, they coudn't pull away far enough to break the draft.

The poor guys on their mildly hopped up 74” bikes would run them into the ground trying to stay in front while I just purred along.

hobot said:

Just don't press close if coming up from behind as might press someone into over doing it on their corner cripples, wait just a bit as once around them can leave em so far behind its their own dam fault after that.

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Aren’t you supposed to wait on an inside line to pass? That way if they dump it they don’t take you out.

I have a lumpy and nasty idle with the JS stage one "as promised", but barely off and it's silky smooth power. Them 1 1/2" pipes sing like Gabriel's horns. Man that's fine!
I might think that anything over a stage one and there will be no idle to be had. If that is a streetability factor for you, then it deserves consideration.

pete.v said:

I have a lumpy and nasty idle with the JS stage one "as promised", but barely off and it's silky smooth power. Them 1 1/2" pipes sing like Gabriel's horns. Man that's fine!
I might think that anything over a stage one and there will be no idle to be had. If that is a streetability factor for you, then it deserves consideration.

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I have just about decided to go W/the straight up 10.5:1 CR installation. I figure that I can reduce compression W/O a significant $$$ penalty. Hell, I can anneal & re-use a solid copper head gasket right? (worked on my BSA) Scuff the cylinders walls W/a hone & re-use the rings if I’m careful. It would be just a small machine shop charge to machine a pocket in the piston crown. Who knows, once I measure the head chambers I might be closer to 10:1 than 10.5:1.

The cam choice is a bit more critical. I’ll be eating $400 if I make the wrong choice. Probably better to err on the side of caution there & stick to the Stage 1..

Bitchin', I don't know if you're refering to Jim's Schmidt's pistons when you said you could dish the crowns to reduce CR but if so you may wish to talk to Jim because I believe his under crown machining leaves his lt. wt. pistons crowns at .170" thick so something to think about...Mark

Matt, About bending gearbox mainshafts. I run very high gearing, however I achieve it by fiiting a smalle rear wheel spocket, and larger gearbox final drive sprocket, rather than larger engine sprockets, If the mainshaft is spinning faster for the same road speed, doesn't that mean the bending moment is reduced ? Plus I believe close internal ratios give everything in the transmission train except the rear chain an easier time.

marksterrtt said:

Bitchin', I don't know if you're refering to Jim's Schmidt's pistons when you said you could dish the crowns to reduce CR but if so you may wish to talk to Jim because I believe his under crown machining leaves his lt. wt. pistons crowns at .170" thick so something to think about...Mark

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Wow! No wonder they're so light. He must do that between the valve pockets. I was assuming that the under crown was uniform across the span & the same profile as the medium compression piston.

So much for that idea if that is so. Look like the only practical way to reduce CR is a thicker head gasket.

The main way in past to decrease CR was fitting a barrel base plate as only .040" copper of slightly thinner Flamering gaskets available. JMS now offers a few top gasket thickness. The side issue is each change in stack height changes the push rod to rocker geometerry so pushrod length may need diddling to center rockers on valve stem travel arc. Once ya do get p-rod dialed in then any change in stack components can just be added or subtracted from new p-rods w/o the tedious fiddling of first time.

I'm taking an educated chance going 10.5 CR with JMS kit and his flat lifter Norris D drag cam in 920 93 mm wide flame front jugs on 87 octane and don't expect to need water or higher octane w/o the blower installed. After long pow pows with Gary at PowerArc ignitions tales of impossible to stop knock on pumped up Harley they ran more power on 87 octane than hi octane tried prior. PowerArch and Boyer are ones I know offer a rev limiter function though costs more on Boyer.

Cyrogenic tempering then dry friction coating can add endurance and extra kix in the seat.

hobot said:

The main way in past to decrease CR was fitting a barrel base plate as only .040" copper of slightly thinner Flamering gaskets available. JMS now offers a few top gasket thickness. The side issue is each change in stack height changes the push rod to rocker geometerry so pushrod length may need diddling to center rockers on valve stem travel arc. Once ya do get p-rod dialed in then any change in stack components can just be added or subtracted from new p-rods w/o the tedious fiddling of first time.

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J&S makes copper base gasket in .021" thickness. That sound just about right to drop CR form 10.5:1 to 10:1

Well I can now say what regular fuel does with a 10.2 to 1 compression ratio. I got a tank full of low octane fuel at a premium pump in Northern Texas. Around 4000 ft elevation.

It was hot and I was riding with my visor up and my earplugs in so I didn't notice the pinging until too late. As I topped the second hill from the gas station one piston seized.

It freed up after a short cool-down and I got some octane booster to stop the severe pinging but the damage is done. I have ridden 600 miles since and compression is down on the left side and it rattles pretty seriously. Definitely going to shorten the trip.
I guess I will be doing that new motor for sure now -at least it happened on the old motor.

I am still doing better than my brother who was accompanying me on the trip. His weld re-enforced Combat cases split about one inch below the cylinder base about 400 miles into the trip. His bike went home on a truck. Jim

After reading your other post Jim I thought you may be lowering your advise slightly,I realise the higher numbers can be made to work very well but even when a highly skilled tuner like your self gets caught out whats Joe Dummy going to do, After working in recon shops for 15 years 9.5-1 seemed to be about a no warranty claim level.
Its not going to look good if you and your brother turn up in the truck is it?

I once found myself in some backwoods town that only had one pump with regular. Bad planning to end up low in fuel in such places, but it happens. My friend with the 10.4 to one bike, normally carries octane boost, but had forgotten to put it in. The bike I was on is only 8 to one, so no worries, I only run midgrade in it normally and it is actually fine on reg. Not so good for my friend, very similar to Jims story, new engine time!
If you always ride in developed areas, premium is easy to get and even super premium isn't that hard to find. If you like twisty quiet old roads, sometimes regular is all that is available.

Glen

Sounds more like bad fuel below 87 octane. We'd need to know what cams were in Jim's and his friend split Combat too. Neither my Combats both a bit above 10:1 d/t missing base plate and 40 over bores [which ups CR] seemed to have issues running on summer time 87 octane 500>2000 ft. I had both engines apart d/t grit worn rings and bores with oil smoke increasing detonation proneness but not evidence of it on plugs or pistons seen, though some blasted bare no carbon surfaces on crowns and head chamber. So as usual its both luck of the draw on what each engine can take and how close to the destructive edge your life philosophy takes you. Seems 10 CR is the magic value to become pensive pinging on. I was as pensive as anyone having ping knocked my share of old V8s but running out of gas lost on unpaved paths more than once saved by farmers lawn mower or tractor gas forced me to try it a see mine could live with it.