cam chosen... build to start

just picked up a ss cam... pn 063536... can I use the standard iner & outer valce springs & spring spacers...or am I going to have spring bind issue... I've ordered new cam folowers to match the cam... I know that I am going to have some issues with jumping the compression up, any ideas with out milling the head ....this bike is a real bastard..... atlas crank...73 850 cases.... 75 850 cylinder & pistions..... RH10 head ( going to port out from 30mm to 32mm .... have Mikuni 32mm flat side carbs...1 1/2 id exhaust... power arc ignition... am I going to run into clearance issues besides valve tappet clearances..... also I imagine I would probally need to raise the compression at least up to 9.5:1 & run hi octane to keep from haveing denotation issues... any tech help ( real life experence ) & part numbers would be helpful ... also what would it hurt to run 32mm carb into a 30nn opening ?..... remenber..... it's not how you ride the storm out but rather how you dance in the rain

I had a Combat cam in mine until it blew 11 years ago. Stock springs and metal spring seats are fine but watch for coil bind on the intake. You probably have to remove the fibre heat insulators there. Clearance is usually ok on the exhaust which is where they are really needed. Easy enough to build up with valve gear on one or both cylinders and measure for coil bind at full lift. Springs should have at least 50 to 60 thou coil gaps.
Sounds like yr compression will be quite low so leave out base gasket. Really you should mill the head as per 750 Combat and 40 thou off would get you near 9:1 +/- with std pistons depending on your start point. Without cutouts valve to piston clearance then needs checking with plasticine/playdoh etc.
I once read (don't recall where) that the tappet guide plates are different for Combat cams though I've only ever seen one type. Cam to tappet tunnel clearance also needs to be checked. Usually with 850 barrels there is no problem, same goes for cam clearance in the 850 cases.

Putting the cylinders on the deck and getting an .021" head gasket from JS will get you pretty close without machining.

tripower said:

just picked up a ss cam... pn 063536... can I use the standard inner & outer valve springs & spring spacers...or am I going to have spring bind issue... I've ordered new cam followers to match the cam... I know that I am going to have some issues with jumping the compression up, any ideas with out milling the head ....this bike is a real bastard..... atlas crank...73 850 cases.... 75 850 cylinder & pistons..... RH10 head ( going to port out from 30mm to 32mm .... power arc ignition... am I going to run into clearance issues besides valve tappet clearances..... also I imagine I would probably need to raise the compression at least up to 9.5:1 & run hi octane to keep from having denotation issues... any tech help ( real life experience ) & part numbers would be helpful ..... remember..... it's not how you ride the storm out but rather how you dance in the rain

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I think there have been some comments about big vs. small ports. IIRC, the smaller ports were getting the bigger horsepower numbers for a street bike. If you are building to race, that's a different can of worms. You might want to run your ideas by Jim Comstock. He has done a lot of practical research, i.e., dyno work, on these very same Norton issues. As for spring bind, it takes accurate measurements to verify. Seat height alone varies considerably from head to head.

"Stock springs and metal spring seats are fine but watch for coil bind on the intake. You probably have to remove the fibre heat insulators there."

Although I have a lot of professional experience with building hi performance and competition auto engines, I have no experience with performance- modifying a Norton motor but I do have one question - is this insulator you mention the only thing between the base of the valve spring and the head? If so, I would not remove it because the spring will just chew up the aluminum. On my commando, when I installed new rings and valves, there were steel inserts under the base of the valve springs; there were no additional heat insulators. So if there's an insert PLUS a heat insulator, removing the insulator should be no issue - can't think why a heat insulator would be necessary but whatever... OTOH, if there is only a steel insert, removing it would, IMO, cause a problem.

Re cams - again, I have no experience with Norton cams but I have seen an amazing number of people who changed a car engine's stock cam to a "performance" cam and hated the results because in real life (other than competition engines), the motor seldom was in the power band where the cam actually helped and the real-world result was, as I used to call it, "a street motor with the special low-performance modification."

mike996 said:

"Stock springs and metal spring seats are fine but watch for coil bind on the intake. You probably have to remove the fibre heat insulators there."

Although I have a lot of professional experience with building hi performance and competition auto engines, I have no experience with performance- modifying a Norton motor but I do have one question - is this insulator you mention the only thing between the base of the valve spring and the head? If so, I would not remove it because the spring will just chew up the aluminum. On my commando, when I installed new rings and valves, there were steel inserts under the base of the valve springs; there were no additional heat insulators. So if there's an insert PLUS a heat insulator, removing the insulator should be no issue - can't think why a heat insulator would be necessary but whatever... OTOH, if there is only a steel insert, removing it would, IMO, cause a problem.

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No, the springs have the bottom cup, with the insulator between the cup & the head.

Another consideration if upping the compression ratio is to shorten the pushrods to suit - the factory never did this for the Combat :shock: and the one I just rebuilt had tappet witness marks heading towards the edge of the valve tip - I think I removed nearly 2mm from the pushrods to get it all back in line.
Worrying, but it seemed to survive that way until I got hold of it :roll:

Have the barrel top indexed to its base as may find its got a slight .003" from Norton so worth a bit more CR. Better sealing-stability w/o a cylinder base gasket. You will be more pleased with 30mm ports and 2S cam across whole power band than 32 mm so maybe just alter the bends and clean up valve-guide area. If not going full 10:1 then smaller ports will help the mix draw in faster for more response from 2S cam. The 30 mm ports will not restrict flow into redline zone but with above the stock carb size will.

Shave head down some and fit JMS thin head gaskets plus natural fiber thread and Hylomar the tunnels and oil drain hole. Trim push rods down so rocker centers on stems. Grind down the very ends of rocker valve ends, mainly for complete ease to place push rods and clean up rest of rocker finish just for sense of fun decorative mechanics to see now and then checking valve lash.

I'm sold on 2>1 exhaust as one least muffler to carry but 2>1>2 should give as much extra response down low w/o hurting top end but may have to degree cam to find sweet spot. Set initial spark so just don't back fire on starts then don't worry about octane unless really enjoying the throttle snaps in taller gears in summer Mt. climbs.

Ive been doing a lot of thinking on launching with the SS Camshaft , and come to the conclusion
that if you let in the clutch at 4.000 and dont let them drop lower , it will be the quickest . :mrgreen:

Matt the mighty 850 torquer might launch well at 4000 but Combats take closer to 6000 to get ahead with hp. CR has a lot to do with what rpm the engine 'comes on cam'. The must ask how lucky ya feel to make some lasting memories before ya taken out.

hobot said:

CR has a lot to do with what rpm the engine 'comes on cam'.

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Can anybody else verify this comment from experience? I've always believe the 'comes on cam' has more to do with inlet and exhaust length and configuration , and the cam timings which set the point where the harmonics get active. What I did not know until recently that when a Molnar manx is changed over to methanol fuel, it can pull from much lower down the rev range, however that might be due to the more forgiving nature of the fuel with respect to tuning errors. Perhaps increasing the comp. ratio has a similar effect to leaning off the mixture so the bike comes on tune ?

hobot said:

Matt the mighty 850 torquer might launch well at 4000 but Combats take closer to 6000 to get ahead with hp. CR has a lot to do with what rpm the engine 'comes on cam'.

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Some of might say that has more to do with the respective cams in an 850 and in a 750 combat.
If the cams were switched, what would that do to this scenario....

acotrel said:

Perhaps increasing the comp. ratio has a similar effect to leaning off the mixture so the bike comes on tune ?

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Engines that are leaned off more than a tad will not make more power.
Sure, they will rev if not under load.
But if you load them on the dyno and lean them off, the torque fades, badly.
If they don't ping themselves to death.
Or melt.....

Manx engines running methanol would/should/could have a very high compression piston in them.
Are we comparing apples with apples ??
Just the extra latent heat of vapourisation of alcohol keeps the internals cooler, which will give better running too.

acotrel said:

hobot said:

CR has a lot to do with what rpm the engine 'comes on cam'.

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Can anybody else verify this comment from experience?

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low compression engines won't really rev, but yes inlet and exhaust length and configuration also add into the equation towards making an motor spin up.

More CR mainly helps hot cams to start and idle and respond to throttle down low because they close intake valve later they don't begin compress till piston a good ways up the bore = 50-75' ABDC is common. Both valves are open nearing TDC and tend to blow back intake or let exhaust back wash so higher CR helps compress what little mixture is inhaled at lower rpms. Hotter cam also reduces need of octane with its effective-dynamic lower CR at lower rpms, but as rpm builds then the ram charge effect kicks in - even w/o attention to the intake and exhaust pulse tuning. As rpm builds less octane also needed as piston spends less time near TDC so less time for heat to build to blow up the mixture before compression spike is dropped fast by retreating piston. Intake and exht length & dia. tuning definitely part of power equation per cam profile but conflicted as what may help down low generally hurts top end power and visa versa. Basically need enough static CR so engine behaves decently down low - but not so much it detonates on available octane and spark timing advance. Once on cam, that is rpm enough the ram fill is happening before mixture can be blown back, higher CR gives a few more percent power - but now in the zone the porting and intake and exhaust really come into play. Approaching 10:1 with the 2S cam seems good compromise to run on 91 octane and behave with good Norton torque down low yet keep on building power till over red line destruction. Can search up CR and cam shaft performance to get more details than I know.

Rohan, the higher latent heat of vaporization does much more than simply keep the internals cool. It freezes the inlet tract which causes the incoming charge to cool. The air becomes denser, and more alcohol is needed to keep the combustion chamber temperatures right and the cycle repeats. That way you get a bigger bang for your buck, however you rate of fuel usage increases. It works at all compression ratios, however alcohol has unlimited antiknock so much higher compression ratios can be used. The effect of raising the compression ratio on an alcohol motor, is much less than the effect from changing from petrol to alcohol. And if you increase the comp. ratio, you then need an ignition system which will cope with the higher combustion chamber pressures. Most speedway solos at 16 to one ratio run magnetos. I had discussions with a guy with a Trident on 14 to one, and the ignition system was its major downfall. You can have all the theories about what should work, however the experience can be considerably different from your expectations.
An another thing - keeping the internals cool doesn't necessarily improve performance. One of the difficulties in using methanol comes when you have aluminium barrels. Sometimes getting the motor warm enough to race, is a pain in the backside. In two strokes, it is easy to crack a piston, and even in a big bore manx the extra piston slap can be a problem, if you don't get it warm enough.

acotrel said:

The effect of raising the compression ratio on an alcohol motor, is much less than the effect from changing from petrol to alcohol. .

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Don't address your replies to me - address all the readers here.

That statement quoted above is nonsense - as we have discussed here before.
Methanol in a stock motor makes very little to no difference than running on pump gas/petrol.

I was involved in someones 650 speedway Triumph running on methanol.
Made no difference to a stock motor power output - but it ran soooo much cooler.
Yes, it needed keeping warm even, on a cool day.
It wasn't until it got high-compression (alcohol) pistons that it came alive.
Thats where the REAL power comes from in alcohol motors.....

Manxes can run a 12:1 piston on alcohol.
And even higher, if you can make those mountains fit in there.

Rohan, I've got a simple question for you. You've obviously seen spark plugs with many different heat ranges - what is the fundamental difference between them and how do you 'read a spark plug' ?

Is this an exercise of psychotic shape shifting ??
Or has your brain slipped a cog.

Running methanol, you don't even NEED plug readings.
Just run it well rich - thats the gorgeous beauty of alcohol.
It can be 50% rich, and it only 'loses' 10% or less power.
No need to worry about melting pistons....

Unless your fuel tank range is important.
Or your fuel taps and hoses don't flow enough fuel...

Rohan, I directed my comment to you because you were the one making dumb statements.

'Methanol in a stock motor makes very little to no difference than running on pump gas/petrol.'

It makes no difference in performance if you make the common mistake of running it too rich. It is a difficult to jet for as petrol, if you a trying to get it right. It works better even at comp. ratios as low as 7 to one. In Australia we have run manxes and Triumphs as high as 12 to one for decades. Alcohol delivers more at those ratios, but it is not essential to go that high, - even with a standard piston a manx is faster on methanol, as long as you jet it right. My brother and I have successfully used methanol in two strokes for about 40 years. We would not dare to raise the comp. ratio above standard even though we reshape the squish bands.