Cam choice?? Decisions, Decisions

CanukNortonNut · Jan 26, 2011

Well I have 2 options for a new cam which my 74 850 Interstate in need for renewal = Soft Cam.

Because of a worn cam it will not go faster than 75 mph and it bogs on induction noise through the Carburettors the more I twist the throttle.
I have a Megacycle 560-N-R or a SS cam (Two SS stamped on cam) for options. Both are scrolled for oil ways and I think that flat tappets can be used for both. I am wondering if the valve tappet clearance is the same as the combat 0.008” intake and 0.010” exhaust using the SS? I don’t plan on shaving the head. So compression will remain the same. Black Diamond valves and new guides with R/N 901-N springs for added trix. :mrgreen:
Have any of you used either of these cams on an 850 and wasn’t the SS cam used for a stage one performance upgrade? I don’t have my Norvil book handy. Any input would be appreciated. Thanks in advance.
CNN

bwolfie · Jan 26, 2011

After you make a decision I would be interested in the cam you don't use, If it is available. I was going to order a new one from RGM, but If I could find a nice used one that would be nice.

1up3down · Jan 26, 2011

With this past summer's rebuild on my 850, I put in a new cam, the Megacycle 5600.

With my cam, Valve clearances should be set at 9thou, both intake and exhaust.

Make sure to send your lifters to megacycle to be matched to the new cam. You may need new ones, I was lucky, just a regrind.

The higher lift lobes, along with the slightly oversize new Black Diamond valves I fitted, caused the valves to just touch.

Had to have a little bit taken off the valves and the seats recessed a bit to make sure nothing would touch.

Be careful of all this when fitting a little "hotter" cam than the stocker.

Please click here and review the various cam choices and clearances, I think your new choice is shown.
http://www.nortonownersclub.org/support ... /camshafts

Hope all this is helpful.

comnoz · Jan 26, 2011

The 560 nr cam will be the happier grind on a streetbike. Almost as good as a standard cam in most applications. Jim

pete.v · Jan 26, 2011

comnoz said:
The 560 nr cam will be the happier grind on a streetbike. Almost as good as a standard cam in most applications. Jim

I agree with this. It might also be said of the SS grind that to perform as intended would require head shaving to increase CR. Without higher compression the true potential of the ss is lost. That's just what I have heard.
560nr is the way to go as far as I'm concerned.
I installed the Stage 1 kit from JS Motorsport this winter. Both intake and exhaust at .005 with BSA radius lifters.
Waiting for the weather to break is particularly difficult this year.

Hobot · Jan 26, 2011

pvisseriii advice agrees with what I've had to study up on last couple years > mild cams workl best with mild CR, more aggressive cams need higher CR to function, especially to start and idle w/o having to blip like a dragster. Also bad to reverse the relationship ie: putting a milder less over lapped less aggressive cam in a higher CR engine can lead to detonation. This was learned hard way by folks trying to detune Combats.

ashman · Jan 27, 2011

Hi
I built my 74 850 to stag 1 specks 32 years ago and got my standard cam built up and grinded to SS cam specks, I still run the same cam to this day, I have just finished total rebuild of motor 4 months ago now, I still run with flat lifters and my head has been shaved 12 thou and running orginal valves but have replaced the springs as well a fair bit of porting, with 40 thou over size Hepilite pistons and balanced crank, this motor hasn't let me down in all this time...

I am very happy the way this SS cam grind works and you know when it kicks in, in my orginal workshop manual that I brought over 32 years ago it had the high performance section at the back of the manual and I did most of the things for the stag I engine for road use, this engine works good at low RPMs as well as high speed running, very happy with my SS cam grind...

Ashley

grandpaul · Jan 27, 2011

The 560 with radiused followers on the alloy tank 850 sure made the front end feel light on moderate accelleration!

I didn't run it too hard because I prefer moderate break-ins, and didn't have it long enough to really put it through the paces before selling it, so I have mixed emotions.

The cam was a good choice.

comnoz · Jan 27, 2011

ashman said:
Hi
I built my 74 850 to stag 1 specks 32 years ago and got my standard cam built up and grinded to SS cam specks, I still run the same cam to this day, I have just finished total rebuild of motor 4 months ago now, I still run with flat lifters and my head has been shaved 12 thou and running orginal valves but have replaced the springs as well a fair bit of porting, with 40 thou over size Hepilite pistons and balanced crank, this motor hasn't let me down in all this time...

I am very happy the way this SS cam grind works and you know when it kicks in, in my orginal workshop manual that I brought over 32 years ago it had the high performance section at the back of the manual and I did most of the things for the stag I engine for road use, this engine works good at low RPMs as well as high speed running, very happy with my SS cam grind...

Ashley

A 2s cam is a fun sporty grind and works well- if you do the rest of the tuning needed to make it work. Simply installing one in a low compression 850 motor usually results in an overall loss of performance.

CanukNortonNut · Jan 27, 2011

bwolfie said:
After you make a decision I would be interested in the cam you don't use, If it is available. I was going to order a new one from RGM, but If I could find a nice used one that would be nice.

Both of these cams are New. So nothing is used. Sorry bwolfie.

CanukNortonNut · Jan 27, 2011

comnoz
How much increase in CR do you need to make the 2s work. I really don't want to peel of .040" and then work on the pushrods/ valve cutouts etc. etc.
Thanks.
CNN

comnoz · Jan 27, 2011

CanukNortonNut said:
comnoz
How much increase in CR do you need to make the 2s work. I really don't want to peel of .040" and then work on the pushrods/ valve cutouts etc. etc.
Thanks.
CNN

To see power similar to a standard cam in the 3 to 5 K rpm range you would need to raise the CR by around 1 point. So .040 or 1mm would be a good starting point. You will see a few extra horses over 5000 then. Pushrod shortening would be needed. Jim

JAYMAC · Jan 27, 2011

I get superb overall results with a PW-3 fitted.

Carbonfibre · Jan 28, 2011

hobot said:
pvisseriii advice agrees with what I've had to study up on last couple years > mild cams workl best with mild CR, more aggressive cams need higher CR to function, especially to start and idle w/o having to blip like a dragster. Also bad to reverse the relationship ie: putting a milder less over lapped less aggressive cam in a higher CR engine can lead to detonation. This was learned hard way by folks trying to detune Combats.

Interesting.................and did studies help you find out the reasons for this?

bill · Jan 28, 2011

Carbonfibre said:
hobot said:

pvisseriii advice agrees with what I've had to study up on last couple years > mild cams workl best with mild CR, more aggressive cams need higher CR to function, especially to start and idle w/o having to blip like a dragster. Also bad to reverse the relationship ie: putting a milder less over lapped less aggressive cam in a higher CR engine can lead to detonation. This was learned hard way by folks trying to detune Combats.

Click to expand...

Interesting.................and did studies help you find out the reasons for this?

116 and one more negative

Hobot · Jan 28, 2011

Carbonfiber is just testing me and that's what I'm all about on my special Peel. Any weakness in her handling or my understanding could well be the end of us.
If you are new to Commandos, there have been a number of people that tried to detune a Combat by putting in standard cam. This raised dynamic CR to point detonation became a limiting factor. Yet with 2S cam detonation was much less if any issue on same octane. You will just have to take my word for it or study up your self why a cam that has both valves open very much at same time needs higher CR ratio to function as power adder, or even idle.

Any one with creek water handy or windshield washer fluid can have 116 octane about anywhere they go. Jim's pistons are 10:5 but Peel will only have 7.5 on start up and slow idle d/t too over lapped a cam for road use : )

Review DynoDaves cam graphs, many are just slight modification off the 2S cam. Increasing engine displacement tends to tame a hot cam made for a smaller engine. Smaller ports tend to tame down a more radical cam. Combined effect would be it comes on cam sooner and behave nicer down low.

bsaboss · Jan 28, 2011

There are a number of good spreadsheets on Harley sites (http://www.bigboyzcycles.com/TwinCamComp.htm is one) that allow you to show the impact cam choice has on corrected compression. Basically the later ABDC the inlet cam closes the more compression bleeds off. Looking at the calculator's variables it wouldn't be difficult to use it to get a pretty close figure for any engine, as long as you know things like the combustion chamber volume etc.

Hobot · Jan 28, 2011

Neat calculator thanks, plugged in Peel data to get static 11.86 and effective 7.84.
Her intake closes 83' ABDC.

BrianK · Jan 29, 2011

Fly on, Little Wing!

Carbonfibre · Jan 29, 2011

hobot said:
Carbonfiber is just testing me and that's what I'm all about on my special Peel. Any weakness in her handling or my understanding could well be the end of us.
If you are new to Commandos, there have been a number of people that tried to detune a Combat by putting in standard cam. This raised dynamic CR to point detonation became a limiting factor. Yet with 2S cam detonation was much less if any issue on same octane. You will just have to take my word for it or study up your self why a cam that has both valves open very much at same time needs higher CR ratio to function as power adder, or even idle.

Any one with creek water handy or windshield washer fluid can have 116 octane about anywhere they go. Jim's pistons are 10:5 but Peel will only have 7.5 on start up and slow idle d/t too over lapped a cam for road use : )

Review DynoDaves cam graphs, many are just slight modification off the 2S cam. Increasing engine displacement tends to tame a hot cam made for a smaller engine. Smaller ports tend to tame down a more radical cam. Combined effect would be it comes on cam sooner and behave nicer down low.

Any idea why exactly a longer duration cam needs higher compression pistons to work properly? I get the impression that this would be useful info for most of those interested in this thread.

Cam choice?? Decisions, Decisions

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