How Do I Check the Lobe Dimensions on MK2 Camshaft

I want to check the lobe dimensions on my camshaft (MK2 Roadster) to see if any appreciable wear has occurred and if I need to replace the camshaft.

Where do I find the dimension for the lobe height so I can measure it?

All I can find in the manual is the Base Circle Dia. @ .885" and the Maximum Lift @ .332" for Intake and .322" for Exhaust.

Is it simply a matter of base circle plus maximum lift to give total lobe height from peak of lobe to other side of base circle.

If this is the procedure then the intake measurement would be: 1.217" and exhaust 1.207".

Is this correct or re there other measurements available somewhere.

Thanks

Don

thunderbolt said:

If this is the procedure then the intake measurement would be: 1.217" and exhaust 1.207".

Click to expand...

That's basically it.

L.A.B. said:

thunderbolt said:

If this is the procedure then the intake measurement would be: 1.217" and exhaust 1.207".

Click to expand...

That's basically it.

Click to expand...

I think I"m missing something here... IF the rocker arm driven points (valve stem and pushrod cup) are equidistant from the rocker pivot point, then the displacement distance of the valve should equal the displacement distance of the pushrod... which would be .322" or .332" because that's the amount of lift. How does the base circle dimension enter into the math if the displacement is always .885" when the valves are closed and only .322" more when it opens??

... I'm sure I'm missing something here... anyone??

o0norton0o said:

IF the rocker arm driven points (valve stem and pushrod cup) are equidistant from the rocker pivot point,

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It's 1.13:1 (according to the factory manual).

o0norton0o said:

then the displacement distance of the valve should equal the displacement distance of the pushrod... which would be .322" or .332" because that's the amount of lift. How does the base circle dimension enter into the math if the displacement is always .885" when the valves are closed and only .322" more when it opens??

Click to expand...

As I understood it, thunderbolt was simply asking for the cam lobe dimensions not the valve lift figure.

The only catch would be if the cam had been been regound at some point, the base circle would be smaller and the total height less.

Greg

I have just measured the lobes on my shaft !!!!!

Curious measurements. According to my calcs the measurement should be 1.217" Intake & 1.207" Exhaust lobes (base circle + maximum lift).

My measurements starting from timing side and working across towards the drive side were as follows: 1.215", 1.215", 1.215" & 1.216".

These measurements ALL tally with what the intake measurement should be. The exhaust measurement should be .010" less. What's happened to these measurements? All the measurements on the lobes of my camshaft are literally the same.

Can anyone explain what's gong on for me?

Thanks
Don

Are there any markings on the camshaft (a letter stamp on the side of a cam lobe for instance)?

Not saying yours is Thunderbolt but I'd say some cam grinders regrind the cam lobes all the same, probably not knowing any different.
Not speaking of the Norton specific cam grinders who no doubt know their stuff when it comes to Norton cams.

L.A.B. said:

Are there any markings on the camshaft (a letter stamp on the side of a cam lobe for instance)?

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Yes Les there is a letter T stamped on the outer face of the lobe nearest the drive side.

Thanks
Don

thunderbolt said:

I have just measured the lobes on my shaft !!!!!
My measurements starting from timing side and working across towards the drive side were as follows: 1.215", 1.215", 1.215" & 1.216".
Can anyone explain what's gong on for me?

Thanks
Don

Click to expand...

I've read through this thread a couple of times, and unless I'm missing something, you state you have a stock cam in your bike.

The lobes on a stock cam are .330" on both inlet and exhaust, so it would appear you are right where you should be with your measurements.

Holmeslice said:

thunderbolt said:

I have just measured the lobes on my shaft !!!!!
My measurements starting from timing side and working across towards the drive side were as follows: 1.215", 1.215", 1.215" & 1.216".
Can anyone explain what's gong on for me?

Thanks
Don

Click to expand...

I've read through this thread a couple of times, and unless I'm missing something, you state you have a stock cam in your bike.

The lobes on a stock cam are .330" on both inlet and exhaust, so it would appear you are right where you should be with your measurements.

Click to expand...

The Norton manual gives the exhaust spec as being .010" less than the intake. According to the manual they are not the same.

From my shop manual

According to the manual, both rocker ratios are 1.13:1 and standard valve lift is the same for inlet and exhaust (0.375").

L.A.B. said:

According to the manual, both rocker ratios are 1.13:1 and standard valve lift is the same for inlet and exhaust (0.375").

Click to expand...

Les,
Is it possible that there is an error in the shop manual? Prior to looking at the manual I also though there is .330" lift on all lobes. The photo I posted came directly out of my shop manual. I just looked at a chart on the NOC site and it also shows .330" across the board.
Should we write this off as another typo in the manual?

http://www.nortonownersclub.org/support ... /camshafts

Deets55 said:

Is it possible that there is an error in the shop manual?

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It is a possibility that can't be ruled out at this time. :wink:

Sorry folks, as I followed the thread with significant amusement....
please note with all the accuracy measurements offered, I would offer (tongue in cheek) you would be better off using a ruler than mic's .
The cam measure rig and Mitutoyo 2358-50 I use to measure my cams is to .0001 resolution. Therefore actually measuring as much as .005 wobble in the base circle diameter even makes setting valve clearance like throwing a dart at a dart board. Or like Dirty Harry..."do you feel lucky sucker- well do ya? "
I have assumed the 06-1084 1S cam and it's predecessor 22729 SS (not 2S) (20M3/atlas/650ss/88ss+) are meant to be the same profile you are all discussing. This is based on actually measuring a lot of the over 2 dozen OEM norton take outs, and 2 NOS 20M3S /06-1084 I have on the shelf. In manufacturing practice, I failed to see the .010 differential being debated. Though I might spot check again!
:mrgreen:

My shop manual also shows the .332 inlet vs .322 exhaust, but then on the next page it declares identical lift of .375
Measuring a new cam I have laying around, with a sticker that says 06-2608 and outer lobe stamped with the letter "P", I cd find no difference in the lobes, all at or near 1.2165
My conclusion is that the manual is incorrect in this respect, should read .332 for both, for a stock cam.

So am I right to assume that this cam will now go back in the motor with the original followers (lifters)?

And in retrospect, did the measurements tell you more than a visual inspection did?

SteveA said:

So am I right to assume that this cam will now go back in the motor with the original followers (lifters)?

And in retrospect, did the measurements tell you more than a visual inspection did?

Click to expand...

Steve, you are correct in assuming this cam will go back in the engine. The reasons for the checking in the first place were that I didn't want any worn parts going back into the engine. Making sure that all lobes were relatively close in tolerance to each other. This cam has a "T" stamped on the lobe nearest to the drive side and Les has suggested that would determine that it is a standard 850 cam. If it had been a Dunstall, Axtell or some other hotter cam it would not have been going back in this motor.I have determined that this bike is going to be done up as close to original as possible. Hence standard parts in the motor. Oh yes, the original lifters will go back into the motor as well. They look in really great condition and have been checked by a mechanical engineer friend that has three Commandos and knows them pretty well. Also same lifters working on same lobes as originally came out of the motor.

In retrospect, the cam lobes looked and felt smooth enough (no grooves from lack of oil, etc). Visual can't tell you everything though so then the measurements were taken with a micrometer for a true indicator of very little wear if any on the lobes. Those two things aside the other sense that is used in checking the conditions of parts is "feel". Amazing how "feel" can quickly feel pitting, grooves, lips on material that is being inspected. All these aspects of inspection process are used no doubt by others as well as myself.

Thanks Don

I run race cams....um....in race motors, but I have a good condition standard 850 type cam which would go in if I built a road motor.

They are a really good choice....for a road bike!