Measuring Cam Wear

Joined
Oct 28, 2009
Messages
1,322
Country flag
I am freshening up the top end of my 72 Combat, which may or may not have a combat cam (2S) in it.
I am wondering about whether the cam is worn and wanted to check on this by measuring valve motion.

Can this be reliably done with a dial indicator on the valve stems while the head is still on the bike?
Or with a dial indicator on the pushrods with the barrel still on?
Or take the barrel off and measure the lifter movement?
I don't want to split the cases and measure the valve lift directly.

I found this link on the NOC site which suggests trying to calculate valve lift using valve motion is problematic. https://www.nortonownersclub.org/node/13848

Any practical advice would be appreciated.
 
I am freshening up the top end of my 72 Combat, which may or may not have a combat cam (2S) in it.
I am wondering about whether the cam is worn and wanted to check on this by measuring valve motion.

Can this be reliably done with a dial indicator on the valve stems while the head is still on the bike?
Or with a dial indicator on the pushrods with the barrel still on?
Or take the barrel off and measure the lifter movement?
I don't want to split the cases and measure the valve lift directly.

I found this link on the NOC site which suggests trying to calculate valve lift using valve motion is problematic. https://www.nortonownersclub.org/node/13848

Any practical advice would be appreciated.
The best , is on the pushrods , not funny because it needs the head off , but better than the head+barrel off ! on the valves apart the rocker ratio calculation and the possible readings error (valves angles ?) it is the easiest .........my thoughts . But if it is only to check wear 'and not the total lift ( to see if it is a 2S or not) the valve method could 'or will ' show you some discrepancies (apart of the above errors ) .
 
I am freshening up the top end of my 72 Combat, which may or may not have a combat cam (2S) in it.
I am wondering about whether the cam is worn and wanted to check on this by measuring valve motion.

Can this be reliably done with a dial indicator on the valve stems while the head is still on the bike?
Or with a dial indicator on the pushrods with the barrel still on?
Or take the barrel off and measure the lifter movement?
I don't want to split the cases and measure the valve lift directly.

I found this link on the NOC site which suggests trying to calculate valve lift using valve motion is problematic. https://www.nortonownersclub.org/node/13848

Any practical advice would be appreciated.
If you really want to know the condition of the cam lobes, take the barrels off. Once you have the head off for refresh, it really isn't that difficult.

With anything else you do, you are still only guessing.

Reduced lift isn't the only thing you need to look for with a worn lobe, you need to see the state of the wearing surfaces, including the follower surfaces.


And if you don't do it when you do have the head off, you will be taking the head off for a second time before too long.
 
With the head off, I used a long reach dial indicator that locates nicely in the sockets on the lifters, and measured lifter motion. It was repeatable, and I am pretty confident in the results. Intake lobe lift is .380 on both sides, exhaust lobe lift is .324 on one side, and .330 on the other side.

I also measured intake lift at TDC: .178,
and exhaust lift at TDC: .200

The NOC has a pretty comprehensive list of spec on Norton cams.

The .380 and .330 are not too far off the 2S and 4S cams. But the TDC lift is way off.

Thoughts?
 
Your best bet is to measure the full cam profile every 5 degrees or so with a degree disc on the crankshaft and a dial guage on the pushrods. With the barrel on. Always turn in the forward direction to eliminate back lash.

Plot them using a spreadsheet and then compare the profile to the set of profiles on DynoDaves site to hopefully identify your cam. The difference in TDC lift may be due to a different cam profile to the 2S your currently thinking. Or else the cam may be installed a bit advanced.

I just used a pushrod when I did mine. Measure all 4 lobes if you have the time because I found a 4 S with different lob centres between side. It's also very worthwhile carefully checking the base circle and the quietening ramps.

Edit. I see the DynoDave site no longer has those profiles listed. Looks like he has had to instal some kind of password system. Maybe contact him by PM To see if he can help.
 
Last edited:
If you measure over the full 720 degrees of cam rotation you will measure the base circle as well. On one cam I measured the base circle wandered up and down up to 3 degrees which means setting tappet clearance was going to be potentially wrong.

Very carefully measuring the quietening curves as the cam starts to open and accelerate onto the ramp of the cam can identify any machining errors and corrections required to the tappet clearance.
 
I had a good look around Dyno Dave's site and couldn't see any Norton cam profile info. Anybody know where the Norton cam info is?

I found Dyno Dave's BSA cam profile info using google, also not on his site, as far as I could see.
 
I just noticed that Dyno Dave's technical articles, including the cam profile info, is now in the Technical Information section in this forum, courtesy of LAB, I assume.
Which is great, as I understand all of the Norton technical content is no longer on Dave's website.
 
I just noticed that Dyno Dave's technical articles, including the cam profile info, is now in the Technical Information section in this forum, courtesy of LAB, I assume.
Which is great, as I understand all of the Norton technical content is no longer on Dave's website.
Thanks for this.
 
Taking off and fitting the head in the frame has to be one of the worst, most fiddly, and generally unappealing jobs on a Commando (well, for me at least).

So having done the hard bit, it just seems real false economy to not pull the barrels. It’s such an easy job, and allows SO much more inspection. You can basically check out the health of (almost) the entire engine.
 
It's generally not a great idea to remove rings from a cylinder after break in and then replace without honing and new rings. You can lose the existing ring seal.
I have done this and had it go OK and I've also had it not work out.
A good friend of mine who is a master machinist and motorcycle builder goes to great lengths to keep the rings in the bore when doing a bottom end inspection. He has made a jig so that he can lift the Vincent cylinders just enough to pull the gudgeon pins and check rod wobble ( Big end bearing wear state) while keeping the pistons and rings in the cylinders, engine still in bike.
This text from a small aircraft engine maintenance article gives an explanation.

General Aviation News
GENERAL AVIATION NEWS
Because flying is cool
MENU

The marriage between piston rings and cylinder wall​

By Paul McBride · June 3, 2012 ·
Q: I am an A&P, and have been in aviation since 1990. I once worked with another mechanic who told me that if you pull a piston out of a cylinder, you must replace the rings and hone the cylinder. He is the only tech I have heard say this — until I read your article What’s best? A flush or overhaul?
You stated: “If oil starvation is suspected, you may want to remove the #1 cylinder (leave the piston in the cylinder so you don’t have to hone the cylinder and install new rings) and remove the connecting rod from the crankshaft.” Can you explain this? Is there a Service Bulletin or other directive that explains this practice? Thanks for sharing your knowledge with us.
TOM THROSSEL, via email
A: Tom, let me start off by thanking you for your question. For the life of me, I can’t recall any Lycoming publication that specifically tells you to do what I stated about leaving the piston in the cylinder while doing an internal inspection in this particular situation. In this case it was for the suspicion of foreign material in the engine. However, as I think back in my career, I honestly believe this is one of those maintenance procedures that one learns from experience.

Let’s take a look at the logical side of the equation. I hope you noticed that the person making the inquiry did not mention how many hours were on the engine in which he found bits and pieces of paper towel. Therefore, I assumed the engine was beyond the normal break-in period of, say, 25 to 50 hours. Given that, I also assumed that if this was the case, then the piston rings would have been seated or bedded in and the oil consumption stabilized. If the piston were removed from the cylinder at this time, the result would be that we disturbed the marriage between the piston rings and the cylinder wall, which is a result of proper engine break-in and which we know has occurred when the engine oil consumption stabilizes. Once the piston is removed from the cylinder barrel, you can never reassemble it and have the same ring to barrel marriage.
 
If I pull the barrels and want to measure ring wear, I will remove the rings from the pistons, drop them in the bore, and check for end gap. This assumes the rings were gapped correctly when new, or the measurement is not meaningful.
What am I missing here? Any other way to detect ring wear?

If I decide to install new rings, can I just order any .020 over rings and install them in the .020 pistons I have? Or do I need to match the new rings to the pistons I have? Is that dead simple, or a freakin nightmare? Why am I thinking nightmare.......
 
Last edited:
"Freshening up" is a term I associate with "reconditioning" when it is used in regards to engines...
What was the reason for removing the cylinder head in the first place...?
 
Back
Top