A, B or "touring" cam?

J

JayJay

Well-known member
I'm tearing into an engine and the camshaft looks to be in pretty good shape (the engine was rebuilt sometime in the past, well before I got the car). I want to rebuild it with a "touring" camshaft, but how do I tell what I have? I suppose I could compare it to the Burtz "touring" camshaft I have for my Burtz build, but are the differences between the various cams in lift height, lobe profile or cam timing? I'm not anxious to regrind a good cam if I don't need to.

Thanks, all.

JayJay
 
JayJay said:
I'm tearing into an engine and the camshaft looks to be in pretty good shape (the engine was rebuilt sometime in the past, well before I got the car). I want to rebuild it with a "touring" camshaft, but how do I tell what I have? I suppose I could compare it to the Burtz "touring" camshaft I have for my Burtz build, but are the differences between the various cams in lift height, lobe profile or cam timing? I'm not anxious to regrind a good cam if I don't need to.

Thanks, all.

JayJay
Click to expand...

The cam needs to be reground either as is or whatever you decide and no matter what, the lifters need to be refaced also.
If you decide to go cheap and not do this, the lifters absolutely need to be kept with the lobe they were running on before.
 
Pete said:
The cam needs to be reground either as is or whatever you decide and no matter what, the lifters need to be refaced also.
If you decide to go cheap and not do this, the lifters absolutely need to be kept with the lobe they were running on before.
Click to expand...
Thanks, Pete, good point. One of the compelling reasons for this teardown was to refresh the valves and to replace the original lifters with adjustable (the gaps are way out of whack). Since I'll be changing the lifters I'll go ahead with a cam regrind as well.

The good news is, at first glance the babbit looks good. (Note: dictionary wants to replace "babbit" with "wabbit", as in "wascawwy wabbit".) Need to check the clearances still but I'm optimistic.
 
JayJay said:
Thanks, Pete, good point. One of the compelling reasons for this teardown was to refresh the valves and to replace the original lifters with adjustable (the gaps are way out of whack). Since I'll be changing the lifters I'll go ahead with a cam regrind as well.

The good news is, at first glance the babbit looks good. (Note: dictionary wants to replace "babbit" with "wabbit", as in "wascawwy wabbit".) Need to check the clearances still but I'm optimistic.
Click to expand...

I recommend the 1 inch dia. lifters with the pinch nut and have the cam reground for the 1 inch lifters.
 
The bearing metal was invented by a guy named Babbett, so it is capitalized.

I personally don't like reground cams and would buy a new one. But that is my opinion and others disagree.
 
The Model B camshaft profile, which is an improvement of the Model A grind, is used by some as a touring grind for the Model "A" camshaft. The Model B camshaft is distinguished by an extra lobe that drives a fuel pump. The Model B camshaft does fit into the Model A engine without any modification.
Camshaft lobes are case hardened to reduce their wear rate. Case hardening does not completely go through the camshaft, so it is considered more of a surface condition. Thus there is a concern the regrinding an existing camshaft may reduce the case hardening which affects the camshaft's life.
My preference would be to use a Model B camshaft, or buy a new camshaft with a touring grind. Perhaps the Burtz camshaft has a profile more suitable for touring, so you may want to consider getting a camshaft with the Burtz profile. I do not know if the Burtz camshaft will fit into a Model A block.
 
There were 3 Model B cams produced, the most common one had .302" of lobe lift. The best one had .339" but these are more rare. The Burtz cam is a little more radical, more lift and duration, and does put the power curve at a little higher RPM.

Original A/B cams are not case hardened, they are just made from really good steel, so re-grinding them does not change its hardness.
 
Heat treat in model A/B cams is adequate as is for a hot rod regrind. They were NOT case hardened from the factory.
What works best for a mild street engine is more lift, LESS duration and MORE lift velocity.
You do not lose low end performance this way. You DO get a slight lopey idle sometimes though which can be offset by certain engine modifications.
 
All very informative but to the original question: once I have the cam out and on the workbench, how do I tell what I have? I get that the B cam will have an extra lobe for the fuel pump, and I can check for that. But as between a stock (original or regrind) grind and a regrind to B (touring) specs, is there any way I can tell? I need to mic the journals and lobes to determine if it's suitable for a regrind anyhow, but other than those raw metrics, is there a way I can see what the cam is ground to? And where is there a listing of what the grind specs are?


Thanks.
 
JayJay said:
All very informative but to the original question: once I have the cam out and on the workbench, how do I tell what I have? I get that the B cam will have an extra lobe for the fuel pump, and I can check for that. But as between a stock (original or regrind) grind and a regrind to B (touring) specs, is there any way I can tell? I need to mic the journals and lobes to determine if it's suitable for a regrind anyhow, but other than those raw metrics, is there a way I can see what the cam is ground to? And where is there a listing of what the grind specs are?


Thanks.
Click to expand...

There is no way to tell what the grind is just by looking at it if you are not experinced in doing that.
If you had a KNOWN hot rod cam to sit alongside and compare or measure lobes then you could tell if it had been modified but not to what specs.
You could NOT tell what the specs were just by looking at it.
There are many websites that list specs for various cams and you can find them by searching "camshaft specs".
To find the specs of a cam without some special equipment the easiest way is put it in the block it is going to be run in and degree it. All this requires is a degree wheel and a dial indicator.
 
Set the cam in the engine with one exhaust and one intake valve and adjustable lifters. Set the tappet gap to 0.010 inch on both valves. Set a degree wheel on the crankshaft with a pointer. Set a dial indicator on one valve and measure the degree duration and lift. Use 0.010 inch lift off the seat for the valves as the start and end of the duration. Do this for both valves. Then compare your results with the specs. Depending on how the specs are listed, whether by crankshaft degrees or by cam degrees, you may have to divide the duration by two.
 
nkaminar said:
The bearing metal was invented by a guy named Babbett, so it is capitalized.

I personally don't like reground cams and would buy a new one. But that is my opinion and others disagree.
Click to expand...

You are almost correct. His name was Isaac Babbitt.
 
You can get a rough idea by measuring lobe lift. The best way is with a dial indicator, but on a stock or near stock cam you can mic the lobe across the nose (fully open) and at 90 degrees from that point, the difference will give you lift in inches. Most, but not all, touring cams have higher than stock lift. I grind a cam that I call a 'C'. It is just a .339" B cam that I've copied and rounded the nose a bit for longevity, it now has .320" of lobe lift, and it makes a great touring cam. It has slightly more duration than earlier B cams, idles like a stocker and performs very well in the RPM ranges that we tour in.
 
Jim Brierley said:
You can get a rough idea by measuring lobe lift. The best way is with a dial indicator, but on a stock or near stock cam you can mic the lobe across the nose (fully open) and at 90 degrees from that point, the difference will give you lift in inches. Most, but not all, touring cams have higher than stock lift. I grind a cam that I call a 'C'. It is just a .339" B cam that I've copied and rounded the nose a bit for longevity, it now has .320" of lobe lift, and it makes a great touring cam. It has slightly more duration than earlier B cams, idles like a stocker and performs very well in the RPM ranges that we tour in.
Click to expand...

I get it that lift means the valve travels higher, and gets more breathing. But what is the duration (in plain english)?
 
Duration is how long the valve is off of it's seat, Usually measured after a certain amount of initial movement of the valve, like .050 after opening to .050 before fully closing. Measured in degrees of crankshaft rotation.
 
nkaminar said:
Set the cam in the engine with one exhaust and one intake valve and adjustable lifters. Set the tappet gap to 0.010 inch on both valves. Set a degree wheel on the crankshaft with a pointer. Set a dial indicator on one valve and measure the degree duration and lift. Use 0.010 inch lift off the seat for the valves as the start and end of the duration. Do this for both valves. Then compare your results with the specs. Depending on how the specs are listed, whether by crankshaft degrees or by cam degrees, you may have to divide the duration by two.
Click to expand...
Makes perfect sense, other than ... I don't have adjustable lifters, which is the primary reason for getting into the valve train in the first place (to install them). I'll just assume that the cam is a stock A cam unless I find the extra lobe, in which case I'll assume it's a B cam. Either way, a regrind is in my future.

Thanks a million to everyone who responded. I have learned a lot, which is usually the case when I go on the Barn.
 
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