Cam lobe issue?

[Warp Speed]

Im sure this has all been mentioned earlier, but there still seems to be allot of confusion so......
All sbc flat tappet cams are ground with their taper at the rear of the lobe. This make normal operation of the cam and lifters push the cam towards the rear of the block. That is why a thrust plate isn't needed in stock configuration.
Sbf used one bank with the taper to the rear, the other bank to the front, hence the need of a thrust plate.
On our Cup flat tappet cams, our specs were a minimum of .020 to a maximum of .055 lobe offset to the rear of the engine in relation to the lifter bore.
You can either shim the front of the cam to move the cam back, or cut the face to move the cam forward to get proper position. There will be a stack up of tolerances between lifter bore/lobe position from front to rear, so checking every lifter to make sure they are all acceptable isn't a bad idea.
The quickest way to do this, is to machine a piece of round stock to the od of the lifter. Next, machine a groove the width of the lobe nose, or just few thou larger. Then, using a dial indicator on the cam gear face, you insert the tool into a given bore and it centers the lobe. Zero the indicator, remove the alignment tool and push the cam back against the block. This will quickly give you the offset location.

[CamKing]

Next time I get a slightly used cam in here, I will post a picture of the wear pattern, so you can see what's going on.
There are many misconceptions.
With a tapered lobe, and crowned lifter, you don't need the lifter to be offset on the lobe, to make the lobe rotate. The rotation is controlled by the amount of lobe taper, and the radius of the lifter crown.
Moving the cam forward or backwards does not change the contact point on the lifter, just the contact point on the lobe.

[cgarb]

Mike, would one be correct by saying a flat tappet with the lobe centered on the lifter bore you would lose half of the contact surface on the lobe?

[houser45]

Not using a cam button on a flat tappet cam is not really the best practice. I use a roller or solid button on all the wet sump sprint car engines I build, You cant retain the cam as snug as you would with a roller but at .010" to .015" end play it allows movement of the cam and at least you ignition timing will be as solid as you can make it. Having no button will cause lots of timing movement. Not what I am looking for

[77cruiser]

Not a low mileage cam, about 18-20,000 miles.
The nose is starting to go away, lost about .006-.008.

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[user-17438]

Not using a cam button on a flat tappet cam is not really the best practice. I use a roller or solid button on all the wet sump sprint car engines I build, You cant retain the cam as snug as you would with a roller but at .010" to .015" end play it allows movement of the cam and at least you ignition timing will be as solid as you can make it. Having no button will cause lots of timing movement. Not what I am looking for

If you use the stock gm timing set on your Sprint car engine, you will not have any of the mentioned problems. You want the cam to find its home at 10,000 rpm.

[houser45]

who in there right mind is going to use a stock gm timing set driving an oil pump, magneto,power steering pump AND a fuel pump? how long do you suppose that chain will stay tight??

[racear2865]

Not using a cam button on a flat tappet cam is not really the best practice. I use a roller or solid button on all the wet sump sprint car engines I build, You cant retain the cam as snug as you would with a roller but at .010" to .015" end play it allows movement of the cam and at least you ignition timing will be as solid as you can make it. Having no button will cause lots of timing movement. Not what I am looking for

If you use the stock gm timing set on your Sprint car engine, you will not have any of the mentioned problems. You want the cam to find its home at 10,000 rpm.

oh crap
reed

[F-BIRD'88]

Plenty of SBC’s failed cam lobes since 1955, many under the initial warranty!

Not by the stock cam running out of fore aft position while running.
Most were a direct result of bad cam manufacturing (porous lobes) example of the infamous 305 cams. Most stock SBC cams run for the whole LIFE of the engine.
Be sure the timing set is made correctly to GM spec and the crank thrust is correct. The cam self aligns when this is right.
Watch the hot rod market timing sets. Many are not made right.

You will find most (the vast majority) old stock OEM cams from old stock motors are in surprising good condition, even the high perf stuff and high mileage.
The infamous 305 motor cams were pretty much a isolated thing and replacing that cam with a new stock 350 cam "929" cam resulted in a full cure. No fooling with cam buttons required. The stock setup works and does not need a cam button or a bearing behind the camshaft. Adding one will not increase cam life.

Of course if the crank's thrust bearing is wrong or the timing set is wrong too then all bets are off.

[BILL-C]

If yor lifter bores are not located properly, or the bores too loose, you are more likely to have a problem. When probing lifter bores in cnc machine it's common to find most within a couple thou and just a few wacked out. All it takes is one to spoil the job.

[racear2865]

If yor lifter bores are not located properly, or the bores too loose, you are more likely to have a problem. When probing lifter bores in cnc machine it's common to find most within a couple thou and just a few wacked out. All it takes is one to spoil the job.

Check a BBC.
reed

[steve cowan]

Not using a cam button on a flat tappet cam is not really the best practice. I use a roller or solid button on all the wet sump sprint car engines I build, You cant retain the cam as snug as you would with a roller but at .010" to .015" end play it allows movement of the cam and at least you ignition timing will be as solid as you can make it. Having no button will cause lots of timing movement. Not what I am looking for

If you use the stock gm timing set on your Sprint car engine, you will not have any of the mentioned problems. You want the cam to find its home at 10,000 rpm.

Guys come on MTE is being sarcastic
Read between the lines

[BILL-C]

If yor lifter bores are not located properly, or the bores too loose, you are more likely to have a problem. When probing lifter bores in cnc machine it's common to find most within a couple thou and just a few wacked out. All it takes is one to spoil the job.

Check a BBC.
reed

Pretty much automatic to correct lifter bores on BBC here. Before i got cnc we used BHJ tooling to correct lifter bores. I didn't have any way to measure, but i'm sure that some holes were .020 or more off. Cam killer for sure.

[racear2865]

If yor lifter bores are not located properly, or the bores too loose, you are more likely to have a problem. When probing lifter bores in cnc machine it's common to find most within a couple thou and just a few wacked out. All it takes is one to spoil the job.

Check a BBC.
reed

Pretty much automatic to correct lifter bores on BBC here. Before i got cnc we used BHJ tooling to correct lifter bores. I didn't have any way to measure, but i'm sure that some holes were .020 or more off. Cam killer for sure.

I have a CNC also and I was damn surprised when I checked my first big block.
reed

[88bluestar]

Inspected lobes, measured base circle and lobe. Cam lift spec is supposed to be .332, this came out to .320 all 16 lobes. I gather this is typical on an Elgin grind?