Cam lobe issue?

[CamKing]

Ow, my head is hurting now...

Any chance Mike you could punch: "cam lobe taper images" into Google, find an accurate one and post the link to it and your matching explanation here?

I looked, and did not find any that were correct.
If you use the diagram you posted, the lobe taper would be correct, if you were looking at the cam from the passenger side of the car. The box that says "Right" would be the rear of the engine.
The lifter offset is on the wrong side. You want the cam to be moved toward the front of the engine(away from the box that says "Right").
This will move the contact point closer to the high side of the lobe, when it's on the base circle, and at max lift. As the lifter accelerates,the contact point will move towards the low side of the lobe, but not all the way to the edge of the low side.

[CharlieB53]

I couldn't tell from the picture if that was an EDM solid lifter. Would that have made a difference?

Would it also be a good practice to 'groove' the lifter bores, either a straight line down or a curved groove to provide a little better oiling supply to the sides of the lifter and bore?

I've seem some cut/grind a very small oiling groove or flat on the lifter from the oil band down to the bottom to provide cam oiling. I don't doubt a modification like this also provide a slight amount of bore lube as well. Care would have to be taken not to radically reduce over all oil pressure.

[MadBill]

Ow, my head is hurting now...

Any chance Mike you could punch: "cam lobe taper images" into Google, find an accurate one and post the link to it and your matching explanation here?

I looked, and did not find any that were correct.
If you use the diagram you posted, the lobe taper would be correct, if you were looking at the cam from the passenger side of the car. The box that says "Right" would be the rear of the engine.
The lifter offset is on the wrong side. (To correct this illustration,)You want the cam to be moved toward the front of the engine(away from the box that says "Right").
This will move the contact point closer to the high side of the lobe, when it's on the base circle, and at max lift. As the lifter accelerates,the contact point will move towards the low side of the lobe, but not all the way to the edge of the low side.

OK, I think I've finally got it and indeed, I was envisioning the front of the engine to the right side of the screen. For the depiction I posted, the builder should shim the cam forward (to the right of the screen) to move the contact point on the lobe closer to its rear edge, but because the taper is a straight line, the contact point on the lifter and the resulting rotational torque will be unchanged?

Regardless, the lobe taper will create a rearward (towards the box labeled "RIGHT") thrust and thus keep the cam sprocket thrust face in contact with the front of the block.

PS: I assume the offset measurement shown below is irrelevant, as it is the offset between the centerline of the lifter and the center of the contact zone on the lobe that affects rotation torque?
.

Lifter-Lobe Relation.jpg

[Brian M]

I don't want to create debate but my head hurts also. I am in the process of doing my final assembly of a sbc 400. Checking my FT cam offset in relation to lifters, my cam is sitting rearward of the lifter holes. The distributor gear is centered in relation to the distributor hole.

The depth of my cam timing gear is .120 so that of course makes my cam stick out of the block .120. I made a pointer with a plastic tip from an old lifter, much like racear's. If I go and place my cam lobe centreline .020 forward of lifter bore centreline I have to move the cam .115 forward. Now I have .235 sticking out of the block and the distributor gear doesn't look in the right position.

A question if anyone cares to bite. Since I am an "old" novice builder, not many engines under my belt but I do pay attention to detail, can the distributor gear be positioned off centre of the distributor hole and if so what is considered safe?

[CamKing]

I don't want to create debate but my head hurts also. I am in the process of doing my final assembly of a sbc 400. Checking my FT cam offset in relation to lifters, my cam is sitting rearward of the lifter holes. The distributor gear is centered in relation to the distributor hole.

The depth of my cam timing gear is .120 so that of course makes my cam stick out of the block .120. I made a pointer with a plastic tip from an old lifter, much like racear's. If I go and place my cam lobe centreline .020 forward of lifter bore centreline I have to move the cam .115 forward. Now I have .235 sticking out of the block and the distributor gear doesn't look in the right position.

A question if anyone cares to bite. Since I am an "old" novice builder, not many engines under my belt but I do pay attention to detail, can the distributor gear be positioned off centre of the distributor hole and if so what is considered safe?

If you had to move .115" to get the centerline of the lobes to be .020" forward of the centerlines of the lifters, that means, right now, your centerline of your lobes would have to be .095" rearward of the centerlines of the lifters. If that's a SB Chevy, that would be the farthest off, I've ever seen one.
I suggest you double check your numbers.

[77cruiser]

Is this the way it should be?

Lifter-Lobe Relation.jpg

[88bluestar]

What must be done to move the cam forward to position it correctly? Pics taken on driver side of engine.

[user-17438]

What must be done to move the cam forward to position it correctly? Pics taken on driver side of engine.

Depending on if it's a block issue. Sometimes you have to put the lifter bores in the right spot.
Or use a cam button from the backside. Or take material off the snout. Or add shims..Etc.

[F-BIRD'88]

You don't need to do anything. Get a correct GM OEM spec timing set and it will SELF ALIGN.. and the lifters will spin. Just like every other GEN1 SBC since 1955.

Only roller cam setups need a cam button and thrust bearing behind the cam
to control cam for aft location.. A flat tappet cam DOES NOT NEED this.
It is designed to self align when its running.

[user-17438]

You don't need to do anything. Get a correct GM OEM spec timing set and it will SELF ALIGN.. and the lifters will spin. Just like every other GEN1 SBC since 1955.

Only roller cam setups need a cam button and thrust bearing behind the cam
to control cam for aft location.. A flat tappet cam DOES NOT NEED this.
It is designed to self align when its running.

[user-17438]

Yes, he is correct.. no need to measure anything. Anything without enough clearance will ad of clearance. Just slap it together


It amazes me garage jockeys get paid what they charge.. yet people can complain about a professional and what they charge..

[user-17438]

Since camking said the high point of taper was rear, I at the very first knew that, the label "right" was really meant to say left.
As far as a sbc to move the cam forward the counter bore that fits over the front of the cam in the sprocket would need to be deeper, and rather than mess with cutting a cam shaft, or some other goofy thing, that is the easy cheaper part to work on. And no reason to even touch the factory bore in that sprocket, just go a bit deeper on the face and a bit over in that area of the bore not cutting anything from the original bore.

I wouldn't move the entire cam if it was only 1 or 2 lobes.

[88bluestar]

Would the easiest way be to resurface the front of the cam face if it needs it after the timing set change? Max rpm is 7000 pill, though it’s geared around 6800 roughly

[user-17438]

I think silver seal or something like that makes a mandrel to easily cut it.

[Keith Morganstein]

You don't need to do anything. Get a correct GM OEM spec timing set and it will SELF ALIGN.. and the lifters will spin. Just like every other GEN1 SBC since 1955.

FBird ,
You are mistaken if you think the cam lobes and lifters will self align. The cam will be forced to the rear of the block by the force on the cam lobes by the lifters and the distributor gear and oil pump load. The thrust surface of the cam gear will limit the travel. That will be alignment and the lifter to lobe contact will be a result of that.

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