Tcheairs38655

I can move the cam with a screwdriver and almost center the lifter on the cam lobe
Ready to put the heads back on my freshly rebuilt (by a reputable shop) short block 427/450. just looking around, I noticed with the solid lifters installed that the lifters are roughly 1/4" off center with the camshaft lobes. I am able to take a big screwdriver and move the camshaft back and forth about the same 1/4" causing the lobes to line up with the lifters (pretty much anyway). So, since I'm wondering why the lateral play in the camshaft and what is going to hold it centered on the lifters? I dropped in the distributor and there is still some play with the distributor gear engaged.

Question: What the flock? is this normal..???? Play in the camshaft back and forth?

Thanks

Avispa

What you observed is normal. The lobes on the cam are tapered in diameter toward the back of the block. This causes the lifters to put backward force on the cam. The backward force is carried by the thrust face on the back of the cam sprocket, so for the most part the cam doesn't "walk" in the block. Without the sprocket on the cam, it can be pushed farther back, so the lifters will be off center with the lobes. Put the sprocket on and try it again. It will look better. The cam will still be able to move front to back, but with the motor assembled the cam will be forced into its normal position in the block.

Cautrell05

The lobes are also off center slightly so that the lifter and pushrod spin in the bore. If they dont spin it will eat the lifter. Normal design for flat tappet camshafts.

Nick

AZDoug

Its normal but not right. Nothing you can do about it.

IIRC, i read once that early BB motor blocks didn't have the lifter bores exactly where they should ideally be. It never seemd to cause any problems in production cars.
Doug

Avispa

They sure didn't. It was common for the lifter bore angles to be off a few degrees rotation. Not enough to be noticeable in a street driven car, but all top $ builds using old Mk IV blocks have the lifter bores indexed for that reason. Let's not even talk about casting flaws near the back of the cam tunnel.....

Kevova

Lifters and distributor supposed to limit cam walking. A bearing style cam button is more effective. There shouldn't be so much tension as to wear cam gear and block face.

Critter1

The energy required to turn the oil pump is what pulls the cam back to make sure the cam driven gear rides on the block surface.

Avispa

If that were the case, it wouldn't be necessary to put in a thrust bearing and cam button on retrofit roller cams. Iskenderian used to publish a really good guide to roller cams back in the pre-OEM roller cam days.

Critter1

So, you're saying the motion I described has nothing to do with keeping the cam pulled back so the cam gear contacts the block?

AZDoug

One can mathematically prove the effect of the oil pump FAR outweighs and lobe slope pressure, as the axial lifter pressure would be the sin of the lobe slope angle x the spring pressure x 16 x (complex math)*, and with a tiny, tiny cam slope angle, the sin is close to zero.

*complex math would seem to be some integral of the spring pressure from zero lift to full lift x 2, minus the base circle.
Doug

Critter1

Yup, it's all about the oil pump.

Tcheairs38655

Thanks for the replies. I understand the physics of the cam centering on the lifters with engine rotation. I do appreciate all the input...Also, the title of this post has nothing to do with love...it's LOBE...sorry for the typo. The edit tool won't let me edit the post title.

Avispa

Maybe you guys are right, but I was sure I wasn't imagining reading about cam walk. The Isky paper is long out of print, but at least one mag says the same thing. And the oil pump still doesn't explain why even OEM roller cam motors have cam thrust bearings. The OEMs don't put those things in for no reason.
http://www.superchevy.com/how-to/eng...apping-roller/

If there's another explanation I'm all ears.

AZDoug

FWIW, I installed roller cam in my 327 several years ago with no thrust bearing and no thrust button. No problems at all.

I suspect the bearing does keep the cam a bit more 'locked down" in one specific location. I also suspect that massive load/unload of the motor may cause the cam to walk a little bit, but it isn't an issue in most street cars. Oil pump starvation under higher RPM could also cause cam walk. I consider the thrust button/bearing more of safety feature against unusual conditions rather than a true necessity. The hot rod your motor books from the '60s and early '70s said use thrust buttons on flat tappet cams, FWIW.

The angle slope on the lobe is to create lifter rotation, the engineers simply made the slope work in conjunction with the oil pump rather than fight against it.

Doug

AZDoug

BTW: just because something is done, does not make it needed or even good. Conventional wisdom used to say that you needed to groove the main journals of a crank in a high performance motor. I ahve even has some engine builders tell me that in the last 10 years. They got very firm and told me I was plain wrong when i said that reduces the bearing load capacity by 10-20%. I avoid places like that.
Doug

larrywalk

I was looking to see if anyone commented on the apparent pitting on the first lobe showing in the picture. I have never seen a lobe's base circle appear like that. Any comments?

Kevova

Only improperly stored - rust.

Tcheairs38655

Guys, I don't know what's going on with the photo, but there is no pitting or rust on this camshaft. It's new right out of the box from Crane...

Westlotorn

I called on a couple hundred Engine Shops in the 90's. Some of the owners or Techs taught me things every time I visited and were always asking what was new. Others refused to accept any new information and stayed with what was know in the 60's.
It was frustrating to deal with those that refused to embrace the improvements that were known to help just because as I heard 100 times. "I have been doing this for 30 years, I know what I am doing."

I agree some of the new fangled idea's did not pan out but that was very few, most were legitimate improvements that enhanced engine life like what you said about grooved crankshafts or bearings.
Have you seen the 3/4 grooved bearings? they give full oiling all the way around 270 degrees of rotation but have full bearing face for the load areas. These came out in the late 90's and were adopted by most racers at first and then some of the OEM's.

domenic tallarita

EXACTLY

Dom