What causes "cam walk"?

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Ricks70Duster340

Ricks70Duster340

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I am a member of another forum and saw a guy with a 440 & hyd roller cam have his engine ruined because the cam walked. He used a bronze drive gear and one of those cam buttons that was two-piece with a little bearing in between (he got it from Manini but 440 Source looks to sell them too). He said he installed it with .005 clearance between the button and the timing cover. The failed cam button made an impression on the inside of the timing cover. When he took the cover off he saw the button had fallen apart.

What would make the cam walk like that?
 
It doesn’t sound like they had it set up improperly……unless there was enough forwards thrust force to bend the timing cover outward(it can happen), then the .005” thrust clearance you had set, ends up being more.
You should use either a pretty rigid timing cover, or have it so the timing cover is nearly touching the back of the water pump.

As for your original question:

How to Prevent Roller Cam Walk

What forum was that discussion on?
 
If he used the stock timing cover, there you go. It distorted the cover and the cam button came apart. You need a billet cover with a roller cam.
 
PRH said:
It doesn’t sound like they had it set up improperly……unless there was enough forwards thrust force to bend the timing cover outward(it can happen), then the .005” thrust clearance you had set, ends up being more.
You should use either a pretty rigid timing cover, or have it so the timing cover is nearly touching the back of the water pump.

As for your original question:

How to Prevent Roller Cam Walk

What forum was that discussion on?
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The article you referenced is interesting, but how would one know the block is out of whack before installing the cam? If there is that much force pushing the cam forward, would even a reinforced timing cover keep it from eventually eating away at the cam button and causing a failure?
 
You don’t know.
You just have to assume it might have some thrust force(fore or aft), and build it accordingly.

I’ve seen a BBC bend a timing cover outward nearly a 1/4” in a few dyno pulls.
 
RustyRatRod said:
If he used the stock timing cover, there you go. It distorted the cover and the cam button came apart. You need a billet cover with a roller cam.
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At somewhere between $250 and $300?! The idea is to have the area where the cam would push forward reinforced to prevent bending, right? Would it be possible to weld a large washer on the outside of the cover so that, when installed, the washer butts against the water pump to prevent it moving any further. Would that accomplish the same thing?
 
Ricks70Duster340 said:
At somewhere between $250 and $300?! The idea is to have the area where the cam would push forward reinforced to prevent bending, right? Would it be possible to weld a large washer on the outside of the cover so that, when installed, the washer butts against the water pump to prevent it moving any further. Would that accomplish the same thing?
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I'm not sure. The rest of the cover is still stamped steel. How much did all that roller valve train cost? How much will it cost when the cam pushes so far forward that the lobes run into the sides of the lifters and break the camshaft into several pieces and no tellin what else? I'm not bein smart, I'm just trying to make sense.
 
"Would that accomplish the same thing?"
I would sure think so. Certainly worth a try. I have seen 1/8 strap steel welded on the outside of covers on bbc and sbc.
 
RustyRatRod said:
I'm not sure. The rest of the cover is still stamped steel. How much did all that roller valve train cost? How much will it cost when the cam pushes so far forward that the lobes run into the sides of the lifters and break the camshaft into several pieces and no tellin what else? I'm not bein smart, I'm just trying to make sense.
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I hear ya' man. Like 33IMP said, may be worth a try. I feel for the guy this happened to. My engine is now in the shop for a rebuild. I'm using a solid roller cam & want the setup to live without spending a whole lot more than I've already done.
 
Ricks70Duster340 said:
I hear ya' man. Like 33IMP said, may be worth a try. I feel for the guy this happened to. My engine is now in the shop for a rebuild. I'm using a solid roller cam & want the setup to live without spending a whole lot more than I've already done.
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I can completely relate. Sometimes it seems like the spendin never ends. If anybody can sympathize with that, it's me.
 
I've made spacers and a bracket that attached using the timing cover bolts. One setup had an adjustment via bolt head and lock it in so the cover couldn't push out. Did those on BB/sb Chevies too.
 
Sounds like the button came apart & the rest was collateral damage. I use the stock timing chain cover. The space between the rear of the w/pump housing & the TC cover where the button is: I make a spacer that is a snug fit, push it into place & secure with silicon.
 
Bewy said:
Sounds like the button came apart & the rest was collateral damage. I use the stock timing chain cover. The space between the rear of the w/pump housing & the TC cover where the button is: I make a spacer that is a snug fit, push it into place & secure with silicon.
Click to expand...
Great idea! A little "JB Weld" to hold it might go a long way!
 
Ricks70Duster340 said:
I am a member of another forum and saw a guy with a 440 & hyd roller cam have his engine ruined because the cam walked. He used a bronze drive gear and one of those cam buttons that was two-piece with a little bearing in between (he got it from Manini but 440 Source looks to sell them too). He said he installed it with .005 clearance between the button and the timing cover. The failed cam button made an impression on the inside of the timing cover. When he took the cover off he saw the button had fallen apart.

What would make the cam walk like that?
Click to expand...
I have always ran .008=.010 on my roller cams , (hemi,406sbc,and now 505) , the timing cover must be reinforced to prevent flexing if using a stock cover...
 
You actually asked what causes it and I've not seen that addressed yet. First, let's cover what stops it. Flat tappet camshaft lobes are ground with a taper. If you look at a used one, you can see where the lifters have ridden on the lobes. It's not in the center. That's because of the taper. This taper does two things. First, that taper engages with the convex face of the lifter and makes it spin in the lifter bore so the lifter will not wear out in short order. It's a normal reaction for the camshaft to be pushed forward in the camshaft bore because of the intermediate gear meshing with the camshaft gear. So that action has to be countered with something. That taper is it. The taper also keeps the camshaft from walking forward.

Now we come to roller camshafts. You guessed it. They have no taper, since the rollers on the lifters must sit squarely on the camshaft lobes. With no taper, the camshaft is free to walk forward, so "something" must be used to keep it in check. That's where camshaft buttons come into play. The factories mostly all use a camshaft thrust plate, I believe. In our pre roller camshaft engines, we have to find another way and the camshaft button is it.
 
RustyRatRod said:
You actually asked what causes it and I've not seen that addressed yet. First, let's cover what stops it. Flat tappet camshaft lobes are ground with a taper. If you look at a used one, you can see where the lifters have ridden on the lobes. It's not in the center. That's because of the taper. This taper does two things. First, that taper engages with the convex face of the lifter and makes it spin in the lifter bore so the lifter will not wear out in short order. It's a normal reaction for the camshaft to be pushed forward in the camshaft bore because of the intermediate gear meshing with the camshaft gear. So that action has to be countered with something. That taper is it. The taper also keeps the camshaft from walking forward.

Now we come to roller camshafts. You guessed it. They have no taper, since the rollers on the lifters must sit squarely on the camshaft lobes. With no taper, the camshaft is free to walk forward, so "something" must be used to keep it in check. That's where camshaft buttons come into play. The factories mostly all use a camshaft thrust plate, I believe. In our pre roller camshaft engines, we have to find another way and the camshaft button is it.
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Excellent info. Yes, my LA engines used a thrust plate to keep things from moving. Appreciate the insight.
 
Ricks70Duster340 said:
Excellent info. Yes, my LA engines used a thrust plate to keep things from moving. Appreciate the insight.
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I wish they all used one. That wouldda made it easy. I've thought of making one for my next slant 6 build on the stand.
 
The chain is the primary piece that stops walk on an oem BB. No plate up front to contain the cam inside the block. You have a drive gear that when under power or decel will want to push the cam forward or aft.

Taper in the cam will not stop cam walk, unless it was an extreme level of taper.
 
Ricks70Duster340 said:
I am a member of another forum and saw a guy with a 440 & hyd roller cam have his engine ruined because the cam walked. He used a bronze drive gear and one of those cam buttons that was two-piece with a little bearing in between (he got it from Manini but 440 Source looks to sell them too). He said he installed it with .005 clearance between the button and the timing cover. The failed cam button made an impression on the inside of the timing cover. When he took the cover off he saw the button had fallen apart.

What would make the cam walk like that?
Click to expand...
I took a look at the thread and I don't know what happened. Looked like a stamped cover which is really iffy with a roller cam. A stamped cover usually needs to be reinforced for a roller cam. I always use a billet timing cover for roller cams but some people don't want to spend the money for the billet cover. In this case it sounds like the guy lost the entire engine due to the cam walking. That doesn't happen very often but it can happen. I've seen a fair amount of damage in roller cam engines over the years due to cam thrust issues. BB Chevy motors chew up the block, other engines eat into the timing cover. Lots of stuff gets destroyed if the cam moves out of position.
 
Reinforced cover.
Timing (5).JPG
 
^^^^ This looks like what I did in post #13. I made the spacer thickness so that it just kissed the back of the w/pump housing. I also had to make an extension for the button to get the 0.005" endplay correct.
 
The timing chain has nothing to do with cam walk. The rearward cam thrust is created by the load of the oil pump! The direction of the helical gears on the cam/pump drive want to drive the cam backwards when the pump starts pumping oil....which should be always. The lifter offset is designed to counteract this force, but the minimal contact area of the lobe/lifter is not a lot so it just 'helps'. Roller lifters do not have this restraining force, so the cam could move forward slightly under the right conditions.
 
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