Roller cam walk?

[eddie jett]

Machine shop called today and was asking if I knew why the Hyd. roller cam walks into the engine? The engine is totally assembled and ready to go other than this. He said he installed the timing set ( show cars Sa gear) the crank and cam gear line up but he can push it into the engine, he said it would walk when running. Anyone know whats going on, and should he know the answer to this???

 

[409 lever]

you need a cam button.goes on the center of the upper sprocket in the timing set.when you install a roller cam you need to locate it front to back in the block.with a flat tappet the lobes are ground so as the lifters rotate it pushes the camshaft towards the rear of the block.

 

[1961BelAir427]

You may want to look into a wear plate or Torrington bearing behind the cam sprocket to keep it from cutting into the front of the block when/if that upper gear walks backwards. You will probably have to machine the back of that sprocket the thickness of the plate or bearing to keep everything in alignment also. Usually around .030", but measure.

 

[eddie jett]

He stated that it walks "into" the engine. He builds race sbc,bbc stuff everday but it had been years since his last W block and never with a roller. He asked if there was something about these engines he wasn't aware of.

 

[eddie jett]

You may want to look into a wear plate or Torrington bearing behind the cam sprocket to keep it from cutting into the front of the block when/if that upper gear walks backwards. You will probably have to machine the back of that sprocket the thickness of the plate or bearing to keep everything in alignment also. Usually around .030", but measure.

Is this common on these engines? I'm no machinist and this is my first 348/409. I'm a little worried that he's asking me.

 

[eddie jett]

You may want to look into a wear plate or Torrington bearing behind the cam sprocket to keep it from cutting into the front of the block when/if that upper gear walks backwards. You will probably have to machine the back of that sprocket the thickness of the plate or bearing to keep everything in alignment also. Usually around .030", but measure.

Forgot to mention he said the gears get out of alignment also, sounds pretty severe.

 

[1961BelAir427]

Is this common on these engines? I'm no machinist and this is my first 348/409. I'm a little worried that he's asking me.

I still haven't gotten my first W together either, but I've heard of this happening several times from other members here AND I've also seen it happen occasionally with sbc & bbc engines.

 

[Fathead Racing]

Roller cams are usually not an issue as much as flat tappet cams. Flat tapped cam lobes are ground with alternating lobes o keep the cam from walking one way or the other but nothing is perfect. Nothing special about the W engine. Thrust button is a no brainer with a roller cam. The distributor gear with the roller cam tends to push the cam forward thus the cam button. Install the cam button, adjust fore and aft .005/.010 end play and use the solid wear plate behind the cam gear. Between the button and the bronze wear plate you should get a fair marriage between the gears. The cam gear and crank gear alignment need not be perfect. Tell your guy to treat it just as you would any other GM block. It's just a generic cam walk. Yes, your guy should know this!

 

[eddie jett]

Roller cams are usually not an issue as much as flat tappet cams. Nothing special about the W engine. Thrust button is a no brainer with a roller cam. Install the cam button, adjust fore and aft and use the solid wear plate behind the cam gear. Tell your guy to treat it just as you would any other GM block. It's just a generic cam walk. Yes, your guy should know this!

Thanks, I REALLY hope that I've interpreted what he said wrong and he does know, but I will pass this along thanks again.

 

[Fathead Racing]

Look at my post again, I added a few things.

 

[409 lever]

if your gears are out of alignment you need to fix that first.the timing cover has to be fairly rigid to keep from flexing outward.once the alignment issue has been straigtened out,install cam button and front cover with a gasket.use a large screw driver and push the camshaft forward with decent force [don't snap a lobe off] and watch the front cover.if it flexes out you need to build a stop in between the cover and the water pump.i have seen people use a good sized gob[technical racing term] of epoxy on the back of the pump and bolt it up and let it harden,now you have a custom cam stop.some performance big and small block water pumps have a threaded hole in alignment with the camshaft for this purpose.
and yes again your engine builder should know this.

 

[eddie jett]

Well naturally it's friday and he didn't call until late in the day so I have all weekend to wonder and worry. I will call him first thing Monday and figure it out, I guess on the bright side after 6 months of gathering parts and 10 months at the shop my engine is finally together.

 

[eddie jett]

if your gears are out of alignment you need to fix that first.the timing cover has to be fairly rigid to keep from flexing outward.once the alignment issue has been straigtened out,install cam button and front cover with a gasket.use a large screw driver and push the camshaft forward with decent force [don't snap a lobe off] and watch the front cover.if it flexes out you need to build a stop in between the cover and the water pump.i have seen people use a good sized gob[technical racing term] of epoxy on the back of the pump and bolt it up and let it harden,now you have a custom cam stop.some performance big and small block water pumps have a threaded hole in alignment with the camshaft for this purpose.
and yes again your engine builder should know this.

I'm thinking about using the electric pump show cars has because of clearance issues, it's going in a 55 chevy and it's a little tight up front. I guess I'll bring this up Monday to him, with what I see going on in his shop I 'm sure he's checked this stuff but if not he will, thanks

 

[Ishiftem]

Pretty much all of the above. You WILL need something between the cover and pump at the minimum. I did and when I brought the rpm up the timing would retard a good 5 degrees because the water pump was flexing and the cam was moving forward. I reinforced the cover and that fixed the issue. You don't need to pry on the cam to check it. Finger pressure is all you need. More will just flex everything and give a false reading. If your engine builder does not know these things, find a new one.

 

[models916]

If it is pushing back into the block, I would think the rear cam plug is not in all the way. Big socket and a hammer to move it a little. If the cam moves too much into the block on de-aceleration, it will bind on the timing chain. Nothing different on this cam tunnel than on the SBC or BBC except the extra rear oil hole. Tell him to make it like a SBC. There is another post here about cutting a slot from the distributor oil ring to lube the cam/distributor gear better. Get that done while you are at it.

 

[63impalass409]

I will second what models just said about the rear plug and if this shop does not know this or how to use a cam button I would find someone else to build it because who knows what else they did not do right!!!

 

[Don Jacks]

What they all said!A suggestion Eddie,if I may.Show Cars lists 2 electric water pumps.On a street engine,I'd suggest that you get the more expensive CSI pump.The reasons are reliability [I ran my small block CSI for 10 years before its first rebuild],and it flows 35 gph,as opposed to the 30 gph on the Pro-Comp version.Pro-Comp's stuff has been less than desireable in a lot of cases.With either one, beefing up the timing cover will be a good idea because the electric pump body sits quite a ways ahead of the cover.

 

[Ishiftem]

The cam should never contact the rear plug. The cam gear is what limits rear movement of the cam. The plug is not a back stop.

 

[Dr Richard Kimble]

if I'm understanding this correctly , it is the resistance from the oil pump that causes the massive force driving the cam forward?
I thought it would be pulling it back?

 

[Fathead Racing]

if I'm understanding this correctly , it is the resistance from the oil pump that causes the massive force driving the cam forward?
I thought it would be pulling it back?

No massive force. That's only one of the problems. Another cause of cam walk can be if the lifter bores are out of square with the cam bore. This can screw the cam in or out of the block. All correctable. Minor out of square is taken care of with the cam button and wear plate behind the cam gear. Just another thing to have checked at the machine shop or take your chances and have it checked if you have issues. I had a flat tappet cam pull the Cloyes trimming gear in to a unprotected block .120". I had a custom wear plate made that took care of the problem.