Can someone explain to me what the deal is with thrust buttons and cam bearings and special timing covers and whatnot?

The whole retro-roller conversion seems pretty straightforward to me aside from this part.

I've been doing searches and absorbing what I can, but it seems like there are multiple ways to do it, and that's fine but I cant tell which are the "bah it'll be a'ight!" methods and which are the correct methods.

But this is what Im thinking is the best way to do it.

I can buy this timing cover:

http://www.summitracing.com/parts/CLO-9-221/?rtype=10

Use my current timing chain. Bolt up a retro roller cam to it... And...

Then am I done? Or do I need some kind of thrust bearing on the backside of the timing gear in case the cam walks backwards? Do I use a roller (torrington?) bearing? Or are there kinds that dont have rollers that can come apart?

I also see cam buttons of all sorts of sizes on summit. Seems like a lot cheaper option than that fancy timing cover... but I just have a regular stamped cover now, so I'm thinking I'll need to replace it anyway. I know Edelbrock makes some water pumps with a built it support to preload the timing cover in that area so it can be used with a cam button, but theyre pretty expensive too so Im not sure that's the right route either.

But could I use a timing cover like this:

http://www.summitracing.com/parts/MRG-4595P/

And use a regular cam button like this:

http://www.summitracing.com/parts/SUM-G003/

That'd allow me to spend a lot more money on other parts of the car that actually matter instead of blingy shiny stuff. But then do I need to put something on the inside of the timing cover or is it acceptable to let the cam button touch the timing cover directly? And then I'm not really sure how to determing the correct size cam button without just doing it trial and error. I came across a clever method of getting the button to touch the timing cover without the gasket, and then you install the gasket and get your proper clearance and endplay. But I also read some people saying that they bought one of those cam buttons and they used a file to fit it... is that acceptable practice?

Sorry for all the questions... I like to understand these things as thoroughly as possible before I dive into them so that there are no surprises.

 

Since no-one else has replied yet, FWIW:

I was having a play with cam buttons during my last cam swap. Was just installing another flat tappet, but I noticed that the previous cam had the chamfer worn off MOST the lobes, not just the one that had obviously gone flat.

As far as my logic determined, this would put the cam in a position where it could have possibly walked forward had let it wear any further, so I decided to play with cam buttons as cheap insurance against the possible carnage this would create. And I wanted to go thru the exercise, to figure this out myself,

I noticed that both the old cam and the one before it, had been thrusting on the rear cam tunnel plug, rather than the sprocket. -There was a bright witness mark around the rear end of both cams, and the rear plug was blingin'. So to space it out, I used a thrust washer behind the cam sprocket. Determined with plasticine and vernier that the cam sprocket thrust face was about 20 thou away from contact the block as is should. Used a 30 thou Comp thrust washer, problem solved.

The I got a new timing cover (2-piece for the next time), and a nylon cam button. Research indicated that the cam button is fine riding directly against the inside of the timing cover - but nylon only, don't use the aluminium ones as they can gall the cover.

Installed the button on the cam gear, and trial-assembled with a blob of plasticine on the button and no gaskets. Found about 65 thou clearance between the cover and the button, removed cover and hammered on it until the clearance was zero. Then final re-assembly with gaskets to get working clearance.

During research several years ago, there seemed to be 2 camps on the timing covers - those who said cheap covers where totally fine, and the others who said they would gauranteed bend under thrust, and u better get a strengthened one like the Cloyes you listed. Go figure. Same deal with the Torrington argument, with fan-boys for both sides.

 

A great deal more noise is made over this subject than it really warrants.

Think about the forces on the cam for a minute... you've got the dist gear with the oil pump load on it, which is trying to pull the cam INTO the block in any type of cam. This is actually QUITE A BIT of force; it's enough that it's what is usually responsible for chewing up the dist gear.

In the case of a flat-tappet cam, the bottom of the tappets (lifters) isn't "flat"; it's actually convex, with a radius of like 5 feet. The surface of the lobes isn't "flat" either; it's at an angle, with the rear edge of the lobe several thousandths taller than the front edge, such that the "angle" that it sits at is just slightly greater than the angle at the edge of the lifter face. The cam and the lifter bores are designed for the cam to go into the block just far enough for the rear edge of the lobes to about line up with the rearmost part of the lifters. The lifter sits on the cam ONLY at the rear of the lobe and the outer edge of the lifter face, which makes the lifter want to rotate in its bore. But, it also adds a small amount of force holding the cam rearwards.

A roller cam doesn't have that tiny extra rearward force.

Therefore: there's no reason that you "need" a thrust bearing in a "retrofit" (original design) roller system, any more than you "need" it in a flat-tappet setup where the forces are greater, or in an OEM roller setup where the forces are the same.

For YEARS, most of us with the "retro" rollers, back before the factory invented their extra whoop-de-doo, used stock timing covers most of the time and either a nylon cam button or a little tiny Torrington one. Entirely adequate in most cases. Obviously having a "better" retention method is .... "better", but it can be argued, not really necessary. Mostly, having a more "perfect" retaining system guarantees that the cam won't ever move AT ALL front to rear, which will make the spark timing more consistent by not jerking around the dist gear so much.

Here's a timing set with the thrust bearing built in. Obviously you can't just add a Torrington to a timing gear without machining an equal thickness off of the back of the gear.



Bottom line: a regular good-quality timing set and that cover with the built-in button, is a completely adequate setup. Set it for about .005" - .010" of cam end-play. If you're worried about where the timing gear rubs on the block for some reason, you can file a VERY small groove (like, .015" deep and about that wide, with like a Swiss pattern triangular file or something) between the front edge of the cam bearing and one of the oil holes in the bearing, to deliver a bit of extra oil there.

 

Okay I'll run one of the nylon thrust buttons then if I go roller.

I'm arguing whether or not I will be better off going with a 280H... will be a $300 swap... or a Roller cam swap, as cheaply as I can justify it, at $800ish. Not sure there will be a huge performance difference but it's the peace of mind of having a roller setup with today's oils that appeals to me.

If I could do roller cheaper then it would be a lot easier decision. The main area I think I can save money is if I go with a used roller cam. But used retrofit roller cams aren't nearly as common as used factory roller cams or used factory-style roller cams.

How hard is it to run, for example, an LT4 hotcam with a retrofit roller setup? I know the factory uses a completely different front piece to control cam walk, but can I still use use a thrust button for it? Is there anything else that needs to be done?

 

I don't know near as much as these other gentlemen but I'm pretty sure a "factory" style roller cam's snout will necessitate a factory style roller cam timing set as it sticks out the distance of the retainer plate which may prohibit the use of a button. And, just my , a roller, if I understand it correctly, is a "twofer": it has lower rotational resistance, (reduced friction), which frees up power and faster ramp rates, (at any given lift/duration), which makes more. So, I'd recommend the roller, hands down.

 

You would have to use a cam gear to suit a OEM roller because the bolt pattern is different

LPE make a OE roller to non roller block kit that includes a spacer to fill the recess for the cam retainer machined
on the nose of the OE roller cam

http://www.lingenfelter.com/mm5/merc...egory_Code=C30

 

For some reason the roller cams seem to have narrower published power bands though, which I find odd. Not by a huge margin, but flat tappet cams seem to generally have around a 4,000 RPM range compared to roller cams being limited to 3500 or so.




So would that kit really be all you needed to make that work? Aside from the new timing chain....

Eh... doesnt seem to be much room for cutting budgets there...

I think Im gonna try to do some clever stuff with the bolts on the back of the water pump to reinforce the timing cover. That will save a ton of money. Gets my expenses down to right around $800...

 

I reckon you could probably make a u-shaped reinforcing bracket out of a bit of flat bar, to sit over the timing cover. Never bothered with it in my flat tappet situation, obviously.

Does this mean that forward cam walk is really a non-event, in practise - even in a roller situation?

 

Basically, yes... the main difference being, in a roller setup, if it DOES occur, the consequences are even more disastrous, making it that much more of a concern in some situations.

YOu used to could get real simple braces for stock timing covers that were essentially just a strap that went across.

And, there have been water pumps on the market, might still be, with a little tab of casting with a bolt sort of thing screwed into it that pressed on the TC. Edelbrock I seem to recall had one for example.

And, all of th ecomments about the factory roller timing set are spot on... but there's one further problem with retrofitting one of those into a non-roller block, and that is, the bolt circle is so small, there's almost no room at all for a cam button to fit among them. Aboout all you can do is take a nylon one and whittle it down small enough to go down in there. I don't know of ANY bearing-type one that would fit.