To clarify the subject, I've got a 70's 350 with a Crane Retrofit roller cam. Pretty much every cam manufacturer says you need a "better" timing cover to keep the cam button from flexing the cover, thus allowing the cam to walk, potentially wreaking all sorts of havoc. I've got a cam button, set it up correctly, and just played with forcing the cam forward a bit...the cover did flex somewhat, which is what I'd expect from a piece of metal that thin.

Did a search, didn't come up with much.

Wondering if the timing covers changed when the small blocks went from flat tappet to roller, and if so, how?

Buddy was telling me there are at least two different stock flat tappet timing cover designs, one of which is "reinforced". This is the one he says I have...has 3 stamped in ridges shaped like spokes from the center of the cover outwards. Apparently there are some without the reinforcing ribs, but I've never really paid attention to this point.

Just curious what GM felt was appropriate with their roller cams and timing covers. This motor won't see over 5000RPM, but I just want to make sure I'm not going to generate excessive cam wear without a "stiffer" cover.

Thanks for any comments on the differences between roller and non-roller blocks in this area.

 

Its fairly had for a cam to walk around any cover would work fine. As far as one being stronger then another I dont there is such a thing unless were talking an aluminum cover. My Dads now brothers 55 has a retrofit kit in it with a solid roller I havent seen any issues with its stock 1967 cover as of 23,000 miles.

 

The reason they suggest a stronger cover is the retro cam needs a cam button, where an OE roller cam block has a thrust plate behind the cam timing gear to hold the cam in place. That's the reasoning, but I have no experience with roller cams in older blocks.

 

I've built a bunch of roller motors over the years (starting long before the factory sodomized the whole concept) and used a whole lot more stock timing covers than any other kind. Never had any trouble.

The natural forces in the enigne are designed to pull the cam rearwards. There's really nothing trying to make it move forwards, unless there's something drastically wrong (in which case retaining the cam is the least of your problems) or you wreck the hell out of the car at high speed into a wall or something. The dist gear is designed to apply the oil pump load in the rearward direction.

Put it together and don't worry about it. Just make sure that the cam has a little free play between the block and the TC, i.e. the TC doesn't hold it smashed against the block, otherwise it will tend to eat up the cam sprocket thrust surface on the front of the block.

 

thanks a bunch for the responses!

I set the clearance as best I could, being that it's impossible with the cam plug in place, to do it the way the manufacturers "preferred" method. I'm confident it's correct.

Anyways, your posts helped reassure me, and have shortened my project, and eliiminated some potential cost.

Again, appreciate it. Always love to hear from real-world experience.

 

Hmmmm....I never thought of it from the distributor gear standpoint! I bet that's enough in itself!

 

<b>The natural forces in the enigne are designed to pull the cam rearwards.</b>

According to Comp can Crane, Flat tappet cams are ground on a slight angle which both causes the lifter (and pushrod) to spin AND pre-loads the cam to the rear of the block..

When installing a roller cam there is nothing to pre-load the cam, according to them. they say it WILL walk, and even if it only walk a little it will cause the spark timing to retard since its pulling the distributor "out" wards on its gear.

They say you want to use a thrust plate (to protect the face of the block) and a cam button (to keep the cam from walking too far forward).

they say nothing about a stronger timing cover, but when i did my engine tear down the inside of my timing cover was DESTROYED from the cam walking into it. i can only imagine another few hundread miles and my cover would have failed. I had a cam button... but aparently it wasnt enough.

 

Not to rub salt in an open wound, but.... I doubt that any of this had anything to do with your problem in that motor, or any of the other ones you've built that have self-destructed. In the case of the motor you mention that IIRC ate the upper half of the cam bearing (the normally unloaded half), the actual problem was most likely misalignment of the gear drive you used because the block wasn't machined for it, not anything to do with the cam or buttons or thrust plates.

We all know about the slight angle of flat-tappet lifters. That does in fact add to the force attempting to pull the cam into the block. You're exactly right about that. So, since a flat-tappet cam has more force than a roller tending to pull the cam inwards, why aren't thrust bearings used with those? There's no logic in your claim.

Incidentally, since the dist gear teeth are trying to pull the cam into the motor; so if the cam slides forward, it tries to advance the timing, not retard it. The cam all the way in its rearward-most position gives the latest possible ignition timing.

I've built roller motors that have gone many years of operation and tens of thousands, some maybe even hundreds of thousands for all I know, with no malfunctions. Been building them probably since before you were born. I have one sitting in my garage right now with about 30k miles on it, and another in the brand-new motor my car right now with about 20k on it. My personal experience with such things dates from the days when I used to do engineering work for Comp, back when I lived in Memphis; nothing I did had to do directly with their actual product ( I didn't design cams for them or anything like that), but I sure got alot of exposure to cams and how they're made and how they work. Got even more from a couple of close friends and 2 of my brothers who worked at Comp.

Take a look for yourself at Comp's recommendations. http://www.compcams.com/Technical/Ca...L/128-169.html Go to page, say, 138, where the Extreme "retrofit" rollers are; see if you find a thrust plate on that page. As a matter of fact, they do offer a timing set with a roller thrust bearing, part # 3100KT; but it's not even suggested as the "premium" choice for use with those cams. Must not be too critical if they don't even suggest it when reaching as deep as possible into your pocket.

 

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ack! slow down. neeeeeveeerrrrrr said your name or that you were wrong. Just pointing out comp cams info! thats why i started with "comp and crane..." not "well i think that..."!!!!!!

And ive never blown a motor! ever! Sure ive lost a cam bearing, ate a cam lobe, and overheated it recently... but never blew it. still using the same crank rods and pistons i started with 4 years ago.

and it does say somwhere that the cam walking forward retards the timing on comp's page.. ill find it...

<b>There's no logic in your claim.</b> and thats not my clain either... was just parroting what comp said. It goes somthing along the lines of "because there is no pre-load towards the rear of the block a roller cam tends to walk forward towards the timing cover... making a cam button necessary to keep it from moving too far."
I beleive the angle on the tappet cam pulls it towards the rear of the block... and...

what THEY said when i called and asked was a roller cam only gets preload forward from the oil, but none backwards according the COMP (not me..) and needs a button to keep it back and a thrust plate because its made of a different metal than tappet cams and can wreck the front of the block where the tappet cams do not because the metal is softer....

so take all that and grind it up or step on it or whatever but dont throw the old "been doing it since before you were born" stuff at me... I know alot of 40 year old drag racers that still drag race and think porting the heads doesnt help when you have a blower... in fact the 52 year old man that helped me build my first motor still drag races, and when he asked me if i had an RV cam i almost laughed in his face.
but no joke, his 360 spins 8000 rpms and lives... so its not like he doesnt know what hes doing...

im still learning.

 

im still wondering how if the force is so great, a lil plastic button is suppost to last 100k...?


this is the only part of my motor i havent decided on yet.... its a 400 solid roller motor, but this is the one nagging detail i dont know how i plan to solve..

the motor will spin pretty darn fast... if it helps, i'll get the cast alum 2 piece timing cover, if it doesnt, im getting the stamped steel 2 piece..


but i would feel soo much better if there was a bearing or somthing other then a lil piece of plastic holding my cam still when its spinning at almost 4k(cam speed)

 

Ask and ye shall receive

http://store.summitracing.com/partde...part=CCA%2D200

This is the one I always use

 

excelent.... thanks....

i really didnt want to put that lil piece of plastic button in my motor

 

Don't sweat the little plastic button- it'll work and work for a long long time. Just go ask the Buick GN 3.8L engine guys. They got a factory cam button even with flat tappet cams. Spring loaded, no less! Tore down an original motor with 129K miles on it- cam button still looked almost brand new. Don't think about this subject for too long- you can go nuts. I almost did.

 

so it wasnt all worn down?

 

I used the "plastic" one as well.

As best I can tell, it's nylon, so it should last a long time, plus it makes it a lot easier to set the "end clearance" on the cam, as the nylon is easy to work with.

 

IMHO for this price, play it safe and use a aluminum cover. Trust me. You'll be happier with one less thing to worry about.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33625

 

coo... i might snipe one of thoes later on....


i wont bother with that one... since you posted it, its going to get more bids.. hehe

 

Yeah, here is another link...
http://cgi.ebay.com/ebaymotors/ws/eB...category=33625
Just save the links and do a "View Sellers Other Items" in the future. Both have been selling one a week for about a year now and you can use the "Buy-It-Now" Option for a reasonable $27 to $35 depending on which seller you use.