Many people have asked about swapping factory roller cams (LT-1, "Hot" cam, etc.) into early (86-down) blocks as well as putting cheap, commonly available flat tappet cams into late model (87-up) roller cam blocks. Lots of questions about what interchanges, how, what parts to use, etc. Much conflicting info, and even fewer answers about "why" certain stuff fits or doesn't.

Earlier tonight I ripped apart, side-by-side, an old flat tappet SBC engine and a late model roller cam SBC engine to see what the real poop was on this subject. Test subjects were a typical 1974 350 truck engine (flat tappet) and a 1987 L-98 350 f-body engine (factory roller cam). Here's the truth....

1. Cam bearings are exactly the same and you can physically shove either cam into either block type.

2. Front end of the block where the snout of the cam sticks out is machined basically the same (no offset difference at all) but the roller cam block has two bolt holes drilled way out on either side of the cam to bolt on the factory roller cam "retaining plate" that fits between the block and the top timing gear.

3. The factory roller cam is notched or "necked down" on the front 5/32" of it's length so that it slides THROUGH the factory retaining plate and has a "shoulder" for the retainign plate to push against to retain it from walking out the front of the block. The snout of the roler cam is also ever so slightly longer overall than a flat tappet in that area becuase it's gotta slide THROUGH the rather thick (1/8") retaining plate and still have just a smidge of length left to fit snugly into it's receiver on the back of the timing gear.

4. The roller cam top timing gear also has a different amount of "offset" to it to compensate for the longer cam snout and the thickness of the retining plate, but keep the chain itself in the same location as a flat tappet cam.

5. The BOLT PATTERN and DOWEL LOCATION on the snout of the roller cam/top timing gear is smaller in diameter than that of a flat tappet cam. THIS IS THE MAIN REASON WHY YOU MUST USE A ROLLER CAM TYPE TIMING CHAIN WITH A FACTORY ROLLER CAM. You can't physically bolt the gear to the front of the cam if you've got the wrong type of timing chain.

6. The lifter bores on a LATE model roller block will accept both flat tappet and factory roller lifters- the oil feed holes to the lifters are in exactly the same location. Flat tappet lifters in a roller block will look a little funny sitting way down in their bores, but they'll work perfectly.

7. The lifter bores on an EARLY block won't take the taller factory roller lifters for several reasons. First, they are not tall enough. The factory "dog bone" retainers will be way too far down on the body of the lifter and they'll get chewed up for sure. Second, there's no way to mount the factory "spider" in the lifter valley to hold them down.

8. The original 1987 L-98 cam DOES have a fuel pump eccentric ground into the cam so you could use a mechanical block-mounted fuel pump on it if you got hold of an appropriate SBC fuel pump pushrod. Later model cams or performance factory replacement cams? No idea of they have an eccentric to drive a fuel pump or not.

Interchange possibilities....

Flat tappet cam in a roller cam block? Easy. Shove the cam in, leave off the factory retaining plate, use a standard flat tappet cam timing chain, drop the flat tappet lifters in the bores, get the right length pushrods and away you go.

Roller lifter in an early block? More difficult. Shove in the cam, install the factory retaining plate (with the "ears" machined off- just use it as a spacer), install factory roller cam timing chain, install cam button (to keep cam from walking forward now that the retaining plate no longer "retains" the cam), and use aftermarket roller lifters, retainers/anit-rotators, and appropriate length pushrods.

 

You can use a factory roller in an earlier block, or an earlier cam in a roller block. A pre 87 flat tappet cam will fit right into an 87 later block, no mods needed. To use a factory roller in an earlier block some guys figure out a way to mod the block to mount the spacer plate to the earlier block. Either cam needs its proper timing set. I wouldn't try cutting the ears off the spacer plate cause it's too loose to work correctly as a spacer.
Some guys wouldn't suggest using a later roller cam in a pre 87 block, it's kinda mickey mouse, but it's been done.

 

That is the reason you DO NOT want to use factory roller lifters in a pre-'87 block, or any post-'86 block that doesn't have the provisions for them.

Good info Damon.

I have both blocks sitting in my basement and I'm fully aware of the differences, but I would have not been able to note ALL the differences as well as you did.

 

why would you even want to use the factory roller cam when there is a much better roller set up from the aftermarket grinders.

 

id like to point out, theres nothing "mickey mouse" about aftermarket rollersetups.


they've been using them for ALOT longer then the factory.. waaay before 87.
id consider using a piece of stamped sheetmetal bolted to the lifter valley alot more "mickey mouse" then what the aftermarket does... matter of fact, if you want some real lift, you cant use the factory lifters... you have to go aftermarket.. either aftermarket "factory style" or regular aftermarket ones.


if you're using a mechanical block-mounted fuel pump you need a roller tipped or soft metal tipped fuel pump pushrod...


now my only question is..... with a pre87 block, why would you need the "spacer plate " at all?

 

The reason you'd need the spacer plate, is because the timing chain itself is in the same place in either a flat-tappet setup or the factory's Frankenstein; and the cam gear thrust boss on the front of the block is in the same place, front to rear, namely in the same plane as the timing cover flange; so the timing gear is in the same place too. But when they mutilated the concept, they added that retainer plate, which means that the thickness for it had to come out of the cam gear. Which means that if you use the stupid system's cam gear, there has to be something there to take up that thickness. And since using the stupid system's special cam means that you have to use the stupid system's special modified cam gear also, then one way or another you have to have something behind the gear to fill up the retainer plate's volume.

Why the factory got it in their head that they had to invent this whole Rube Goldberg is totally beyond me. It's so grossly inferior to the system all the rest of us had been using for all these years, plus it ran up the cost of production, in tooling and design and manufacturing changes. IMHO it's a poster child for bad management in American manufacturing and for why the import car mfrs (who seem to apporach their job with a bit more practical common sense and less job security padding) have managed to take so much market share away from domestics. The "Big 3" (?) use up too much of their cost on things like redesigning blocks, that produce no tangible benefits to their customers.

 

mmk, thanks.

my roller cam (that i just resold for $50 more then i paid for it *wooot*) was made for the non factory setup... it was a solid roller cam anyhoo..
i didnt see the need for it with that one.... i only had it for a week before i bought a supercharger (and now have diffrent cam requirements) so it got sold before i looked to deeply into it..

with nonfactory solid roller cams that dont have the smaller "snout" on the end of the cam, you use regular timing chains with a cam button right?
this is my first roller motor, so i wanna be sure...

 

[QUOTE]Originally posted by MrDude_1
[B]id like to point out, theres nothing "mickey mouse" about aftermarket rollersetups.

What I was saying is that, to some, it's kind of mickey mouse to try to mount a late factory roller setup into an earlier block. Spacer plate and all... but it has been done.
Just defending what little credibility I've got.

It's all a lot easier to grasp when you have the two different types of blocks and all their related parts sitting on the floor in front of you to piece together and see what fits where.

 

Correct. Use a good quality real roller chain, such as a Comp 3100 or equal, and a cam button, either the solid plastic type or the roller type.