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Old 01-29-2013, 12:18 PM
BogiesAnnex1 BogiesAnnex1 is offline
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Originally Posted by zildjian4life218 View Post
I wonder if its worth it to see if my machinist has a timing chain for a vortec that I could mock up real quick to check. I have only seen older blocks, vortec blocks and my block and I would definitely agree that mine looks like the vortec one. Idk what GM did differently between the flat tappet, the pre vortec rollers and then the vortec rollers.

Thanks for the input guys. Sorry took me so long to get back to you Ive been swamped with school and work.
The Vortec is pretty much the same as the other OEM rollers, it adjusts the gears and chain for the plastic timing cover that comes on those engines. It should fit the older roller blocks with the sheetmetal timing cover but the thrust depth should be the same as the camshafts and thrust plates interchange at least insofar as the two different bolt hole distances used between the very early roller blocks and the later ones are concerned.

Still there is no harm in trying different gears to see if a better clearance can be had.

Generally the configurational difference between non roller, roller, roller optioned but flat tappet equipped are:

- Flat tappet blocks have no provisions for a roller i.e. no spider mounting bosses (3), no face machine or drillings for the thrust plate, low height lifter bores, flat face on cam. Thrust is taken between the backside of the cam driven gear and the block face. The cam will always have a fuel pump lobe.

- Roller blocks have three bosses on top of the main oil galley to mount the spider, the block face is machined to accept two mounting bolts for the thrust plate, there is a thrust plate, the lifter bores are raised to provide support for the longer lifter, the lifters are tied in pairs by a gadget called the dog bone, the cam has a stepped face that protudes about 1/4 inch forward of the flat tappet cam so it can pass through the thrust plate, the cam gear is modified in the hub so it can accomodate the thickness of the thrust plate which it now reacts against instead of the block face. The cam may or not have fuel a pump lobe. The push rods are shorter to accomodate the taller roller liftesr.

- Roller provisioned blocks with a flat tappet cam have all the unique provisions for a roller cam but use a standard non roller cam with the flat and short face. This uses standard length flat tappets with the older standard length (longer) push rod. It uses the older timing gear that reacts thrust aganist the block instead of a thrust plate. The cam may or not have a fuel pump lobe.

- The Vortec block used in the L31 Vortec is the same as the preceeding roller blocks whether those blocks had a roller or flat tappet cam. The Vortec block (880) actaully was used in late 1995 production and some 1996 Vans with a flat tappet or roller tappet cam, sheetmetal timing cover, Swirl Port or L31 Vortec heads, with Throttle Body Injection (TBI). Where the L31 in pickups starting with 96 production all used Central Multi-point Fuel Injection, L31 Vortec heads (two versions), a plastic timing cover which drives a unique timing gear and chain set for clearance (narrower gear teeth and chain) because the plastic timing cover accomodates often but not always a built in crank seal and always a crank position sensor.

As you can see where the roller provisioned or equipped and the L31 blocks are concerned there is a lot of interchange between them and they can use the flat tappet cam, lifters and timing set from older Gen I engines when all this stuff comes in a set of equipment. The L31 Vortec plastic timing cover does require a unique narrowed timing set as it uses up space for the crank position sensor. If you're using an L31 Vortec with carb or TBI it's simple back date the engine to use the sheetmetal or even a cast aluminum timing cover from the earlier engines.


Last edited by BogiesAnnex1; 01-29-2013 at 12:25 PM.
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