I installed a double roller timing chain. Tried to crank the motor it was near impossible to turn. As it turns out the double roller was too thick for the timing cover. does this mean I can only use the single roller? or could I buy a different timing cover? It is on a Gen VI 454. it's the 6 bolt timing cover.

Another issue, I got a hold of some Oval BBC heads, casting number 3999241. They have the 2.07 intake valves. would there be a big difference in HP if I get the 2.19 valves and how much would that run me?

Not sure what to do about the timing cover.. Perhaps you can measure the clearance you need and make a spacer of the right thickness using steel sheet. Your local laser/plasma cutter would do a beautiful job using a gasket as a template.
But maybe there are double row chain sets especially for Gen IVs..?

The old "How To Hot Rod Big Block Chevys" book talks a lot about the improvements of the larger valves in the oval port heads.. (I looked for a dyno chart I thought I remembered seeing in there, but didn't see one.)
Anyway, I'd suggest fitting the bigger valves and blending the bowls. This really wakes them up.

However, I was in this exact position and did my sums first. After all the expense of valves, springs, retainers, locks, seals, new guides, new hardened seats, the labor involved in crack testing, decking, replacing seats, honing guides, porting, valve grinding & lapping, etc, etc, plus the money I'd have if I sold them, a brand new pair of Edelbrock 60459s were not much more than what I'd be spending anyway..
..and they're aluminum..
..and they're brand spankin'..
..and they're fully assembled and ready to bolt-on..
..and they'll make 540hp with 9.5:1 c/r, a dual plane and a hydraulic cam!
I've got a pair and I reckon they're hard to beat.. :thumbsup:

Most double rollers hit the block just behind the top gear at 12:00. Just remove the gear and cover the oil pan and cam good and file or grind the top edge of the castin off. It only takes a little. Also when the chain hits the block it moves it foward and might hit the cover.

GM recommends replacing the plastic six bolt cover with a stamped steel cover after you drill and tap the additional four holes (using the cover as a template) if you desire to run a double roller chain. Because there is less drag with roller cams in Gen V and Gen VI blocks the factory went with a single roller chain and gear set. I would only swap over to a double roller if you plan on running some hefty valve springs; as in solid roller camshafts (which would collapse the hydraulic roller lifters).


Larger Dave

Thanks for the great input, I will stick with the single roller. I plan to put on the stock oval port heads with 2.19/1.88 valves, I don't know the spring pressure, but I'm sure the single roller will handle it.

SixtyEight