Big block oiling design deficiencies?

[G B.]

Please don't read this if you think everything designed by GM engineering is perfect. You will just get cheesed off.

I think that sixties big blocks might get inadequate oil volume to the valve train. I haven't worked on enough of them to know for sure. I'd like to hear the experiences of others to possibly confirm my suspicions and suggest a good fix.

I've never encountered a stock small block that needed more than a stock oil pump. Not only is stock oil pressure sufficient for street performance use, the volume spurting out of the push rods (at the downstream end of the system) is significant. If you rev a stock small block with the valve covers off, you will quickly have a mess.

The sixties big blocks I've worked on have been noticably different in this regard. The oil pressure readings have been about the same as the small blocks, but there is little oil coming out of the push rods. On all of these engines I was able to adjust the rocker nuts without even using a splash shield. Even when run at 2,000 rpm, the oil would barely trickle out of the push rods.

Big blocks had a reputation among my friends as being 75,000 mile engines during the late sixties. At about that point, something in the valve train would fail. The cam would go flat, a rocker ball would burn, a valve would seize in the head, a pushrod would bend, that commie/plastic cam gear would strip, whatever... but it was usually something in the valve train. I never cared enough to find out why, but now I want to know.

[Clem Z.]

Re: Big block oiling design deficiencies?

big blocks with solid mechanical piddler valve lifters put a EXCESS amount of oil to the rocker arms and caused the stock pans to run low at high RPM because the oil could not get back to the pan fast enought. my 65 396 and my 66 427 did this so i ran 1 quart over full when drag racing. the fix i used later was to use small block edge orifice solid lifters which cut the oil to the rockers by 20% but you needed to use full roller rockers because of the cut back of the oil supply could starve the stock rocker balls on the exhaust and cause them to run hot. i have no experence with hyd lifter big blocks

[Clem Z.]

Re: Big block oiling design deficiencies?

big blocks with solid mechanical piddler valve lifters put a EXCESS amount of oil to the rocker arms and caused the stock pans to run low at high RPM because the oil could not get back to the pan fast enought. my 65 396 and my 66 427 did this so i ran 1 quart over full when drag racing. the fix i used later was to use small block edge orifice solid lifters which cut the oil to the rockers by 20% but you needed to use full roller rockers because of the cut back of the oil supply could starve the stock rocker balls on the exhaust and cause them to run hot. i have no experence with hyd lifter big blocks

[Clem Z.]

PS

the oiling systems on the BB was opposite of the SB because the BB oil fed the mains first and then to the cam,lifter area,where the SB the oil fed the the cam lifter area first and then went to the mains.with modified SM you needed to open the grooves behind the cam bearings and the size of the oil hole that went to the mains to get enought oil flow to the crank.

[Clem Z.]

PS

the oiling systems on the BB was opposite of the SB because the BB oil fed the mains first and then to the cam,lifter area,where the SB the oil fed the the cam lifter area first and then went to the mains.with modified SM you needed to open the grooves behind the cam bearings and the size of the oil hole that went to the mains to get enought oil flow to the crank.

[Bill Clupper]

Re: PS

Depending on the year of the engine, there are some special considerations in the early engines to get oil upstairs. Also the placement of the rear cam bearing is critical as I recall. I'm with Clem, my race engine had plenty of oil in the top end, but it was a mechanical lifter engine (L-88, then Cam Dynamics Roller)

[Bill Clupper]

Re: PS

Depending on the year of the engine, there are some special considerations in the early engines to get oil upstairs. Also the placement of the rear cam bearing is critical as I recall. I'm with Clem, my race engine had plenty of oil in the top end, but it was a mechanical lifter engine (L-88, then Cam Dynamics Roller)

[Joe L.]

Re: Big block oiling design deficiencies?

Jerry-----

As Clem pointed out, the basic design of the small block and big block oiling systems are different. For small blocks the main oil gallery is located above the camshaft. For MOST Mark IV big blocks, the main oil gallery is located in the left side oil pan rail. This feature is the fundamental reason for the other pressure oiling differences which Clem mentioned.

While most Mark IV big blocks used this system, not ALL did. The ZL-1 aluminum big blocks used the small block-type oiling system with the main oil gallery above the camshaft. In 1990, when the Mark IV big block was replaced by the Mark V, the "ZL-1" oiling system was incorporated. This, of course, continued with the Gen 6 big block which followed and, as far as I know, the new 8100 big block introduced last year.

The "ZL-1" oiling system is far superior to the system used in the vast majority of 1965-90 Mark IV big blocks. In fact, other than weight reduction, it's one of the primary reasons that I selected the "ZL-1" aluminum block for my engine project. The "ZL-1" block is an order of magnitude more expensive than a cast iron Mark IV block, but, in addition to the weight savings, the "ZL-1" oiling system makes it worth it. In my opinion, anyway.

[Joe L.]

Re: Big block oiling design deficiencies?

Jerry-----

As Clem pointed out, the basic design of the small block and big block oiling systems are different. For small blocks the main oil gallery is located above the camshaft. For MOST Mark IV big blocks, the main oil gallery is located in the left side oil pan rail. This feature is the fundamental reason for the other pressure oiling differences which Clem mentioned.

While most Mark IV big blocks used this system, not ALL did. The ZL-1 aluminum big blocks used the small block-type oiling system with the main oil gallery above the camshaft. In 1990, when the Mark IV big block was replaced by the Mark V, the "ZL-1" oiling system was incorporated. This, of course, continued with the Gen 6 big block which followed and, as far as I know, the new 8100 big block introduced last year.

The "ZL-1" oiling system is far superior to the system used in the vast majority of 1965-90 Mark IV big blocks. In fact, other than weight reduction, it's one of the primary reasons that I selected the "ZL-1" aluminum block for my engine project. The "ZL-1" block is an order of magnitude more expensive than a cast iron Mark IV block, but, in addition to the weight savings, the "ZL-1" oiling system makes it worth it. In my opinion, anyway.

[Clem Z.]

Re: Big block oiling design deficiencies?

one problem with the BB orignal oiling system was that with main oil gallery at the bottom of the block it limited the length of ths crank stroke that could be used because you could not grind into the block in that area very far before you were into the oil gallery.

[Clem Z.]

Re: Big block oiling design deficiencies?

one problem with the BB orignal oiling system was that with main oil gallery at the bottom of the block it limited the length of ths crank stroke that could be used because you could not grind into the block in that area very far before you were into the oil gallery.

[G B.]

Thank you both

I didn't realize the two oiling systems were so different. I've always dealt with hydraulic lifter engines, so maybe that particular lifter design bleeds off too much volume to leave enough for the rockers.

I'll probably try a high volume oil pump to see if that makes a difference at the rockers. I hesitated to do this before because I've seen them pump a small block pan dry at only 3,500 rpm (sustained).

[G B.]

Thank you both

I didn't realize the two oiling systems were so different. I've always dealt with hydraulic lifter engines, so maybe that particular lifter design bleeds off too much volume to leave enough for the rockers.

I'll probably try a high volume oil pump to see if that makes a difference at the rockers. I hesitated to do this before because I've seen them pump a small block pan dry at only 3,500 rpm (sustained).