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I put in or helped put in, a lot of engines in a lot of cars over the years, but never built one. So this is my first rodeo. Three years ago, I brought a bare small block that had been already been prepped and bored .030 over for $400. The block sat along with a forged kit, that I got in 2016 and the reason for that, is there was nothing wrong with the original L48 that was in my C3 then. That L48, as some of you might remember had the aluminum L98 heads off've the early C4's. Those heads have tiny 58cc chambers and bumped up the compression at least a point to a point and a half. Forward to last Fall. My C3 started not running right. It would start right up, drive, etc, but something was wrong and a compression check, showed 68 PSI in the #1. As an example of how much the compression increased using the L98 heads on the stock dished piston L48 block, #3 and #4 were 175 and 180 PSI! I flogged this C3 mercilessly for five years and I couldn't complain about a 44 year old bottom end, finally giving up.

The replacement block is an '87-'91 factory roller cam block, with the one piece rear seal, built in cam thrust plate (no retrofit roller needed or buttons), plus the intake valley is set up for the lifter retainer and the lifter bosses are machined flat at the factory. The crank for these blocks is different, because of the one piece rear seal. Also, I had to buy the factory rear seal holder, that attaches to the back of the block along with five fasteners. There is a four inch viton donut that goes into this and around the machined rear of the crank. It is exactly the same as the '68 through '86 SBC's in all other respects. It is not a Vortec. It is commonly referred to by it's stamp number, a 638 block. I picked this, because with a roller cam, you get the advantage of running a higher lift, faster ramp profile and none of the problems that a flat tappet cam has, like having to break it in or worse, wiping it out, despite all precautionary measures.

The forged engine kit was purchased at a circle track shop, that gave me a deep Hot Rod Magazine discount (like 50%!). $1,380 got me a forged 4340 steel crank, along with Icon forged 4130 pistons and forged H-beam rods, with ARP fasteners, along with a steel flywheel and even came with gaskets and bearings. The whole thing was balanced and blue printed as well. I also watched numerous YouTube vids and discovered a series of engine build up videos from an old and very experienced road and circle track racer 'cartapes'. This guy showed how to prep the bare block, because you'd be surprise at what there is to fix on a regular SBC. The oil passages often have casting flash obstructing nearly half the passage. A good example is the oil drain hole in the back of the lifter valley. Mine was just like his, a whole lot of casting flash and I went ahead and purchased a set of grinding bits from Kodiak Tools and went to work. The cartapes guy, also stress relieved every hard line on the block, inside and out, because hard angles hold the stress, versus rounded ones, spreading it. Sounds excessive, but what the heck?

638 block, below. Note the flat machined lifter surfaces and the three posts that are tapped for the cam retainer. Note the front of the block, that has the holes tapped for the cam thrust plate (there are two sizes of these thrust plates and they only differ by mere hundreds of an inch!). Also some of these 638 blocks, came from the factory set up with flat tappet cams, so make sure, to look for the tapped holes in the indicated areas. If you want to replace your tired or underpowerd SBC, why not get this block, and have a factory roller, versus an expensive retrofit kit with spacing problems and nylon buttons?

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Wow. This is what I did to my SBC as well. Superb oil flow, back to the pan!

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You've got to go with air tools doing this. Battery operated or electric drills have too much torque, not enough speed. Torque means it's harder to control and you don't want to damage delicate bearing or cylinder surfaces doing this!

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Note the difference between the one side and the other. The hard angled surfaces concentrate the stress and the rounded ones, spread it. Makes sense, doesn't it? It was a lot of work!

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The Kodiak Cutting Tool set was over $100! But they never dulled or went to crap. They cut very, very well. You had to be careful with them. Here are the main caps. One is stress relieved and the other is not.

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Did this to my block too. You had to use a hand file at times, or be super careful with the air grinder...

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Here's a good example, of bad casting flash, that can easily flake off at some time, destroying your engine. You can actually break it off, with your fingernail. I removed all of the obvious stuff like this, but actually found a pocket of casting flash, mixed with crusty foundry sand in one of the deep pockets of the engine! I could actually crumble some of it off. Needless to say, I went to town with the grinder and removed all of it!

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You can get them from the junkyard, or buy them, brand new, from Pace Performance at about $3.42 apiece. They hold the roller lifters in place and stop them from rotating (which would be really bad!). They sit on top of the flat machined surface in the intake valley. That flat machined surface, is not on early '68 to '86 SBC's. I also purchased the 'spider' and the bolts, brand new, from Chevrolet Performance as well. That spider or retainer actually came a little warped, but not to worry, you have to torque this thing down to the center of the block and it goes flat, with a lot of spring pressure on top of the dog bones. This set up is good to 6,000 rpm. Beyond that, you should actually get the roller lifters that are attached to each other with a bar.

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Just want to share this, because you may consider this for your next build. The factory roller cam set up, is a better way to go and along with the one piece rear seal, makes for less leakage. As mentioned, the 'spider' didn't sit flat on the work bench, but installing it, took all that out and made for some serious pressure of those arms, on top of the dog bones. There is very little in the way of documentation on the web or even youtube on this. I had to look really hard to figure out some of this, because most of the SBC builds are the early blocks. These 638 blocks accept any regular SBC style head as well, and have the exact same engine and trans mountings, along with a standard water pump setup and timing cover (unlike the Vortec, which uses a weird plastic cover).

Jebbysan

Good write up.......the "Cartapes" guy is correct......the factory oiling system on a small block has a lot of flash and sharp edges......
The reason a lot of people do not use the factory roller setup is that the dogbones hit the lifters somewhere around .540-.550 lift.....so it is limited.
A lot of the work you did was unnecessary, but like you said...what the hell, right? One thing you have to remember is that a s&%tload of oil goes to the heads.....the drainback holes in the heads are as or more important than any other drain aspect.......make sure your holes are large enough......
Did you chamfer the rear main cap oiling feed hole? This is a common racer block prep item.
The real skinny is that even though the oiling system on a SBC is probably the best design there was for 50 years.....the system is flawed in several ways....one being that it oils the cam first.....and because of this.....the verticle feed from the pump to the lifter feed is too small as well as the whole feed from front to back that pressurizes the lifters. It works fine to about 6000 rpm or so.....but it starves for volume after that. Even factory Bow-Tie blocks from GM were not right.......but this is splitting hairs as very few run dedicated racing engines here. But on a SBC you will run out of oil before the block moves around so the whole 4 bolt main thing is an Urban Legend too......
The 87-91 blocks are great....and you can't beat that main seal for function.....but that is another thing......you have to separate the engine from the trans to change a main seal....2 piece you do not....(Although it is a pain).
Keep the posts and pictures coming.

Jebby

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Note the very rear part of the crank. Usually, there's some kind of offset flange hanging off the end, but not here. Definitely a different deal and you must have the block that matches, because there's a casting that holds the viton donut that seals the crank to the block.

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Here is a good example of what the seal looks like, attached to the block.

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Indeed, I did hog out the rear main cap oil passages, both where the oil pump goes and also where the oil exits the inner passage

. It was worth it, because even where the oil filter mounts, there's a lot of room for improvement! I did all the mods that were on that tape. Also, you're correct on the lift limits with the dog bones, versus the bar links and thanks for providing that info for others here. When I spec'd a camshaft, I called Howard Cams, looking for something with about 0.525 lift and the guy was super knowledgeable. He told me, I should run a wide LSA, because C3 Corvettes have built in vacuum leaks (via the headlight system!). With 10.2 compression, he told me, that with the cam he spec'd for me, that it'd be no problem to get 400 to 425 HP easy. I'm happy with that, because it was a blast with a little over 300 with the old L48 motor. Ran low 14's and pulled hard through all the gears, really well. Not the fastest time, but I learned something from that (and also driving my buddy's numerous vintage Austin Mini's). I came up with this: "It's not how fast it goes, it's how it goes fast!"

jackson

Have you considered GM's LT4 Hot Cam swap? With 1.6:1 rar it's .525/.525 218*/228* and wide LSA 112...genuine steel roller ...very popular pn 24502586 ...under $300 ...seen a Wilhoite regrind of same under $150

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Thank You, but I already have the cam in place and am running 1.5 ratio rockers. Might've considered it, but this will work, along the same lines and it worked out to the same lift.

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The timing chain cover wouldn't fit over the timing chain. Take a look at the guide pin for the cam. The reason Howard Cams sells them like that, is because that same cam is used in the LT1, so it has to be that long (not sure why). So I had to grind it down. Just an FYI, when you're installing a performance cam in an 87-91 roller cam block.

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We don't any metal chips in there, do we? That's the 100 mph tape, that's used in aerospace and on the battlefield to patch bullet holes in air vehicles. It's not cheap, but it sure does the job well!

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After taking the grinder to it. Yes, I shaved a tiny little bit off the top of the ARP bolt, but I damn sure wanted to make sure it didn't protrude, whatsoever.

jackson

The GM Hot Cam's pin is same for same reasoning. Don't know about Howard's but you can tap-drive GM's pin deeper into cam snout.
In the same manner as you might check valve face-to-piston clearance, you might've used Play-Doh to check between cam bolts & timing cover.