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SBC Top End Refresh

1/12/2018
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Sometimes you find yourself working on the same things over and over. For me and my Sedan Delivery, it seems like it’s always the engine. I am not always easy on it, but I don’t quite thrash it either. A few weeks ago I managed to bend an exhaust valve when the piston said hello to it at about 6,000 rpm. I concluded that the reason for this was because it was cold outside, the valve guides were nice and tight (as they were supposed to be on a new engine) and it saw more rpm than it needed at that moment.

Here we can see that even with the rocker arms removed, the valve doesn’t want to close all the way!

So, to pick up the pieces, I decided to pull the top end off of the engine and have the valve replaced and of course replace all of the gaskets that are involved. Lots of guys may need to do this for various reasons other than a bent valve, but the process is the same regardless.

My first step, especially if I wasn’t the one to put the engine together, would be to rotate the engine to top dead center on the #1 cylinder. Then I remove the distributor cap and see where the rotor tab is located. It is typically pointing to the front terminal towards the driver’s side slightly. I mark this position on the distributor body so that I can get the timing really close upon reassembly. At this point, you can remove the distributor, intake manifold, exhaust manifolds (or headers) and start removing the rocker arms and pushrods. A lot of people ask me if they need to keep the rockers and pushrods in order. It isn’t absolutely necessary, but why not and one of our valve train organizer trays (part number 2514394) comes in very handy here! If you remove the lifters it is absolutely critical to keep them in order!

Here is the mark the valve left on the piston. Fortunately, it didn’t do any more damage than this!

After removing the cylinder heads I saw that pesky valve that couldn’t get out of the way of the piston fast enough. At this point, the heads went off to the machine shop and I started cleaning parts. I can’t stress enough how clean everything needs to be. I take the time to scrape the gasket surfaces with a nice carbide scraper, clean the threads in the block with a thread cleaner and NOT a tap as the tap can actually remove material resulting in less thread engagement and a potential problem down the road. The next step was to clean all of my bolts and other gasket surfaces in preparation for putting everything back together.

I got my cylinder heads back from the machine shop and was now ready for reassembly. On this particular engine, I used Fel-Pro shim head gaskets to get a little bit more compression and get the quench correct. I believe in using copper-coat anytime steel shim gaskets are used to ensure they seal properly. Small Block Chevys (and lots of other engines) typically use head bolt provisions that are exposed to the water jackets underneath the deck surface. It is really important to use thread sealer on these bolts so that no coolant finds its way up the threads of the bolts. I used aviation thread sealer for this and made sure the threads were super clean before reinstalling. You want to work quickly once putting the heads on and starting all of the bolts because the thread sealer is drying by the minute. I torqued all of the head bolts to 40 lb. ft. initially and then followed up with 65 lb. ft. to make sure they were evenly torqued.

At this point, I reinstalled my pushrods, rocker arms and poly locks and adjusted my valves. I won’t go into great detail about how to do that because it is covered in this article - Setting Valve Lash on Hydraulic Lifters. Historically I have always set my lifter pre-load with ½ turn past zero lash with a hydraulic camshaft, however, I happened to be using a Comp Cams hydraulic roller conversion with this engine and they recommend 1 full turn of preload with their lifters.

It’s all downhill from here, so after putting the intake manifold back on with some nice new Fel-Pro 1204 gaskets and a small amount of RTV on the water ports, I was ready for my distributor, exhaust manifolds and the rest of my accessories. After filling it with coolant and fresh engine oil it was time to bring it back to life! I have had this engine running before, and so I happen to know that it likes around 38 degrees of total timing with the relatively inefficient combustion chambers these heads have. I fired it up, let it warm up a bit, quickly set the timing and locked the distributor down. It was running great so after a few minor adjustments, it looks like the 55 is back in business!

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