Block Prep

For engines of not too much more than 200hp there is nothing special required, unless of course you plan on using a different type of crank. The age of these blocks dictate that you should give any block a good clean and check it out thoroughly for cracks or any other damage before you invest any time or money in it. Line boring isn't usually required, though cutting material from the deck might be be needed to get the squish/quench clearance down - more on this later. Keep an eye out for cracking around the head bolt holes which is quite common, though minor cracks here don't seem to cause any problems. These holes also tend to strip threads so consider fitting inserts and/or studs while you're at it. A honing plate must be used for the final honing operation to ensure the bores are round when the head is fitted. Bore finish is quite important, and should match the rings requirements. Generally a 280 grit stone will be best for chrome rings and a 400 grit for moly or moly-plasma faced rings. It's generally accepted that an automatic machine can give a better, more consistent result than hand honing.

We touched on the importance of maintaining the maximum possible cylinder wall thickness earlier; trouble is it's getting hard to find blocks that haven't already been rebored several times, and anyway you could argue that a very high HP engine would benefit from walls stiffer than those in a virgin block. This can be achieved through sleeving with high-strength thinwall sleeves. The success of such an operation though rests almost entirely on the person doing the machining. If the job is done properly, a sleeved engine will make more power, have more strength and last longer than a normal unsleeved block. If the machining isn't 100% though, it will fail quickly and this is probably why sleeved blocks have a poor reputation with some. The sleeve and block must be machined to very close tolerances, and the sleeve must press up against a step or shoulder to ensure a reliable seal with the head gasket. It's not practical to use sleeving as a means to enlarge the bore; in order to maintain a reasonable thickness of material around the sleeve and in the sleeve itself you'll probably end up with a bore no bigger than standard and possibly a bit smaller. The improvement in wall stiffness will more than compensate for the smaller capacity, especially with very highly tuned engines. Sleeving a high revving high output engine is a different matter altogether to sleeving something like a worn out tractor engine - you might have to talk to several engine machinists before you find one with the experience and competence to do it correctly. Properly done though, there are definite strength and performance benefits to be had.