The Crank

There are quite a few different types of cranks for the little Holden. There are two stroke lengths; the 202 engine uses a 3.25" stroke while everything else from the 138 red up to the 186 is 3" stroke. There are also two different materials used; the 3" cranks made before the introduction of the HK in mid '67 are steel, plus the 186 X2, the 186S and the 186 XU1s used steel as well, while all 173s and 202s are cast. Strength and durability doesn't seem to be an issue for either type, and remember Brocky won Bathurst in a cast cranked 202 Torana so I wouldn't be too concerned about the lack of steel 202 cranks. Big end journal size is the same with all engines, but the 202 and the later (blue) 173's use a bigger main journal than the others.

The later 12 port 202 (but not the 173) engines had fully counterweighted cranks that make life quite a bit easier for the mains and the block. Strictly speaking they still aren't quite fully counterweighted, but they are certainly an improvement over the red cranks. For a street motor or any engine that is subject to sustained high revs I'd go for the counterweighted crank, though for some forms of short-duration racing the lighter non-counterweighted crank might have an advantage. See the section on balancing for more details on this. Besides the different main journal diameters mentioned earlier there are also variations in rear main seal dimensions so if you are planning to use a 202 crank in an earlier block (perhaps to make an engine that's bigger than the numbers on the block indicate) you will have some machining to do. The rope seal cranks have a slightly bigger diameter seal journal than the lip seal cranks, but the journal can be ground down to the smaller size if necessary. This allows a late fully-counterbalanced 202 crank to be used in a red neoprene-seal block. The neoprene seals seem a bit more prone to leaking than the rope seals but either will work if installed very carefully. Installing a 3-1/4" stroke crank in a 3" block requires the main tunnels to be line bored or alternatively the cranks can have their main journals turned down, apparently with no ill effects. Bearing clearances should be no more than .0025" to .003", which might be considered a little bit on the tight side for hi-performance engines. Similarly, you want to keep the rod side clearance fairly close to the stock figures in order to prevent throwing too much oil around. When scrounging for cranks keep an eye out for units that were used with an auto transmission - the manuals had a tendency to wear out the thrust faces fairly badly.

Drilling and tapping the crank snout is worth considering; not only does it enable the use of a balancer retaining bolt it also lets you pull the balancer onto the crank gently instead of driving it on with a hammer. Don't make the thread so big it weakens the snout - 3/8" UNF is enough.

Some of the earlier cranks had smaller diameter oil holes, and while these cranks were fine for normal use they were prone to bearing problems at high speeds. Later 202s etc. were drilled 15/64" and this is sufficient for competition use. Definitely do not crossdrill the journals. It's normal practice to slightly chamfer any sharp edges or corners on the oil holes but don't get carried away and flare them too much - it just reduces the bearing area.

Some people like to run knife-edged cranks, where the outer circumference of the counterweights are bevelled back to an edge. Sometimes the leading edges of the counterweights are bevelled too. The idea is to reduce the windage and drag on the crank, and it also reduces the rotating mass. While this sounds cool I'm not sure it's worth it on a horsepower-per-dollar basis. I know that the oil wrap-around effect on the crank can cause drag and sap power at high revs, but unless you plan on going the whole hog with a special sump design and scrapers and so on I suspect the gains from running a knife edged crank on its own would be minimal. There's another even better reason to avoid knife-edging: it will be impossible to balance the crank to a 50% balance factor with so much material removed from the counterweights and this makes the knife-edged cranks unsuitable for any high rpm work where block and crank durability is important.

Knife Edged Crank
A knife edged crank. Don't do this unless you can afford to compensate for the reduced counterweight with lots of Mallory metal.

You could probably get away with using a new standard balancer on a 3" stroke engine or a mild 202, but for high RPM work you'll have to use a competition style balancer as an absolute minimum, especially on a 3.25" crank. If you decide to use a stock balancer consider fitting some sort of retaining ring or flange to the front to stop the rim from walking off the hub. There are a few different types of heavy duty balancers around and while they aren't cheap they can be good insurance. A stock balancer may come apart at high speeds, with possibly disastrous results. Depending on what combination of balancer and timing cover you are using, the timing marks may not actually indicate TDC so remember to check it and re-mark it if necessary. More info in the next section..