Datsun SRL311 Cylinder Head from Rallye Enterprises, Ltd.


Datsun 2000 Partial Cylinder Head Assys
These units were left when we stopped rebuilding heads awhile back. Haven't found time since to finish them so we are selling them as they are. Heads typically include new valves, seals, springs and guides. Check photos and descriptions of each particular head for information accurate to that head. Bottom and top of head have both been milled flat to correct previous warpage. It will be necessary for you or your shop install your old studs, dowels and cam towers.

A little background on heads...they don't like being run low on coolant or anything else that allows them to overheat; faulty distributor, improper removal of "smog devices" some of which protect the engine...; lean mixtures, plugged radiator, bad pressure cap, plugged exhaust; the normal things that engines don't like.

When they overheat and warp; both top and bottom warp; putting a cam back in a warped head usually results in it either binding and "blueing" the towers; or breaking if the stress is severe enough.

We did some of the earliest "engineering" adventures with oven straightening heads in the 70s; when most machine shops had not seen many; if any; aluminum heads. Our methods were crude and done out of desperation. We learned in addition to warping the heads can sink, twist and "shift" themselves. Cool.

When a head is cut it is important that only the slightest amount be removed; you don't even need to run the cutter to the ends of the head to make the top suitably flat. Removing material top or bottom puts the cam closer to the jackshaft which creates chain slop and alters the cam timing. It is uncommon to have a problem with valve to piston contact because the valves have been moved too close to the pistons; it is usually due to the valve timing being altered. (When they open and close in relation to the piston position) Various methods have been used to counter this situation. We typically used cam tower shims. Lowering the cam; or raising it more on the top than it was originally to make up for bottom cutting alters the valve train geometry...basically this means the cam lobes will not be running in the center of the cam follower (rocker arm) lobes. You can "cheat" and let them go to the edge; but if they go over that the cam says bye-bye in short order.

Altering the placement of the wear pattern on a cut head typically involves changing the rocker buttons' thicknesses. (sometimes not all of them). If the valve is sunk more in the head due to multiple valve jobs; it can help or add to the problem.

Nissan's service instructions were to never remove cam towers from a head. This is due to the fact that you can take a new head; remove the towers; reinstall them; and find the camshaft bound up. It can be a rather tedious process to reinstall cam towers and have the cam turn freely. Your goal is to get it so the cam will turn with two fingers with the journals oiled (and of course the rockers out!). Getting it to turn as easily as possible involves tightening the towers evenly, unevenly, and/or banging on some offenders with a plastic mallet. Even with the extensive use of locating dowels that Nissan provided it can be work. Using "plastigauge" we were usually able to locate the problem tower or cap. Normally if you get it correct on the workbench; it will stay correct when the head is torqued to the block; but not always. There are all kinds of tricks like clamping them into the towers and then bolting the towers on; but this can drive one to temporary insanity as any other method...

In a perfect world; the car would not overheat and the head not need to be milled. In a perfect world you would just as Nissan suggests get rid of the head when it is cut the slightest amount. In a perfect world the new castings would cost $80.00. They were $440 as far back as 1980 so ways had to be found to make it all work. If everyone that "needed a new head" in 1980 had only that choice; there would be a lot less roadsters out there today.

Once a head has had it's top milled to true the surface; it does not matter which towers go back on it. You will usually have an easier time if you keep them in order; but they were originally bolted to a flat surface; so this sometimes doesn't matter except #1 and #5 of course. You want to get the cam as relaxed as possible in it's "bed" and if need be you can always have the cam journals "align-bored". Some shops call this "line boring" but it's purpose is to ALIGN the towers not to bore a hole. If it is done properly the tiniest amount of material will be removed. And again; this must only be done if all attempts by a proficient individual have been undertaken beforehand.

The original thickness of the U20 head is 4.528" (115mm). They can typically do fine up to about .020" off without a cam chain problem; assuming the chain and gears are in good shape. After that point you want to think about dealing with the situation.

If need be we have used towers, studs etc.


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