Datsun U20 Cylinder Head Info


Datsun 2000 Used Cylinder Heads

CYLINDER HEADS unless specified otherwise are "just off the engine" and have had nothing done to them. They haven't been cleaned or anything else except for those measurements and comments we have provided on the individual pages.Click on the info link or part number for each head to see the head and information for that particular unit.

Any parts listed are only in whatever condition they are in. Heads may be offered at different prices depending on what parts are included. Used heads would need to be ordered by a mailed in order accompanied by a money order. Please inquire for delivery costs. A US Postal Money order is by far the quickest if you have any kind of time constraint.

We check for current thickness on all four corners as some heads were not leveled properly either before milling took place or releveled during the process if necessary. Critical spot is of course on both sides of the forward (#1) cam tower. We also check if there is a top "crown" that needs to be knocked off; and existing bottom warpage. Sometimes the top "crown" measurement if slight can be ignored as some are measured end to end. Strictly speaking; for cam related problems; you only need to put a straightedge across the five cam tower spots; not the entire gasket surface. Typically the "crown" figure is derived from taking one-half the gap noted on the opposite end of a straightedge that is held down on the other end of the head. This is assuming the head is warped evenly upward along its length but this is not always the case. The measurement is a good indicator though. Minor crowns may not cause cam to bind. It is not a good idea to remove towers unless you absolutely have to.

We look for anything obvious; broken studs etc. I can't say though that some thread problem somewhere won't get by us as we don't run every open hole for problems. There may be missing nuts, bolts, studs, washers etc. Suspect any stud at least on the manifold to need replacing. Much easier to do before you install the head than with head on car! Many of these heads have sat in our storage for 10 20 30 years and they may have sat somewhere else before that. Some were just pulled from cars or engines and bugs, dirt, rust all have found a pleasant home on some of them.

Always assume cam towers have been off and reinstalled improperly or out of order. Never assume a cam turns freely (assuming top of head is not warped). Always check and take necessary measures to correct the situation. Always have heads cleaned out and passageways checked. The first thing you do with a head to be worked on is to mark all towers and caps. Sadly many roadsters get worked on people who may have good intentions but poor technique.

Unfortunately; when a head is warped .020 or whatever; many machine shops would just set their cutter to some arbitrary figure and go to lunch. I've seen lots of heads that were cut .060 to clear a .020 warp. And I have seen a shop take a head and say "Oh it only needs to be cut .15; it will be great...and NEVER measure the head to see what was taken off PREVIOUSLY. The shops that wouldcheck the top warp were few as well. I guess they figure since they weren't putting the cam in it wasn't their responsibility.

Some of these we've taken off engines ourselves; or have been from cancelled projects we've purchased or have fallen out of the sky and landed here. They range from near pristine to "Why are they listing that?" Truly the good, bad and the ugly. Some of these would have been scrapped 20 years ago; lately quite a few people are putting together roadsters out of junkyard cars and piles of parts and are looking for any way to lessen their cost. At least this way I won't be burdened by second thoughts when I do toss a part out later!

In the 70s and early 80s there was a big demand for cylinder heads; mainly due to problems with the cars that could have been corrected very easily. No easy way of communication back then; but service update signs and info in the dealerships WOULD have been possible. Similar information could have been provided by ALL vehicle manufacturers in car mags; or their own publications. The only owners that learned of the simple ways to keep their cars running were those mechanically inclined enough to figure it out themselves; or had their car worked on by someone like myself; who would sit them down on an apple crate and bore them to death over the details. (Or who would coerce, entice, beg them to sign up for our next catalog/owners guide if I ever could actually stop working on someone's car to finish the thing...)

By this time Nissan had lost or threw out/converted the tooling for the heads. A complete new tool was created at a cost that must have been unbelievable.

Tech Info on 2-litre 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 and almost always when towers and/or caps are swapped.

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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