u20 head cam tower question

[Gregs672000]

Also, there are different torque values based on lube and type of lube (dry vs oil vs assembly lube), and it's important the threads are cleaned with a tap. If you have studs, ask the vendor or contact ARP if not listed somewhere in the tech wiki. The stock head bolt torque is listed in the manual along with the process and sequence. There may be torque values listed for the other nuts and bolts on the head (like the cam caps) somewhere but I've just used "common sense" when tightening those nuts (other makes, like modern BMWs, list torque values for just about every one on the car!)

[DCroadster]

I asked for the wrong values. There are 3 studs that hold the cam in place on each tower and the 2 studs that hold the cam tower to the head.

Is there a torque chart on this site I'm missing?

Rob

[jhayden]

"Tightening torque of camshaft bearing cap nuts is 13 ft-lb for large nuts and 5.1 ft-lb for small nuts." Lower camshaft bearing nut not specified, but the following caveat is: "Caution: Never remove Lower Camshaft Bearings unless you have a suitable machine for boring camshaft bearings in line. If you once remove camshaft bearings, the bearing centers will be out of alignment and the recondition is very difficult without center boring."
Yours were removed by a p.o., so the best advice here is to follow the procedure previously described by Mr. Premo.

The pictured roadster resource manuals are strongly recommended, and the Clymer (the first) gives all the torque values you will need.

Jon

[DCroadster]

Thxs Jon,

I have now added these to my list of Datsun docs.

Luckily I think that they have only disturbed the cap nuts because the towers are still stuck hard even though the nuts have been loosened.

But I will make sure when I get everything back together.

I don't see how there is room for extra cam bearings since the cam takes up all the space when I tighten the upper nuts. But will start looking at the docs.

Rob

[Gregs672000]

There are no cam bearing shells like a rod bearing. When installing the cam just keep doing everything progressively when it comes to tightening nuts... install all, slowly tightening the nuts on each tower and cam cap without synching them down firm, rotating the cam by hand (lubed) with each change to find if it binds and if so (likely) moving towers and caps to relieve that binding, then continuing the tightening process until the cam rotates without binding when all nuts are synched down. This can take a fair amount of time, especially with mixed towers. There may be a little resistance but nothing that requires a lot of force to turn the cam by hand... you'll clearly feel bad binding. It was probably a lot faster and more accurate for nissan to have mounted up raw parts and line boring them in the assembly process vs having a worker do this very slow process.

Like I said about the torque... use common sense, they don't require much (make sure you set to 5.1 lbs and not 5.0... ha!).

[david premo]

So here is how it works, when the head is made dowels and pins are placed on each of the cam towers. I believe it’s one dowel and 2 pins per each tower, then it’s machined in place to achieve perfect alignment. If the head is true and in-cut then the cam will turn easily with no rockers installed with just a light twist of your fingers. If it does not turn easily, loosen all of the caps and try it. If that fails then take all of the caps off and try again, BE SURE TO NUMBER THE CAPS THEY ARE LOCATION SPECIFIC! A common problem is some machine shops only surface the bottom of the head and the top and bottom warp together as they are the same piece of material. I have always preferred to straighten the head and remove as little material as possible so as not retard the cam timing. The heat the while pressing it flat, then when it cools they surface the minimum amount of material keeping the head as close to full thickness as possible. So the fastest way to know if the problem is a warped head is to place a straight edge on the head with the valve cover off. I have see quite a few heads over the years with this problem. Also is the cam in the head originally from that head? Sometimes when cams are changed the replacement cam are slightly different size and need to be micro polished on the bearing surfaces so they will turn freely.
Dave

[DCroadster]

Thanks Dave and Greg!!

I follow what you are saying. So I can not assume that the numbers on the caps are correct, in order. They start out that way from the factory numbered in order, but from then on It is purely a manual process to get best fit or least resistance to the cam during installation.

Theoretically, wouldn't a new head on a brand new engine be lined bored already with cam caps in order. The issue is then replacement of the cam, hopefully it is within a spec that doesn't require moving the caps around.

So the setup 5 - 2 - 1 - 4 - 3 maybe correct based on the current cam.

Rob

[Gregs672000]

Hard to tell Rob... mine are all stamped in order, with #5 being unique of course but all the others are the same I believe (is that right Dave?). I think in the long run you're just gonna have to play with it until you're sure you hit the sweet spot. If they came off that way and were matched to the cam, assemble it that way and see what's what... I don't think there's any magic... things align or they don't. I've heard of one broken cam in a U20, and I think the conclusion was a warped head. Things must have been binding a lot for that to happen I think. If the cam seems pretty good but holds up (a little) consistently in a spot, then find that spot/tower/cap (by loosening those nuts slightly one cap at a time and tapping on it, seeing if that fixes it, and if not retightening before moving to the next tower to test), examine it for high spots and use a little emery cloth to gently polish the surfaces as that may clear that up. It's aluminum so be nice.

[Gregs672000]

As I understand this, all your towers are mismatched "unknowns" being installed on to a different head, right? I think alignment is going to depend a lot on how well the towers align together with each other when they are bolted down onto the pins. It may be necessary to see if they will move even fractionally side to side. It may be necessary to try the towers in different places (?). It may be necessary to try the caps on different towers... ahhhhaaaaaaaa, lots of combinations! I'd start with whatever was the last known assembly (as much as you may know), or if nothing is known you'll have to just pick and choose your way through it until it's right... cause it must be right or it's a no go. Let us know... be patient!

[Gregs672000]

I'm trying to visualize how I would do this... I think I'd use the cam to help me set the towers by installing the towers but not tight, then laying the cam down (lubed) on them and tightening the nuts while pushing down a bit on the cam. Then, turn the cam without the caps and see if it seems smooth and completely without issue. If not, then loosen tower nuts until the bind goes away and try again or move towers. Then try the caps on whatever tower you think is potentially right... just a thought... there are many many combinations and ways you may need to try (or maybe it will work first time! )

Also, have you ever heard of "bluing"? It's a blue grease-like material that you wipe on metal parts that slide together in order to find high and low spots or to see where parts are wiping together (like your cam to rocker arms pads). If you can find some at a parts store that may be helpful in finding high spots or points where things are binding.

[david premo]

Greg 1 and 5 are different from the other three towers. 1 is taped for the cam chain guild and 5 is a small diameter journal with thrust surfaces to keep the cam from moving fore and aft.
Dave

[Gregs672000]

Greg 1 and 5 are different from the other three towers. 1 is taped for the cam chain guild and 5 is a small diameter journal with thrust surfaces to keep the cam from moving fore and aft.
Dave

Thanks Dave! I just glanced at them... hopefully he's got all the right parts!

[redroadster]

I missed the word interchangeable
I'd see if the machine shop can line bore it / bearing it ( if the babbitt bearings are available