How easy should a cam turn?

[Ben's Z]

I have seen posts that say "spin with 2 fingers". "Spins freely" leaves a lot of room for error.  My cam turns over by hand but its not like it keeps spinning or snot on a glass door knob.  Thoughts? 

[redzedturbo]

If you have lubed all the towers before you put the cam in it should turn with very minimal effort. If you can put a finger on a cam lobe and turn it 360 deg it should be fine. Main thing is all the towers are straight and inline. You will know if one is out of line it will feel like the cam is dragging when turned. Good luck.

[Ben's Z]

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[Ben's Z]

If you have lubed all the towers before you put the cam in it should turn with very minimal effort. If you can put a finger on a cam lobe and turn it 360 deg it should be fine. Main thing is all the towers are straight and inline. You will know if one is out of line it will feel like the cam is dragging when turned. Good luck.

Damn.  I ain't there. Call me crazy with this thought.  Could one use valve lapping compound to get that cam to spin a little easier?  I will use the dead blow hammer a few more times and see if I can get it to spin a little better.

[Tony D]

One could.. But one would screw the pooch in doing so.

[Ben's Z]

Took it to another machine shop. They agreed with my presumption that they did not mill the top either. They thought that the cam would be fine once the motor is warm. I suggested torquing the head to the block and checking to see how it spins with it torqued properly. Any other thoughts?

[Tony D]

"Cheap Machine Work Rarely Is..."

"Quick Machine Work Rarely Is..."

 

Etc.

[NewZed]

You could have had it running and blown up by now, and been on to another head.  You know it's going to self-destruct anyway.  Just run it.

[Ben's Z]

Ok ok. Find another shop and insist they mill the top too? It's not that it's that tight. When I put the cam gear on yesterday it seemed to spin but about 20% of the rotation was tighter regardless of cam. I wish nothing more than to find a machine shop here in Houston that has nothing but L series Datsun blocks and heads waiting for machine work. I may show Doug at Awesome z and get his input. This really has been hell.

[Ben's Z]

Well I tried a few things this morning.

1) I took my NA cam out of my P90 and put it back in my NA head which is still on the block to get an idea of how free the cam should spin. Knowing that I took it back out.

2) I installed my P90 head with the head gasket with the theory that perhaps with the head torqued the cam might spin easier. Sort of a reverse torque plate theory when machine shops bore cylinders. I put the cam towers on loose and put the cam in. I did the torque sequence checking the cam for spin after each sequence. I torqued it to 20 ft lbs first go around and then tightened the cam towers to 14 ft lbs. The cam was even tighter than my bench top spin. Went once more around to 40 ft lbs., no change. Still too tight, I stopped there.

My question is this. When Nissan align bored the cam towers at the factory did they torque the head to spec first?

I believe they did straighten the head but if they didn't resurface the top the I am pissing in to a 100mph head wind and torquing the head made it worse.

I am going to take it to a shop and have them plane the top.  Is there anyway they should simulate the head being torqued to the block when they do this? 

Edited December 8, 2012 by Ben's Z

[Xnke]

No. If the bottom surface of the head is flat, then they don't need to torque it to anything when they mill the top.

[NewZed]

If you read around the internet, which you've already done, then you'll find that getting a good fit when swapping towers seems to be hit and miss, after lots of trial and not-working.  Some have reported that they swap tower positions when trying to get things to work.  You might even trying mixing and matching towers from the two heads and spinning them 180 degrees.  Who knows.  Nissan says to junk the head and get a new one if the cam towers are damaged, they don't have even have an option for making new towers work.  In the factory's view, onced the towers are installed and line-bored they are part of the head, never to be removed.  So there is no machine shop procedure to fix the issue.  It's luck.

 

Have you tried the damaged P90 cam in the P90 head?  You have two heads and three cams right? The P90 cam with the cracked dowel hole might have the best odds of success.

[Ben's Z]

Did a little more looking.  I took all my cam towers off and used my potentially not perfectly straight Stanley 18" level and found that a .010 feeler gauge has a little drag under where the center cam tower would bolt down.  I put in 1,2,4,5 cam towers and torqued to spec, and it really didn't seem to make a difference.  Odd.

[Xnke]

That means the head was NOT straightened before being shaved. You will need to have the top of the head skim cut to correct this issue.

[Ben's Z]

Thanks my man. That is the next move. Will keep you posted.

[Xnke]

Overhead cam heads get the shaft in most machine shops that don't deal with them often...long L6 heads, especially. The proper way to recondition one is measure for flatness, and then STRAIGHTEN it, not just mill it flat. Once it's been straightened, then the deck can be milled to clean it up, and the cam bores need to be line-honed, unless like the L head, they are removable. If they are, they would then be removed, the valvetrain completely dissassembled, and the top of the head milled flat. The head can then be reassembled, and the towers WILL realign...it's pretty hard to disassemble a mated assembly that was produced with a flat surface, and then reassemble it on a flat surface, and have it come out less than flat. I don't understand the big deal about not removing the cam towers...they're doweled into place, as long as they are carefully reassembled and aligned onto the cam such that it spins freely when they are torqued to the required value, then there is no reason to remove them.

[srgunz]

I would also wonder if the shop removed the towers for some reason and reinstalled

a couple not in their original position?

[Tony D]

Saying repair procedures don't exist for this is just plain wrong.

This is all basic machine shop work.

But people go and buy on price from myriad shops providing 75% of what SHOULD be done when remanufacturing a head.

 

Top AND BOTTOM of the head when warped must be returned to true. That means milling top and bottom. After straightening.

 

Now we got somebody adding different steps guessing how its done at the factory making matters worse.

 

The original L4's had iron towers with inserts. You don't "line bore" a non-split bearing bore without an oversized cam journal! You must weld the bores, and turn on a vertical mill.

 

Everyone here is assuming these cam towers are line bored at the factory when strong evidence exists no such thing occurred. It was simply a jig (arbor)-assembled piece fom bins of pre bored, dimensionally identical cam towers in a box.

 

You don't want to mess with the "mallet and turn" method of installation?

 

SIMPLE AS PIE FOR A PRODUCTION MACHINE SHOP:

 

Make a steel arbor of sufficient length, and 0.0005~0.00075 undersized the journal BEARING diameter. Stick them on the arbor like meat on a shush kebab and stick them on your head. Bolt them down, remove the arbor (some shops will GUNDRILLED the Center of the arbor o allow a shot of CO2 to shrink the arbor and allow the removal to be easier as line-to-line fits easily bind if you don't pull exactly straight...

 

THERE YOU GO:ALIGNED PERFECTLY!!!

 

If your head isn't warped, that is!

 

This is building on a bad foundation, a warped head that was short-cut repaired, and now it's compounding itself with "make-it-fit" methodology.

 

Any wonderment as to WHY Nissan said to simply replace it now is removed. They realised most customers will not pay for proper machine work, at a competent shop. They will go low-bid and their reputation (Nissan's) will be impacted as a result for any work done in the first 10 years of ownership.

 

This is part of he reason they nixed the triple Mikuni package (165Hp) on the 240Z (emissions was #2, but that didn't stop Toyota using them north of the US Border on 2TG's in Canada!

 

 

[Tony D]

For production, you tool a pneumatic arbor to clamp them in-line and sink the attaching bolts.

 

String towers, air on, position on head, bolt down, air off...retract. Next station.

[PMC raceengines]

i do this every day lol we have a bar that runs thro the towers , most datsun race shops do , the cam spins with a flick off the fingers when done right  ,,, but the head has to be dead flat before you start , this seems to be hard lol for some  , all simple engine building work .