Stripped cam tower bolt

[ttodhunter]

Hey all, 

 

I'm assembling the top end and came across a couple of stripped bolts in the cam towers.  These are the bolts directly next to the head bolt, so I'm hoping they are just there for assembly purposes.  With the head bolt sharing a deck less than an inch away, does anyone know if these bolts are necessary?  Part of me thinks they are there for a reason, another part thinks the head stud will apply all the clamping force necessary.  

 

Thanks!

[madkaw]

You might actually get away without having to repair that with the big head bolt right there

[ttodhunter]

I just went ahead and put helicoils in and put it back together only to find another stripped.  So I helicoiled them all.  Quick note- if you mess up on a helicoil, if you can pick the end out and grab it with a needlenose, you can pull the whole thing right out.

[NewZed]

Somebody probably used the torque values in Monroe's Rebuild book.  Apparently there's a typo in the book, the value is too high.

 

Make sure you do the tap-and-rotate alignment when reassembling.  Nissan considers the cam towers as non-removable.

[ttodhunter]

I have to ask...  What is the tap-and-rotate alignment?

[NewZed]

Can't remember but I think that it might actually be in Monroe's Rebuild book.  But here is a writeup that a past member put together.  The towers are bored for the cam after they are installed.  When they are removed any mismatch on reassembly can cause cam binding.

 

I've never done it myself I just remember reading about it.  He doesn't mention the tapping, I must have seen that somewhere else.  Basically, if rotation gets tight a couple of light taps on a tower or two can loosen it up.  The goal is to get everything torqued and have a cam that rotates freely.

 

 

Edited April 25, 2022 by NewZed

[ttodhunter]

Thanks NewZed and madkaw!

[Tony D]

Those bolts are there for alignment off-block. The towers are NOT line-bored, they are assembled on a mandrel. If you make an installation mandrel you can get them installed in one shot-but you need those bolts to secure the towers in the proper orientation. The production mandrel was expandable, so it held them centered till pulldown, and then retracted into itself for production removal. To make one you just duplicate a cam bearing diameter minus about half the normal clearance. It is a BITCH to get the mandrel out if the head is not properly decked and warped on the top! You can set it up near full clearance but the real answer is to align them properly on a properly decked head and then effortlessly install your cam without any adjustment necessary. 

You can centerless-grind the mandrel, but the one I made was just turned on a lathe. If you find the right size of pipe/heavy walled tubing (like Schedule 80) you can set up the mandrel (tight clearance tolerance) and then pack the core with dry ice and alcohol and pull it right out loose as a dockside er... "sporting lady"...