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The Engine Saga continues - Help!


bobc

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Ok, after an extra week from the date promised, I drove over to the machine shop to pick up my head today. As the machinist was going over the work he did, he mentioned that I needed to torque the camshaft bracket bolts. I didn't have my manuals with me, but I told him I didn't think he was supposed to take the brackets off. He assured me that it was ok, but he didn't know what to torque the bolts to.

Well, when I got home I checked the original Datsun manual and my Clymer book because I was pretty sure I was right and it states:

" Never remove camshaft brackets from the cylinder head, even though removal looks easy. If the brackets are removed, it will be extremely difficult, if not impossible to realign the bearing centers."

So, I think my head is now royally toast. Is there a way to realign the brackets properly or am I just going to wear out the cam or cam bearings if I go with their work. I put a stop payment on the check until I can speak to the owner, but I think my head is ruined.

Thanks for your advice,

Bob

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Hi Bob:

Pay the man - after you take the head back to him with the Torque Spec.'s. Ask him to torque it down as he shows you how it's done.

He will most likely put the cam in the support towers, and as he tightens the bolts down, he should be constantly turning the cam by hand.. to feel the resistance if any. He will follow basically the bolt tightening torque sequence that is used to bolt the head down on the block.

This is done all the time by professional shops. I believe that Nissan's warnings in the Field Service Manuals, as well as those in the after market manuals (that copied the FSM's) had more to do with Dealer Service Personnel, that had little experience and very little need to ever remove the supports. There is also the possibility of getting them mixed up (not put back in the same location as they were).

In the aftermarket "performance" field - the situation was quite different right from the beginning. Milling heads and decking blocks commonly resulted in the need to put shims under the cam towers - to put the cam/crank centerlines back in the proper relationship. So of course they always had to take the cam towers off. The one thing you do not want to do is mix them up by location on the head.

I'd say let him do it - so if he screws it up... he's holding the bag not you. Just plead ignorance and fear.. and ask him to do it. It is most likey he has the bolts close to their final torque settings anyway, and he has most likey already assured the cam is freely turning in them.

FWIW,

Carl B.

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Carl beat me to the punch, but you are fine. I had a similar experience. If you do it yourself, follow the directions I was given here:

http://www.classiczcars.com/forums/showthread.php?t=10257&highlight=cam+tower

By the way, I now see that I mentioned an earlier thread, but back then I didn't know how to link to it. I do remember that I tightened the mounting bolts in three steps to 13 lb-ft of torque. I started with the center tower and then worked my way out to the ends, just like tightening head bolts. (I may have used the same order in fact.) The trick is to keep turning the cam by hand between tightening the bolts, and if it gets tight to back up and try again. When you are done it should spin free.

Edited by Walter Moore
Left out details.
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Thanks Walter and Carl. I'm feeling much better now. I was really p.o.'d earlier. This guy was a week late, charged double what he estimated and then I ran into this. I think my objectivity was out the window by then.

Bob

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Zak,

See this link:

http://www.classiczcars.com/forums/showthread.php?t=10076&highlight=cam+tower

That is the thread that I referred to in the thread that I linked to earlier.

So essentially, to re-install the cam towers you must have the rocker arms removed.

Put the towers back with the bolts finger tight and the towers in the same order that they were when you took it apart.

Slide the camshaft into the towers and make sure that it turns freely.

Tighten the mounting bolts slowly to a maximum of 12 - 15 lb-ft of torque starting with the two in the middle and working your way out to the ends in a spiral pattern. (Just like torquing a cylinder head... middle tower, tower to the right, tower to the left etc.)

Keep turning the cam shaft between tightening the bolts. If it begins to bind, loosen the last bolt tightened and try again. It seems like perhaps I had to tighten both bolts on a tower before it went free sometimes, but certainly if the cam is in a bind after tightening any two bolts on a tower you have a problem.

Having the camshaft in a slight bind while tightening the other bolt on a cam tower will not hurt anything, but never just give up and put the engine back together and run it that way.

After the final torque setting is achieved on all bolts, re-check that the camshaft rotates freely.

If you are not comfortable risking the engine to your own skills, pay a trusted professional to reassemble the head for you. That is why they are in business.

Edited by Walter Moore
Incomplete response.
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As you can see from the previous replies, the only real issue surrounding the removal of the cam towers is preventing/resolving any "binding" issues on re-installation. When I did my first head, way back when, I read "somewhere" about an easy way to eliminate any binding. Reinstall the cam towers and cam as described above, ensuring that the towers are in the right sequence. Torque the first (front) tower to about 10lb-ft. If you rotate the cam as you're torquing it down you'll notice if it starts binding. If you do encounter any binding give the top of the that cam tower a sharp rap with a hammer. You may have to hit it more than once, and harder than you think reasonable but it works like a charm and will NOT harm the tower or cam. The sudden shock helps properly seat the tower. When it's moving freely again retorque to 12lb-ft and move on to the second tower and repeat the sequence til all are done. It's easy to accidentally over-torque the cam towers so be carefull. You don't want to strip threads on a head.

I know, I know, hitting the towers with a hammer sounds completely whack but there was a reason the older manuals recommended "not" removing them. They can be a royal PITA to reinstall and you definitely DON'T want your cam binding. This method allows you to remove/replace the towers with a minimum of frustration. Hope this helps.

p

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