Camshaft replacement

Revision as of 03:26, 6 March 2011; view current revision
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Replacing the Camshaft in a Datsun 1200 is not difficult, but like any engine requires careful measurements and expert use of tools.

The first step in an a series cam swap is remove engine from car. The reason is so the lifters can be fitted. You have to turn the engine upside down to clear the cam for removal and installation. Otherwise the lifters fall into the bore hole, and possibly into the sump when the cam is removed.

Lifters

With a new cam, new lifters (aka tappets, sometimes called cam followers) should always be used. Otherwise failure *will* occur after a while (days to months). Replacing or resurfacing them is really just cheap insurance as you will kick yourself if you save a few bucks, only to find later that the cam has an excessively short service life as a result of out of spec lifters.

It isn't recommend to resurface liftesr since they are very cheap from Nissan, even light Nismo (Datsun Competition) ones are pretty cheap.

You could alternatively have the old lifters "radius ground" (resurfaced) and harndess-treated (?) before putting in a new cam or reground cam. The lifters have to turn as the cam lobes are ground at an angle to the axis of the cam and are not parrallel with cam axis. The slight roundness of the lifter face causes the tappet to spin and not wear in one spot. The lifter face should have a slight convex curve, so that the lifter spins and is not in the same position all the time. This helps avoid excessive wear on the the cam lobes.

The basic idea is to have the cam contacting the lifter with a center of pressure off to one side of the dead center of the lifters axis. This allows the lifter to rotate as the cam passes underneath, minimising wear on both the cam lobe and the lifter face.

It will usually rotate the pushrod as well which causes the balls & sockets to wear much more evenly by eventually creating a near perfect spherical contact point at each end of the pushrod, which maximises the life of these components.

Discussion: resurfacing tappets (lifters)

Additionally, to match the lifter design, the camshaft lobes should be ground with an ever-so-slight taper across its face when viewed from the side. This is way too small to see with the naked eye.

On the other hand, if the cam and lifters are both used (and matched together -- don't mix and match used ones), as long as they are serviceable, with no discernable wear, there is no need to replace them.

So how do I know if I need to have the lifters resurfaced? They look fine to me - very smooth surfaces with no scoring or visible marks of any kind. Is visual smoothness enough or is it not worth the trouble to have them resurfaced unless there are major problems?

If your lifters are in good servicable condition you should be able to place two of them together, with the flat faces touching & you should be able to see that they have a curved surface as one rocks over the other. From memory, these things are often ground on something like a 36" radius, so the curvature is very subtle.

Removing Camshaft

1. Remove engine from car
2. Put engine on a stand
3. Remove rocker cover and loosen each rocker arm
4. Remove rocker shaft assembly
5. Remove pushrods, numbering each one with a bit of tape (#1 is at front of engine, #8 at the rear)
   • For best wear, they should be replaced into the same spot to match the rocker arms and lifters.
6. turn engine upside down, remove the sump. Being upside-down, gravity will hold the lifters of the camshaft.

Be sure not to turn the engine right-side up or the lifters will fall out.

1. Carefully pull camshaft out of its bore. Don't let the lobes or bearing surfaces be nicked by the edge of the bore hole. You don't want to damage the bore hole.

Replacing Camshaft

1. If installing a new cam, be sure to fit new lifters or failure *will* occur after a while (days to months)
2. Put cam lubricant on the bottom of the lifters
   • Cam lube can be anything from a good quality engine oil to special moly cam lube. The idea is to stop the cam lobes wearing on the initial start up. Most auto stores will have something to do the job. Don't be afraid to use ots either. As the saying goes 'oil is cheaper than metal'.
3. Put cam lube on the camshaft lobes and bearing surfaces
4. Carefully insert the camshaft into its bore. Don't let the lobes or bearing surfaces be nicked by the edge of the bore hole.
5. Perform camshaft timing procedure
6. Turn engine right-side up
7. Insert pushrods
8. Bolt on the rocker-shaft assembly
9. Perform Valve adjustment
10. Install rocker cover
11. Replace engine into car
12. IMPORTANT: Before starting the engine, review the camshaft break-in procedure

Replacing Cam - Engine in Car

Is there any way to put the camshaft in without removing the engine? Know any shortcuts? Perhaps by removing the sump and inserting the lifters from below?

EDIT: Here is a way to do the cam change with the engine still in the car: http://datsun1200.com/modules/newbb/viewtopic.php?topic_id=50410&forum=1&post_id=359036#forumpost359036

Possibly. Perhaps you can take the rocker gear off then the pushrods out then turn her over and push the cam followers down or up if you know what I mean and slip it out and then the new one in. The followers might be a bit hard to get to go down far enough so you might have to give the old cam a fast spin to knock them down. Its worth a try and let us know (click Edit) how it works out.

Or, You could put your 1200 on one of these:

Then turn the entire car over, like this:

Alas if only there was a magic device that held the lifters in place we could leave the motor in and just swap cams.