camshaft replacement

[orange 73]

Hi, I want to replace my cam on my 73 240z and want to know if it is possible to do it with the head still on the car. Just to preface my question I have done a head change before so I know about the wedge in the timing chain and torque specs and all. I guess my main question is can you remove the camshaft with the towers which will involve removing the 5 long head bolts and in the process not have to "re-torque the head bolts" in the typical 'center out' pattern. If anyone can help it would be great!

Thanks, Mike

[Jeff G 78]

Yes, the cam can be replaced with the head on the car. You do NOT remove the towers. What you need to do is remove the trans mount and lower the rear of the engine. This points the cam up enough to slide it out the front and clear the radiator support. You will need to remove the hood and radiator as well as loosen the fuel rail and move it up or down to clear the cam path. It isn't easy, but beats removing the head, manifolds, etc.

[orange 73]

Jeff thanks for the quick response, I understand the proceedure you are decribing but how do you deal with the spring tension/pressure on the cam lobes to slide the cam out?

Thanks, Mike

[Arne]

You need to get a service manual, it will describe the process. Removing the cam towers is a last resort and not recommended unless you need to shim them.

[Jeff G 78]

If you are only replacing the cam and leaving the springs alone, you can simply use a large flat blade screwdriver to remove the rockers. After you remove the springs at the adjuster end of the rockers, pry the valve spring caps down with the tip of the screwdriver while the shaft of the screwdriver is against the cast part of the cam - NOT the lobe. It's very easy with stock springs. Once removed, lay each rocker out on a clean towel or board in order so they can be reinstalled the same way they were. You will have to turn the cam such that the lobes are up while you remove the rockers.

Once all the rockers are removed, set the engine to #1 TDC and wedge the chain before removing the gear and cam retainer plate.

The manual can be downloaded from xenons30.com. It doesn't matter what year manual you download as the base engine disassembly is more or less the same.

[orange 73]

Thanks guys for the info. it makes sense now that you describe the process. One other question I have: Can camshafts be interchanged from the different L-series engines ie, 280 cam into the 240 head and vice versa, and what if you are using the old rockers on a new cam, will the new cam break in correctly?

Thanks, Mike

[e_racer1999]

Short answer: yes, all 6-cyl mechanical rocker camshafts are interchangeable. Slight difference in lift/duration/profile across years, I believe. I recommend to ALWAYS keep rockers and camshafts together, or have your existing rocker arms resurfaced.

If you've never taken a cam/head off of a tension-type OHC engine, find a who has. Trust me when I say some experienced hands to help you out will save you hours of frustration. If the timing chain slips you will be hating life for hours.

[Diseazd]

Don't put an L24 cam in an L28 w/o a spray bar.....L24 cams don't have oil holes in the lobes.

[Jeff G 78]

Yep, like Guy said, if your Z does not have a spray bar, you must use an internally oiled camshaft. They can be identified by the oil holes in the lobes. If you do have a spray bar, you can use either style cam, but if you have a weak oiling system, your pump might not be able to support internal and external cam oiling. With a tight bottom end and a turbo oil pump, using a spray bar with an internally oiled cam is fine. An alternative is to use an internally oiled cam and buy the MSA block off plates for the towers. They are cheap and eliminate the spray bar.

Given the choice, I like the spray bar, but it needs to be in good shape.

[orange 73]

Thanks guys for the info, I am just trying to get my 73' 240 running so as to have a driver car while I am restoring my 280. It's coming along but I have a long way to go. Happy new year to all.

Mike