Camshaft button wear

bill_si · #1 11-03-2006, 06:04 PM

I have an '86 3.8 that lost the camshaft magnet. Keep in mind on this model the magnet bolts on to the camshaft gear. I have pulled the timing cover (it was not as terrible a job as I imagined) and found several things. There is lots of debree around the cam gear from a chewed up magnet assembly. I do not see how this could have been hit as the mounting assembly was still tight to the gear unless the cam came forward. The entire portion of the magnet enclosure is sheard off. I also found the timing chain to be slack. I will put it back together with a new chain and gears and magnet assembly and tensioner.

My biggest concern is the camshaft button. The boss on the cover on which the button rubs is worn with a peak in the middle and the appearance of galling on the entire service. I suspect the boss is somewhat shorter than it was when new. I am not sure if the button assembly I have is complete or if parts are missing. I found just a spring and the spring seat that wears on the cover boss. The spring seat had a mating wear pattern with the boss.

My questions are: Is my button assembly complete and should the cover boss be machined flat or possibly even be built back up? Is this wear normal? The engine has about 97k original miles. Is the button needed? And the last question, how did the magnet get damaged?

Thanks in advace.

Bill

maxwedge · #2 11-03-2006, 06:22 PM

Welcome to AF.I'd get a new cover or an unworn used one, thrust button and spring here, or the cam will be walking out of the block, that is the purpose of the button of course. Magnet probably hit the cover with the button worn.

bill_si · #3 11-03-2006, 06:46 PM

Maxwedge,
Thanks for the quick response!

You have confirmed what I was thinking. I suspect that GM will want more for a new cover than the car is worth. That is why I was wondering about welding it back up to heigth and machining it flat. Of course I do not know what the heigth should be.

In fact I was wondering if the boss was supposed to be a counterbore to help keep the button centered and it might all be worn away. And I suspect that a used cover may not be any better than what I have and might be a lot of work to find or remove at the local pick n pull just to be dissapointed in what I find after a lot of work.

I will price the cover just to cover all the bases but GM needs to make a buck somewhere so I suspect old parts would be gold from them.

maxwedge · #4 11-04-2006, 11:47 AM

Tough job welding that cover and getting the right contact surface!

Alibi · #5 11-04-2006, 04:24 PM

you'd be better off getting a cover from a junkyard motor than trying to find a NOS one. I doubt GM even carries this part anymore anyway.

bill_si · #6 11-05-2006, 10:59 AM

I wish to thank everyone for their suggestions and valuable insights. I have obtained my new parts and here is my plan.

The new cam button is of an entirely different design. Instead of having a plastic cap that wears on the cover (with the case losing) it has an internal bearing assembly so there will be no rubbing on the cover (unless it fails). If it fails it will be steel against aluminum so I would expect a quick failure of the cover. I hope the new button design is reliable.

I am not going to replace the cover. However, it is available aftermarket at a very reasonable price (under $100 my price, my kid works at a parts store). But since I have a mill and lathe (and I am cheap), I am going to mill the boss in the case down about .35 inches and then drill a blind center hole. I will then machine a new aluminum extension with a mateing shaft for the center hole. I will press and locktite it in and reassemble. If I screw up it will be new case time. The part should never come lose as there is no torque on it with the new button design and there is always pressure on the new extension so it should not be able to come out if it becomes loose.

I think the sloppy chain had more to do with the cam coming forward than the worn button and it seat. The button spring just does not have that much pressure.

maxwedge · #7 11-05-2006, 01:05 PM

Quote:

Originally Posted by bill_si

I wish to thank everyone for their suggestions and valuable insights. I have obtained my new parts and here is my plan.

The new cam button is of an entirely different design. Instead of having a plastic cap that wears on the cover (with the case losing) it has an internal bearing assembly so there will be no rubbing on the cover (unless it fails). If it fails it will be steel against aluminum so I would expect a quick failure of the cover. I hope the new button design is reliable.

I am not going to replace the cover. However, it is available aftermarket at a very reasonable price (under $100 my price, my kid works at a parts store). But since I have a mill and lathe (and I am cheap), I am going to mill the boss in the case down about .35 inches and then drill a blind center hole. I will then machine a new aluminum extension with a mateing shaft for the center hole. I will press and locktite it in and reassemble. If I screw up it will be new case time. The part should never come lose as there is no torque on it with the new button design and there is always pressure on the new extension so it should not be able to come out if it becomes loose.

I think the sloppy chain had more to do with the cam coming forward than the worn button and it seat. The button spring just does not have that much pressure.

Good plan, do it!

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