I recently hooked up the Durametric to look at cam deviation. My 99 C2 has about 92k miles, many of which are track miles. As you can see from the attached screen shots, I revved the warmed up engine to about 5000 - 6000 rpm and let the rpms vary a little. The cam deviations indicated zero until I let the engine idle. What I thought was strange is that the initial set of readings - bank 1: -4 and bank 2: -2 changed over time as the engine continued to idle and ended up at -6/-3. I repeated the Rev sequence and the deviation numbers stayed the same. Is it time for new pads?

Edit:. I do see that I barely got the rpms over 4000 on the other set of revs i posted in the screen shot. I did do a third set at 5000+ rpm.

 

The only way to know for sure is to pop the valve covers and have a look.

 

Keep in mind the specs are +/-6, so you are not in any trouble right now. I have 99 C2 w/144K miles. I recently checked my cam deviations and they were still within spec (I don't remember what they were).

 

Good to know. I will change them when it's convenient then. I will do an "engine out" later this year to do a bunch of preventative maintenance.

 

I checked my cam deviations with the Durametric and came up with -7.7 and -4.6.at idle. I'm not sure that the car was warmed up properly but it wasn't cold. I've read a few posts where people with high numbers replaced their pads only to find that the old ones weren't very bad.

How accurate is the correlation between cam deviation and pad wear?
Assuming the engine is out of the car for other work, what's a ballpark figure for a shop to replace the pads at the same time?

 

I think the cam deviations are related to the wear pads, chain stretch and tensioners. I know there are updated 1, 2, and 3 chain tensioners. That being said, I am by no means a master mind mechanic like Jake. Maybe Jake or Charles could weigh in. They are the experts.

 

I think the best indication of when to replace the vario chain guide pads is by watching the debris in the sump/oil filter.When a significant amount has been found they should be replaced.

The vario chain guide pads are colored tan or brown (different colors exist), the other chain guides for the IMS and long chains are black plastic.

The cam deviations can be caused by the initial settings not being precise, or by chain wear/stretch, so not necessarily a good indication of pad wear. The pads are cheap(like $20 bucks) so if your are ever in the vicinity, a good time to replace them.

 

As I wrote earlier. The ONLY way to be sue is to pull the valve cover everything else is just speculation.

 

I have found that the older I get, the more time I have to speculate, and the less time I have to pull things apart to just look. And that speculation ( with the proper background knowledge) saves a lot of labor and $$$. More times than not, my speculations are correct. YMMV

 

Nothing wrong with speculating but you need to verify. In this case, the owner will have to get his hands dirty or get his wallet out.

 

Thanks for the responses. I don't mind getting my hands dirty. I actually enjoy fixing broken stuff. I have rebuilt engines and transmissions in the past, although not an M96, and this work is not beyond my capabilities. I will definitely plan on taking the covers off and replacing the guides. I will dig this thread up in a couple of months when I do the work and post pictures of the guides along with the "after" deviation values.

 

Tensioner ?? FWIW ,, a couple of the guides cant be done just pulling the valve cover.. At least that is what it looks like in my Bentley manual.

 

 

You are correct that at least one of the tensioners cannot be replaced without major surgery in a 1999.

 

I'm hoping it's not a tensioner, given their price.