geostasis

I took my somewhat long in the tooth (1988) 911 to the shop earlier this week for a service and a new clutch. Since the engine was dropped anyway, I also asked for a valve adjustment since I have been getting some distinct clacking/ticking.

Got the call yesterday PM: one of the lobes on the right cam has a pit (wear?) and needs to be replaced. Since one needs to be replaced, I'm getting advised that I should replace both cams, all the rockers, all the chain rails, valve springs, and the valves.

I'm in 3K right now and would like to spread the repair cost over some time, so a couple of questions:

1) What is the risk of driving with a pitted cam lobe?
2) Would cam pitting cause excessive ticking, or should I be suspicious about other causes such as valve guide wear?
3) What questions should I be asking as I figure this out?
4) Are there any engine rebuild shops which are highly recommended for street vs race/track cars? Price is important, but not the only consideration.

I have the Wayne Dempsey "How to Rebuild and Modify Porsche 911 Engines 65 - '89" and will be reading it cover to cover this weekend.

Other stats:
* 1Qt Oil per 1000 miles or so
* Car is a weekender vs daily driver, but I do occasionally take longer trips

Thanks all

Rotten Robby

1.) there is no risk. The damage has already occurred.
2.) Yes, but you should be aware that this could be a combo of problems.
4.) In San Jose see Jerry Woods. In Oregon see Jeff Hines.

This was probably caused by improper cam break-in or improper geometry. That is why they are talking about replacing everything.
My advice, spend the money now.

Loaded

Im backin Robby here cam issues have always seemed to snow ball in to huge issues address it now

geostasis

Very much appreciate the info -- Scott

SeattlePorsche

I would take a picture of the damaged lobe and show it to the pro mechanics like Steve Weiner and Pete Zimmerman on the board first. They might say you can wait. Also, John Dougherty of Dougherty Racing Cams has a website. I am sure you could email him a photo for another opinion.

Having said that, I showed them all (SW and PZ) my cams and they said to remove it, so I went the regrind route. My friend John Walker told me he sees some wear on cams during valve adjusts and he doesn't always think removal at the time is necessary. But I think, sadly, it is just a matter of time.

SW told me it is from a combination of heat and dirty oil, and today's crappy oil formulations. SW told me I only needed to regrind the cams and rockers. They only take off 3 thousandths from the rockers. My cams were ground to a different profile so JD took off 15 thousandths max.

The advice that you should replace everything seems a bit harsh. You either have a tremendous amount of damage, or your mechanic is just being over conservative. Cams can be reground for 245$, rocker faces reground for 40$. I don't know why they want you to replace all the valve springs and valves. Good luck!

Daniel Dudley

The risk of driving with a pitted lobe is that you will ruin the cam, and possibly spread metal. Talk to the big boys.

If I thought I might get 20+ K on my guides, I might do them now or I might wait on that . I know I spent a lot of money on a valve job on a 928, much more than the head gasket replacement warranted. In the end it ran the same. When I was younger, a lot of the 6 cylinder Jag boys used to say if it uses a little oil, you know the oil is getting everywhere. Made them feel better. I have seen some really stout engines that ran a little oil past the guides, and had good compression.

The big boys will know what to tell you.

Steve Weiner-Rennsport Systems

Correction: (3) Jeff Hines is in Seattle,...good guy, too.

Rotten Robby

Thanks for the correction Steve... I have a Jeff Hines motor in my 914-6 conversion... I met him in Portland and I just assumed....

pjc

Depends what you mean by "pitting". If its gone through the hardened surface there is only one solution - replace; a re-grind is no good to you. Followers etc should be OK. Having got the engine down this far I would look at everything else - certainly replace chains and followers, no point in not and relatively cheap.

You definitely need advice on how far the cams have gone.

Had a new pair ground by John Dougherty - great guy, offered lots of technical info on the process, billets, machine he uses etc.

PJC

Peter Zimmermann

Your risk factor is low, but once hard metal starts coming apart those tiny bits start circulating inside the engine, which is never a good thing. Regarding doing a valve job, your consumption is perfect so don't bother. Your valve train noise is a chicken or egg thing. It's quite possible that lousy valve adjustments are responsible for both the noise and pitting. If rockers are left too loose they will slap the cam, accelerating the wear. Also, crummy oil can factor into the situation as well, as can aggressive driving with a cold engine. Cam replacement can be done with the engine in the car, and in many cases rocker arms can be re-faced and used again. While the cams are being replaced the chain ramps (aka guides) are easily accessible. Again, if your oil consumption figure is accurate it's possible that your engine (valves/guides) still has many thousands of miles of life left. If your consumption was a quart/300 miles or worse I'd say take it apart, but in your case I just don't see a need. Regarding new vs. re-ground cams, apparently improvements have been made to the process since I sold my shop. You should have a long talk with Steve W. about your engine, and the variables involved!
Pete

Doug Hillary

Hi,
just to add another dimension and without seeing any pictures of the cams in question, most cam pitting commences as a result of corrosion. It is a common problem in low use engines of almost any make

Using an engine lubricant with a high Total Base Number (TBN) and changing the oil as the Manufacturer recommends is the best insurance. Pitting does NOT show up on in a Used Oil Analysis (UOA) but can often be detected by cutting open the oil filter at oil change time and inspecting its contents

Many 928 engines (especially GTs) have pitted cams and have been used with this condition for several years where no associated wear is evident (eg the cam still has a "normal profile within limits". Cam pitting is not always associated with cam wear as we normally know it - it can be said it is "damage" rather than wear in most cases

Regards