This was written by a man named Jim Allen (jimallen@onlinecol.com) and seems to be an excellent and authoritative description of the cam wear problem in our stock 3.5 liter Rover V8s. It's worth reading.
For about 4 years, while I worked at a Rover dealership ('87-93), we had a cam wear problem on 3.5L engines. It dated back a ways (prior to the USA intro), according to many sources, and was common on any engine with the "detox" or "low lift" cams (the NAS '87-88 3.5L had the low lift cams). To a much lesser degree, the other 3.5Ls were affected as well. A lot of cams were warranteed on 3.5L Rover engines from '87 until the last of those vehicles went out of warranty.
Most engines affected
We discovered the problem while repairing a rash of intake manifold coolant leaks. The bad lobes were often readily visible. After that we started checking when the engine was down. The earliest cam failure I saw was at 1,100 miles but I have torn apart about 50 NAS 3.5L engines in my career and only a handful did not show abnormal wear.
The 3.9, 4.0, 4.2 and 4.6L engines seem immune to the problem to a large degree, due to better designs and manufacturing. In the course of doing an article on cams a few years back, I queried 8 cam manufacturers, including some in the UK, about the problem. I was told it was due to two situations; the small diameter of the cam (which leaves less surface area when the profile is ground) and poor heat treating. Lack of maintenance, internal coolant leaks or subgrade oil made the problem worse. The surface area problem was solved by using more of the material in the blank when the cam was ground and the heat treating was improved.
Check with dial indicator
As to checking, the bad lobes can be identified visually but if you don't know what to look for by experience, you will only spot it when it gets very bad. The best method with an assembled engine is via a dial indicator. You will need to remove the rocker arms to do this, as the lifters will bleed down via valve spring pressure and give inaccurate readings. You can use the pushrods to measure from. Put the cam on the center of the heel to zero the dial and then rotate the engine to the peak lift point and record the results. Test each lobe a couple of times until you can dublicate the results exactly each time. Since the hardening is little more than .010-012" thick, if the readings vary more than that, lobe to lobe, you are into the soft stuff somewhere. Also, you can compare the reading to the lift specs in the manuals. If you have a cam out, you can mike the lobes, compareing differences between the lobes or to a new cam of the same grind.
Bad timing!
from Century Rover
As to checking timing chains, I tested the cam timing of about 30 vehicles in the course of my Rover dealership work. Any time I had the front cover off and had a few extra minutes, I checked with a degree wheel.
I was curious as to why one engine could be a rip-snorter and the next a dog. I found that only five or six of the engines I tested were at, or close enough to, the factory spec. About a third were advanced a few degrees (up to about 4 degrees- making them the rip-sporters) and the rest were retarded (the dogs) to varying amounts (up to 8 freaking degrees). Going farther, I checked to find where the errors came from and found that every cam I checked was dead on and the end result was that the timing gears were the cause. The keyways were machined incorrectly. After that, I did not trust the factory timing gear. The few (maybe two) I replaced under warranty (no, they would not replace the units for timing errors unless the engine was grossly effected), I checked for accuracy and swapped sets with the parts dept to get a good set. If the customer was buying, I installed a Cloyes True Roller set**. I know of one customer who could feel the difference, seat of the pants!
** You would be better off to consider a duplex chain other than
Cloyes. (Webmaster)