Diesel RVs: Re: [diesel_mercedes] Fuel Economy, Power & Cam Timing

Well, yeah; dial indicators and degree wheels and all that stuff can let you know exactly where your cam timing is at, and I've done it that way, too. But you can be sure that any, and I mean ANY engine with 150,000 miles or more on it will have a stretched timing chain, and the longer the chain the more the stretch. You can put in a 3- to 4-degree offset key in these engines without worrying about going through that whole degree-ing procedure.

As far as difficulty, I would rate this job somewhere below setting the valve lash:

Once the cam cover is off, move the crankshaft to where the number cylinder is at TDC, and use baling or other type of wire through the holes in the cam gear to hold the chain at the top of the gear. Release the chain tension by removing that big nut-like thing just forward of the manifold assembly, and take out the spring and plunger that's inside. Remove the cam gear bolt. This could be the most difficult step. I use a long wrench and a good sized hammer to strike the wrench and pop the bolt loose. They've always come right off, in my experience. What you don't want is for the engine to turn over. Not that anything will be damaged if it does; it's just that the bolt is not coming loose. Now the cam gear will come right off with maybe just a tap or two from behind. Remove and replace the Woodruff key, making sure the offset is installed such that the camshaft itself will be a clockwise in relation to the gear. Then, reassemble, moving the crankshaft just enough to allow the cam gear to slip back on. There is a torque specification for the cam gear bolt; don't tighten it until after the tensioner is re-assembled. Again, I use the long wrench, and give a couple of quick, medium-hard strikes to secure the bolt. There isn't a lot of tension on it, and the torque specification isn't critical. Oh, and don't forget to remove the baling wire....

Mark (currently) in Clearwater, FL (returning to Covid-free Centennial, CO today)

On 06/26/2020 11:14 AM Nate vwnate1@yahoo.com [diesel_mercedes] <diesel_mercedes@yahoogroups.com> wrote:

Yes Mark, you did ;

The thing is : I'm not comfortable fooling with the OHC, I worry I'll screw it up or damage things .

I'm keenly aware that cam timing is critical and shuffle keys offer the solution .

The V-8 Hot Rodders did this all the time using dial indicators to make sure they had the timing perfect .

I have never done it .

-Nate

LIVE in the world as it is, WORK to make the world as it should be

Rob wrote :

Mark

Thanks for the reminder.

Cam timing is on my to-do list. I already bought a 4* offset key, so next time I get in there, I'll swap it out.

Rob

MARK wrote :

I've said years ago what the problem is, Nate. Cam timing. Anyone who's had to advance their Injection Pump timing has proven to themselves that their timing change has stretched. Setting the IP is doing only half the job. Now, both of you, check the position of the timing marks by setting the crankshaft at "0" with both of the valves at cylinder one closed, and see where the notch on the camshaft timing gear is in relation to the notch on the first camshaft bearing tower. The woodruff keys are available in one degree increments up to 5-degrees. They're available from autohausaz.com; part numbers are:

6219910067 - 5-degrees

6219910167 - 4-degrees

6219910267 - 3-degrees

6219910467 - 2-degrees

Make a guess as to the number of degrees it's off, then, get the off-set key, and install it such that the camshaft is now a bit clockwise from where it was originally. I wouldn't go any less than 3-degrees, maybe 4, as these engines with the mileages they've covered are going to be at least that much off. AND, having the camshaft a bit advanced doesn't hurt anything.

If you had to make a big adjustment to the IP to get it timed correctly (like 10-degrees? WOW!), you may want to first advance the camshaft gear a whole tooth on the chain, then recheck the position before installing the offset key, retarding the camshaft back to get it to the desired position.

If you think advancing the IP improved mileage and power, wait till you see what happens after you get the camshaft correct in relation to the crankshaft.

Mark in Centennial, CO

1979 300SD (27 mpg combined, with 4-degree offset camshaft timing key)