No key on camshaft drive sprocket?

Color me surprised on my 1998 Jetta A3 AHU, but I just pulled the drive sprocket off of the cam shaft and was amazed that there was no key between the gear and the camshaft. Why not? The camshaft has a key slot in it, and everything about this motor requires exact alignment between the cam and the crank or very expensive events take place, yet there is nothing in there as insurance. That seems strange.

Any idea why VW would choose to do it that way? Because it gives you a little more leeway in how the injection pump is timed in it's relation compared to the cam and motor or just because they can't control the distance from the crank or something like that?

Is it typical to loctite the cone or bolt with anything stronger than blue loctite? Has it ever slipped on anyone because the camshaft bolt got loose? Mine wasn't super tight, maybe 40 ft lbs when I took it off and there is no kind of locking washer under it. If that bolt ever backed out 1/2 turn, it would all fall apart rather quickly.

Just seems like a good place to go with a little extra insurance...

Assuming that your car is like my 2003 which also does not have a key all is good. Refer to your Bentley repair manual and www.Metalnerd.com and www.ross-tech.com for tools to properly set up your new timing belt. Many vendors have a deluxe timing belt kit for your car. Same kit for 98-03 so I am going to assume your car is like mine. No Loctite, no lock washer. design has worked fine for many engines. That pulley should require a pulley puller to pop off the tapered fit sprocket.

It's a cone/tapered fitting between the cam and sprocket. Use the proper lockdown tools, run the timing belt around the crankshaft and injection pump, then also the tensioner and place the cam pulley in the belt and fit it to the end of the camshaft.

Before tightening the bolt on the end of the cam, set the tensioner at the correct tension, then tighten down the bolt (official manual calls for only 33 ft-lbs, Frank06 and others on the forum prefer 45 ft-lbs for various reasons...). This allows the belt to be under the least amount of stress. The teeth aren't loading up in on direction or another so much. This is important with a belt that is under so much stress from fighting 19.5:1 compression and also has to drive a very high pressure fuel injection pump.

After you get it all set, remove all the locking tools and rotate the engine by hand twice. Then lockdown the cam and injection pump again, double check how close the TDC mark is. If the cam locking plate does not slide in and out very easily when you're perfectly at TDC, rotate the engine so the cam plate does slide in and out easy, then loosen the cam pulley bolt, but don't remove it (using the counterhold tool, NEVER allow the locking plate to take up the torque) and knock the pulley off the taper again using a punch through the access hole. Then go ahead and rotate the engine to exactly on the TDC mark, then re-torque the cam pulley (again you must use the counterhold tool).

Remove locking tools and rotate the engine again. Double check locking tools vs. TDC mark once again, this time it should be perfect. If not, repeat steps above until it is.

Chubber said:

....everything about this motor requires exact alignment between the cam and the crank or very expensive events take place,...
Any idea why VW would choose to do it that way? ...

Click to expand...

because it requires exact alignment, that's why. A key with one fixed position isn't exact enough.

The 40 lb*ft on the thread is multiplied by the helix to a greater force pulling the bolt head towards the cam shaft. Then the taper effect further increases the friction fit between the sprocket and cam. That 40 lb*ft torque is multiplied many times over by the combined forces of fine threading and taper. Do NOT overtighten that cam bolt. The stressing forces imparted on the sprocket from exceeding it can crack it.

p.s.: I believe the factory torque on that bolt is closer to 35 lb*ft...

Matt-98AHU said:

After you get it all set, remove all the locking tools and rotate the engine by hand twice. Then lockdown the cam and injection pump again, double check how close the TDC mark is. If the cam locking plate does not slide in and out very easily when you're perfectly at TDC, rotate the engine so the cam plate does slide in and out easy, then loosen the cam pulley bolt, but don't remove it (using the counterhold tool, NEVER allow the locking plate to take up the torque) and knock the pulley off the taper again using a punch through the access hole. Then go ahead and rotate the engine to exactly on the TDC mark, then re-torque the cam pulley (again you must use the counterhold tool).

Remove locking tools and rotate the engine again. Double check locking tools vs. TDC mark once again, this time it should be perfect. If not, repeat steps above until it is.

Click to expand...

Matt, thanks, that is what I figured. You just did a better job of explaining it in writing. It's to allow it to be set just right and even out manufacturing tolerances in the engine.

In aircooled VWs you can do the same thing with special washers for the cam-to-gear that are slightly off-center. But that isn't as accurate.