M108 Valve adjustment procedure?

[muleears]

I want to adjust the valves on my '67 250 S (M108). I have searched and can't find the procedure or proper clearances anywhere. Is it not posted here, do I just need a repair manual? I adjust my own valves on my diesels so I think I have the skill needed. Just not the instruction. I have learned I need a special wrench. Any direction is appreciated.

[muleears]

I'm guessing it is straightforward. I remove the valve cover, loosen the locking nut (with the special wrench) adjust to proper clearance with another nut and re-tighten. Am I far off, or does it use shims for the adjustment?

[daidnik]

There are no locknuts. The cam followers sit on top of the valve on one side and on top of a 'ball pin' on the other side with the overhead cam sitting over the cam follower. The friction mechanism for keeping the ball pins in place is two sets of external threads on the ball pin that are slightly out of phase, thus when these two sets of threads are simultaneously engaged in the ball pin seat, there is friction. Friction enough so that they can and should be rather hard to turn, and with the carbs on one side, there isn't a lot of clearance to get a spanner in there. Thus the special tool for adjusting these has a crows foot bottom and and a sort of offset extension to go around the end of the cam follower and connect with a driver. You'll need that tool to do the job. The size is 17mm. I've not found the standard Sears type crowfoot spanner bit to be satisfactory at all; they tend to spread open under the required torque and lead to rounding of the hex on the ball pins and that's a problem you don't want to have.

Clearances between cam and follower is usually set COLD.

Exhaust: 0.008 inch

Intake: 0.004 inch

I always make two passes, adjusting only Intakes on one and only Exhausts on the other. You don't want to mix any of them up as a tight Exhaust adjustment WILL lead to problems.

When adjusting, you also need to look for cam followers worn thru the hardening by the cam. These will have lines/steps worn into that surface that will make the feeler gauge sticky/loose as you slide it back & forth in the direction of the axis of the cam.

Worn followers will eventually cause wear on the cam lobes and that's an expensive repair. The cam followers alone are ~$30 apiece. Finding 3 or 4 bad ones on a 40+ year old motor is not unexpected.

[muleears]

Originally Posted by daidnik

There are no locknuts. The cam followers sit on top of the valve on one side and on top of a 'ball pin' on the other side with the overhead cam sitting over the cam follower. The friction mechanism for keeping the ball pins in place is two sets of external threads on the ball pin that are slightly out of phase, thus when these two sets of threads are simultaneously engaged in the ball pin seat, there is friction. Friction enough so that they can and should be rather hard to turn, and with the carbs on one side, there isn't a lot of clearance to get a spanner in there. Thus the special tool for adjusting these has a crows foot bottom and and a sort of offset extension to go around the end of the cam follower and connect with a driver. You'll need that tool to do the job. The size is 17mm. I've not found the standard Sears type crowfoot spanner bit to be satisfactory at all; they tend to spread open under the required torque and lead to rounding of the hex on the ball pins and that's a problem you don't want to have.

Clearances between cam and follower is usually set COLD.

Exhaust: 0.008 inch

Intake: 0.004 inch

I always make two passes, adjusting only Intakes on one and only Exhausts on the other. You don't want to mix any of them up as a tight Exhaust adjustment WILL lead to problems.

When adjusting, you also need to look for cam followers worn thru the hardening by the cam. These will have lines/steps worn into that surface that will make the feeler gauge sticky/loose as you slide it back & forth in the direction of the axis of the cam.

Worn followers will eventually cause wear on the cam lobes and that's an expensive repair. The cam followers alone are ~$30 apiece. Finding 3 or 4 bad ones on a 40+ year old motor is not unexpected.

Thanks Daidnik, that's some valuable information for me. A couple questions though; I looked at the "specialty tools" section of Fast Lane and they had two Mercedes valve adjustment wrenches, one 17mm it said was for the V8's and one 14mm for the "early six cylinder models". Which should I use? I'm assuming the 14mm? Second question; a standard crows foot wont work because it won't fit around the cam follower? Do I need a MERCEDES brand tool or do others make them? How long should this job take, with the right tool? Thanks again.

[daidnik]

The only ones I've seen with the 14mm size were earlier like on the W111 cars of the early 60's.

A quick removal of the valve cover will answer the question definitely as you'll be able to get a spanner on some to check fit. You just won't have enough range of movement to turn the ball pins.

[white280SE]

I had to cut a spanner ( cheap China ) and weld it to a bolt this then worked a treat.. ( just the open ended part )

Car was quite and much better ... just the valve guide then went 200 miles later but that's due to plonker mechanic that ripped the old girl off for $3000 of head work :-/ grrrrr