Another valve adjustment question

[jedwards]

I am adjusting the valves on my early 250SL which has travelled 60,000 miles so there is some normal wear on the cam lobes and the tappet faces to be expected.
I have a good set of 13mm wide feeler gauges but these are not wide enough to cover the entire surface, so I have a centre zone on each cam that reads slightly loose and edges that read slightly tight.    These differences are not large, perhaps ½ thou, but there is a difference.
How should I set them up?
According to the centre or according to the edges?

Jeff

[stickandrudderman]

Set them up at the centre and you'll be fine.

[jedwards]

From what Dr Benz has written on the subject, plus your comments, suggests it I should should tighten them until the gauge is well trapped in the centre and then back them off until it just pulls free.

If that is correct conclusion, then I have mine clearances far too wide at the moment.

jeff

[stickandrudderman]

Yes, the force required to extract the feeler guage is relatively high compared to other cars when the gap is correct. Do this with a Ford engine and you'll have rough running.

[garymand]

There should be a 'slight but significant' pull force or drag as you slide the feeler out. I've never measured the pull, but compared to pulling a trigger, I think its a few onces.  I always go a little too tight first, snug the feeler so it on't move unles I yaw the feeler(move you hand sideways and pull to get it to move.  then back it off until I can just pull the feeler out without horizontal rotation.  the cam lobes never wear perfectly flat, so ther is a valley and a hill filling the valley.  You are working the feeler between the two slightly 'un-flat' surfaces.  Very normal that it isn't flat on both sides cam lobe wear.   One surface will always be just a little softer and wear a little faster and the two surfaces adjust to each other.   No biggy, you are feeling ~.000X inch and it won't make much effect, but for consistancy between the valves, use the same amount of pull force to drag the feeler out and don't be afaid to go back and check each one. 

AND, the balls wear into the rockers, so if you haven't turned the balls in a long time, you may find the valves are a little loose again in a few K due to the re-mating of the ball serfaces. 

[Benz Dr.]

I kind of look at how the cam and the rockers look. If they're smooth I will set them fairly tight./ If there's some roughness I set them even tighter. On worn engines that require .007 I sometimes use a .006 feeler and set it so so it slides through nicely without much drag. If I set this same engine to .007 as perscribed it will end up being .008 or more sometimes. Anything more than .008 and you will hear it start to make noise.
Remember,you will not be able to hear a tight rocker arm. If the engine has been in service for a while, a light film will form on the base circle of the cam lobe. If the lobe is clean and shiny all the way around, you're way too tight!

[jedwards]

Fantastic advice and really helpful.
Many thanks to you all.
Jeff

[ja17]

Pull your valve adjustment wrench off and away from the adjuster for the final feeler gauge measurement. The wrench can alter the measurement if it is in place.