Valve Adjustment Clarification - PeachParts Mercedes-Benz Forum

leathermang · #1 08-20-2014, 10:20 AM

The CAM NUT is stong enough to rotate the engine with....
The REASON not to use it is that the whole system is designed with respect to keeping the timing chain tight between certain points in the rotation... the slack being addressed on the passenger side of the engine by a combo spring,ratchet and oil pressure.
This is why the FSM specifies that when ' rolling in' a new chain pressure is to be kept on the combined chains...
If you use the CAM NUT then you are PUSHING A CHAIN... thus not keeping the designed tension on the side of the engine meant to keep the chain in contact with the sprocket of the timing pump and things like chain rails.
We have had many reports from people who thought they ' just replaced' the chain... and found the timing pump a tooth off afterwards...
But some people do not believe the FSM.... after all it was only written by the people who built the car...
TCane and I spent an hour taking a PS nut off a car he bought ....with oxy acet and many heatings and lots of force..... that is when we found out it was tapered...

funola · #2 08-20-2014, 11:34 AM

Quote:

Originally Posted by leathermang

....................
TCane and I spent an hour taking a PS nut off a car he bought ....with oxy acet and many heatings and lots of force..... that is when we found out it was tapered...

OK so you have verified the PS nut is tapered. Usually a taper is used for an application where precise timing is needed such as in a VW camshaft or injection pump shaft. Why was a taper used for the Mercedes PS pump?

ROLLGUY · #3 08-20-2014, 11:55 AM

I don't know what the big deal is about using the PS pump pulley. I have never had to remove a PS pulley, and don't ever plan to do so. It is not worth the effort to rebuild a PS pump when there is so many good ones available. Like most everything else on these cars, it is designed and built very well, and should last the life of the car (in most cases they do). I have had almost 30 of these cars, and only once have had a leaky PS pump that needed fixing/replacement. I have several laying around, so finding a replacement is not hard. I would not bother removing the pulley for any reason, I would just replace the entire pump. As far as using the crank pulley over the PS pulley, most always I am able to use my 27mm deep socket on a 1/2" ratchet just fine. If I do it just right, it stays on the bolt and does not fall off while I am adjusting valves. In fact, it has happened several times that I left it on the crank bolt and started the engine minutes later after putting everything back together. I have gotten the valve adjustment down to about a half hour total now. The times I can't use the crank bolt, I used the PS pulley and it worked just fine. I see no problem with doing it whatever way works best (easiest). I am not going to NOT use the PS pulley bolt for fear that I won't get the pulley off, because I probably will not ever have the need to remove the pulley in the first place........Rich

mach4 · #4 08-20-2014, 01:14 PM

Quote:

Originally Posted by ROLLGUY

I don't know what the big deal is about using the PS pump pulley. I have never had to remove a PS pulley, and don't ever plan to do so. It is not worth the effort to rebuild a PS pump when there is so many good ones available. Like most everything else on these cars, it is designed and built very well, and should last the life of the car (in most cases they do). I have had almost 30 of these cars, and only once have had a leaky PS pump that needed fixing/replacement. I probably will not ever have the need to remove the pulley in the first place........Rich

I'm with ROLLGUY on this one. I've got a spare pump (actually an entire spare engine) so dealing with a failed pump is a simple swap...nothing to do with swapping a pulley.

leathermang · #5 08-20-2014, 12:16 PM

Quote:

Originally Posted by funola

OK so you have verified the PS nut is tapered. Usually a taper is used for an application where precise timing is needed such as in a VW camshaft or injection pump shaft. Why was a taper used for the Mercedes PS pump?

Actually I think that where precise timing is needed a key is more often used..
A tapered (friction ) fit is often used to protect something in the power line...as with using the friction of a Morse Taper in a lathe... where you WANT it to give way under certain drastic situations and limit the damage by letting the power go on down the line..

funola · #6 08-20-2014, 12:49 PM

Quote:

Originally Posted by leathermang

Actually I think that where precise timing is needed a key is more often used..
A tapered (friction ) fit is often used to protect something in the power line...as with using the friction of a Morse Taper in a lathe... where you WANT it to give way under certain drastic situations and limit the damage by letting the power go on down the line..

For timing a VW diesel engine, the cam nut is left loose while engine is rotated to TDC before the cam nut is tightened. In the VW, the taper on the cam is for precise timing, not for protection of the cam, which bends valves and breaks the cam if the engine goes out of time for whatever reason. The taper IMO is for precise alignment of the pulley for less pulley run out and wobble, same reason the morse taper is used in morse taper drill bits.

leathermang · #7 08-20-2014, 02:12 PM

Quote:

Originally Posted by funola

For timing a VW diesel engine, the cam nut is left loose while engine is rotated to TDC before the cam nut is tightened. In the VW, the taper on the cam is for precise timing, not for protection of the cam, which bends valves and breaks the cam if the engine goes out of time for whatever reason. The taper IMO is for precise alignment of the pulley for less pulley run out and wobble, same reason the morse taper is used in morse taper drill bits.

Well, you don't believe the Mercedes people who wrote the FSM...
and you have not been reading the same books on machine design that I have.. or you did not believe them either...
I can't help you under those conditions.

Bio240D · #8 08-20-2014, 02:41 PM

Hi Everyone!
Regarding the valve adjustment procedure, the base circle on these camshafts is Not really a circle at all. This means that you cant really set the valves with the lobe pointing randomly away from the follower (ie the 90deg method). It needs to be in a specific position.
I set mine one lobe at a time with the lobe pointing at the oil squirter tube.

I would suggest that you prove to yourselves my statement about the base circle not really being round, and it is very easy to do. First, Set the valve clearance with the lobe pointing at the tube. Then rotate the cam untill it is pointing Straight up or about 11 oclock. Check your valve clearance again! It will be quite different! Then turn the cam slightly past the tube, say 2 oclock. Once again, check the clearance, and it will be different. Please don't just take my word for this, but rather actually do the experiment next time you set the valves. I wish the FSM was a little more specific about EXACTLY what position the lobe should be in to set the clearance, but, sadly it is not.

I hope this helps!
Cheers!
Chris

leathermang · #9 08-20-2014, 02:52 PM

Quote:

Originally Posted by Bio240D

I would suggest that you prove to yourselves my statement about the base circle not really being round,
I hope this helps!
Cheers!
Chris

OR they could just assume that the Factory Shop Manual specifies a certain procedure for a good reason... LOL

vstech · #10 08-20-2014, 02:57 PM

You are correct, on a worn cam there will be various degree wear that is why I said "on a cam that is not damaged" the reason the FSM doesn't specify position is because when the car is built there is a perfect base circle for the cam...

Quote:

Originally Posted by Bio240D

Hi Everyone!
Regarding the valve adjustment procedure, the base circle on these camshafts is Not really a circle at all. This means that you cant really set the valves with the lobe pointing randomly away from the follower (ie the 90deg method). It needs to be in a specific position.
I set mine one lobe at a time with the lobe pointing at the oil squirter tube.

I would suggest that you prove to yourselves my statement about the base circle not really being round, and it is very easy to do. First, Set the valve clearance with the lobe pointing at the tube. Then rotate the cam untill it is pointing Straight up or about 11 oclock. Check your valve clearance again! It will be quite different! Then turn the cam slightly past the tube, say 2 oclock. Once again, check the clearance, and it will be different. Please don't just take my word for this, but rather actually do the experiment next time you set the valves. I wish the FSM was a little more specific about EXACTLY what position the lobe should be in to set the clearance, but, sadly it is not.

I hope this helps!
Cheers!
Chris

funola · #11 08-21-2014, 08:01 AM

Quote:

Originally Posted by Bio240D

Hi Everyone!
Regarding the valve adjustment procedure, the base circle on these camshafts is Not really a circle at all. This means that you cant really set the valves with the lobe pointing randomly away from the follower (ie the 90deg method). It needs to be in a specific position.
I set mine one lobe at a time with the lobe pointing at the oil squirter tube.

I would suggest that you prove to yourselves my statement about the base circle not really being round, and it is very easy to do. First, Set the valve clearance with the lobe pointing at the tube. Then rotate the cam untill it is pointing Straight up or about 11 oclock. Check your valve clearance again! It will be quite different! Then turn the cam slightly past the tube, say 2 oclock. Once again, check the clearance, and it will be different. Please don't just take my word for this, but rather actually do the experiment next time you set the valves. I wish the FSM was a little more specific about EXACTLY what position the lobe should be in to set the clearance, but, sadly it is not.

I hope this helps!
Cheers!
Chris

Whenever I check valves clearances, I always check a few at different points of the base circle (valve pointing up or at the oil rail) and found no difference. This was with cars in my sig. Small sample size but data nevertheless.

funola · #12 08-21-2014, 07:50 AM

Quote:

Originally Posted by leathermang

Well, you don't believe the Mercedes people who wrote the FSM...
and you have not been reading the same books on machine design that I have.. or you did not believe them either...
I can't help you under those conditions.

Help? I did not ask for help. Maybe you are confusing me with someone else? We were discussing why a taper was used on the PS pump and you go on a rant that I do not believe in the FSM and that I have not read the same books you have been reading.

leathermang · #13 08-21-2014, 08:13 AM

Quote:

Originally Posted by funola

Help? I did not ask for help.

You asked me why a taper was used on the PS Pump.

and I said I do not know specifically about that..but that in machine theory books I have encountered... one use of the friction taper involves protecting the tool from unexpected problems in the material being dealt with... as an example you can see that a set of Silver and Deming drill bits used by the typical post drill of old times.... all the drill bits had the same size shank.. and a flat on one side... this fit quickly and accurately into the hole in the drill shaft... which had a lock bolt to keep the drill bit in place... a fast and accurate change of bits was thus accomplished..
BUT... if you hit something hidden in the drilled item... it broke the drill bit... or stripped cogs from a gear... or burned a flat on the drive belt...
Most people who need help do not realize they need help.

Here is one possible guess as the the thinking of the MB engineers.... they saw the ps pump as something which could lock up... and ruin the belt driving it... and did not want the ps pump to be an Achilles Heal in terms of the car making it home... or to safety... as the car can be steered ( with great effort )without the power steering pump working...
So they put a emergency slip clutch into the drive line of the PS pump.