Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help




Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Diesel Discussion

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 05-11-2009, 04:14 AM
Registered User
 
Join Date: Jul 2007
Posts: 517
Timing chain and replace vac pump at same time?

Hi folks,

I don't plan on doing the timing chain work, but I may attempt to check the stretch myself. Also, I have not looked at the R&R work for the vac pump, but I don't imagine it would be difficult. That might be something I'd do.

My question is should both be done at the same time or can one be done and then the other done later?

Bob
Reply With Quote
  #2  
Old 05-11-2009, 11:16 AM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
it is 100 times easier and safer to roll in a new chain with the vacuum pump removed
__________________

Reply With Quote
  #3  
Old 05-11-2009, 11:19 AM
vstech's Avatar
DD MOD, HVAC,MCP,Mac,GMAC
 
Join Date: Mar 2006
Location: Mount Holly, NC
Posts: 26,198
Quote:
Originally Posted by jt20 View Post
it is 100 times easier and safer to roll in a new chain with the vacuum pump removed
Why?
__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!
Reply With Quote
  #4  
Old 05-11-2009, 11:22 AM
compu_85's Avatar
Waiting for his Model 3..
 
Join Date: May 2008
Location: Springfield VA
Posts: 5,174
You can see you've got it seated on the IP's cog easily I suppose.

-J
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000).

2013 Fiat 500E. 20,000 miles, 80 miles at a time.
2012 Passat TDI. 95,000 miles. More space, power, and fuel economy than the Benz
2004 Touareg V10 TDI. 150,000 miles. One of 450.
1999 Jetta TDI. 310,000 miles.
1992 Jetta ECOdiesel. 156,000 miles. 1 of 48. Sold.
1991 Jetta ECOdiesel. 430,000 miles. 1 of 700. Sold to VeeDubTDI, totaled in front of our house
Reply With Quote
  #5  
Old 05-11-2009, 11:22 AM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by jt20 View Post
it is 100 times easier and safer to roll in a new chain with the vacuum pump removed
I have the same question............why?
Reply With Quote
  #6  
Old 05-11-2009, 11:26 AM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
the force from the vacuum pump on the timing gear pulls the chain down into the recess causing many of the well-known inaccuracies.

if this, and compression are removed, the timing chain is under complete control by the movement at the crank only (and the chain's own weight, of course..).
__________________

Reply With Quote
  #7  
Old 05-11-2009, 11:31 AM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
Quote:
Originally Posted by compu_85 View Post
You can see you've got it seated on the IP's cog easily I suppose.

-J

the chain cannot come off the IP gear unless the entire set of safety pins is removed. I believe there are two and one bolt on the side of the casting facing the fender.
__________________

Reply With Quote
  #8  
Old 05-11-2009, 12:07 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by jt20 View Post
the force from the vacuum pump on the timing gear pulls the chain down into the recess causing many of the well-known inaccuracies.

if this, and compression are removed, the timing chain is under complete control by the movement at the crank only (and the chain's own weight, of course..).

Is it the vacuum pump...........or just the compression of the engine?

I agree that the elimination of the "forward jump" is desirable.
Reply With Quote
  #9  
Old 05-11-2009, 12:13 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
it is certainly both*.. but the vac pump is not mentioned in the manual. So anyone following the manual (as a novice) will not be aware of this force.

Manual says to remove the glowplugs and tensioner.

If you happen to set your engine in such a way that one of the two lobes on the timing gear are near the max compression of the VP bellows, you will find a considerable opposing force.

People doing this for the first time will not imagine that pulling up with force is a good idea to remove slack thus created.


*this is not to say that the crank will jump forward at the speeds involved
__________________


Last edited by jt20; 05-11-2009 at 12:26 PM. Reason: added clarity
Reply With Quote
  #10  
Old 05-11-2009, 12:33 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by jt20 View Post
it is certainly both*.. but the vac pump is not mentioned in the manual. So anyone following the manual (as a novice) will not be aware of this force.
Where is this opposing force coming from? Is it from the vacuum in the system? If so, the system could simply be opened and the lack of any vacuum would kill that deal in a hurry. Why bother to remove the pump?
Reply With Quote
  #11  
Old 05-11-2009, 12:37 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
you would have to APPLY vacuum to the pump in order to remove the force of the spring on the IP gear lobes.
__________________

Reply With Quote
  #12  
Old 05-11-2009, 12:44 PM
Banned
 
Join Date: May 2002
Location: Blue Point, NY
Posts: 25,396
Quote:
Originally Posted by jt20 View Post
you would have to APPLY vacuum to the pump in order to remove the force of the spring on the IP gear lobes.
Well, in that case, you'd definitely need to remove the pump.

I'm curious as to whether the pump can push back on the chain, and drive the engine backward during the process and thereby cause an issue with the feed of the new chain.............the act of compressing the spring will simply require more force at the crankshaft, but won't create any catastrophe if the engine doesn't move in reverse.

I've not encountered the desire of the engine to move in reverse when it's slowly advanced to set the valves. The speed of rotation might be the issue here.
Reply With Quote
  #13  
Old 05-11-2009, 01:42 PM
sasquatchgeoff's Avatar
Cascade Foothill Lurker
 
Join Date: May 2007
Location: Portland, OR
Posts: 561
My experience (which is "once") is that the pump makes the crank that much more difficult to turn, at least when the lobes of the timing gear are pushing on the spring of the VP. The process of threading the chain is already so precarious that an extra amount of opposing force creates conditions where error is more likely - when the opposing force releases is a moment where the ill-prepared could make mistakes. Forward rotation of the chain/sprockets can cause the chain to jump teeth as well - especially if the MB chain retainer tool is not used as is the case with most of us. Many variables have to be taken into account and prepared for so that the chain can be replaced with maximum accuracy. For me, removal of the vacuum pump is insignificant on this scale of importance.
__________________
327K on 1986 W201, 602.911, 722.414 2.5 190D ("The Red Baron")
139K on 1993 W124, 104.942, 722.433 2.8 300E ("Queen")

http://farm5.static.flickr.com/4081/...0bb92d3c_m.jpg http://i370.photobucket.com/albums/o...g?t=1325284354

Do not worry about your difficulties in Mathematics. I can assure you mine are still greater.
- Albert Einstein

take a walk down memory lane...
Reply With Quote
  #14  
Old 05-11-2009, 02:10 PM
ForcedInduction
Guest
 
Posts: n/a
Quote:
Originally Posted by jt20 View Post
the force from the vacuum pump on the timing gear pulls the chain down into the recess causing many of the well-known inaccuracies.
The injection pump, compression/expansion and the camshaft has far more to do with that than the vacuum pump.
Reply With Quote
  #15  
Old 05-11-2009, 03:51 PM
Registered Hack
 
Join Date: Mar 2008
Posts: 4,612
Quote:
Originally Posted by Brian Carlton View Post
Well, in that case, you'd definitely need to remove the pump.

I'm curious as to whether the pump can push back on the chain, and drive the engine backward during the process and thereby cause an issue with the feed of the new chain.............the act of compressing the spring will simply require more force at the crankshaft, but won't create any catastrophe if the engine doesn't move in reverse.

I've not encountered the desire of the engine to move in reverse when it's slowly advanced to set the valves. The speed of rotation might be the issue here.

I am not advocating the removal of the VP for chain renewal procedures. Just to fulfill the OP's Question.

I doubt the VP can pull the crank backwards, but it will definitely put tension on the chain along that length (from crank to timing gear)

But I see what you're getting at with the speed of rotation.. compression must be removed to avoid this.

If all precautions are met, and the installer makes no error in turning the engine and laying the new chain on the cam sprocket, this force is negligible.

..it is when a small mistake is made in laying the new chain and removing the chosen clamps from the sprocket that this force becomes an obstacle. The installer pulls on the chain until it is taught, not until he overcomes said force and removes ALL slack on the IP side of the engine.
__________________


Last edited by jt20; 05-11-2009 at 04:11 PM.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On




All times are GMT -4. The time now is 10:37 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page