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 ShopForum > Technical Information and Support > Tech Help

Reply
 
LinkBack Thread Tools Display Modes
  #1  
Old 02-27-2003, 12:39 PM
jmdunn
Guest
 
Posts: n/a
No compression on cylinder #8. Will this cause no start?

My timing chain jumped a couple of teeth on the left cylinder head because of a bad tensioner. I replaced the tensioner, rails, and gears inside and outide the timing cover(huge job). The chain has 40,000 miles and shows no stretch. Timing marks on both cams line up when the harmonic balancer points to 0 degrees. I tried to start the car and allit would do is pop and backfire. So I checked the distributor rotor was pointing to the #1 plug wire at 0 degrees on the harmonic balancer and both cam lobes pointed upward. Still no start. Now the heart wrenching part. I checked compression on the cylinders. All show 145-150 psi in 20 degree outside temperature with new10W-40 oil except #8 which is not showing any compression at all. How bad is the damage likely? Is this compression normal. It was around 125-130 psi on all cylinders last fall when I checked but the engine was warm and the air temp was around 60 degrees?

Thanks again,
jmdunn

Last edited by jmdunn; 02-27-2003 at 12:50 PM.
Reply With Quote
  #2  
Old 02-27-2003, 12:48 PM
WRM WRM is offline
Registered User
 
Join Date: Jun 2002
Location: BURBANK CA
Posts: 151
engines need at least 100 psi to run. it looks like you might have alot of bent valves or the valve are not seating correctly.
Reply With Quote
  #3  
Old 02-27-2003, 12:52 PM
jmdunn
Guest
 
Posts: n/a
sorry wrm,
I should have looked more closely before I posted. The post is edited now. my current readings should have read 145-150 psi on all but # 8 cylinder which reads 0 psi.

thanks
Reply With Quote
  #4  
Old 02-27-2003, 04:08 PM
Registered User
 
Join Date: Jul 2001
Location: SoCal
Posts: 1,303
The crank revolves twice for every camshaft revolution. You could be 180 degrees out of phase with the ignition. Check that your spark isn't occuring while valves are actually open.

Steve
Reply With Quote
  #5  
Old 02-27-2003, 04:17 PM
jmdunn
Guest
 
Posts: n/a
When the cam lobe are pointing up which=valves closed on # 1 cylinder. The timing marks are in alignment and the rotor points to # 1 spark plug wire.
Reply With Quote
  #6  
Old 02-27-2003, 04:20 PM
Super Moderator
 
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
Still should start and run poorly to terribly.

Try advancing the timing - 0 is kind of retarded.

Dumb questions:

What are you calling #1? Should be right (passenger side) front.

Did you get the plug wires on correctly according to the firing order?
__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
Reply With Quote
  #7  
Old 02-27-2003, 04:21 PM
moedip
Guest
 
Posts: n/a
No compreesion on #8? - You have a bent valve stuck open. Take off the valve cover and look at the cam lobes as they contact when you crank engine over by hand. I will bet one valve or both on #8 are not moving. Time to pull the head. DO NOT TRY TO START THE ENGINE UNTIL THIS IS RESOLVED. As it is an interference engine - the stuck valve can puncture the top of the piston.

Last edited by moedip; 02-27-2003 at 04:31 PM.
Reply With Quote
  #8  
Old 02-27-2003, 05:12 PM
sixto's Avatar
smoke gets in your eyes
 
Join Date: Jun 2000
Location: SF Bay Area
Posts: 19,744
I had a 78 450SEL that ran reasonably well with no plug in #4 so no compression in one cylinder will not make it impossible to start.

Backfiring means you're getting fuel. It's a continuous system so there's no fuel timing to check. Recheck cam and ignition timing.

Sixto
91 300SE
87 300SDL
83 300SD
Reply With Quote
  #9  
Old 02-28-2003, 01:20 AM
Member
 
Join Date: Feb 2000
Location: seattle, wa
Posts: 87
when you jump timing on a v8 99 % of the time the exhaust valves are bent on the left head. if you want to be sure it's simple to find out. remove the rockers on the cyl with no compression. run a test again to confirm the obvious. paul
__________________
Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.
Reply With Quote
  #10  
Old 02-28-2003, 04:41 PM
Super Moderator
 
Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,316
If you run a compression test without the intake valve opening, there won't be anything to compress.
__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
Reply With Quote
  #11  
Old 03-01-2003, 01:39 AM
Member
 
Join Date: Feb 2000
Location: seattle, wa
Posts: 87
sorry for not being clear.as to preforming another test it would be injecting air into that cylinder(leak down) you'll hear air going out the tailpipe, big time, or you'll hear it if you push down on the airflow meter if it happens to be a bent intake valve.
paul
__________________
Paul Roberts
Mercedes Centrum Inc.
Bellevue,WA.
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 10:17 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2011 Pelican Parts - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page