Help! - 86 420SEL Idle misfire after timing chain guide replacement - PeachParts Mercedes-Benz Forum

jodeven · #1 12-31-2006, 01:48 PM

Hi Folks,

Well got the car running, however, Idle is not so good. Feels like rapid misfire - (high frequency) at idle. Off idle engine runs fine. Power seems okay - I think. I may be paranoid and it may be down as well.
Off idle the engine seems smooth. -no misfires. Full throttle no misfires.

Everything I did is as follows.

Guides
Tensioner
Spark plugs
Ign Wires
Belts
Cam Oilers
v. cover gaskets.

The spark plugs are Bosch Super WR8DC+ gaped at .032 thousands.

I lost time when replacing the guides. Spun the motor by hand and the pistons and valves were interfering. So I removed the rockers and retimed motor. I don't know if this is a problem but when I got the crank and the right cam lined up to marks the left cam is now 1/2 tooth retarded. Before I began the repairs I set the motor up at TDC and all marks lined up. I don't know what changed - why I now have the left cam 1/2 tooth off.

Ran compression test all cylinders on left side were at 160 psi. The right side was 165 - 175.

Can anyone give me an idea. Is the spark plugs the resistor type and causing the problem? or do I have a valve timing issue? or something else?

Thanks,

Joe

Strife · #2 12-31-2006, 02:31 PM

1/2 a tooth is a lot. Mine never lined up "perfectly" when I was done, but probably not that much. If I had more know-how I would have put in compensating Woodruff keys for the cams (gear wear and just engine-to-engine variations account for a few degrees, apparently). I'll bet your misalignment is actually less than 1/2 of a tooth. If you were actually one tooth off, you would know by now, IMHO. I think a tooth is a large number of degrees (remember, cams move at 1/2 crank speed) and this would be, uhhh, "very bad".

Resistor plugs are NOT recommended (and yes, I know non-resistors are hard to find but they can be found). I'd look there, and also look at the routing of your ignition wires, and whether or not they are really on the plugs well (stupid mistake, but I've done it).

Did you replace the cap and rotor? Just disturbing an old one can make a marginal set-up bad.

Did you line up the distributor properly (the rotor to the mark on the distributor casting)? I assume that you removed it to do this job.

Strife · #3 12-31-2006, 02:32 PM

P.S. Did you disturb any vacuum hoses (like the one under the air cleaner?).

Another "stupid" question: Did you remove one link from the old chain when you ran the new one through (I hope so).

jodeven · #4 12-31-2006, 03:10 PM

Hi Strife,

I did not replace cap and rotor. Just cleaned. I don't know if the plugs are resistor or not. Also did not replace chain. It appeared to not have stretch when I checked it. (all marks were aligned perfectly before I took it apart)

I double checked all connections (wires and vac hoses). All apear okay. Although it is always still possible I missed something. Right now not the most likely.

I just don't know if the plugs are causing the issue or the cam timing.

Thanks,

Joe

Strife · #5 12-31-2006, 03:22 PM

Those definitely are resistor plugs. Apparently Bosch is not making non-resistor plugs anymore (see other threads).

garymand · #6 01-02-2007, 08:48 PM

Plugs are not the proble. I had the very same problem on a 380 and never got a good answer to why or what to do.

I do know this adjuster is probably taking up the slack in the chain and that pulled the cam back a little taking up the slack in the chain. I think the adjuster ratchets as it moves out. You can't just push on it to compress it.

I'm sure you've done this but, starting over with the valve covers off. Ensure the crank is pulling the "right" cam with the chain as it comes up on TDC. I'm assuming you call the right cam the one on the right as you look at the car. I think it should be from the driver's perspective, but anyway. The driver's side cam is pulled directly by the crank: as the crank comes to tdc so should the cam come to the mark. assuming #1 compression, the right cam #6 should be lobes down pushing the valves open. Then the pasenger side follows lobes up. Ensure the chain is tight with the cams both at #1 TDC compression. For sure, the driver's side should be right on and the other not far off. All the extra chain is pushed out by the tensioner. One cam should not be right on and the other 1/2 tooth behind.

I'm thinking if I remember right I used one offset key to move the one cam. The gear is still behind but the cam is closer.

jodeven · #7 01-03-2007, 06:44 AM

Quote:

Originally Posted by garymand

Plugs are not the proble. I had the very same problem on a 380 and never got a good answer to why or what to do.

I do know this adjuster is probably taking up the slack in the chain and that pulled the cam back a little taking up the slack in the chain. I think the adjuster ratchets as it moves out. You can't just push on it to compress it.

I'm sure you've done this but, starting over with the valve covers off. Ensure the crank is pulling the "right" cam with the chain as it comes up on TDC. I'm assuming you call the right cam the one on the right as you look at the car. I think it should be from the driver's perspective, but anyway. The driver's side cam is pulled directly by the crank: as the crank comes to tdc so should the cam come to the mark. assuming #1 compression, the right cam #6 should be lobes down pushing the valves open. Then the pasenger side follows lobes up. Ensure the chain is tight with the cams both at #1 TDC compression. For sure, the driver's side should be right on and the other not far off. All the extra chain is pushed out by the tensioner. One cam should not be right on and the other 1/2 tooth behind.

I'm thinking if I remember right I used one offset key to move the one cam. The gear is still behind but the cam is closer.

I put a new set of plugs in last night. Non Resistor Bosch plugs that I got from the dealer. No change. I guess I am going back in, however, don't know exactly what to do.

Anyone else run into this problem. Any solutions?

Thanks garymand for the insight.

Joe

p.s the cam that is off half tooth is the drivers side cam (left). Crank and passenger cam (right) is on the marks

Tomguy · #8 01-03-2007, 08:34 AM

I don't understand something:
How do you get 1/2 tooth as a reading you're off by?

You rotate the ENGINE (counterclockwise) until the cam is showing to be lined up correctly, then you read the degree stretch on the crank hub. Is it off by 10°? That'd be 1/2 of a tooth, but 10° is a more accurate measurement. You CANT move the cam until it shows TDC, then check the engine. It will never show correctly, and the reading is typically not consistent either. You also can't move the cam close, then move the engine to TDC to finish it. You must move the engine by the crank soley to do this check.

If you're off by less than 10°, it's possible you have an offset tooth in that cam (put in by a previous mechanic)

david s poole · #9 01-03-2007, 09:46 AM

how far into the engine did you go?did you remove the cam sprockets?if i understand correctly the drivers side cam is off by a half tooth and this is the opposite from what it should be.i think you have that [drivers]cam retarded and hence the bad idle.if you call me i can walk you through it.

jodeven · #10 01-04-2007, 07:16 PM

Quote:

Originally Posted by david s poole

how far into the engine did you go?did you remove the cam sprockets?if i understand correctly the drivers side cam is off by a half tooth and this is the opposite from what it should be.i think you have that [drivers]cam retarded and hence the bad idle.if you call me i can walk you through it.

First, I would like to say a big thanks to David. He took the time with me over the phone. He knew exactly what was wrong. Okay now for details.

The problem was retarded cam timing on left cam (drivers side). This caused the bad idle. The reason:

I installed the "timing mark washer" on backwards.

This washer is keyed to the cam. The washer fell off when I removed the cam sprocket.

I looked at the washer and it appeared it could be put on the cam either way as long as the key was up. I now know that is not correct. (thanks again David) The woodruff key slot in the washer is off set relative to the timing mark (barely noticeable) and therefore when installed backwards caused the left cam to be off time. Forum Members this is very hard to detect. I am posting this so that you don't make the same mistake I made. I can tell you this, I will never forget it.

Also, unless I missed it, the service information does not have any reference to the proper orientation of that washer.

I installed the washer correctly (flipped it over) - All marks lined up perfectly. Re-assembled the vehicle and by 10:30 last night started her up and she ran perfectly.

Joe

ctaylor738 · #11 01-04-2007, 09:19 PM

Nice wrench, guys.

david s poole · #12 01-05-2007, 09:44 AM

all's well that ends well.