A great big THANK YOU to all that helped - PeachParts Mercedes-Benz Forum

JBR · #1 03-24-2006, 06:23 AM

The 73 450sl started last night, 1st turn of the key. YAHOO
I did what I said, new vac line to MAP. New plugs. Gave the air slide valve a rap with a hammer. And WA LA.
Now with the dist. turned full cloclwise the timing is at 0 (TDC). That is the closest I have been able to get to 5* ATDC.
I turned the idle air mix screw out, to increase idle. Now here is a few more questions.
How do you test the, water temp sensor (EFI control).
And the Therm-o-time switch.
And the cold start valve. Are all these tested with resistance. What would be the OLHM value for each @ what temp.
Also to achive perfect timing 5*ATDC which way would I turn the rotor to retard it even more? Thanks again.

t walgamuth · #2 03-24-2006, 07:20 AM

now to change the timing you cant move the rotor, you need to move the body of the distributor. and to reason it through here is how i think of it. i look at the direction the rotor turns, and if i want to advance the spark, i move the body of the distributor so that the rotor reaches its completion event sooner. so if your rotor turns clockwise, to advance the spark you would twist the body anticlockwise, etc. to retard you turn the body the same direction the rotor turns. so that it reaches the event later.

hope that helps

tom w

JBR · #3 03-24-2006, 07:44 AM

Thank you for your imput. I do beleive I need to retard the timing. But I can not turn the body of the dist. The hold down bolt is all the way at the end of the slot, no more turn is allowed. I beleive I need to lift the dist. out an inch or so, and turn the rotor. But which way do I turn the rotor? Then put the dist. back in with the bolt centered in the slot. Thanks

nhdoc · #4 03-24-2006, 08:27 AM

Quote:

Originally Posted by JBR

Thank you for your imput. I do beleive I need to retard the timing. But I can not turn the body of the dist. The hold down bolt is all the way at the end of the slot, no more turn is allowed. I beleive I need to lift the dist. out an inch or so, and turn the rotor. But which way do I turn the rotor? Then put the dist. back in with the bolt centered in the slot. Thanks

I believe the normal direction of rotation of the rotor is clockwise in this car (you can double check it by watching the rotor turn whilst cranking the engine over with the cap removed). If that is the case, and you are trying to retard the spark further you would turn the rotor counterclockwise one tooth after lifting the distributor, then reseat it and retime it.

It's possible that in the past someone removed the distributor and replaced it with the rotor one tooth off. It's also possible that the timing marks on your crank pulley have shifted and you're not even reading the right timing at all...but assuming that's not the case and all you want to do is time the engine to the mark you can turn the rotor and reseat it. If this results in unsatisfactory performance I would confirm the timing marks are correct by manually turning the engine so #1 is TDC (you can use a dowel as a "feeler" in the spark plug hole) and check that the timing mark on the pulley corresponds correctly to 0 degrees at TDC.

Unless you're the only one who's worked on this car its entire life you cannot assume anything is correct. Over the years it's had a lot of hands under the hood, and some have probably tried to undo what others have done wrong...that's usually the challenge in fixing up old cars...trying to get it back to manufacturer's spec first, undoing all of the workarounds others have done to "re-engineer" it.

t walgamuth · #5 03-24-2006, 08:29 AM

that is right.

tom w

Tomguy · #6 03-24-2006, 10:43 AM

I don't think it's possible for timing marks on the 4.5 to ever be off without the entire hub falling off?

Before you pull the distributor to reset the rotor, check to see if vac is being supplied to your distributor. If it isnt getting vac, timing should be 7° BTDC, not 5° ATDC. Easiest way to tell if it's affecting your car is pull the vac line while it's running - if the engine speed jumps up, the vac retard works. If there is no engine speed change, find out why - Make sure your AC is switched off, does the line have a vacuum on it? If so, but it doesn't retard the ignition, the unit on the distributor is bad. Plug the line, set timing to 7°BTDC until you replace it. Lots of threads on this. Do a search, most of them are probably in the Vintage forum.

JBR · #7 03-24-2006, 12:01 PM

Hi Tomguy: The line does have vac. it will stick to your lip when the car is running. Also The diaphram does work when you suck on it.
But isn't it true, that if the timing is set too advanced already then removing the vac retard line will show very little difference.
The reason I,m saying this is last week when the car was really screwed up, I remember setting the timing as retarded as possible and when the vac line was removed the idle went up. Then turned the dist. to advance it, then removed the line again it had no effect. Right now with all the work being done and set to TDC ( can not get to ATDC) when the vac line is removed there is some increase idle but not much.

Tomguy · #8 03-24-2006, 12:54 PM

No, that shouldnt be the case. It should provide about 12° of advance regardless of where it was set. Set it at 0° and you should get 12°BTDC with the line off. There might be a TINY noticeable factor from the mechanical advance advancing it MORE when you pull the vac line off - in other words, at 1200RPMs, you might see 13-14° as opposed to 12° - but it should always cause at least 12° of advance. If it doesnt, there is something amiss with either the retarding unit, or the top plate's movement in the distributor.