Setting the Timing on a '71 250 - Mercedes-Benz Forum

 
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post #1 of 8 (permalink) Old 07-22-2005, 08:06 AM Thread Starter
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Setting the Timing on a '71 250

Okay, so I think I have determined that the timing on my '71 250 is off. The picture below is from a book I have showing how the timing marks should line up, my lines do NOT line up, they don't look like the lines in the picture and they are off just a tick, how do I set it, I would appreciate some really basic step by step directions. This would probably explain the reason the car is hesitant on start up and also backfires through the carbs when underload like on a hill, right? All help is appreciated. Thanks
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post #2 of 8 (permalink) Old 07-22-2005, 08:12 AM Thread Starter
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RE: Setting the Timing on a '71 250

here's the picture
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post #3 of 8 (permalink) Old 07-22-2005, 02:16 PM
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RE: Setting the Timing on a '71 250

You're not going to like this.

Take off spark plug #1.

Bring engine to TDC. Piston #1 all the way up.

In the picture you have there is a bolt on the camshaft wheel.

Remove it

Turn the cam shaft until it lines up.

Replace the wheel & bolt.

It may not fire after that. So open your distributor and there is a timing mark on that. Point the rotor to the timing mark with engine at TDC.

Hope that helps.

BTW where did you find that picture?

Thanks

George
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post #4 of 8 (permalink) Old 07-22-2005, 03:51 PM Thread Starter
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RE: Setting the Timing on a '71 250

Thank you thank you thank you! That is exactly what I needed, Being that this is my first time setting the timing when I was checking it I forgot to make sure it was at TDC so it might not be off, but I am pretty sure it is off. As for the procedure it doesn't seem that totally painful, it's pretty much what I expected. I got the picture from a book I ordered thru a local bookstore it's called Mercedes Benz 250 1968-72 owners workshop manual. It's printed by Autobooks owners workshop manual. It's a great book with a lot of stuff the Haynes manual doesn't cover, it's also a lot easier to understand because it's written in american english compared to uk english. It cost me about $45 bucks including tax.
Once again Thankyou [:D]
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post #5 of 8 (permalink) Old 07-22-2005, 03:55 PM Thread Starter
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RE: Setting the Timing on a '71 250

one more question, turn the camshaft to align the marks or turn the wheel to align?
Thanks
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post #6 of 8 (permalink) Old 07-22-2005, 04:22 PM Thread Starter
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RE: Setting the Timing on a '71 250

sorry, one more question. TDC is determined by putting your finger over the spark plug hole and turning the engine be hand and when you feel the increase in pressure it's at top dead center?
Thanks
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post #7 of 8 (permalink) Old 07-22-2005, 09:40 PM
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RE: Setting the Timing on a '71 250

Ok. TDC, Top Dead Ceter, is when piston #1 reaches it's full compression stroke. In this situation, the valves must be closed. The piston will have reached it's apex, (the highest it can travel), The timing mark on the cam will be ligned up, and the ditributor rotor will be poiting to the spark plug that connects to cylinder 1. Typcaly this is where a running engine would fire the combustion chamber, which would follow the remaining cycles of a 4 cycle engine, power, exhaust, intake and back to compression.

TDC is determined by removing spark plug #1.
Cover the whole with your finger and turn the cam by hand. When the piston comes up and it is in the compression stroke, it will build pressure, if it does not then you're in the exhaust stroke.

It will build enough pressure to push your finger off the hole.

put a straw in the cylinder. This will help you to visualise where the piston is. As the engine turns the piston will go up and down and you'll be able to see that with the straw. makes sense?

Read the timing wheel and when it reaches 00. the straw should be at the highest point. Turning the engine any further will cause the straw to come back down.

At this point, the cam shoulde be aligned, as is in the picture, and the rotor on the distributor should be very close to the timing mark on the distributor housing. It's a little line not found anywhere else on the housing. Remove the ditributor cap.

if the cam timing wheel is not lighed up when you're at 00 and is actual at the bottom, you're at the exhaust stroke. Rotate the engine 180 degrees.

if it is off, then leave the engine, crankshaft, at 00, remove the cam wheel bolt, then the cam wheel, then put the bolt right back in there and use ut to bring the timing mark back to center.

If you have any questions, email me your phone number and a good time to call you and I will be happy to walk you through it. You can email me at ggenovez at gmail dot com.

Now if you don't mind, I also have a 250 and a haynes manual. It does not go into too many details on how to remove the rocker arm. Would you mind email me the directions on the book.

Also the ISBN # on the book would be very helpful as well.

Thanks and good luck

George
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post #8 of 8 (permalink) Old 07-23-2005, 07:11 AM Thread Starter
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RE: Setting the Timing on a '71 250

Thanks everything is much clearer now, I feel pretty confident that I can set the timing with no problems.

The ISBN number for the boook is 1-58850-031-4

I will make a scan of the rocker arm removal process and the picture that goes with it and email it to you aswell as post it so if anybody in the future needs help with it.
Thanks
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