Setting the Points on a 3.7L Merc

ta400man

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Last night I replaced the points on my 87, 3.7L, 165hp, 224CI straight 4 motor. I never set the points before and I looking for some advice on setting the gap. I was unable to get the engine running.<br /><br />I set the gap bye turning the engine so that the points were on the high side of the disturber lobe and set the gap to about .020. I also made sure that the points were touching on the low side of the lobe. I assume there is a tolerance for that gap. Some advice would help.<br /><br />Thanks,<br />Shawn
 

Bt Doctur

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Re: Setting the Points on a 3.7L Merc

it should run, .018 preferred.<br />12V at the + side of the coil?<br />was it running before you changed the points?<br />tach or shift interlock could be killing the spark.
 

ta400man

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Re: Setting the Points on a 3.7L Merc

Where is the shift interlock located, I noticed that the tach was jumping when I hooked the battery back up after adjusting the points. What is the shift interlock?<br /><br />Does any one know where the Dwell is suppose to be set, I read on this forum that the dwell for a 4 Cylinder merc is around 34.<br /><br />Thanks in Advance,<br />Shawn
 

Haut Medoc

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Re: Setting the Points on a 3.7L Merc

Points .022<br />Dwell 31*-34*.....
 

ta400man

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Re: Setting the Points on a 3.7L Merc

I set the points to a gap of .022 and I measured a dwell of 30. I figure that is close enough. <br /><br />The manual specified a gap of .022, Haut Medoc you were right on the money.<br /><br />But my motor still does not run. But I think that the points are still set right.<br /><br />Thanks,<br />Shawn
 

Don S

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Re: Setting the Points on a 3.7L Merc

I set the points to a gap of .022 and I measured a dwell of 30. I figure that is close enough.
It should run, but it won't run right. We are not playing horse shoes or hand grenades, so "Close Enough" isn't GOOD Enough.<br /><br />What kind of distributor do you have, Delco Remy or Prestolite? Makes a big difference in dwell and timing.
 

Bt Doctur

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Re: Setting the Points on a 3.7L Merc

interlock is located on the plate that holds both cables. small micro switch .interupts the ign. to ease shifting.tach is connected to the ign, system,it goes bad, shorted, grounded ,no spark.
 

ta400man

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Re: Setting the Points on a 3.7L Merc

I am not sure what distrubutor I have, I belief the distributor is stock.<br /><br />Did the stock merc come with several different distributors?
 

Buttanic

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Sep 25, 2003
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Re: Setting the Points on a 3.7L Merc

Did you replace the condenser when you replaced the points. If you did try putting the old condenser back. Lately I have seen several cases of new condensers being bad.
 

ta400man

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Re: Setting the Points on a 3.7L Merc

I did try to start the motor with the new and old condenser. I even tried to put the original points back in.<br /><br />How much will the dwell change from running at the speed of the start versus at idle. I am reading a dwell of 30 when the starter is cranking the motor.<br /><br />Thanks,<br />Shawn
 

Buttanic

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Re: Setting the Points on a 3.7L Merc

Dwell should not change at all with engine speed.<br />It is possible if you left the ignition on for a while and the points were in the closed position that the coil might have burnt out. Do an ohm reading between the + and- coil terminals. resistance, should be 1.4 to 3 ohms.
 

bruceb58

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Re: Setting the Points on a 3.7L Merc

You put the rotor back in right? I made that mistake once! <br /><br />Pull off a spark plug wire and check for a spark there and work your way backwards.<br /><br />Did you do anything else?
 

ta400man

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Re: Setting the Points on a 3.7L Merc

I don't think I put the rotor on backward, the rotor is sloted. Maybe I put the wires on the reverse order. Which way does the rotor turn.<br /><br />Thanks Again,<br />Shawn
 

bruceb58

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Re: Setting the Points on a 3.7L Merc

I meant putting the rotor back in!<br /><br />You didn't say that you changed the wires at the same time! You are talking about the spark plug wires...right?<br /><br />I always do one thing at a time so that if I mess up, I know what caused my problems.<br /><br />Pretty easy to see which way the rotor turns when you crank the engine with the cap off.<br /><br />Turn the engine to TDC. You will either be at the top of the compression stroke or the exhaust stroke. Your rotor needs to be pointing at the wire that goes to cylinder #1 at the top of the compression stroke. You can then see if the wires are going to the correct cylinders in the correct order.
 
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