4.3LX Merc distributor not turning

Manta13

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May 12, 2020
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1993 4.3LX merc 0F073610 with Thunderbolt IV. Thought it was the ignition sensor after going thru the troubleshoot flow chart. Replaced that and tried to fire up. No spark at the plugs so I took off the dis cap and cranked. No spin....

My next thoughts are pull off the front and check the timing chain. Any other things to recommend before I start ripping off parts? I haven't pulled out the distributor either. I was reading about a pin on the shift but I'd need help understanding. Thought it was a solid shift down to the gear.
 

Bondo

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I was reading about a pin on the shift but I'd need help understanding. Thought it was a solid shift down to the gear.

Ayuh,..... Welcome Aboard,...... The solid metal gear is pinned, with a roll pin to the solid steel shaft,.......

If you pull the distributor, 'n the gear is still pinned, do a compression test,.....
 

Scott Danforth

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Could be bad dizzy gear, cam gear could be worn, timing chain may be gone. Pull dizzy and look like Bondo stated. If gear is intact, look down dizzy hole.

If cam looks ok, then crank motor while looking at cam. Cam sould turn.
 

Manta13

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Rain has me in and out. I figured the compression check would be to validate if the valves are moving so I cranked it over while using the oil fillopening as a visual. Rockers are moving so I see that as the chain is intact. Once rain subsidies I'll be pulling the Dist to check gears and pin. If the pin is sheared will the gear drop off the shaft?

Would it be safe to assume I am narrowed down to pin, dist gear, cam gear as the trouble?
 

Rick Stephens

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Would it be safe to assume I am narrowed down to pin, dist gear, cam gear as the trouble?

I would probably not ask it that way. You are the only one there. and pulling the distributor is the only way to answer that question. Reality is. You have ruled out the timing chain. Anything else is still possible.
 

Manta13

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Dist gear is worn down bad. And without a snake scope I can't get a good look at the cam gear, but at a top glance they didn't have the shine of worn parts like I see on the dist gear. Are the two gears designed where the cam gear is more hardened and the dist gear would be the sacrificial part?

I know the convention answer is change it all, but I'm not outfitted to get into the camshaft as easily.
 

Rick Stephens

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Some say that the disty gear is softer than the camshaft so it wears instead. They even had a bronze gear on distys for flat tappet motors that had a softer camshaft. I think the only choices you have are swap a new gear on the disty and try it, see how it wears, or pull the camshaft and look. Not sure either path is perfect.
 

Manta13

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Appreciate the advice. Waiting on parts. Doesn't appear that is a regularly stocked item.
 

Bondo

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Dist gear is worn down bad. And without a snake scope I can't get a good look at the cam gear, but at a top glance they didn't have the shine of worn parts like I see on the dist gear. Are the two gears designed where the cam gear is more hardened and the dist gear would be the sacrificial part?

I know the convention answer is change it all, but I'm not outfitted to get into the camshaft as easily.

Ayuh,...... Welcome Aboard,....... When ya get the new gear, 'n pin, you'll be lookin' over the distributor pretty good,.....
Be sure it's all up to snuff,....
Make sure the gasket is under the distributor body, as that effects the distance for gear mesh,....

'n change the oil,..... All that metal went somewhere,.......
 

Manta13

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Tried NAPA. I have had success with them in the past. They couldn't cross reference the part for me at a few stores. Digging through myself it looks like ECH DG501 is darn close, but the O.D. (1.5) seems a bit too much looking at the existing part. Even with the metal sheared off. Any sites you all are successful with cross referencing part numbers?

part #8M0115498. Not asking anyone to do it for me, just figured it would be a question that came up.

(Edited.. missed a few letters in the NAPA part#)
 

harringtondav

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Stating the obvious here, but don't forget to time the camshaft when you reinstall the repaired dist. #1 cylinder (front left/port) at top dead center as indicated on the timing marks. Be sure #1 piston is up or you will be 180 deg off. Best way is to remove that rocker cover and insure the intake valve is closed. ...you may be able to feel the piston through the spark plug hole with a probe. ...I haven't tried this on this engine.

Reinstall the dist with the rotor pointing to the #1 spark plug wire. It may take a few tries to get the dist in the original orientation since the dist gear is helical and will rotate the shaft as it's lowered into the cam gear.
 

Manta13

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Stating the obvious here, but don't forget to time the camshaft when you reinstall the repaired dist. #1 cylinder (front left/port) at top dead center as indicated on the timing marks. Be sure #1 piston is up or you will be 180 deg off. Best way is to remove that rocker cover and insure the intake valve is closed. ...you may be able to feel the piston through the spark plug hole with a probe. ...I haven't tried this on this engine.

Reinstall the dist with the rotor pointing to the #1 spark plug wire.

Appreciate it. I have a pretty solid Clymer Shop Manual that I have used on this boat for years. Suggests removing the spark plug on #1 and feeling for compression. Was going to give that a go first before taking off the rocker cover. Book has a good pattern lay out for EI valves if I have to take that route.
 

Manta13

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So as I am installing the distributor back into the engine following the TDC and #1 point for the rotor, the distributor is going it 90 deg clockwise from where it was positioned upon removal. The alignment of the oil pump slot was the limiting factor here. Not usually an issue but the ign. amplifier mounted to the dizzy is basically against the breaker.

Could I get a long slot screwdriver and turn the oil pump 90 degrees so it lines back up to having the ing. amp in the back?
 

Scott Danforth

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Yes you can.

You can also clock the rotor the same amount it turns (in opposite direction), and the crank the motor slightly to drop the dizzy onto the onto shaft
 
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