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Old 09-26-2010, 07:07 PM   #1
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Default how to check if my engine jumped the timing chain

95 4.3 mercruiser. I tried to time it to 8 deg before top dead center but It wouldn't start. It will start if its about 25 deg before top dead center. How can i check to see if the timing chain jumped? or is the only way to take off the water pump and timing cover?
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Old 09-26-2010, 10:56 PM   #2
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well...I'm going to ask a simple question...did you do a full up tuneup...???...meaning did you replace the plugs/wires/distr. cap/rotor???..if so..when you replaced the distr. cap and the wires...did you replace it one for one???...meaning plug one went to the exact same place as it came off on the distr. cap???cuz to me it sounds like your one hole off the distr cap.....
to check the timing...put the crank on tdc...make sure the distr rotor is pointing to #1 plug....if the rotor is pointing to something else....then either the plug wires were installed incorrectly or the timing belt jumped....I seriously doubt timing jumped....the way the engines are designed now days ..it's danged near impossible...

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Old 09-26-2010, 11:12 PM   #3
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yep I did a full tune up dist cap rotor, wires, spark plugs, rebuilt carb, new fuel lines and filters. I have gone over it and over it many times to verify that the correct plug wire on the dist cap is going to the correct cylinder. in the correct rotation. but I will check it again tomorrow just to be sure. It will run smooth at idle when its not in the water but like I said the timing is over 25 deg out, being it runs ok at idle and doesnt backfire when out of the water. but under load is a different story. tomorrow I am also going to check to see if the dist has play in it by turning the motor back and forth by hand to see if the rotor moves immediatly or is delayed. I was told by doing this it will tell me if my timing chain is streched
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Old 09-26-2010, 11:50 PM   #4
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actually no..there is some play between the crank and distr...it's minimal..but you won't see it...you need to stick a degrees dial on the crank before you'll notice a change....humor me....take all the plugs out...put the crank on tdc....check to see if intake closed....that should be tdc on the compression stroke....then pop the distr. to see where it's pointing.......if it's 25degs off...you installed it onto the wrong plug.....I'm betting it is...

let us know how it goes..

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Old 09-26-2010, 11:50 PM   #5
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would a week coil make the motor not run at the proper 8 deg? and allow it to run at 25 deg btdc?
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Old 09-26-2010, 11:51 PM   #6
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nope...weak coil would either fire a weak spark or not work at all...the distr is what fires the spark at the right time.

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Old 09-27-2010, 12:47 AM   #7
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i have heard that the higher the compression the hotter spark is needed if the engine will run at 25 deg before tdc (piston hasnt compressed the air fuel mixture completly) but wont run at 8 deg btdc full compression. in theory if it was a week coil sending a week spark it might not be enough spark to ignite the air fuel mixture at full compression......
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