does a rebuilt engine mean the original specs don't apply ?

[splatter]

I have a 1984 140 HP mercruiser its in a 16' sting ray if that matters . Any way the boat use to run great then it quit cranking . It was obvious the electrical parts needed replacing so I replaced everything except the coil and the distributor . I made note of how everything was set before I took it all apart because I didn't know if I would be able to find the specs for a motor that old . So I did find the specs and set the points to .022 and the timing to 6 degrees BTDC . Now the boat runs like crap . Its hard to get it up to speed and it spits and sputters doesn't have near the power it did before and theres no way it would pull a skier up .
So i set the points to what they were before . .025 and the timing to what it was before 13 degrees BTDC . Now the boat runs almost as good as before but not quite . I think the timing before was set more like 16 degrees BTDC but when it gets that far over its just a guess because the pointer on the motor doesn't go that high .
The guy I bought the boat from said that the engine had been rebuilt . while he lied about a multitude of other things I think he was telling the truth about that because of how good it has always ran and the fact that it doesn't burn any oil . So i'm wondering whats the deal . I was expecting the boat to run better than ever after the tune up .Does a rebuild negate the original points and timing settings ? If not then could someone enlighten me as to whats going on with this .
Thanks in advance

 

[Silvertip]

Re: does a rebuilt engine mean the original specs don't apply ?

No! The only thing that changes is the cylinder bore diameter if the engine is bored oversize to take care of cylinder wear. It changes the engine displacement by a very small amount. Timing and dwell (point gap) settings and all other adjustments remain the same. the harmonic dampener may have slipped which means the timing mark is no longer in the right place. To check this, remoe #1 spark plug and turn the engine by hand to get #1 cylinder at TDC on the compression stroke. Don't go by the timing mark. Use a wooden dowel or a similar soft device through the spark plug hole to determine TDC. Now see where the timing mark is. If it is not at "0" the harmonic dampener has slipped, meaning the bond between the rubber and the hub and the outer ring has broken.

 

[84EdH]

Re: does a rebuilt engine mean the original specs don't apply ?

if the rebuild was done correctly, meaning the timing chain and camshaft installed correctly, the timing spec would be as original, unless harmonic balancer slipped as silvertip said. seeing as the coil and distributor are integral parts of the electrical system, what is "everything else" points, plugs, wires, capacitor ? Your cranking problem was not related to any of those parts, so I am not sure what you were after.

 

[RollinEarly99]

Re: does a rebuilt engine mean the original specs don't apply ?

No! The only thing that changes is the cylinder bore diameter if the engine is bored oversize to take care of cylinder wear. It changes the engine displacement by a very small amount. Timing and dwell (point gap) settings and all other adjustments remain the same. the harmonic dampener may have slipped which means the timing mark is no longer in the right place. To check this, remoe #1 spark plug and turn the engine by hand to get #1 cylinder at TDC on the compression stroke. Don't go by the timing mark. Use a wooden dowel or a similar soft device through the spark plug hole to determine TDC. Now see where the timing mark is. If it is not at "0" the harmonic dampener has slipped, meaning the bond between the rubber and the hub and the outer ring has broken.

^^^^ Agreed ^^^^

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

if the rebuild was done correctly, meaning the timing chain and camshaft installed correctly, the timing spec would be as original, unless harmonic balancer slipped as silvertip said. seeing as the coil and distributor are integral parts of the electrical system, what is "everything else" points, plugs, wires, capacitor ? Your cranking problem was not related to any of those parts, so I am not sure what you were after.

points, plugs, wires, capacitor, distributor cap . yes that is everything else . And why wouldn't my cranking problem be related to any of this . I was no longer getting spark before I replaced these things .

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

No! The only thing that changes is the cylinder bore diameter if the engine is bored oversize to take care of cylinder wear. It changes the engine displacement by a very small amount. Timing and dwell (point gap) settings and all other adjustments remain the same. the harmonic dampener may have slipped which means the timing mark is no longer in the right place. To check this, remoe #1 spark plug and turn the engine by hand to get #1 cylinder at TDC on the compression stroke. Don't go by the timing mark. Use a wooden dowel or a similar soft device through the spark plug hole to determine TDC. Now see where the timing mark is. If it is not at "0" the harmonic dampener has slipped, meaning the bond between the rubber and the hub and the outer ring has broken.

Thanks , I will check it this weekend . so is this something that MUST be repaired or should I just set it where it will run good and forget it ?

 

[84EdH]

Re: does a rebuilt engine mean the original specs don't apply ?

Theres the confusion. A no spark condition is not called a cranking problem. Cranking refers to engine being turned over by starter. Did you set dwell?

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

Theres the confusion. A no spark condition is not called a cranking problem. Cranking refers to engine being turned over by starter. Did you set dwell?

Oh ok,sorry for the confusion ,the engine turns over fine . I had a starting problem . No i didn't set dwell , I don't have a dwell meter . I set the points with a feeler gauge,this is how I didn it back in the old days when cars and motorcycles had points and it always worked fine . i am obviousely not a mechanic I'm a parts swapper at best but I did do my own tuneups back in the day and never ran into anything like this .
thanks

 

[Volphin]

Re: does a rebuilt engine mean the original specs don't apply ?

Personally, I'd just adjust advance the timing a bit more and call it a day. Look at the distance between 6 and 12 degrees BTDC and eyeball it to 16-18. I run about 23 BTDC on my V6.

 

[Alumarine]

Re: does a rebuilt engine mean the original specs don't apply ?

The motor must be at the proper idle speed to set the timing correctly.

 

[Walt T]

Re: does a rebuilt engine mean the original specs don't apply ?

Check firing order , then check it again. Verify you know which way the distributor rotor is turning.

 

[Volphin]

Re: does a rebuilt engine mean the original specs don't apply ?

Invest in a small dwell meter from harbor freight. They aren't that much. You will need it once a season anyway.

 

[Southtowns27]

Re: does a rebuilt engine mean the original specs don't apply ?

Make sure the mechanical advance in the distributor is working correctly. Check the timing at idle, then increase the engine speed up to about 3000 RPM. You should see the timing mark advance. If it stays in roughly the same place at idle and at speed, the mechanical advance is seized and would cause issues like you're describing.

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

Check firing order , then check it again. Verify you know which way the distributor rotor is turning.

have done this multiple times

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

Make sure the mechanical advance in the distributor is working correctly. Check the timing at idle, then increase the engine speed up to about 3000 RPM. You should see the timing mark advance. If it stays in roughly the same place at idle and at speed, the mechanical advance is seized and would cause issues like you're describing.

the mechanical advance is the springs on the bottom of the distributor right ? If this is the case can I just remove the distributor and free them up by hand ?

 

[81 Checkmate]

Re: does a rebuilt engine mean the original specs don't apply ?

Yes.....springs/weights are in the distributor, and yes remove the distributor to replace them. The internals have to move freely to advance. Just freeing them up will not be enough.

If they are all rusted up... it's better to replace them or...... better yet go with a newer electronic ignition.

 

[Bt Doctur]

Re: does a rebuilt engine mean the original specs don't apply ?

Try .018 on the points and 6 deg BTDC on the timing.

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

No! The only thing that changes is the cylinder bore diameter if the engine is bored oversize to take care of cylinder wear. It changes the engine displacement by a very small amount. Timing and dwell (point gap) settings and all other adjustments remain the same. the harmonic dampener may have slipped which means the timing mark is no longer in the right place. To check this, remoe #1 spark plug and turn the engine by hand to get #1 cylinder at TDC on the compression stroke. Don't go by the timing mark. Use a wooden dowel or a similar soft device through the spark plug hole to determine TDC. Now see where the timing mark is. If it is not at "0" the harmonic dampener has slipped, meaning the bond between the rubber and the hub and the outer ring has broken.

So if I have the timing set to 6 BTDC then when the #1 cylinder is at the top the timing mark should show 6 BTDC correct ?
If that is the case then the harmonic damper hasn't slipped because thats what I had today when I checked it .

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

Make sure the mechanical advance in the distributor is working correctly. Check the timing at idle, then increase the engine speed up to about 3000 RPM. You should see the timing mark advance. If it stays in roughly the same place at idle and at speed, the mechanical advance is seized and would cause issues like you're describing.

I did this today and I could see it advance some but I didn't know how much it should advance . So I took the distributor off .( I thought the mech adv was on the bottom of the distributor not under the points where I found it )And the springs and weights move freely as they should . So I don't think this is the trouble .

 

[splatter]

Re: does a rebuilt engine mean the original specs don't apply ?

after doing both of the above today I took the boat to the lake and set the timing at approx 18 BTDC . The points are still at .022 . The boat ran good like this except at the very top of the throttle I could feel it lose power . Also before I changed the parts it would top out at 4800 RPMS and 40mph . now it tops out at about 4500 RPMs and 37 MPH . I can't get back to the lake until a week from tomorrow and I think when I go I'm gonna go to about 20 BTDC and see if that won't get it back where it was before.
I really don't know what to make of the fact that it won't run correctly when set to spec . I'm thinking over the winter that I'm gonna go to electronic Ignition and see what happens .