1984 Mercruiser 140 repeatedly needs timing readjusted

[stikboyy]

I have a 1984 Mercruiser 140 serial # 6712267
I was out the other day for a couple of hours and on my way back in the motor started to run rough and was low on power. When i got back home i checked the timing and it was at 4 degrees ATDC. I reset the timing to the factory spec of 6 degrees BTDC and took the boat back out. The motor ran perfect for 2 hours and then experienced the same symptoms. I once again checked the timing and it was at 6 degrees ATDC. I am absolutely certain the distributor bolt was tightened down properly. I pulled the distributor to inspect the gears and the distributor gear and the cam gear look good. #1 cylinder piston is at TDC when the timing mark on the balancer is lined up the 0.
Any ideas on what could be causing my timing to change?

 

[alldodge]

I would look at the pin which holds the gear on the distributor. If that's good the look for any play in the shaft an up/down

 

[Bondo]

Ayuh,.... Welcome Aboard,... To continue AD's advice, also check whether there's any shaft wobble,.... as in worn bushin's in the housin',....

Is the points wear block, wearin',..??

Lastly, rotate the crank shaft backwards, 'n forward abit, while watchin' the distributor shaft, to see how worn the timin' gears are,...

 

[kenny nunez]

Hold the distributor body just above the gear and try to see how much play there is and watch the points and you will see the problem. Have a machine shop install a bushing in the area above the gear and a new one in the top. Or buy a new Mallory.

 

[stikboyy]

The roll pin in the gear is in good shape and the gear is tight on the shaft. There is no side to side play in the distributor shaft (its also not acting like side to side play does. the timing isnt wandering. its going from the correct setting and moving to a different spot and staying there). Ill check for wear in the timing gears tomorrow.
Thanks for your input so far!

 

[kenny nunez]

Just as AD posted on the pins that support the flyweights I have seen some so bad that the weights almost cut the top off the distributor body.
The bushing that is worn is the one in the block above the oil pump. Not a very good design.

 

[Scott Danforth]

im going with wear block wearing on the points because they were installed without grease on the wear block. therefore the point gap changes, which changes the dwell, which changes the timing

 

[Fishermark]

It would take a lot of wear to make the timing change that much just from the points changing gap. I too suggest disassembling the top part of the distributor (under the points plate) and see if there is any wear.

What gasket are you using under the distributor? It sounds to me like the distributor body is moving on you. I know you said the bolt was tight... but maybe take out the hold down tab and see if the bolt goes down smoothly. Maybe the threads are binding or something. I know I once used a gasket I had cut from some cork material once and that was a mistake. The distributor would loosen and do exactly as you describe.

 

[stikboyy]

I think i'm going to replace the distributor. There is no play in the timing gears. when i move the crank forward and than backwards the rotor responds instantly. I have .068" of end play in my distributor shaft; which must be too much. The points block does seem to have some wear on it but i didnt check that before it happened so i have nothing to compare it to.

 

[Fishermark]

If you do replace the distributor - go ahead and buy a new AC Delco Voyager kit. You can shop around for the best price. It is the best thing I ever did when replacing the ignition system.