1967 Merc 650 Jumping timing??

J

JasonC

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Aug 5, 2007
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I have a Merc 650 1967, s#2167229. Last year jumped timing so I replaced timing belt and upper crankshaft bearing )felt like it had play by wiggling the flywheel)... then winter came... So after getting it running fine in a 1/2 50 gal drum, I took it up to the lake a couple times, started and ran great. Yesterday I took it out again and about 20 mins out on the lake it cut back from WOT to about 20% power... Turned it off on the lake to try and see what the prob was. Couldnt figure it out. Would only start with throttle pushed all the way forward... (neutral safety switch is apparently not working either..)anyhow, I putted back to the boat ramp and went home... Put it back in the bucket and screwed with it.
Long story short, It had apparently jumped the timing belt a tooth or two again. I cant figure out how/why.
It only takes about 15-20 mins to disassemble, adjust the belt and reassemble, but I can only imagine the scene if it happens while out with the wife and kids...

Any ideas on what it could be? Like I said, I replaced the upper crankshaft bearing and the timing belt recently (less than 10 running hours) and theres not the play in the crankshaft (flywheel does not wiggle anymore) I'd be ever so grateful for anyones ideas on this. (Doubly so if I can get it fixed by the long weekend...)

Thanks in advance
Jason Carney
 
J

JasonC

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Aug 5, 2007
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Re: 1967 Merc 650 Jumping timing??

Hmmmm... I'll pull the distributor out and replace that bearing. Anything else you would suggest I should service while I have it apart? (I've only owned the boat for a year and know nothing of the service history prior to that)...
Thanks again for your help.
 
L

Laddies

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Sep 10, 2004
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12,218
Re: 1967 Merc 650 Jumping timing??

I didn't mean it had to be changed only checked, it's the only thing besides a upper main that can cause slack.
 
E

emckelvy

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Jan 16, 2004
Messages
2,506
Re: 1967 Merc 650 Jumping timing??

How tight is the belt? The distributor bearing would have to be terribly worn out before it would be loose enough to make the belt jump time.

I had one motor where it jumped time like that. After much head-scratching I found that the belt sprocket on the flywheel was split. So, it would "walk" around the flywheel.

Replacing the belt sprocket fixed the problem.

Note that this sproket is keyed to the flywheel so if there was a problem with the keyway or the pin in the flywheel it could lead to a "jumping time" issue.

Anyway, strange problem, just something else to check. You'll probably have to pull the flywheel to get a good look at it.

HTH & let us know what you find................ed
 
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