Resolved: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

[yorab]

Motor in signature. Fresh rebuild. I finally got to go out on the lake this evening. Break-in procedure for this motor requires running at approximately 3000 rpm for the first hour. It ran great at 3000 rpm for about 45 minutes. Then I heard a misfire or something similar. This went away when I dropped the rpm down to about 2000 rpm. I shut the motor down for a few minutes and when I tried to restart, no luck. I pulled the cowl off and noticed that the timing belt was very loose. The distributor bracket had shifted. I guess that I didn't tighten down the bolts enough. I think that I'll put some lock washers under the hold-down bolts. The original set up used only flat washers.

I believe that the belt had jumped a tooth, but I couldn't see for sure because the flywheel guard was in the way. I'll check the timing tomorrow. If this is what happened, could this have caused any damage? I also checked for spark at the starboard plugs but I wasn't getting any. I would think that even if the timing had jumped, there should still be spark on all cylinders. Is this correct?

 

[Willyclay]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Sorry you had a problem during your first outing. I had a similar problem with my 1962 Johnson 75 and found a damaged distributor shaft that I believe was caused by my failure to properly tighten the shaft nut. Hopefully, yours was just a tension issue. Agree that you should get spark if the timing has "jumped" or just shifted from the proper setting. Hang in there, you can whip it!

 

[yorab]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Okay, I'll first make sure that the timing is correct and that the distributor shaft/other parts are not damaged. That will be one problem solved. Then I'll move on to checking for spark. I'll update later today.

 

[hidef]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Fortunately you are dealing with a two stroke so a jump in the timing will mess it up as far as starting goes but there is nothing internal that would be hurt. You bracket most likely loosened and then the belt jumped a tooth. Check the torque on all the bolts.

 

[yorab]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

When I checked for spark after reassembling a few weeks ago, I simply pulled a single plug wire and used my spark tester from the auto parts store. I left the other three leads attached to the plugs and moved to each cylinder consecutively. At that time, I had not introduced fuel to the motor, so I didn't need to worry about it starting without water. Now I have fuel in the system and it could start. With this motor (non-magneto, battery-distributor type) can I simply pull all of the plug wires off the plugs and out of the way (so that it can't possibly start) and then test for spark one at a time? Do I need to ground the leads in order to prevent damage to the condensor, points, etc?

BTW, I'm a bit paranoid about removing the plugs if I don't have to due to recent issues with a thread insert. I'm hoping to test for spark without removing the plugs. But if I have to, then I certainly will.

 

[F_R]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Ground the plug leads that aren't under test, so you don't strain the coil or rotor.

Speaking of rotor, that could be the problem. They sometimes arc through to the shaft.

 

[yorab]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

So the timing belt was definitely loose due to the distributor bracket hold-down bolts being loose. No question about that. But, the belt did not jump. Timing was still spot on. I looked at the distributor components and everything checked out okay. I grounded the leads and checked for spark on each lead. Very random and spotty at best. I then checked for spark directly from the ignition coil. Also spotty and random.

I bought my coil a few run-hours before I decided to rebuild, so I knew that it should be fine. However, I forgot what it looked like. That was almost 4 years ago afterall. Therefore, I made a guess as to which one was the coil that I bought and which was the coil that was on my parts motor. I must have gotten it wrong. Once I switched coils, I tested for spark at the coil. Very consistent and strong. I then checked for spark at each of the leads. Also very consistent and strong. I believe that this problem is corrected. I will know for sure this evening as I am taking the boat back to the lake for more testing and break-in. Thanks to all for the advice.

 

[ezmobee]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

I want video!

 

[yorab]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

There will be video-a-plenty, oh yes, video-a-plenty!

 

[yorab]

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

Re: 1963 75hp Possibly Jumped Time (But Not Like Marty McFly)

The ignition coil worked out well. Ran great...for a while. I'll post about my new problem(s) in a new thread.