Odd Mariner 20 (Yamaha 20) fault

[Scrottocks]

Have recently carried out a thorough stripdown, cleanout and overhaul of the timing/magneto ignition/carburation on a 1977 (or slightly later) engine. Set cb gaps to 35 thou as per manual and fully set up including all throttle linkages, etc . But wouldn't start. No spark!! None at all - I could hold the plug leads - nothing. Eventually traced it to the cb points movement/lift being minimal and when set at 35 thou they wouldn't even close - hence the lack of spark. Only by setting the gap down to about 12 thou would they close and open as required and then the engine ran - pretty well, actually.​

Have not yet had the opportunity to get the boat and engine into the water to try a 'power test'. In the past it has always run reliably.​

The problem was that the 'lift' from the cam on the flywheel boss was very small, insufficient to raise the cb points cam follower and produce 35 thou opening on the cb points. (New points by the way but that wouldn't change this effect). This is odd. I can't believe that the steel flywheel boss would wear - not caused by the points cam follower. Initial (and imprecise) vernier measurements on the flywheel boss indicate a lobe of not much more than 10 - 15 thou; not the 30-40 thou I was expecting.​

Has anyone else had this problem? And a solution? - remachine the flywheel boss? Buy a replacement? Aaarrghhh!​

 

[Willyclay]

Re: Odd Mariner 20 (Yamaha 20) fault

You might check the Sierra website for their CD conversion kit. I know it fits older J&E motors with points. Only works on magneto type ignitions without alternators under the flywheel. Good luck and let us know what you do!

 

[Willyclay]

Re: Odd Mariner 20 (Yamaha 20) fault

Another thought after re-reading your post is that most breaker-point ignition systems I am familiar with use .020in gap, not the 35thousanths you mention from your manual. We are talking inch scale, not metric? If so and your cam lobes mike at 10-12thousanths, the resulting gap at the points should be greater due to the leverage of the breaker points arm. I agree with you that the wear on the cam lobes should not be drastic but the motor is 30 years old. FYI, I do not have a manual for your motor and am speaking from experience only.

 

[Scrottocks]

Re: Odd Mariner 20 (Yamaha 20) fault

WillyClay,​

:redface::redface::redface: Note to self - RFM - carefully! Whoops, a whole post based on a false premise. Checked the manual when setting the points, saw 035 and as it's an American manual assumed that it must be 35 thou. NOPE! It really is 0.35mm = 0.014 thou. Having been used to working on car and motorbike engines over the last 3-4 decades I should really have realised that something was odd.​

Hence reducing the gap was the correct action, no probs with wear on flywheel boss; I could have saved myself soooooooo much time!! And then I publicised my ****-up in public for the world to see. :redface: Anyway, all's well that ends well.​

Thanks again for your advice. ​

Scrottocks​

 

[Willyclay]

Re: Odd Mariner 20 (Yamaha 20) fault

Good show! I love situations when I thought something was wrong and it turned out to be correct. Now your peace of mind matches how well your motor runs. Glad I could help. I am no expert like so many contributors to this forum; just an old guy with some experience. Best regards. WC