59 Super Thunderbolt

bholmes7

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Oct 11, 2008
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Hello,

I recently purchased a Glastron with a 40 HP mercury, which I believe is a 1959 model. The previous owner indicated when he takes it out, it runs for approximately 15 minutes, then shuts down and won't start.

A mechanic in town explained he believes the impeller has been damaged, probably from the engine being operated out of the water, hence the engine overheats and shuts down.

Does this sound like the most logical explanation related to this problem? What other conditions may exist to recreate this issue?

Thanks in advance!!
 

Laddies

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Re: 59 Super Thunderbolt

You should be able to tell if the engine is cooling by the telltale on the port side or by checking the exhaust cover for heat. I would think that there is a good chance that when the engine gets warm the magneto is failing have you checked it for spark when it is acting up?
 

bholmes7

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Re: 59 Super Thunderbolt

Thanks for the follow up.

I have yet to get the unit in the water, as I purchased based on the seller being a friend of a friend. I thought the same thing (electrical), and shared with one mechanic I thought it may be the magneto, based on comments noted on this forum.

A marine mechanic is diagnosing this week. He is confident he will have an answer by tomorrow.

I'll let you know, once I find out.

Thanks again!
 

Chinewalker

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Re: 59 Super Thunderbolt

Bad coil or condenser would be my guess...
- Scott
 

bholmes7

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Re: 59 Super Thunderbolt

Ok, Here's what has occurred to date, after the mechanics have tooled around:

- After taking to shop, they ran for 20 minutes plus with no obvious issues after supposedly cleaning up some wires (note: owner commented this was one of the cleaner/better condition units of this model year he had ever seen)
- Took out on lake; motor ran for five minutes then cut out - same problem as before
- Took back to shop. They worked on for a bit, then noted no spark. Note: They tested all four cylinders during the first visit and had good spark/compression. They could not tell me why there was no spark after they started working on the unit the second time
- They wanted an arm and leg to take apart the magneto, to determine if the points/condenser was the problem. I told them I could do this at home. I proceeded to take apart the unit. (I have average to good skills in basic engine repair, IMHO)
- Renewed the breaker assembly (400 grit SP).
- Noticed condenser appeared old and smelled a very slight tinge/residual smell of smoke.
- Replaced with new condenser
- Replaced plugs with Autlolite 303's
- Cleaned up dist cap "prongs", rotor cap, and all other contact points
- Gapped points at .09
- Tested spark plug wires to dist cap for continuity - all good
- Put back together; tried to start, no luck
- Tested for spark; none
- Pulled off wire to primary ground screw on the magneto - Tested for DC voltage while cranking; appx. .02 volts (positive line from voltmeter grounded to block, neg to wire leading to ground screw)

So, it appears there is some electricity happening at low levels. At this point, I am totally lost. I did order a new breaker assembly which should arrive this week. Is there any other testing I can do to determine why I am getting no spark?

Thanks in advance!!
Bob
 

Laddies

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Re: 59 Super Thunderbolt

You need to find a shop with a magneto coil tester, also make sure it has the right condenser not a will fit. Your trouble was either the cond or coil to begin with.
 

bholmes7

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Re: 59 Super Thunderbolt

I'll take the magneto in to have it checked out.

Thanks much.
BH
 

bholmes7

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Re: 59 Super Thunderbolt

Laddies,

I got to looking at the old condenser and checked it for continuity. No continuity between lead and body.

The marine shop supplied me with a new condenser; part number 70660 (Sierra Supply) I cannot match up this condenser part number with the original (394-1130A1), anywhere.

However, I get several cross references for condensers at different sites, one through Sierra Marine, 18-5169 for my motor, S/N 1315728.

If the 70660 condenser is the incorrect part, would this cause the motor not to have spark? Do you know of a way to cross reference this specific condenser? I could not locate any info. Interesting side note, Sierra Marine's website pulls up this part #, but does not list what motor it is designed for.

Additional quest., where is the coil located on this motor?
 

Laddies

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Re: 59 Super Thunderbolt

I don't know what the cond. that they sold you is but thats not a Sierra number the number that you listed is the right cond number but sierra don't list the points you need. East coast marine is a great place for the parts for the older motors as mad props said. We nornal test coils and condensers rather than just replace them but if you can't find a service place with a tester I guess your stuck with replacement.
 

Chinewalker

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Re: 59 Super Thunderbolt

Also - to save some hassle down the road - test the mag outside of the motor before reinstalling. You can test in two stages - without then with the cap & rotor in place. Without the cap in place, hold the body of the mag against a bench vice or car bumper, keeping the coil tab about 1/2-inch away from the vice/bumper. Spin the mag over (clockwise looking down). Spark should jump that gap. With the cap & rotor in place, put a set of spark plugs in the boots and clamp the plugs in your vice. Again ground the body against the vice and spin it over. You should get spark in all four plugs.
- Scott
 

bholmes7

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Re: 59 Super Thunderbolt

A new condenser and breaker assembly is on its way. I'll let yoou know what happens!
 

bholmes7

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Re: 59 Super Thunderbolt

Ok. Replaced breaker assembly and condenser. Gap ad .010. No luck. Tested mag by Scott's methods (both), no spark. Thought maybe was not turning fast enough, put a small cordless drill on slow speed with voltmeter to Mag - no reading.

I take it the Mag can go at anytime?! Can I safely predict the Mag is shot? If so, can someone suggest the best place to obtain a new/rebuilt replacement, short of a wallet busting price?
Bob

(See attached photo of Mag assembly)
 

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Laddies

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Re: 59 Super Thunderbolt

You might check the local dealers for a used coil that they have tested or ebay has some complete mags most the are called rebuilt they polish the point to get them to work but at lest you have new points fot them, you don't need a complete mag in less you can find one cheap. Other than that ck old mercs for a new coil.
 

bholmes7

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Re: 59 Super Thunderbolt

I replaced the coil, condensor, and breaker assembly. It runs rather good, but probably needs some minor adjustments to the carbs, which I will get to.

However, when I put it in gear, the engine stalls. When out of gear, it runs well at slow and fast throttle settings. Back in gear slowly, stalls, like the unit us under some undue torque, or the throttle is not engaging promptly after it is put in gear. In addition, I also tried to put it into gear with (somewhat) immediate 2/3 to 3/4 throttle and it also stalls.

The mech. put on a new throttle clip (don't know the part name), the red plastic housing over the throttle cable at the motor that has clips to keep the cable from sliding when the interior is sliding back and forth to initiate the fuel system. Not sure what adjustments or issues that may have caused?!
 

Laddies

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Re: 59 Super Thunderbolt

Usually if the engine stals when shifting the idle mixture is either lean or a little slow.
 
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