advice on older 85 horse merc thunderbolt ignition motor.

[Rodrunner]

Hi guys, I'm seroiusly considering buying a 16' jonboat with an 85 hs mercury thunderbolt ignition motor. lower unit is jet drive. I believe it is early 70's model but not certain. Outer shell has red and chrome labeling vs the blue and chrome. Any advice on the motor would be greatly appreciated. Really needing to know if I should spend the 2500 the guy wants for the boat and motor? Boat is in pretty fair shape. Owner says motor runs good but wont know for sure untill spring. Thanks a bunch for any and all input.

Jason

 

[Rodrunner]

Re: advice on older 85 horse merc thunderbolt ignition motor.

Not even sure if this is an inline 4 or 6 at this point. Provided the compression is good and the thing runs, is it worth the investment?

 

[Chris1956]

Re: advice on older 85 horse merc thunderbolt ignition motor.

Well, That motor is from the early 50's I would think, by the cowling color. Second, I had a 12 Jon that was rated for a max of 7.5HP, so it sounds like it is real overpowered. Third, I think the price is outrageous, given that the motor is about 60 years old.

 

[Rodrunner]

Re: advice on older 85 horse merc thunderbolt ignition motor.

Motor is either late 60's or early 70's . Boat has re- in forced transom to handle motor. Does anyone have any experience with the thunderbolt motor

 

[jbjennings]

Re: advice on older 85 horse merc thunderbolt ignition motor.

There is nothing wrong with the thunderbolt ignition, other than the parts are expensive, the wiring is likely 40 years old, etc. The drive shaft on that motor will be mild steel, and is prone to having rust pitting at the sealing surfaces. I wouldn't even consider paying $2500 for such an old rig. It just isn't worth it. The jet drive, if that old, wouldn't be something I'd be interested in AT ALL. Jet drives have very precise tolerances that must be right for the drive not to cavitate. The powerhead also has no cylinder head, and corrosion in the water jackets can be a problem, along with corrodes exhaust cover baffles. The rig you describe has very little value at all.
JMO,
JBJ