Replace pull start with starter motor on 1982 Johnson 7.5HP (J8RCNR)

[csilvest]

Greetings all! I would like to change the rope pull start on my 1982 Johnson 7.5HP (J8RCNR) motor with an electric starter motor. I use it as a trolling motor on an 18' Starcraft. Works like a charm once started, but due to ever-increasing arthritis, I'm enjoying the starting ritual less as time goes by. I'm hoping there is a starter motor that will due the job. I'm not sure such a thing exists.

I've attached a pic of the existing pull start mechanism. From much search, I think this:

http://www.iboats.com/mall/partfind...&gd_poid=242414&gd_row=2&session_id=670016441

might work, but I'm not sure of 2 things:

1. The pinion on the existing pull-starter is 13-teeth, but all electric starters I've seen are 9- or 10-teeth; I'm guessing (hoping) the gear pitch is "standard" and the starter motor pinion is just smaller diameter.

2. Mounting points; the existing pull-starter has 2 bolts at the bottom and 2 at the top. I need to know the dimensions to be sure it will fit.

So, if anyone has done this upgrade, or knows for certain what part# will do the job, I'd sure appreciate your help.

Best Regards!

 

[flyingscott]

Pretty sure that motor was never offered with electric start there is no retrofit for it. Find a motor that has electric start already on it. If I am wrong somebody who knows will be along.

 

[racerone]

++++++ ---Agree with post # 2 above.

 

[oldboat1]

also don't think it can be done (and could be wrong) -- this might work as an alternative: http://www.ebay.com/itm/173523-Top-...ash=item1a2e1f00b9:g:5rYAAOSwfVpYnKN7&vxp=mtr

 

[Scott Danforth]

here is conversion to electric start on that motor in 3 easy steps:

sell old motor, convert to pile of cash
open wallet, dump contents to add to pile of cash
take new bigger pile of cash, buy motor with electric start

 

[oldboat1]

Y'know, a portable drill might work, applied to the flywheel nut.

 

[just_james]

Y'know, a portable drill might work, applied to the flywheel nut.

You might have to have a few drills cause when it catches might throw it overboard lol

 

[oldboat1]

Don't think so. (But don't use your best drill for the first try....) With the improvements in batteries, might be able to motor home using the drill!

 

[csilvest]

Thanks top all for your replies. The concensus seems to be "get a new motor with electric start". I've started searching for a suitable replacement in the used market... as much as I'd love a new motor, I simply can't justify the cost of a new one (new motors tend to be more than I paid for the boat!).

In the meantime, I'm keeping my eyes open for a cheap solution. oldboat1's suggestion of a portable drill motor is an example of the "out of the box" thinking I like. Correct me if I'm wrong, but all I need is a motor that will turn the flywheel, ideally disengaging once the motor starts.

For that matter, can anyone explain the need for the starter motor to disengage after once the motor starts? Is it just to reduce wear on the flywheel and starter pinion? I suspect electricity will be generated by the start motor being driven by the flywheel, but can't see why this is a problem.

 

[fhhuber]

There is always a way to put electric start onto an engine... It may cost more than a replacement engine that already has electric start.

the drill idea is close to one solution, but 7.5 hp engine needs a 4 hp drill and Arnold Schwarzenegger on a good day in his 20's to direct drive the flywheel nut. You need a reduction gear of some sort.

2.5 hp or below might get away with the direct drive with a common 18v cordless drill.

I deal with RC models and we retro-fit home-made electric start on engines as small as 10cc or .61 ci (actually capable of 2+ hp at 14,000 rpm) there are also kits for that which cost about 2X to 3X the cost of the engine.

So...
1) Can it be done? Sure.
2) do you REALLY want to do it? Probably not.

*********************

to start the engine the starter motor has to spin the engine appx 10 to 20 rpm. Sizing the gear reduction for that and selecting the correct electric motor for that means a high rpm electric motor and significant gear reduction.
Then run the outboard up near 5000 rpm and you're spinning the starter motor at 250 to 500 times its rated RPM.
That won't end well.
You need the starter motor to disengage from the gear like the "bendix" in a car's starter.
We use one-way bearings and other tricks in RC model conversions to remote electric start.

 

[fhhuber]

Note... the direct drive to the flywheel nut... you need something to kick the drill loose before the engine tries to break your arm when it starts... because a 7hp engine will break your arm if you don't. 2.5 hp might break your arm...