Johnson 4HP twin

[petrolhead]

our tender uses a 4HP twin Johnson I bought new in 1994, its throttle cable needs replacing andit is £100 including carraige!

So, just bought a faulty motor complete, 1996 model, identical motor, for less than that on basis it has a cable and loads of other useful stuff. The spare motor, starts easy, runs perfect and is super super clean........shame to scrap it really BUT bought with prop not turning when in gear and when I fired it up it pumped no water so the problem was narrowed down. As expected top of drive shaft is chewed with a smooth spline shame it was not simply snapped.

Does anyone have experience of this on these little motors, Why has it dne it and is it even worth taking the power head off to inspect the crankshaft end? if it were ok in theory a driveshaft would fix it.........though a throttle cable would still be required

Maybe I should just pull it apart for spares, I have been here with cars bought to break/scrap and end up tempted to sort them out

[floater]

Not had a smooth spline before but have experience of the driveshaft rotted into the end of the crank. It must have hit something solid although I would have thought the prop and shear pin would have taken the damage. I wonder if the gearbox or pump seized?

I imagine the crankshaft is hardened steel and the propshaft is softer stainless so there may be a chance you can extract the propshaft remains and swarf from the crank and still end up with a usable powerhead.

[petrolhead]

just back from phase one of our holidays........for once sun, no gales and lovely boating

when I say smooth splines, well they are maybe half chewed off which is more worrying, cvos on that basis maybe the other half of damge is in the powerhead. It is very strange, gearbox not seized it seems. I can turn drive shaft and pump/prop turn. I cant ascertain if neutral works off the motor.....its one of those the gear rod stays in the midsection and pushes thru a seal in the gearbox on refit.

Prop which is plastic perfect, spare shear and split pins still in powerhead unused.

I will take a pic sopmetime of the drive shaft and may well take the powerhead off, its so clean all nuts bolts undo and its a simple little thing. If it is usable it only needs a drive shaft to be a good'n. (plus a starter rope, thumb screw and gear cable now pinched for my existing motor!) all of which could come off a breaker fairly cheaply.

[MAW]

This is the weak spot of what was a very handy, light weight engine. I used two or three over a number of years to propel a Broads yacht. They were ideal as very light and easy to lift on and off the back - even when under way. But in the end, they all succumbed to stripped splines. Obviously, I was pushing a boat weighing beyond the spec. Opening the throttle slowly made them last a bit longer.

I have one - splines stripped - in my garage if anybody has a use for it...

[petrolhead]

intertesting, I spent 20 minutes yesterday and took the power head off. The crankshaft splined hole has indeed stripped........smooth as a babies botty useless.

There is a huge lump or crankshaft visible and the bodget side of me looked and contemplated welding a drive shaft in and devising a coupling low down its not worth the bother though. shame, its a much cleaner motor all round than mine which we bought new so maybe I will transplant the power head over some time. Ran lovely in the dustbin!

It is as you say a super motor, very light and quite powerful for its size. Has powered our tender for 18 years now.

[gfgarland]

Don't toss it in the rubbish! Weld a 3/8 drive socket to the spline end of the crank and grind the driveshaft to match the square drive of the socket. The engine will never notice the difference and neither will you! I have done tons and it works a treat.

[Alacrity]

Listen to George Petrolhead - he one of our Canadian cousins & really knows what he is talking about, I am familiar with him from Johns Old Mercs forum.

[petrolhead]

I just saw this post and its a FAB idea.................I was not so wrong welding to it! The motor is in lots of bits in a box but kept so I still have a spare power head if I need one They are cracking buzzy little motors on song and light for the power.