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A Little Bit Of An Engineering Challenge....


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Picked up an outboard motor thursday on a bit (huge) of a gamble, it was advertised as for spares and stated that the cylinder block was knackered so no issues with the deal, I recon I'm gonna have a wee bit of a challenge but going to have a bloody good go at rebuilding the block (with a lot of help from Pete the welder at work).

When I got it home I hooked up the fuel tank and gave the primer bulb a few squeezes and tugged on the pull cord and away it went sweet as a nut so has to be worth a go at saving, it's a honda BF6B with the throttle stop removed to make it an 8HP, it's the same motor other than the restriction.



Not sure how it's not showing signs of major overheating with the level of crud blocking the water jacket but it all looks good other than the corrosion issue.

The crank, rods, and pistons look like they've barely run, main bearings look immaculate, these have not been cleaned they are as lifted out, the bores still show signs of the cross hatching, not bad for a 2005 motor.


Wish me luck....


The clean up process so far, will be better when I get into the blasting cabinet at work.



I'm thinking a bit of aluminium bar drilled and tapped to replace the missing thread and the radius of the missing water jacket looks close to the skirt of a lycoming piston (this bit came to me in the pub after a few beers, lots in the scrap bin at work and a good grade of aluminium) welded into place will cause much less distortion than building it all up in weld.

If I can get it up and running with no leaks for less than £200 I'll be chuffed, that includes the £80 I gave for it.


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  • 2 weeks later...

Didn't use the piston skirt in the end, had a couple of otherwise scrap magneto housings that had an almost perfect shape section so chopped them up.

Had a skim down today till the rest of the face just started to show signs of the cut then finished off with a sheet of emery on a surface table by hand.



That'll do it I recon, can consider buying the gaskets now.

Gonna give the water jacket another blast out then paint inside with a couple of coats of urethabond 104 as it sets rock hard and resists most things and will sort out any porous bits in the welds.

Got a couple of small bits in the exhaust ports to weld and dress then the head will be sorted.

Looks like I got myself a cheap outboard.



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12 minutes ago, Tobster said:

You could always liquid penetrant test (Die Pen) the welds to make sure it’s sealed (water tight). Any local NDT company should be able to help you.

I can do that at work myself but gonna coat the inside as protection anyway so not going to worry about it, it's not as if the cooling system runs under any real pressure on a small outboard.

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34 minutes ago, Bikertov said:

Wow, looks like new !

The internals looked like new when I stripped it, no signs of wear anywhere just the corrosion issue, the thermostat was caked in crud but a quick blast with ground walnut shells bought it up like new and after a soak in duck oil and a few heat cycles in the oven it appeared to work fine so got away with that, £98 for the gaskets and £25 for new mounting rubbers (industrial price not honda price) and £5 for the welders breakfast and job a guddun!

A 6/8hp honda for >£220. :default_biggrin:

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Mounting rubbers arrived, £23 industrial price not honda's idea of £135 I must add.

A quick fettle this evening and it lives :default_party0042: only tried briefly as the rubber grease around the impellor will only go so far and it's raining and geting dark so I'm not getting a water tub sorted tonight, the main bit is it runs and oil pressure light does as it should, had to re-check the book as a lit oil light says problems to me but on the honda it has to be lit to be ok.

If the weather plays fair at the weekend I may wrestle my rib and trailer out of the garden for a test run on the local river, or I may just have a hangover.....

I am a happy bunny!

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