Does anyone service their own 2 stroke outboard?

[DonkeyApple]

I assume so as it's pretty straightforward but I wouldn't mind some basic pointers.

I've a Yamaha 4AC which was bought by my father in the mid 80s and has never seen much action as it was stored in the hold really for emergency purposes as we'd tow a dory or my lugsail dinghy if going anywhere a tender was generally needed.

Anyway, it has always been well looked after and for the last 20 years has been used occasionally but on fresh water and again stored appropriately.

The plan is to use it a bit this summer with the children so I figured that after over 30 years it ought to have a service. Plan being to clean the plug, change the gearbox oil, check the cooling impeller and re grease the main Points etc.

Fitted the outboard to a wheelie bin last night and it fired on the second pull as it always has done. And the water jet seemed healthy and in general all was good. The only negative would be that I'm sure it's not running as smooth on idle as it would originally.

Step one this morning was the spark plug. Generally good, gap ok but covered in black goo. I suspect this is a result of the last few times it was used I think it was running on 50:1 rather than 100:1 so I'm not worried about that. I think I'll end up putting a new plug in anyway.

Next the gearbox oil. None of the fittings have ever been undone and the I've not had any joy yet with the screws so I whipped the propellor off and removed the front of the box to release the oil. It wasn't sludgy but it was certainly a dirty brown. I'll order some oil along with the plug.

So far so good and nice and easy. I'm not going to bother servicing the carb unless the new plug has no impact on the idle. For the amount of use that it's had and that it's always been drained down I simply don't imagine it's not in fine condition.

The water impeller. Where is it? That's the bit I'm stuck on. It's not behind the black rubber plug half way up the shaft is it?

Also, greasing the shaft, I can see the lower nipple but is the upper one the one on the underside of the case itself?

Thanks.

[hidetheelephants]

The impellor is on top of the gearbox; to access you need to remove it, usually three fasteners and perhaps a clamp on the gear shift rod. Some photos would help. They don't idle very smoothly although fresh fuel and a new plug would help, as would cleaning the carb bowl of the 20 years of crap that will be in there.

[DonkeyApple]

Thanks. I recall the engine being bought in the mid 80s but it's never really been used. Until about 2000 it just sat in the hold of my father's yacht along with a new Avon Redcrest, neither of which were used more than a few times. Since 2000 they have both been in my garage, again being used a few times on the Thames in the last 20 years.

I suspect that the outboard hasn't seen more than 50 hours use in its life.

On tick over, as you say, it was never the smoothest of things and being a fixed to a wheelie bin doesn't make for the most stable of environments but the idle wasn't as consistent as I seem to recall it being. I do suspect that that will be resolved via a new plug. If not then I'll consider stripping the carb.

It all works beautifully though but as the water impeller is plastic I figured that after 35 years it made sense to change it. I'm very happy to row the length of the Thames with a kaput outboard but it's not so peaceful if there is a brace of 10 year old girls onboard.

[Matt Harper]

My first 2-stroke boat had a Force, 4 cyl motor that was in reasonably good shape, but had a very lumpy idle. This cured it.

Make sure you liberally lubricate the rubber impeller with silicone before reinstalling it, or it'll get torn-up in seconds.

[DonkeyApple]

Thanks. Murphy's Law has struck in the interim. Stripped it all down and galleys all clear of crud and impeller is fine. Sheared a bloody stud though!!





Clean shear right at the surface. That's going to be a bugger to extract.

[hidetheelephants]

Have a go at it with a left-hand drill, you might be surprised. You could just ignore it, 3 out of 4 is ample for holding the water pump together.

[DonkeyApple]

Thanks. I reckon that it could be left, especially if I make a rubber gasket for it. Will pop down to a friends in the week and stick it in the pillar drill. Hopefully he'll have some left hand bits also. In the meantime I've put some wd40 on it to hopefully release it a little

[paintman]

Your impeller needs replacing.
The wear plate under it needs replacing, looks well pitted.
What does the insert inside the cover look like?

Random Google with pics of parts:
https://www.bhg-marine.co.uk/yamaha-4ac-6e0-17-c.a...

This also came up, worth considering?
https://www.ebay.co.uk/itm/Water-pump-impeller-kit...

Lightly grease inside the cover when refitting & don't start unless the leg is in water - I use a workmate & a dustbin for my 4hp & a hosepipe & muffs for the 135hp.
I use Quicksilver 2-4-C multilube to grease the inside of the water pump. As recommended in the factory workshop manual. It's used to grease most other things on the engine as well!

FWIW the water pump housing bolts on my 135 are torqued in lbs/inch (50 and 35 which are 5.6nm & 4.0nm). Be worth checking what the figure is for yours.

Edited by paintman on Sunday 28th March 00:21

[DonkeyApple]

paintman said:

Your impeller needs replacing.
The plate under it needs replacing, looks well pitted.

Random Google with pics of parts:
https://www.bhg-marine.co.uk/yamaha-4ac-6e0-17-c.a...

This also came up, worth considering?
https://www.ebay.co.uk/itm/Water-pump-impeller-kit...

That's just the crud prior to cleaning. There's no pitting. It's like new after cleaning. I'd ordered a basic service kit in the morning but had to add a water pump kit just to get the bolt!

[GliderRider]

After twenty years, the crankshaft seals could be drying out or perishing. These seal the crankcase to prevent air being drawn in after the carburettor, which would weaken the fuel mixture. If after doing the rest of the servicing, you are still getting poor idling, flat spots on acceleration, or difficulty tuning in general, they would be worth investigating Worn seals may also weep oil from unburnt fuel mix when the engine is not in use.

Yamaha Outboard Crankshaft Oil Seal

Yamaha Outboard Crankshaft Oil Seal +identification info

It is likely that there will be a seal on each end of the crankshaft.

[Pistonsquirter]

An impact screwdriver is usually best for those oil fill/drain bolts. And one would usually confirm the fill plug can be removed before draining the oil

As you mention, a solvent based carb cleaner should help with the rough idle, its the float mechanism and the needle assembly that need to be un-gummed up.

Crank seals don't sound like fun btw!

[dhutch]

Love a good two stroke! I would certainly replace that impeller, looks well goosed which is not a supprise for a 30yo rubber part.

[DonkeyApple]

Pistonsquirter said:

An impact screwdriver is usually best for those oil fill/drain bolts. And one would usually confirm the fill plug can be removed before draining the oil

As you mention, a solvent based carb cleaner should help with the rough idle, its the float mechanism and the needle assembly that need to be un-gummed up.

Crank seals don't sound like fun btw!

Will be fettling with those plugs today. First attempt was half arsed as I knew the blade I was using was not large enough and there's nothing worse than having to look at chewed up screw heads that serve as a perpetual reminder to ones own incompetence.

Carb really shouldn't be an issue as it's never once been left with fuel in it and simply hasn't done many hours.

[DonkeyApple]

dhutch said:

Love a good two stroke! I would certainly replace that impeller, looks well goosed which is not a supprise for a 30yo rubber part.

It certainly resembles a dead spider. Had no joy removing the sheared bolt so when the new impeller arrives I'll be migrating to plan B which entails a minuscule skim of silicon sealant and three bolts instead of 4. Will ponder today whether to retap.

[DonkeyApple]

GliderRider said:

After twenty years, the crankshaft seals could be drying out or perishing. These seal the crankcase to prevent air being drawn in after the carburettor, which would weaken the fuel mixture. If after doing the rest of the servicing, you are still getting poor idling, flat spots on acceleration, or difficulty tuning in general, they would be worth investigating Worn seals may also weep oil from unburnt fuel mix when the engine is not in use.

Yamaha Outboard Crankshaft Oil Seal

Yamaha Outboard Crankshaft Oil Seal +identification info

It is likely that there will be a seal on each end of the crankshaft.

Thanks. Hopefully not. It runs as always off idle I just felt that the idle wasn't as smooth as it once was and I'm pretty sure that it will be down to the plug which I'm pretty sure is down to it being run on 50:1 the last couple of times.

[dhutch]

On our single cylinder 2hp yamaha 2-stroke one of the corner bolts has lost all its thread, cross thread or otherwise seized when I first removed it many years ago and doing something about it is still on the list. The only saving grace is its a 6-bolt interface (two lines of three) not a four bolt job.

If the oil plugs are like the huge cheese-heads on the 2hp we have, if stiff and you dont have an impact option, a mole wrench might work for you.


Daniel

[DonkeyApple]

dhutch said:

On our single cylinder 2hp yamaha 2-stroke one of the corner bolts has lost all its thread, cross thread or otherwise seized when I first removed it many years ago and doing something about it is still on the list. The only saving grace is its a 6-bolt interface (two lines of three) not a four bolt job.

If the oil plugs are like the huge cheese-heads on the 2hp we have, if stiff and you dont have an impact option, a mole wrench might work for you.



Daniel

Gave up on extracting the stud. Took the whole lot apart and even with a bit of heat it wasn't going to budge. New impeller arrived so rebuilt it using a smear of silicone sealant. Be surprised if it leaks.

Waiting on the gearbox oil before getting it back up and running. Currently wondering whether to fit a plug for an external fuel tank as its one of those little jobs that might transpire to be of use.

[PushedDover]

As it happens- yachting monthly have an article on it this month

Can scan if still required
And video

https://youtu.be/jRtMlUxEQX0


ETA
Failed-it’s re:four strokes

[paintman]

DonkeyApple said:

Gave up on extracting the stud. Took the whole lot apart and even with a bit of heat it wasn't going to budge. New impeller arrived so rebuilt it using a smear of silicone sealant. Be surprised if it leaks.

Waiting on the gearbox oil before getting it back up and running. Currently wondering whether to fit a plug for an external fuel tank as its one of those little jobs that might transpire to be of use.

My Suzuki 4hp has one factory fitted.
I've never used it.

TBH it would be too much trouble as I would need somewhere to put one & I can't connect direct to the two 25 litre main tanks for the big engine as it's oil injected not premix.

I have two standard plastic 5 litre cans & premix in them using them to fill the engine's internal tank. Use one until it's empty then start on the other. Next time I go to the garage refill it & just keep rotating them to avoid any stale fuel issues.

[DonkeyApple]

paintman said:

My Suzuki 4hp has one factory fitted.
I've never used it.

TBH it would be too much trouble as I would need somewhere to put one & I can't connect direct to the two 25 litre main tanks for the big engine as it's oil injected not premix.

I have two standard plastic 5 litre cans & premix in them using them to fill the engine's internal tank. Use one until it's empty then start on the other. Next time I go to the garage refill it & just keep rotating them to avoid any stale fuel issues.

Yup. I've a pair of 5L cans that I keep 100:1 in. Filling up on a river, which is where I'm going to use it will be fine. I have memories of filling it up in the Solent and various harbours where it's quite messy work. I've fond memories of refilling while the Red Funnel Ferry was attempting an assault.

Fitting a plug and using a 12L tank might make things a little easier in general. Easier to lug one tank instead of two and no faffing about.

All that would be required is drilling the blank out in the casing and fitting a T piece to the fuel line with the cut off switch becoming the fuel switch when the tank is attached and remaining the cut off when it's disconnected.