Yamaha 50 DETO lower mount

[SimonStDavids]

Hi all,

When I was dropping the gearbox off my yam 50 to change the impeller I noticed that a portion of the mid section has blown away around the lower mount.



And here is a closer look



Is it easy to change the mid section? Do I need to remove the powerhead or can I just leave the powerhead in situ and get a new mid section?

[Nos4r2]

Your powerhead is bolted to the midsection.

[two stroke mick]

Before you change the mid section you would want to figure out the cause of the failure. It looks like a corrosion problem to me.

[beamishken]

The mid section is kind of the first bit to be assembled to the saddle therefore everything else comes off first powerhead , lower unit,top mounts getting the powerhead and top mounts off can be a world of pain due to bolts snapping in the sandwich plate
It's doable but not an easy job

[beamishken]

Actually thinking about it you might not need top mounts off but once that far probably worth doing as they do fail

[SimonStDavids]

Thanks, I thought it might involve major surgery!

Would a weld and a new lower mount work as I have found the bit that has blown off?

Agree I need to find the source of the corrosion. During one of the September storms the little sr4 was swamped and the battery submerged, could the corrosion have been caused by the current earthing through the leg?

[phantom 19]

I worked as a Yamaha engineer for 18 years.

The cause of the problem is a design fault - All electric start Yamaha 40/50D have this problem sooner or later. It is caused by corrosion sandwiched between the large stainless plate of the lower shock mount and the leg casting. It has been festering there for many years.

I must've changed at least fifteen legs in the mid to late 90's when this issue started to appear. We even used to keep a brand new leg casting in stock it was that common. You need to strip it down and replace it ideally. There will be too much rot to be able to weld it.

Yamaha eventually redesigned the leg for the later 3cyl 40hp (40V I think) with a much better lower mounting. If you can find a scrap one from 98 or so onwards then your power head will fit straight on to the newer leg (don't get a leg from the later 50G as this is different it is the 60/70 leg)

The manual start 40/50 seemed to not be affected as much as the electric start models.

[Davie]

I know where you can get all the bits for £100 .....

If you can collect

[SimonStDavids]

Hi Davie.

Tell me more [emoji2]

I believe you are in Scotland and I am in west Wales, but as luck would have it my wife is in Stirling until Thursday!!!!! Is this anywhere near where you are?

Ps- you sorted me out ptt switch a while back and can't recommend your services enough [emoji106]

[Davie]

jeezo. Son was at Blair Drummond yesterday.

[SimonStDavids]

Hells bells! That is just down the road from the inlaws in Dunblane!!

Are you in Glasgow?

[beamishken]

Dundee opposite direction

[stul]

I have a Yamaha 40 HP 1986 3 cylinder.(blown piston)
lots of spares stripped down.
Im in Stoke on Trent,but often in North wales
If your stuck get in touch Pm or 07888 738217
Also have a Seloc repair Yamaha manual for years 1984 onwards
Stuart