OMC 40hp Gearboxes - late 1960s

For pre 1975 outboards and race motors only.

Moderators: Alacrity, Rapier

User avatar
floater
Posts: 1011
Joined: Fri Feb 06, 2009 6:47 pm
CMBA Member: 90
Location: Southern England

Re: OMC 40hp Gearboxes - late 1960s

Post by floater »

I've run my early 70s Evinrude 40s in test tanks, Typically up to 1/2 hour at a time much to the neighbours delight. They are always quite smokey and there's a good old black sludgy mess in the tank after, which is of course the remains of the oil. The first question is therefore are you sure you've mixed the oil ratio correctly?
Regarding the main jet it's entirely possible that over the years a friend of humanity has cleaned it with a drill so although it's stamped as a certain size it may now be way past that.
Your video seems to show the motor running reasonably well as far as I can tell, it's not four stroking which indicates a very rich mixture.
Another thing to consider is whether the synchronisation is set spot on.

I once had a Honda motorcycle that was running rich and wouldn't rev out. I had the carb apart a few times, in the ultrasonic tank at work and on the 120psi airline, no better. In the end I fired it up and squirted Redex into the carb with a syringe, that got it, whatever it was.

Sorry if you have already been through all of my suggestions, just trying to offer help based on some of my experiences.

User avatar
LitchboroughLitchbor
Posts: 36
Joined: Sat Apr 25, 2020 1:08 pm
CMBA Member: 0

Re: OMC 40hp Gearboxes - late 1960s

Post by LitchboroughLitchbor »

Many thanks for your suggestions. It didn't look so bad in that video, but it got worse - eventually stopping. I presume the plugs were too fouled up to continue.

I've wondered about my oil calculations, but every way I do them I come up with same answer - 4% - so 25:1. This early '60s model was supposed to run on 24:1, so close enough.

I wonder whether the oils are different. I think I've used up my stock of OMC 2-stroke oil, so I'm just using whatever the filling station or Halfords have on the shelf.

But I think the problem lies in the carb, because I've got a couple of videos of my trashed '67 running on both carbs. Both are smokey, but one is more smokey and more coughy than the other.

I'm also hoping to upload a couple of boat test videos of the '62 engine last Summer - sounding sweet - and this Summer - not sounding the same. I wasn't planning to do much to the carb this year, but when I ran the engine, it quickly stalled. I found that the cork washer gasket had disintegrated, and gathered in the base of the jet, blocking it completely. Since then I've cleaned it out - not too aggressively - but perhaps the hole is now a bigger than it should be?

But I'm planning another barrel test, now the new float is installed, and hoping it will be back to its old self again!

User avatar
LitchboroughLitchbor
Posts: 36
Joined: Sat Apr 25, 2020 1:08 pm
CMBA Member: 0

Re: OMC 40hp Gearboxes - late 1960s

Post by LitchboroughLitchbor »

Here are the two videos.

Summer 2020 - running fine
https://youtu.be/s4f4Oh2xT4M

Summer 2021 - not very happy
https://youtu.be/w8cNfxVa7TM

User avatar
floater
Posts: 1011
Joined: Fri Feb 06, 2009 6:47 pm
CMBA Member: 90
Location: Southern England

Re: OMC 40hp Gearboxes - late 1960s

Post by floater »

Yup, second vid is certainly chuffy, so I think you're right to be looking at the carb. Regarding your oil, that's probably why your test tank is sludgy, marine two stroke oil (TCW-3) spec is formulated to break down in water, general two stroke isn't. When your motor was made there wasn't much choice and it could run on pretty much anything including general motor oil, I'd avoid anything with a picture of a chip pan on the packaging though.

I can't remember for sure off the top of my head but doesn't your motor have adjustable slow and fast mixture needles?

User avatar
LitchboroughLitchbor
Posts: 36
Joined: Sat Apr 25, 2020 1:08 pm
CMBA Member: 0

Re: OMC 40hp Gearboxes - late 1960s

Post by LitchboroughLitchbor »

Here it is running with the new carburettor cork float

https://youtu.be/B1RFwbUe8ao

I'm much happier with this now. The plugs look much cleaner too.

Yes, I definitely need to change back to normal marine 2-stroke oil, because the stuff I got from Halfords stays black, and does not seem to break down in the water, in the normal way.

I've got a couple of '62 Johnson 40s and a '67 Evinrude 40, and the carbs are basically the same - fixed jet high speed tubes, needle adjustable jets for low speed. The '62s also have a hot water automatic choke, although I never use it.

I was fascinated to read about Nick's travails with the twin needle carb on his Evinrude ski twin. I've got a couple of smaller '50s Evinrudes I haven't looked at yet. Perhaps they are like this?

User avatar
floater
Posts: 1011
Joined: Fri Feb 06, 2009 6:47 pm
CMBA Member: 90
Location: Southern England

Re: OMC 40hp Gearboxes - late 1960s

Post by floater »

That looks like it's running much better with the new float.

I have a few Evinrudes and johnsons from 1960 to 70, 3 to 40hp, trouble is I've not touched them for a couple of years which is why I'm struggling to remember what's got what.

User avatar
Rapier
Site Admin
Posts: 12440
Joined: Thu Feb 05, 2009 5:16 pm
CMBA Member: 569
Location: West Glos

Re: OMC 40hp Gearboxes - late 1960s

Post by Rapier »

Seems a lot better. Non marine 2-stroke won't help either, especially when slow running. I've now gone down the route of semi synthetic / biodegradable TCW-3 if I can find it.

I have been having similar issues (at Cardiff last year and Hamble this) swapped out the float valve for a used spare which seemed to cure it - problem is the ethanol does nasty things to the tips... I have a new float valve and seat kit (p/n 396521) to be fitted soon - I bought a multi-pack of 5 at some stage.

Swapped out a poor gearbox repair in the day between Neyland and Cardiff. I'd been too optimistic regarding the level of wear on the gears / dog clutch on the rebuild; they were too far gone and any load meant it jumped out of gear and spoilt my boating plans.
Fasten bra straps and remove dentures...

User avatar
LitchboroughLitchbor
Posts: 36
Joined: Sat Apr 25, 2020 1:08 pm
CMBA Member: 0

Re: OMC 40hp Gearboxes - late 1960s

Post by LitchboroughLitchbor »

Hi.

Thanks for advice on 2-stroke oil and the carburettor repair kit part number. I asked Bob at South Coast about kits - so hopefully the part number will help.

I used to be the proud owner of one 1960s Johnson, but things have got a bit out of hand since then. Chris Tate has a lot to answer for........

https://www.youtube.com/watch?v=xatqmgBgybQ

I so enjoyed the video of his 1959 Johnson 75, that I've ended up with not one, but three of these (and a 90 and 115 thrown in for good measure).

But they're all a bit heavy for my Tremlett 15, so I've added another '62 Johnson 40 (which seems like it will be quite good) and thought a '67 Evinrude would complete the collection.

All of these have been bought on spec as non-runners. But they all turn smoothly enough. All that is except one. There was always going to one bad apple, and it turned out to be the '67 Evinrude 40. It looked okay in the advert, but when I took the cover off, it was a true Hammer House of Horrors!

I wondered what to do and considered scrapping it - but I had a set of piston rings on the shelf, so decided to have a go.

I doubt it will ever be very reliable, but it's now running and growing on me. I thought it was worth saving, and it's been an interesting learning exercise.

https://youtu.be/1aOAT4Gqaqg
Attachments
IMG_7718_1000px.jpg
IMG_7686_1000px.jpg
IMG_7680_1000px.jpg
IMG_7700_1000px.jpg

User avatar
Rapier
Site Admin
Posts: 12440
Joined: Thu Feb 05, 2009 5:16 pm
CMBA Member: 569
Location: West Glos

Re: OMC 40hp Gearboxes - late 1960s

Post by Rapier »

Even I would have run from that one. By the way, my other issue with the '64 was the float bowl gasket had perished and 'bits' were floating around.

I replaced the valve and seat today - my replacement gasket has already distorted with the lousy fuel we have.
Fasten bra straps and remove dentures...

User avatar
LitchboroughLitchbor
Posts: 36
Joined: Sat Apr 25, 2020 1:08 pm
CMBA Member: 0

Re: OMC 40hp Gearboxes - late 1960s

Post by LitchboroughLitchbor »

Yes, the fuel does seem to be causing all sorts of problems doesn't it.

I found your discussions on gearboxes very interesting. I'll try and dig out the worn parts I took out of my '62 Big Twin years ago. Both the dog and shifter fork were worn on the forward gear side, so I replaced both. Bottom end gear changes have been fairly reliable ever since. I still get a few problems at the top end of the gear change, due to worn parts, between the inner and outer casing, and the 2 screws which hold the outer shift lever, working loose. You noted some of the changes between the early '60s gearboxes and later '60s - in particular the detent ball bearing? My '67 Evinrude seems to have the detent, because it shifts more positively than the 2 older models.

Lots of other interesting little changes - like hex bolts on the thermostat cover, instead of slotted screws; a beefier exhaust cover with larger bolts; a cheaper pressed steel lifting eye; simpler fuel pump etc. etc.

A little quirk I'm working on at the moment is the tiny drain hole low in the gear case, from the water pump area. I noticed some cracking on the '67, which appears to have been caused by a blockage and corrosion in this drain hole. Now I've found the same thing on one of the '62s - so I've just bought a long 4mm HSS drill bit, to try and clear them. A similar problem cost me £300 for a new gear case my V6 merc, so I want to catch this before any more gear cases are wrecked.

I did feel a bit foolish - starting on the '67 Evinrude, and not cutting my losses and abandoning it. 'The worst bit was getting the seized pistons out - just hard slow work. I think the top main bearing will probably need to be replaced, but I'm not hearing too much complaint from it yet.

I finally got to the bottom of why the water pump was not working. Corrosion in the lower unit was preventing the cover from seating properly. Another lesson learnt - and maybe the reason why I've had problems with some other water pumps in the past.

Now pumping plenty of water. No thermostat at the moment. Next steps - hopefully repair a damaged helicoil thread for the lower spark plug, and fit a new cylinder head gasket.

https://www.youtube.com/watch?v=4kUjXoBm_yo

Post Reply