Vintage Tohatsu M9.8A fires right up! Impeller & fuel line options?

[daveh77]

You guys are right, this could get addicting, lol.
After sitting in a shed for 8+ years, cooking in triple digit summer heat, this 'obsolete' M9.8A fired right up! There is gas sludge in the fuel bowl so I expected the carb to be gummed up too but with gravity fed fuel directly to the carb, it started and ran ok.
Water was coming out of the back of the column, and out of a small hole in the base of the engine right behind the rear mounting bolt.
Is that a normal telltale hole or a drain for water that's not supposed to be in the motor base? (second pic)
After only a few minutes, both the water streams stopped, so I assume the impeller died?
Shut it down before it could get too hot.
Does the mostly outside corrosion indicate salt water use?
Information on the A version of these 9.8s is almost nil but I did get a genuine Parts List book. Haven't found a service manual anywhere, only for M9.8B or C models.
How much difference is there in the A or B models?

Personally, being new to outboards, I really like this design: Easily accessible simple dirt bike style carb, fuel bowl & pump, coils, etc.. I love accessible common sense engineering on machinery. Not sure about the bottom end, but the top end couldn't be easier to work on.

This short shaft fits the boat much better than the '59 Evinrude 5.5 LS and has more power, easier to work on, not to mention 10 to 20 years newer. Guessing it must have needle bearings instead of bushings, etc...
Not having a B model to compare it with, I don't know how much of the A carried over or was changed.

Just exactly how rare and obsolete is this A model?
As someone stated in the other thread, I must be able to retrofit some other impeller.
Is that fuel connector obsolete or is it the same as other Tohatsu or Nissan, Honda, or?

All suggestions and input are greatly appreciated.
Thanks, Dave

 

[Sea Rider]

That 9.8 HP oldie of yours has nothing to do compared to any modern 9.8 HP, it's one of its kind. So impossible to swap new spare parts for it. Swipe your tongue through the lower unit, will know if was used in salt water. LOL !!​

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Happy Boating​

 

[daveh77]

Sea Rider,
It never occured to me to lick the darn thing! Thanks for the old salty dog tip!

I know its unique and obsolete but they built them for 20 years '76 to '98 before the B model came out in 1999. I know that no "modern" parts will fit but didn't realize that a 1999 or 2000 M9.8B would be considered "any modern 9.8 HP".
It is just so simple to work on I hate to give up on it.

So just wondering how much different a model B is, what might work, or is model B a completely new design where almost nothing would cross over.
I was hoping some of you Tohatsu gurus like you or Paul could tell me about the differences in Model A vs B but I suppose its possible these were before you took an interest in Tohatsu. No problem, no offense intended, I get it.

My Grandpa bought a $1475 EMF car in 1912 when everyone else were buying $400 Model T.
I started riding and racing KTMs back when they were Pentons and almost no one knew what a KTM was.
So I don't mind a 'one of its kind' if it has some advantages over more common stuff. Like real easy to work on.
I see folks running OB motors waay older than this thing, many with obsolete unavailable parts, and harder to work on.
I just wish I had a factory service manual. (and a better budget, lol)

Thanks for your input, I learn something from every post.
Dave

 

[Sea Rider]

You're welcome Dave,

I like working on oldie motors myself as long they can still work without needing any new part, worse if extremely obsolete and with NLA or hard to find part for them.​

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If the current motor still works fine use it as is, wouldn't worry too much about finding new spare parts for it. Assume it won't be used as a main motor powering aything that floats ?​

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If all the other mechanical an electrical parts are doing their respective homework right, the only part that will be of concern is the impeller. For peace of mind drop the lower leg and have a look at the impeller condition, if has wear on one side of the vanes check if you can flp it and use the other side which should remain virgin, works well if the impeller its whole and flexible, not dried or hardened whatsoever. Compared to other impeller motor brands Tohatsu ones are one of a kind in duration and the material they are made of.​

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The liner can be micropolished with toothpaste in circular motion even with the tip of your finger till smooths out, impeller will last longer and pump water much better upwards.​

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Tried to find a spare parts manual for your motor but it's non existing due to its obsolescence. Checking your posted pics definitely no other modern 8-9.8 B2 model from 2002 upwards will match. Couldn't find anything realted to a 9.8B Tohatsu changed the old design for a much better model...​

Happy Boating​

 

[daveh77]

Thanks, I assumed since it quit pumping water, that the impeller had given up the ghost. Is there anything else that would have stopped it from spitting water?

I did get a factory parts manual off ebay but no luck yet for a service manual.

Good to know that B2 model is completely different design of engine. Is that also true of the lower end?

I have noticed the newer models all have the ignition advance plate connected to the throttle, also high & low adjustment knobs, like all other outboards.
This 9.8A has none of those, making me wonder how it worked as an outboard at all?

Any newbie advice for dropping the lower leg?
(without a service manual or OB experience)
I'm very mechanical, more inclined to that than most, started wrenching on the farm at a very early age. I have always said I'll work on anything IF I have the FSM, not some chiltons or other generic manual.

Primary motor?
Nah, that would be my son on the oars, or the 55# MinnKota, lol.
We got these old motors and a 12' aluminum boat at a barn sale for $300. My fishing crazy 13 yr old son wouldn't let me pass up a boat for $300. Around here this boat without a motor goes for $600-800, up to $3,000 with a running old motor, so 300 wasn't a bad 'investment'. lol
He is so tired of bank fishing and hauling in weeds instead of fish, me too.
He insisted we need to "get out there" where we can catch fish instead of weeds! LOL

We also were gifted a 16' Aire cataraft that can take up to 10hp. The MinnKota does ok on it but would like to try a gasser on it too. The MinnKota does ok on the Yakima River but not enough grunt for the Columbia River.
For safety until we get more experience and reliability, I only go upstream so we can drift back down to the ramp if we have an issue.

Thanks again, Dave and Allen

 

[Sea Rider]

Don't know that precise model as never have physically seen one. To remove the lower leg check for a round brass tube joint that holds both upper and lower rods together which is located between the lower and the middle leg, remove the upper spring pin banging hard with a round punch tool with same or bit les diam that of the spring pin to release the upper shift rod. If never have been removed expect to find any of them amazingly seized. In that case drill the upper one with a HSS drill bit dampen in oil for the tip to last longer. Posted pic says it all, install a new pin, a nail cut to same tube diameter and width, a plastic tie wrap...​

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Look for 4 bolts located under the upper lower leg that holds both legs in place, remove them, if the drive shaft is not seized to the lower crank shaft which hope not, wiggle the lower leg sideways pulling it downwards, should come down... ​

Check if the current installed prop is a non exhaust or exhaust one, if the latter could install a less prop pitch to bump wot revs towards the max rpm range factory stated to push any of both boats more efficiently specialy running up stream. A 9.8B2 exhaust prop will probably match ?​

Happy Boating​

 

[daveh77]

Thanks for that detailed instruction.
Pic of the shift rod attached.
Has to be in forward gear to tilt. N & R tilt is locked.
Assume the protruding vent behind the prop is the exhaust and the screen on the side of it is the water intake, correct?
Does that fuel connector look like anything still in use?
What is the electrical connector?
Thanks!

 

[Sea Rider]

Sorry, the detailed lower leg removal corresponds to the 9.8B2 model which totally differes from your current 9.8. Must unscrew the exagonal tube to release the shift rod, for the lower leg remove all bolts found under AV plate at different locations. The prop corresponds to a non through hub exhaust one and any screen/s seen are water intake/s..​

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Does third pic corresponds to the fuel connector mentioned ? As an alternative and if with sufficient pan space can install a modern fuel intake male valve along a complete fuel line and an external 3.5 gal tank. Reference page 9, items 13-14-12 : fuel related page 43 items 1-2.​

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With respect of the water pump impeller compare the 9.8/A parts manual with the attached 9.8B2, page 23 and check if probably are compatible, if so order a new impeller assuming the liner is in good working order.​

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Happy Boating​

 

[daveh77]

THANKS Sea Rider, that M9.8B parts book was exactly what I needed so I could compare with my M9.8A parts book.
You and Paul were right, (as expected), this A model is obsolete and truely one of it's own kind! After working through comparing all the parts diagrams, I don't think there is a single part that would interchange except screws or bolts!

 

[Sea Rider]

So 9.8 impeller is 100% different ? In that case use the motor as is till the motor drops dead due to a severe overheat, impeller "giving up" issue. LOL!!

Happy Boating​

 

[daveh77]

As long as everything else works ok, I think I should be able to get an impeller from somewhere that could work better than this fried one.
The B model impeller looks like the common long thin fins with a bit of bulb on the contact end.
My A impeller is more of a longer, taller star-shaped 8 pointed gear.
That is IF the drawings are accurate.
They MAY actually be the same size, just different shape.

I see a difference I missed, the A impeller is keyed by a Woodruff key and the B looks like a lengthwise pin without the D shape of a Woodruff or a hole in the shaft to fit cross-ways.
Have to pull mine, measure, and search for something similar.

Do any other brand of star-gear shaped impellers come to mind?

Thanks again, Dave

 

[Sea Rider]

Yep the 9.8B2 uses a round dowell pin whereas other models use woodruff key. Assorted impellers types...

Happy Boating​

 

[daveh77]

Thanks for those examples.
Here are the A and B parts diagrams.
Do you suppose the A type looking like a 8 pointed star is the accurate actual shape or just a draftsman's rendition?
Has anyone seen other impellers that are the actual star gear looking design?

Most impellers I have seen in pictures and videos are like the B model drawing and the picture you posted of the 3 different "normal" looking ones.
Are those 3 all Tohatsu or other brands?

The A model doesn't show a separate pump case, only the cast housing.

Definitely have to get mine pulled out and measured to verify the actual shape and dimensions.

 

[Sea Rider]

The 9.8 B2 impeller it's a medium tall 6 vane one, similar to the middle one as seen in pic, have never seen one physically as we don't have 9.8 B2 models, we run 18 HP and up. Pull the lower leg and check what's inside the liner. If the current impeller it's still fresh and flexible, with no line cracks can invert it and use the other side...

Happy Boating​