Tohatsu M25c3 Leaking Head Gasket?

Alacat

Cadet
Joined
Mar 12, 2010
Messages
12
2001 Manual model. It sat up for 18 months due to a broken heel (mine of course). Took it out last spring and it cranked right up with new gas but smoked like a steam engine with white smoke for a few minutes but then cleared up to a lovely two stroke blue. Ran fine at idle, stumbled at speed. Tracked down an airleak on the bulb and replaced the fuel line and bulb. Cranks and runs, adjusted idle speed to 700 in gear, thought nothing else wrong and went fishing. Time to go home and it won't cough at all. Now with this engine, I've never had to choke it after the initial crank which takes one to three pulls. After warming up, I've enjoyed one pull starts for 7 years. After getting home on the troller, I pulled the plugs and they were wet. Dried them and let the motor sit overnight before putting them back. Put the motor back in the water the next day and no joy in muddville. Towed home and got some new plugs. Cranked up ran fine at low speed which was all I needed at the time. Thought I had it covered.
Six months later, new gas, cranked and ran fine at low speed again. Idled out to the middle of the river a mile from the launch, caught some bait and was getting ready to catch a biggun. Idling around watching the Finder and the motor just took a nap. Got real quiet real quick. Pull, pull, pull... cuss... pull, pull, pull... cuss... choke, pull, pull... really cuss... fish, fish, pull, fish, fish, pull, pull... point the troller home, drink beer, drink another beer... cuss some more. Got home and pulled plugs, wet again. Shine light in sparkplug hole and see a brand new piston looking at me. Not bad for a 10 year old motor. OH WAIT! That's not good!

Lots of corrosion on the bolts and it appears like some leakage through the gasket. Must have had some salt in it's earlier life.

Now I'm not a spring chicken and I surely don't enjoy pulling on a starter rope, much less being stranded miles from home. I'm going to order a new head gasket with new bolts, thermostat, and gasket.

What I need from you guys, if you please, is instructions on the proper way to put this thing back together. I see the bolt holes are numbered. Is that the torque sequence? 24.5 Ft Lbs stamped on the Head. I'll need a torque wrench, i guess. What about gasket compound or glue? Any particular kind? I've already cleaned the old gasket off, thanks to Dremel for that.

Has anyone suffered a similar fate? What's the prognosis? Anything else to look at while I've got it apart?

BTW, It's been 4 or 5 years since I was last here. Name's Alacat, the fisherman previously known as ToonTime and I'm a boataholic. Happy Thanksgiving to all!
 

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Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Re: Tohatsu M25c3 Leaking Head Gasket?

After 10 years use , it's time for a full maintenance, strip carb and soak in carb cleaner, if changing head gasket, will need gasket thermostat & thermostat as well, clean well all water passages, as you will need to remove head to change gasket and torque all nuts, change base gasket, check impeller housing and impeller for wear, grease upper shaft splines when assembling. Change LU tail oil. Check, clean/replace fuel pump diaphragms.

Happy Boating
 

Alacat

Cadet
Joined
Mar 12, 2010
Messages
12
Re: Tohatsu M25c3 Leaking Head Gasket?

Thanks Rider

I have done the Carb and Impeller routine a few times. Diaphram is due.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Re: Tohatsu M25c3 Leaking Head Gasket?

Thanks Rider

I have done the Carb and Impeller routine a few times. Diaphram is due.

Check that both faces of the engine head (where head gasket sits) are completely clean with smooth surfaces so to have new gasket properly seated when torqued as specified. You could take advantage and decarbonize piston head if heavily carbonized.

Happy Boating
 

Alacat

Cadet
Joined
Mar 12, 2010
Messages
12
Re: Tohatsu M25c3 Leaking Head Gasket?

Got the gaskets replaced. Cleaned the Carb. New clamps on all fuel lines. Put it in the water, pumped her up, and pulled and pulled and pulled. Cussed some more. Wait a minute... why is the kill switch laying on the floor? Kick self.

Got her dried out and finally cranked. Twenty mile run, adjust idle to specs. Runs like a hummingbird. 10 inch pull to start once warm. Very sensitive to throttle position. needs no gas at all to crank. just pull.

FWIT, I got 29.2mph GPS with a moderate load. ME, 150lbs, battery, full 6 gal tank, 60 lbs of assorted gear and cast nets, troller, etc.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
Re: Tohatsu M25c3 Leaking Head Gasket?

When these babies are correctly adjusted and maintained starts with 5 inch rope pull :D Nice to read that your baby is back on water. One issue, looking at fifth picture, see that you have the engine still mounted at base, how did you torqued both bottom cylinder head bolts, did you use a special tool/adapter to do so ? A normal socket wrench won't fit, you'll need to remove complete head from base to torque all bolts properly when changing a new head gasket.

That motor would have much better final speed and carry more load at wot if you pass the 25 to 30 HP, for peanuts. Just swap 25 carb gasket for the 30 HP model.

Happy Boating
 

Alacat

Cadet
Joined
Mar 12, 2010
Messages
12
Re: Tohatsu M25c3 Leaking Head Gasket?

Drilled two holes in the Lower Cowl big enuff to get an 3/8 extension through it, into the socket and onto the bolthead. When done, put two 1/2 inch drain plugs back into holes. No harm, no foul!
 

RadarRick

Petty Officer 2nd Class
Joined
Jun 30, 2010
Messages
189
Re: Tohatsu M25c3 Leaking Head Gasket?

Brilliant! I'll bet that saved you 4 hrs and 1 or 2 skinned knuckles.

Thanks for the tip & happy boating!
 
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