Tohatsu carnage - one little piece of rubber can cause all that??

[beto998]

Well, I do have a question here, but let me get through my story first. Boat sat for about 2 years, and I decided this year was the time to clean her up and take her out. 25HP 2 stroke Tohatsu is the motor I'm dealing with. Well, fresh fuel, fresh oil, fix a fuel leak here and there, replace fuel pump, new plugs, clean out the carb, check the lower unit oil level, pees on muffs...good to go right?

I got it down to the lake and warmed it up, did some moderate 1/2 throttle test runs for a few minutes, adjusted the idle speed, and then went to go for a little trip. Well, not 3 minutes into near full throttle operation, a sudden loss of power and a sound that I did my best to ignore at the time - a kind of muffled clang-clang-clang. Now she won't idle, and won't start without a fight. I narrowed it down to the lower cylinder, and verified that the spark was strong. Running at part throttle in neutral, it would run rough and then backfire every once in a while. I packed it up and went home.

After a compression test, I found that the lower cylinder was low (35 to 50 psi, vs. 120 psi on the upper). I did everything I could - couple of soaks in oil and carb cleaner, even penetrating fluid down the spark plug hole to free up what I hoped were sticky rings. No luck, still a lousy 35 psi. Pulled the head off and holy smokes. This just amazed me. I still haven't pieced together all the events here but, looks like a broken off piece of water pump impeller plugged the small port to the lower cylinder cooling inlet, then I guess things expanded until the piston clipped the ports on the exhaust and cracked the cylinder sleeve. Carnage ensued. I'm still not sure what got stuck on top of the piston and caused all that damage, as no pieces appear to be missing from the intake side or the bottom end.

I've found all the parts to repair - two new cylinder sleeves, new pistons, rings, bearings, and all the seals, and most importantly A WATER PUMP. But, has anyone ever pulled a sleeve out themselves on one of these? Any advice on how to go about this, or just let the machine shop worry about it (it'll have to be decked and possibly honed after anyways)?

I've posted a .pdf of the pictures to get the size down. See the attached. Any ideas on what to look for as far as what got stuck in there would be appreciated too.

 

[NorthportTroller]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

Yikes, is it confirmed that it is a piece of the impeller? That's a good example to use for replacing a impeller.

 

[beto998]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

Yep, it's impeller alright. I have a couple of them in my toolbox and I compared it to them, it has the little round end-piece visible on one side. All this being said, I may be vindicated once I pull the bottom end off and see the condition of the currently installed impeller. I remember several years ago when I bought it, the first thing I did was replace the impeller and it was toast. I never did find all the little bits that were missing. Could it take a few years for those bits to work their way deep enough into that port to cause this serious issue? Still no excuse for not changing it this year, but the one that I put in there might not be the culprit.

Also very important to note: the pee-hole and the little dribble port under the engine were normal when this happened, and continued to be normal chugging along with the dead cylinder. Just because you see water doesn't mean you have cooling...

 

[pvanv]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

That chunk of impeller didn't help, but it was probably not fatal. There was a hunk of something metal or glass in the cylinder that did your motor the death blow.

 

[TOHATSU GURU]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

No one replaces the sleeves as Tohatsu only offers a block. Aftermarket sleeves are problematic due to the difficulty of proper placement and likelihood of it being done incorrectly...It's a BS shortcut to save a dollar and I would advise against it.

 

[Sea Rider]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

Were you runing 25:1 fuel/oil ratio when that happened ? It's nearly impossible for rubber parts to pass directly to combustion chambers as water paths are just adjacent cooling paths to chambers, you could have water path obstruction from previous broken impeller somewhere inside crankcase leading to overheat of some kind that ruined piston and sleeve. Or even a thermo failure, A experiemeted machine shop that knows well 2 stroke engines can do the work at a fraction of the cost of a new crankcase. Being engine woonded to death already, nothing to lose and big money to save.

Happy Boating

 

[beto998]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

Were you runing 25:1 fuel/oil ratio when that happened ?

Uh, 40:1, and I thought I was being generous. The specs I have (pic of manual attached) call for 50:1, I've run this motor for 4 to 5 years at 40:1, never an issue, till now that is.

It's nearly impossible for rubber parts to pass directly to combustion chambers as water paths are just adyacent cooling paths to chambers, you could have water path obstruction from previous broken impeller somewhere inside crankcase leading to overheat of some kind that ruined piston and sleeve.

Exactly, in one of the pictures there you can see a bit of rubber inside the cooling water chamber-thingy on the side of the block, what you can't see is the smaller bit of rubber jammed into that tiny hole just behind the bigger piece of rubber. This hold leads directly to the water jacket on the lower cylinder -- it seems to be the only water inlet to the lower cylinder jacket. The rubber did not enter the combustion chamber. I'm with you, I think overheating happened first, then what - did the sleeve crack and damage the piston, or did the piston seize, break a piece of ring and take out the sleeve with an impact?

A experiemeted machine shop that knows well 2 stroke engines can do the work at a fraction of the cost of a new crankcase. Being engine woonded to death already, nothing to lose and big money to save.

Well, I'm certainly going to check around with some bike shops around here as this seems to be quite a common procedure (and frequent) on two-stroke performance bikes. A guy at work said he used to have a collection of damaged pistons from his 2 stroking off-roading days. Maybe if someone tried to put a sleeve blank in and port it all out themselves there would be major concern for error, but I can't believe that a pre-ported sleeve that is custom made for the application would be all that hard to put in? Check out this link: http://www.advancedsleeve.com/2010_ASC_Catalog.pdf - mine is down on page 13. The difference here is about $600 in parts + whatever the machine shop charges, or $450 in parts plus a new block, plus machining. So, call it $800 or $900 vs. $1200 - $1500. at $1200 to $1500, I think this outboard gets retired.

 

[Sea Rider]

Re: Tohatsu carnage - one little piece of rubber can cause all that??

Hard to tell which part broke first due to an overheat, but definitely an overheat due to water path obstruction of some kind in that area, the correct fuel/oil ratio is 50:1, no issue running 40:1 at wot, just more plug fouling at idle. Have reconstructed several sleeves down here, perfectly machined and with new pistons and rings working excellent.

Happy Boating