Broken down 90 TLDI Tohatsus

[lots of boats]

Hi,
I just retrieved my stack of four dead 90 Tohatsu TLDI motors from my Tohatsu dealer. The dealer, and his mechanics, and I took apart four blocks, plus there was another one from another customer. On one of my the engines the piston pin was worn down smaller in diameter. The bearings had departed at some point, and the lengthened stroke didn't agree well with either the top of the piston, or the head.

What are some of the possible causes of piston pin failure?

 

[ziemann]

Re: Broken down 90 TLDI Tohatsus

I am assuming that you have eliminated the obvious culprits already....

Over revving? Is it pushing a load then is the prop ventilating causing a severe over rev? I would think the rev limiter would kick in to prevent anything like that from occuring.

Are there signs of lack of lubrication? I would assume that there would be...

Are you thinking it is a defective wrist pin?

 

[lots of boats]

Re: Broken down 90 TLDI Tohatsus

Hello, I wondered where you went.

The obvious things have been eliminated.

Just to clarify for reference what we did. We took the head off one engine that was really smashed up, this is the one I mentioned in this post. The wrist pin had separted from the piston. This engine has a hole in the top of the piston, which Tohatsu called detonation. However the hole is punched out from below as the rod broke before it came through the side of the block, hit an oil line and caused an explosion. I can't check those oil lines. The wrist pin in question is worn to a smaller diameter where the rod bearings sit.

As far as the over all cause of the TLDI 90 engine failures: there were three mechanics, one was the dealer. Also a former employee and Tohatsu mechanic stopped by and looked at the dismantled engines. The previous business owner i.e. the previous Tohatsu dealer and mechanic stopped by and looked at the dismantled engines. Also I showed some of the pieces to mechanics from another business. Everybody went away puzzled.

I can measure the pin diameter, I haven't looked to see if all the pins are stepped. Of course I don't think Tohatsu parts are defective. They just fail and I am looking for suggestions why. Would overrevving an engine, put enough stress on a wrist pin to cause wear?

 

[chevyjet]

Re: Broken down 90 TLDI Tohatsus

That would be a bearing failure, there is no way that pin was steped. Pulll the other rod bearings and have a look at tham and tell us what you find.

 

[walleyehed]

Re: Broken down 90 TLDI Tohatsus

I can see the direction this is headed so let me add my 2 cents...
Both ends of rod run on needle bearings....if the proper oil is used, these bearings only have problems if the engine has set for many years without use.
2nd., beings nobody here can give you the answer that you want without things getting hostile, call customer tech and present this question to them.
And yes, it IS getting old...

 

[lots of boats]

Re: Broken down 90 TLDI Tohatsus

Hi
I think I have attatched a picture of the pin, rod parts and piston. The pin measures about .785, or 20mm where it was in the piston and .759 on thewrist pin journal. .026" of wear.

 

[whitewater90]

Re: Broken down 90 TLDI Tohatsus

Hi LOB,
Nice piston, Shure looks like the bearing died, My gess is that the pin bearing went and the extra travel of the piston caused some detination which caused the piston to stick and the rod to rip free from the piston. How is the bottem rod bearing? is it still tight? how do the other pistons look?

 

[chevyjet]

Re: Broken down 90 TLDI Tohatsus

You know if i remember right they changed spark plugs about the same time the outboards changed form silver to black, if all the failures are on one particular batch of engines you might check the heat range and see if the ones that have been blowing have hotter plugs.