'99 DT115S Blown Powerhead...Options?

[ScubaSteve]

Was running about 4000 rpm and something let loose. Catastrophic metal sound. Had been hearing a slight knock earlier in the day. Motor still runs but sounds like marbles are jumping around inside.

Pulled the cowling and noticed that I've consumed hardly any oil since my last fill-up. First thought is oil pump malfunctioned/plugged and stopped delivering oil (i.e. lean condition)?

Need to pull the head/lower to get a good idea of what went wrong but I'm thinking crank/bearing/piston rod. I pulled the plugs and can't notice anything out of the ordinary.

Initially it doesn't sound like this is worth rebuilding (17 year old motor with unknown hours). Has anybody had a similar experience with this motor?
Also looking for a contact familiar with these motors who could give me some good insight on a path forward.

[Solarman]

You should stop running it until you know what is wrong.
If a crank, or rod bearing, and it comes loose, it will be too late to repair? Have you looked under the flywheel? It is possible for loose magnets to make terrible sound before they eat up the magneto?

What ever you do, don't run it till you know what the sound is.

Good luck, post back when able.

[ScubaSteve]

Thanks for the reply Solarman.
Won't be able to dig into it until next week.
Will post an update once I get the head off.

[seaox230c]

One of your pistons seized in the block and you snapped a connecting rod. Not worth rebuilding

[ScubaSteve]

Finally got around to turning a wrench on the powerhead. Removed the lower unit and cylinder heads, snapping 5 head bolts in the process. My next step is to remove all attachments to the powerhead and remove it from the mid-section.

The shop manual says to remove the mid-section cowling in order to reveal the powerhead bolts but I can't figure out how to do that. Anybody have any tips on accomplishing this?

I have my sights on a used powerhead that I may be able to swap in once I get this one removed.

[Solarman]

Buying used powerhead may be a bad risk. If powerheads sit for a few months in humidity the chance of rust setting in is very good. The internal parts of the motor if not run regularly will start to rust, because the oils will dry up. The only time 2 strokes get oil, is when running.

On your motor, turn the flywheel back and forth, to see if all pistons move the same. Chances are the needle bearings on the lower piston wrist pin have come apart, My guess.

Good luck, post back what you find out.

[seaox230c]

turn the flywheel with a wrench...the piston that doesn't move is the bad one...do you really want to spend that kind of money to rebuild a 18 year old motor

[Lunchmoney]

Buying a used powerhead is likely buying somebody else's problem. Repowering with new is crazy expensive. Parts are cheap. Labor is what makes it not worthwhile on rebuilds. Avoid that part by doing it yourself with a factory service manual and find a guy to re-sleeve the block for you. Just an option.

[ScubaSteve]

Well now things are getting interesting.

Got the powerhead off today. When turning flywheel, all pistons move smoothly.
Don't hear anything abnormal inside the block like what I was hearing when it was running.

Now I'm starting to think it's a driveshaft/lower unit issue. I tried to force the lower unit into gear (F & R). The propshaft doesn't move when turning the driveshaft in gear (or vice versa). It feels like the gears are binding and I just feel some clicking.

I also noticed that the shift cable linkage to the motor was bent.

Is it possible tht the motor was stuck "in between" gers and the loud sounds I was hearing were coming from the transmission?
I could've sworn it was the top end.

Since I've rebuilt this lower unit once before, I'm going to pull the prop shaft and see what the gears look like. The LU oil is very dark but no presence of metal fragments or water that's noticeable.

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[Solarman]

If shift rod/linkage is bent, it might be the gears did not go fully into position to engage properly. It will cause noise like raking gears. Or jumping out of gear in one direction.

You need to find the source of the noise. Can you feel any play in the bearing at the bottom of the crankshaft (female spline gear that crankshaft slides into)?

You might need a stethoscope to listen while someone turns the crankshaft for you.

Good luck. Post back when able to let us know what is going on.

[ScubaSteve]

In hindsight, I should've run the motor with the lower unit off.

Don't notice any play in the female spline where the driveshaft enters the powerhead. All pistons and cylinders move freely and smoothly. Can't hear any metal sound like I was hearing when it last ran.

I'll work on the lower unit this week but may be in my best interest to fully tear down the powerhead to inspect the crank/bearings.

I still have no clue what I'm doing but at this point I'm in too deep to go back now.

[Solarman]

Might try moving flywheel back-n-forth to see if there is any end-play on each piston (possibly the wrist pin needle bearings are worn too much?)? It might not make noise except when running?


Good luck, post back if you find anything.

[ScubaSteve]

Might try moving flywheel back-n-forth to see if there is any end-play on each piston (possibly the wrist pin needle bearings are worn too much?)? It might not make noise except when running?

Looks like the LU may be the culprit. The pinion gear is toast. Half of it completely gone and the mating gear also has some damage.
When taking the prop off, the end of the prop shaft also broke off right at the end where the hole for the cotter pin is located.



Seems this may have been my issue all along. Now I need to decide A) if it's worth fixing (sourcing parts or new complete LU) and B) how this happened in the first place. The shift rod under the powerhead was bent so perhaps this cause the motor to be stuck "in-between" gears?

I'll play with the flywheel some more and look for any play/abnormal noises there as well.
My feeling is that I should just slap some new gaskets on, reattach the powerhead and run it without the LU. Can I run it temporarily without the water pump and use the flush connection?

[Solarman]

You can connect a hose to the water tube that the water pump sends water up to the powerhead, then run the motor. Do not use the flush port, that port is used to flush the powerhead when not running.

How is it you had no metal in oil of lower unit? Did you remove lower plug when checking oil? With that kind of gear damage, there will be other damage in those gears, maybe even in the casing itself.

Good luck.

[ScubaSteve]

I did remove the plug and only saw a few small specks of metal.
What's left of the gear is still in big chunks so I guess they were too large for the drain hole or just settled somewhere else.

I'm now onto the driveshaft removal.
Do you have to remove the nut at the bottom of the driveshaft in order to pull the whole shaft?