Overheated for the first time...will it be ok? '85 rude 70hp

[rtpassini]

Nearly made me crap my points. never had this happen!

Before the season, I changed the impeller. Didnt have any problems. Took it out tonight and made it probably 300 yards out (no wake speed) and the thing started screaming. I didnt even know it did that. So I shut it off right away. Looked back and started it up again, no tell tale. So I put the trolling motor in and turned it back around. Got home and tore it apart. The only thing that looked strange was the keyway for the impeller. Here is a picture of it

https://dl.dropboxusercontent.com/u/28917583/20140808_201050.jpg

Im thinking it got somehow got caught and it "elongated" it out and eventually jammed it up like a door stop. What do you guys think? How/why did it happen?
Im going to order all new stuff including a housing. But do you think I cooked anything else for it getting hot? I dont know how forgiving these things are when the alarm comes on.

 

[jakedaawg]

I doubt you hurt it if you shut it off right away but a compression test will tell you the answer.

 

[Bosunsmate]

as above^
Check your motor drops far enough into the water , ie the cavitation plate is at least a few inches under water at idle

 

[F_R]

Since you managed to shut it off quickly, it may not have hurt it. But just so you know, overheating can ruin the head gasket, and worse yet those 3 cylinder loopers will warp the exhaust baffle plate which will cause it to leak and squirt water into the cylinders, which destroys the powerhead. At the very least, re-torque the cylinder head and keep a sharp lookout for any signs of water intrusion.

Personally, I'd be yanking the powerhead and replace that baffle plate. Maybe I'm being overly cautious, but I've seen too many trashed powerheads and I'm scared..

 

[rtpassini]

We'll see how I feel once I get the parts and put it back together if I feel like checking everything over.

A new question arises though. Why did this keyway fail? has anyone seen this? I dont want to have to deal with this happening again

 

[Tim Frank]

Not sure what you are calling a "keyway"
That looks more like one of the impeller vanes has broken off.

 

[PaulCT]

It looks like the key slipped out of it's notch in the shaft and yielded under load.. I imagine it was tough getting the impeller off (incidentally, I have a post about a stuck flywheel I'm trying to remove, it might be a sheared woodruff key...).

Did you install the impeller and key in the proper orientation as per the instructions? This might have been installed reversed. The key is installed in such a way that as the shaft rotates, the key "tightens" up between the shaft and impeller due to the shape of the key (one side "sharper", the other side "rounded"), essentially the mechanics of a wedge. If it is installed improperly, you might end up with your symptoms.

Also, the instructions call to pull up and rotate the shaft to seat the key properly. I'm sure you'll have an eagle-eye on these details the second time around

Good luck,

Paul

 

[rtpassini]

im 99% sure i put the keyway in right. but im not sure about pulling up on the shaft....

The other bad part about this, since I yanked it all off, im not sure how to properly install all the parts and gaskets again. not that there is too much to it. Last time I had used a parts exploded view to make sure. Do you have a "proper" installation step by step, paul?

 

[PaulCT]

I assume you are referring to the lower exhaust housing which has two seals (upper, connecting to the upper exhaust housing, and lower, connecting to the gearcase). On my 1989 120 hp Johnson, the lower housing came out along with the gearcase, along with the upper and lower seals. My recollection with a couple of 3 cyl engines similar to yours is that the configuration was similar (gearcase - lower seal - lower exhaust housing - upper seal).

For my 120 hp, the manual indicates to apply rubber adhesive to the seal inner surfaces and install them on the lower exhaust housing, and to apply triple-guard grease to the outer surfaces of the seals (both), then install the housing on the gearcase. Other than ensuring that the seals and housing remain aligned in position, I don't think the adhesive and grease is critical (for that matter, they say to install new seals). I just did this job earlier this year myself using the adhesive and grease (but re-using the old seals), and with a helper to assist, made sure everything lined up properly. I suppose it worked out well, because it's not any louder than it was before the job

Regarding the key (the manual more properly refers to this as a cam). The manual shows an illustration with the sharp edge of the cam leading rotation of the shaft (clockwise when viewing from above). Note when putting the impeller in the housing, you are looking at the impeller upside-down, so in this orientation the rotation of the impeller is counter-clockwise. The slot in the impeller for the cam should be facing out ("bottom" side of the housing). Hold the cam in place on the flat of the driveshaft using some grease... The sharp edge should be on the clockwise (leading) side (view down the driveshaft toward the gearcase). Slide the impeller and housing down the shaft, align with the cam, and ensure it engages the impeller properly.

My manual doesn't mention anything about pulling the shaft upward... Maybe this was in the waterpump instructions, I don't recall for sure...

Now if I can just get my damn flywheel off...

Good luck,

Paul