Chinewalker
Fleet Admiral
- Joined
- Aug 19, 2001
- Messages
- 8,902
With some help from DHadley, my local OMC guy, and my service manual, I was FINALLY able to get all the bugs ironed out of my 1984 Johnson 90! I rebuilt it over a year ago - oversize pistons, rings, etc. I also installed a new waterpump impeller.
I ran the motor briefly after the rebuild, running it on an old trihull I had in the yard. Seemed to run alright and it spent most of its time at the dock, running at idle in gear to put some break-in time on it.
Flash-forward a year. I am finishing up my 1976 Starcraft rebuild and have the motor all rigged and ready to go. An easy run from the ramp to the dock (less than 1-mile) and the wife & kid are ready to go for a ride. Two miles downriver the motor starts to lose revs and I hear a bit of knocking. I pull back the throttle and kill the key. Steam is coming from the motor and I am shaking. Didn't even have the boat out for 5 minutes and I've killed it.
I pull the cowling and the block is definitely hot, but the flywheel moves alright. I kick the key and the motor fires right off and is pumping plenty of water. The block and heads are warm but not hot. We idle back to the dock and now the head scratching begins.
I pull the thermostat housing - all is good and clean. I pull the cylinder heads. No blockages. No apparent damage from getting hot. Replace the heads with new gaskets. I pull the thermostat hoses off and start the motor - GALLONS of water are pouring into the belly pan. Definitely pumping water. Start thinking it might have been a plastic bag in the water, and I take it on another run, watching for steam the whole way. Less than a mile later it's steaming again. I back it off in a hurry and it stops steaming.
So, it is pumping at idle - not pumping on plane. Got me hanging...
I bend my local OMC tech's ear and he asks if the tiny passage in the pump housing, at the top of the dome where the o-ring sits between the cup and housing, is open. I dunno. 10 minutes later and I have the unit off and sure enough - plugged passage. Plugged of my own doing as I was a bit too liberal with the sealant when I put it together. Doh!! I also had wear grooves on the base plate and cup - I only replaced the impeller, not the whole assembly. Doh!!! Soooo, I invested in a new pump kit and OPENED MY MANUAL for the step by step. I've replaced several hundred impellers and it has been years since I felt I needed a manual to get one to pump. Well, it pumps now! Burned a whole tank through it last evening!
The motor runs great - stays warm, not hot, and really makes a nice package with the boat. The boat is rated for 150 and I thought maybe it would be a little underpowered, but it is a lot faster than I thought it would be. Had no problem getting out of the hole and was in the 40mph neighborhood at WOT. So far so good!!
Thanks to all who offered encouragement and suggestions...
- Scott
I ran the motor briefly after the rebuild, running it on an old trihull I had in the yard. Seemed to run alright and it spent most of its time at the dock, running at idle in gear to put some break-in time on it.
Flash-forward a year. I am finishing up my 1976 Starcraft rebuild and have the motor all rigged and ready to go. An easy run from the ramp to the dock (less than 1-mile) and the wife & kid are ready to go for a ride. Two miles downriver the motor starts to lose revs and I hear a bit of knocking. I pull back the throttle and kill the key. Steam is coming from the motor and I am shaking. Didn't even have the boat out for 5 minutes and I've killed it.
I pull the cowling and the block is definitely hot, but the flywheel moves alright. I kick the key and the motor fires right off and is pumping plenty of water. The block and heads are warm but not hot. We idle back to the dock and now the head scratching begins.
I pull the thermostat housing - all is good and clean. I pull the cylinder heads. No blockages. No apparent damage from getting hot. Replace the heads with new gaskets. I pull the thermostat hoses off and start the motor - GALLONS of water are pouring into the belly pan. Definitely pumping water. Start thinking it might have been a plastic bag in the water, and I take it on another run, watching for steam the whole way. Less than a mile later it's steaming again. I back it off in a hurry and it stops steaming.
So, it is pumping at idle - not pumping on plane. Got me hanging...
I bend my local OMC tech's ear and he asks if the tiny passage in the pump housing, at the top of the dome where the o-ring sits between the cup and housing, is open. I dunno. 10 minutes later and I have the unit off and sure enough - plugged passage. Plugged of my own doing as I was a bit too liberal with the sealant when I put it together. Doh!! I also had wear grooves on the base plate and cup - I only replaced the impeller, not the whole assembly. Doh!!! Soooo, I invested in a new pump kit and OPENED MY MANUAL for the step by step. I've replaced several hundred impellers and it has been years since I felt I needed a manual to get one to pump. Well, it pumps now! Burned a whole tank through it last evening!
The motor runs great - stays warm, not hot, and really makes a nice package with the boat. The boat is rated for 150 and I thought maybe it would be a little underpowered, but it is a lot faster than I thought it would be. Had no problem getting out of the hole and was in the 40mph neighborhood at WOT. So far so good!!
Thanks to all who offered encouragement and suggestions...
- Scott
