Hi All,
My sincere thanks to everyone that has posted all the helpful information here. After scouring this forum, I successfully diagnosed and solved my higher RPM overheat problem on my 10 year old Yamaha 90 hp 2 stroke. So here is a rundown of my experience. I hope it provides someone with some beneficial info.
I ended up pulling the cylinder head. Despite religious flushing it looked like the National Geographic cave diving special.
Turned out I had a clogged water port and a heavy sweater of nasty mung. After some serious cleaning and a nice new set of gaskets, I feel like I have a new motor. Pics below.
First step - do yourself a favor and buy the manufacturers service manual! Next, you can follow the directions to test the thermostat and temp sensor. You will look like a mad scientist at the kitchen stove, but it might be a simpler solution to your overheat problems.
After reading all the horror stories about busted bolts, I was very nervous about trying to pull the head. So my approach was to set my torque wrench to 5-10 lbs more than the torque spec and start backing bolts off. I was very fortunate and everything came out without incident.
The cylinder head cover has a number of pry tabs that I was able to gently work with a large screwdriver and a block of wood to get it off. However, the cylinder head took a lot more force. But I found I could get a good grip on the bottom pry tab with square shank screwdriver wedged against the engine block and gave it a HEAVY yank. Those Yamaha gaskets are sticky!
Then came the fun part of trying to clean it up. After several hours of busting my knuckles using CLR and a wide assortment of nylon brushes, I still had a decent layer of crud. That's when the wife chimed in with "why don't you use hot vinegar like we use on the cookware". So I heated up some vinegar to just boiling, and gently poured it onto the cylinder head sitting in a tub. My wife then gave me an "orange stick" - the wood sticks the chicks use to push back their cuticles on their fingernails. After a few minutes of soaking, and some gentle scraping with the wood stick, the mung just slid right off and I could see Yamaha blue again. Around the pistons I used a stiff round nylon brush with the vinegar in a squirt bottle.
With the pistons visible I cleaned off the carbon and took my time to clean the gasket surfaces with the 3M Scotch-brite pads. If I had to do it again I would order the 3M 2" Scotch-brite pad holder for the drill and a box of pads. My fingers were completely raw after doing it the hard way. Despite shoving rags in the cylinders, I still had a lot of gasket junk and pad debris that I sprayed out with combustion chamber cleaner and clean rags.
With a fresh set of Yamaha gaskets (boats.net) in hand, and any corrosion wire-brushed off all the bolts, I was ready to put her back together. I rubbed a little oil into the cylinders just in case anything dried out and oiled the cylinder head bolts as required in the manual. Then simply bolted it back together while carefully following the tightening sequence and torque settings. After I put everything else back together, started her up and, thankfully, everything ran great.
Today I sea-trialed and no more overheat problems! So thanks to all of you who have posted here and helped guide me through the process!
Cheers,
Bud
Here's my list of key equipment and supplies that might help out the next guy:
My sincere thanks to everyone that has posted all the helpful information here. After scouring this forum, I successfully diagnosed and solved my higher RPM overheat problem on my 10 year old Yamaha 90 hp 2 stroke. So here is a rundown of my experience. I hope it provides someone with some beneficial info.
I ended up pulling the cylinder head. Despite religious flushing it looked like the National Geographic cave diving special.
Turned out I had a clogged water port and a heavy sweater of nasty mung. After some serious cleaning and a nice new set of gaskets, I feel like I have a new motor. Pics below.First step - do yourself a favor and buy the manufacturers service manual! Next, you can follow the directions to test the thermostat and temp sensor. You will look like a mad scientist at the kitchen stove, but it might be a simpler solution to your overheat problems.
After reading all the horror stories about busted bolts, I was very nervous about trying to pull the head. So my approach was to set my torque wrench to 5-10 lbs more than the torque spec and start backing bolts off. I was very fortunate and everything came out without incident.
The cylinder head cover has a number of pry tabs that I was able to gently work with a large screwdriver and a block of wood to get it off. However, the cylinder head took a lot more force. But I found I could get a good grip on the bottom pry tab with square shank screwdriver wedged against the engine block and gave it a HEAVY yank. Those Yamaha gaskets are sticky!
Then came the fun part of trying to clean it up. After several hours of busting my knuckles using CLR and a wide assortment of nylon brushes, I still had a decent layer of crud. That's when the wife chimed in with "why don't you use hot vinegar like we use on the cookware". So I heated up some vinegar to just boiling, and gently poured it onto the cylinder head sitting in a tub. My wife then gave me an "orange stick" - the wood sticks the chicks use to push back their cuticles on their fingernails. After a few minutes of soaking, and some gentle scraping with the wood stick, the mung just slid right off and I could see Yamaha blue again
. Around the pistons I used a stiff round nylon brush with the vinegar in a squirt bottle.With the pistons visible I cleaned off the carbon and took my time to clean the gasket surfaces with the 3M Scotch-brite pads. If I had to do it again I would order the 3M 2" Scotch-brite pad holder for the drill and a box of pads. My fingers were completely raw after doing it the hard way. Despite shoving rags in the cylinders, I still had a lot of gasket junk and pad debris that I sprayed out with combustion chamber cleaner and clean rags.
With a fresh set of Yamaha gaskets (boats.net) in hand, and any corrosion wire-brushed off all the bolts, I was ready to put her back together. I rubbed a little oil into the cylinders just in case anything dried out and oiled the cylinder head bolts as required in the manual. Then simply bolted it back together while carefully following the tightening sequence and torque settings. After I put everything else back together, started her up and, thankfully, everything ran great.
Today I sea-trialed and no more overheat problems! So thanks to all of you who have posted here and helped guide me through the process!
Cheers,
Bud
Here's my list of key equipment and supplies that might help out the next guy:
- Yamaha manual
- Torque wrenches for light duty (in-lbs) and heavier duty (22 ft-lbs)
- Small (1/2 to 1/4 in) stiff, round nylon brushes for cleaning around pistons
- An assortment of other nylon brushes
- A gallon of vinegar and a tub to soak the head (don't forget to get it HOT)
- Wood sticks the chicks use for doing their nails
- 3M Scotch-brite pads to clean the gasket surfaces without scratching or sanding. I'd buy the 2in drill adapter and a box of pads to save your fingers.
- A can of Yamaha spray combustion chamber cleaner
- Lots of clean rags.
- Yamaha gaskets (I've had good luck with boats.net)