115hp Merc. power loss

[wrechin2]

Powerhead is in hand. Call me when you can pick up. emoToast

 

[glasstream]

Got the cylinders bored and de glazed, crank and pistons installed, and the block is finally closed. Going to start putting the distributor, starter, fuel pumps, ect on tonight emoDance
Thanks to Wrechin for the block and all the much needed advise. Still have to service the lower unit and change the water pump once the engine is done but I may actually be back on the water before fall. You were right MoonMan.. VERY rewarding it is!

 

[wrechin2]

emoToast emoToast emoToast Good deal! Keewp us up to date.

 

[glasstream]

I got the motor back on the boat and all hooked up. Going to replace the water pump tonight.

Wrechin, If you could help me out with one last thing... I never did pinpoint what originally caused the damage to the #3 piston/cylinder. The gas wasn't too lean, and I figured that lean fuel or a bad impeller would cause damage to all pistons, or am I wrong. There was a bolt in the water jacket that had backed out but the cover was still tight. Is there anything else that I should check or change before I fire it up?? Could it have been a problem with one of the carbs or something? I just don't want to fire it back up and have the same problem.

 

[wrechin2]

Without seeing the piston for type of failure, it is hard to tell. By design,all engines will havesome cylinders that will run hotter than others and will fail first when the temperature rises or the fuel gets a little lean or the quality is poor. When the one "hot" cylinder fails, it will basically sacrifice itself and save the others. I always replace the impeller, thermostats (your's don't have),rebuild the carbs or clean the injectors, and replace switch boxes (yours don't have) to ensure that I don't kill the same cylinder or another one follows soon after. Another thing on this particular engine is, what octane fuel are you running??? This engine was designed in 1976 and the fuel was leaded. This was higher octane. This engine has pretty high compression compared to most. If you also notice on the new piston, the deflector (dome) was .100shorter. This was to lower the compression. So here is a rundown......</p>

1) Fuel quality..... Octane too low. If you read in the fuel system section of the manual I gave you. It talks about using a aviation mix in this engine to combat the drop in octane from then to now.
2) Lean mixture... Even though 2 cylinders feed off one carb, if #3 is running "hot" it will be effected/fail first
3) Impeller... Doubt your issue but may have agitated the "hot" cylinder. DO REPLACE or can lead to future issues
4) Timing... Even though it uses a distributor, timing may vary from cylinder to cylinder due to terminal spacing in the cap. This can be verified by indexing the flywheel. So you can set #1 to 23* and #3 can actually be 26*. <font color="#ff0000">It is important that you also Verify the pointer with a dial indicator</font>. If it has been moved, the timing will be incorrect. </p>

5) Wrong heat range of plug.....This can cause detonation and damage the pistons. </p>

</p>

Hope this helps!!!!!!!!!!!!!!!!!!!!!</p>

 

[glasstream]

Got the rebuild done and started the engine for the first time Sunday emoDance. New impeller is circulating good, (more spray from the exhaust ports than ever). Three of the 'fins' on the old imeller were facing the wrong direction. I'm sure this was part of the problem. I've still got a few more hours in the test tank (50gl drum emoSmile ) to break it in before I move on to the timing & sync. phase, but so far everything seems to be good!
Thanks again to wrechin for the manual and advise. emoToast I should be back on the water in about a week.

 

[wrechin2]

You do know the time you are running it in a 50 gal "test tank" doesn't count because it is "unloaded" time and the only thing you are doing is "seasoning" the new piston with the heat up and cool down cycles. The Link-and-Sync needs to be done now. The hardest part is the max timing which will have to be set in the water.

 

[glasstream]

wrechin2 - 7/15/2010 9:40 PM

You do know the time you are running it in a 50 gal "test tank" doesn't count because it is "unloaded" time and the only thing you are doing is "seasoning" the new piston with the heat up and cool down cycles. The Link-and-Sync needs to be done now. The hardest part is the max timing which will have to be set in the water.

No, I didn't know that. But I noticed last night that I'm leaking oil from the lower unit seal. I guess I fouled up something when I re-assembled it after changing the water pump. Going to pull it back off tonight. Is there a gasket there to change? Figure I need to get that solved before I try to sync it.

 

[wrechin2]

It may just be the addition oil in the fuel. The majority of exhaust comes out of the prop and would cause engine oil to run out behind the prop and down the skeg. You would have had to remove the lower water pump housing to disturb any oil seals.

 

[glasstream]

O.K. That may be it. The mix is 25-1 right now & with the barrell being filled with water up above the gear housing, it could be just floating to the surface and settling there. So there's no gasket/seal to replace when you remove the lower unit housing?
When I reassembled, it took a good bit of pressure to re-seat the unit (it didn't just slide right on). I had to progressively tighten each bolt to pull it up, but I figured that was normal since it didn't just slide right out.
Could I run it with just the flushing muffs and water hose to check for leaking or would that not be a good idea?

 

[wrechin2]

Sometimes they don't just slide up real easy. But it should be fairly easy to go back up using the nuts. If you lowered the gear case and remove the 4 bolts holding the water pump housing on and lifted the housing and replaced the impeller and put the top back on, you did not disturb any oil seal or "O" ring. If you removed the impeller and then removed (using 2 screwdrivers) the lower portion of the water pump housing, then yes you disturbed the oil seals. At 25:1 you will have a lot of extra oil in the exhaust flow and with it in a drum, it will accumulate easily. I have ran them in big storage totes at a 50:1 and they will get a oil film. If you pull your plugs after idling for a minute or so, you will see at a idle they are covered in fuel and oil. When I modify a engine and have to get it jetted correctly, I have to run WOT for 30+ seconds ( this allows the excess fuel to burn off and the plug to change colors) then simply cut the key off and pull a plug and read it. They will be dry and will change color. If I allowed it to idle, the additional fuel will wet the plug and give me a incorrect reading. In short they are VERY rich at a idle and will be putting out a lot of raw fuel and oil into your water. That is probably all that it is. Change the fluid in the lower and keep a eye on it if you suspect a issue. Just my .02