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80hp 2-stroke water issue

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NeilShand

New member
Hi all, Im new to the boating scene, and bought a Swiftcraft half cabin with a Yamaha 80hp 2-stroke outboard. Its had a few problems then it started running on 2 cylinders. Had a quick check and found the lower cylinder had water contamination which was leaning the mixture out and stopped it firing until the revs picked up. Removed the cylinder head, found it was spotless clean, like it had been power washed. Cant see any obvious issues with the head or gasket. Can anyone on here give me some direction as what route to take, or anywhere else to check for the water getting into the cylinder? Thanks in advance!! :D
 
You should have done a compression test before removing the head. Water in the cylinder usually points to the head gasket problem.
 
The boat had been lying out of the water for a few years and picked it up cheap. So had it around 8-months, originally the steering shaft was seized, so stripped the leg and painted and re-built with new bushes/gaskets/water pump/fresh g-box oil. Leaving the engine complete as was running fine before I stripped it. Got it out on the water, then starter motor gave trouble, so re-con starter, new battery cables and battery. Next was it running on 2 cylinders and removal of the head. Yes I admit it was a bit silly buying my first boat that had been out the water for a few years, but I`m a diesel mechanic and thought I could bring it back to life!
 
Well re-fitted the cylinder after being machined, started it running on 3, then put the muffs on and switch on the water and the lower cylinder dropped, getting a good spark, but obv water still getting in somewhere!! HELP!
 
On the port side of the motor is an exhaust cover.On the inside of that is an inner exhaust plate which some times corrodes through.You will have to remove the powerhead to get all the bolts out and you are going to break a few.While the powerhead is off , inspect the part where the exhaust gasses go into the leg.That could also have corroded.If none of these is the problem , then you might have a cracked block.
 
Thank you very much for the advise, will strip it this weekend and let you know my findings. And since you mention it could be a water back feed through the exhaust, I noticed markings on the affected piston next to the exhaust port.
 
Let me know what you find. I had two 60HP yammies witch both had the inner exhaust covers corroded through.The one was a 1992 model and the other a 1995.On both the corrosion was on the bottom cylinder.Regards Pieter.
 
Hi, pulled off the exhaust cover and found a hold in the intermediate plate next to the lower exhaust port! So glad I found the fault, welding it at work and ordered a new gasket. Thanks for every ones help!
 
Neilshand, did the weld work? Did you use might, Tig or stick? I'm having the same issues and will be pulling the motor apart soon.
Can the part be bought and replaced?
Thanks for your help
 
NeilShand said:
Hi, pulled off the exhaust cover and found a hold in the intermediate plate next to the lower exhaust port! So glad I found the fault, welding it at work and ordered a new gasket. Thanks for every ones help!
Click to expand...

Hey there I pulled my exhaust apart and it was clean, pistons look good and I'm holding between 118-122 psi on all three cylinders. I have water getting into the lower cylinder, was the hole prominent and easy to see in the exhaust? Any help is greatly appreciated
 
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