Hi, I am currently running a 1977 70HP Evinrude 3 Cyl on my 1972 17' Baja... When I first got the boat about 5+ years ago I had discovered it wasn't making full power.... I did new coils, plugs and wires, rebuilt carbs, and found compression low on #3 cylinder (lowest one on powerhead)... pulled head off and found cylinder walls were scored up from corrosion due to a leaky muffler gasket that allowed salt water (oh did I forget to mention I run in salt water) to enter #3 cylinder over time from the PO...Pulled muffler off, fixed leaky gasket resealed it and went on my way...
I opted to nurse her along for the next few years, realizing that at low RPM's she would miss a bit and at WOT she's not make full power, but since I am not racing the boat, and just go out to "putt" around just on plane, it wasn't an issue...I knew eventually I would have to decide what to do with the OB...
Fast forward to this season... upper motor mounts after 40 years finally gave way and required changing... I dreaded this because now I had to remove a powerhead that probably hadn't been off the exhaust housing in 40 years of salt water duty...
Two weeks of careful work and four gallons of penetrating oil and the powerhead and lower unit were both liberated form the exhaust housing and I replaced the motor mounts and did some mods to the adapter plate which also had shown signs of aging... (the exhaust port from the powerhead had eroded the wall of the port and was leaking into the lightening pocket next to it and I had a small surface issue with one of the cooling water discharge ports... I filled the lightening pocket up with high temp epoxy putty and lightly milled the adapter plate back to flat, put new gasket on it for powerhead) All new stainless hardware, plenty of never seize and powerhead was back on, lower unit was also refitted with new stainless hardware and reassembly was complete....
Started her up, three cranks and sprang to life, ran it for a while on the cuffs and satisfied that all was complete too her out to the launch ramp and the bay for a run...
Now's where the interesting problem begins, the last time I had her out just when the motor mounts gave way, she bogged down a bit (I had myself and three other adults on board, and would have expected this to be an issue with the added weight and lack of full power) and had trouble getting up on plane... eventually I coaxed he up on plane and everything was good, had good speed, and we had a great time scooting around the Jones Beach area here in LI...
After the new motor mounts went in when I took her out that first time I couldn't get her to throttle up at all... bogged down bad... I knew it wasn't related to the repairs, but after a couple of drop into neutral, goose her up a few times, and then back into forward, she came back to life and got up and went...
I attributed it to possibly being a fuel related problem that might have come up from moving the powerhead around with the engine hoist while working on the motor mounts...I tapped the choke while bogged and it almost died, so I knew it wasn't fuel starvation, but couldn't determine if it was flooding or overfueling.
So I chived on and enjoyed the rest of the day and returned home..
I inspected the carbs, found #2 had weepage around the bowl gasket, so I removed it, cleaned it out and checked all the jets and ports, and put it back on... Engine started right up one crank (after priming) and ran a bit stronger and sounded smoother...
I decided then it would be a good time to see how cylinder #3 was doing... as I still have the low speed miss and #3 doesn't really start firing until about 1100 RPMS... I tried a method I use for other types of engines to see how well a cylinder is firing by adding propane to the intake air in front of the carburetor to listen to the engine change running characteristics... Cylinders 1 & 2 both showed drop off when propane was added to intake air, cylinder #3 had no change in RPMS... It's kind of like a spark drop test, but uses fuel supply to drop the cylinder...
Now I am left with the possibility that I am going to need to rebuild the powerhead....
Soooo (here's my question, sorry for the long build up), has anyone done a successful bore and sleeve on one of these antiques so I can reuse (if possible) the original pistons,(with new rings of course) and give the old girl a little more time on this earth???
Any suggestions on procedures (cut ports after sleeves installed, etc) and recommendation on machine shops here on Long Island NY where I might bring the powerhead to have it done... or am I just "barking up the wrong tree here" and should start to consider other power for the boat??
Sorry for the epic novel, and thanks in advance for any advice...
Rich
I opted to nurse her along for the next few years, realizing that at low RPM's she would miss a bit and at WOT she's not make full power, but since I am not racing the boat, and just go out to "putt" around just on plane, it wasn't an issue...I knew eventually I would have to decide what to do with the OB...
Fast forward to this season... upper motor mounts after 40 years finally gave way and required changing... I dreaded this because now I had to remove a powerhead that probably hadn't been off the exhaust housing in 40 years of salt water duty...
Two weeks of careful work and four gallons of penetrating oil and the powerhead and lower unit were both liberated form the exhaust housing and I replaced the motor mounts and did some mods to the adapter plate which also had shown signs of aging... (the exhaust port from the powerhead had eroded the wall of the port and was leaking into the lightening pocket next to it and I had a small surface issue with one of the cooling water discharge ports... I filled the lightening pocket up with high temp epoxy putty and lightly milled the adapter plate back to flat, put new gasket on it for powerhead) All new stainless hardware, plenty of never seize and powerhead was back on, lower unit was also refitted with new stainless hardware and reassembly was complete....
Started her up, three cranks and sprang to life, ran it for a while on the cuffs and satisfied that all was complete too her out to the launch ramp and the bay for a run...
Now's where the interesting problem begins, the last time I had her out just when the motor mounts gave way, she bogged down a bit (I had myself and three other adults on board, and would have expected this to be an issue with the added weight and lack of full power) and had trouble getting up on plane... eventually I coaxed he up on plane and everything was good, had good speed, and we had a great time scooting around the Jones Beach area here in LI...
After the new motor mounts went in when I took her out that first time I couldn't get her to throttle up at all... bogged down bad... I knew it wasn't related to the repairs, but after a couple of drop into neutral, goose her up a few times, and then back into forward, she came back to life and got up and went...
I attributed it to possibly being a fuel related problem that might have come up from moving the powerhead around with the engine hoist while working on the motor mounts...I tapped the choke while bogged and it almost died, so I knew it wasn't fuel starvation, but couldn't determine if it was flooding or overfueling.
So I chived on and enjoyed the rest of the day and returned home..
I inspected the carbs, found #2 had weepage around the bowl gasket, so I removed it, cleaned it out and checked all the jets and ports, and put it back on... Engine started right up one crank (after priming) and ran a bit stronger and sounded smoother...
I decided then it would be a good time to see how cylinder #3 was doing... as I still have the low speed miss and #3 doesn't really start firing until about 1100 RPMS... I tried a method I use for other types of engines to see how well a cylinder is firing by adding propane to the intake air in front of the carburetor to listen to the engine change running characteristics... Cylinders 1 & 2 both showed drop off when propane was added to intake air, cylinder #3 had no change in RPMS... It's kind of like a spark drop test, but uses fuel supply to drop the cylinder...
Now I am left with the possibility that I am going to need to rebuild the powerhead....
Soooo (here's my question, sorry for the long build up), has anyone done a successful bore and sleeve on one of these antiques so I can reuse (if possible) the original pistons,(with new rings of course) and give the old girl a little more time on this earth???
Any suggestions on procedures (cut ports after sleeves installed, etc) and recommendation on machine shops here on Long Island NY where I might bring the powerhead to have it done... or am I just "barking up the wrong tree here" and should start to consider other power for the boat??
Sorry for the epic novel, and thanks in advance for any advice...
Rich
