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It’s hard for me to admit that an old 6hp has kicked my butt, but it surely has….
I bought this 69 Johnson 6hp years ago, previous owner told me his kid had dumped it overboard then just hid it in the basement…. I bought the engine, it freed up pretty easily, looked as if water had only entered one combustion chamber. I pulled the intake, crank looked as if it hadn’t gotten wet at all. Don’t know what made me probe the rings, but did, and found that they were stuck from rust on one cylinder. The engine sat around my basement for years, even bought a replacement powerhead for it, along with rebuild parts for the original powerhead.
Finally decided to stop kicking this engine around the shop and repair it this spring. I dismantled its original powerhead, replaced the rings, crank bearings, honed the cylinders, replaced all gaskets and seals (pulled exhaust cover also). While working on the powerhead, I noticed the center main crank bushing seemed worn/scored, but the crank seemed OK, so figured it would be OK this way. I ripped the gearcase apart, oil was milky, replaced clutch dog, seals and orings. And of course, it failed the pressure test, driveshaft seal surface was grooved….So ripped it all apart again and spent money for a new driveshaft. New impeller, and crank seal components. Cleaned and checked magneto, rebuilt carb.
Should have known things weren’t going to go well when the waste oil I brought to my friend’s shop leaked all over the trunk, and the recoil rope pulled out in my hand while attempting to start this thing in his test tank…..
Finally straightened out recoil rope and fired it up. Seemed to run OK, idled just “OK”, new rod needle bearings seemed sloppy and noisy though, my eyes and shaky hands probably messed up the tiny 30 needle bearing installation job. The engine lacked power at WOT with a 7″ prop installed while running in the tank….Thought it was running on one cylinder, but both cylinders seemed to be contributing equally when plug wires were pulled. The engine did not run rough/rich/lean at WOT, just had no power. We even installed the correct test wheel, would only turn up 3000RPM. Was totally depressed by my failure here, the ribbing from Gary and the gang didn’t help much either…. Took it home to think about what I must have done wrong.
The only thing I could come up with was that I ignored that damaged center main bushing ignoring that it might cause a crankcase leak between the two cylinders. The mag plate was advancing fully, and the butterfly was opening fully also.
So decided to write off my rebuild job and install the used powerhead I had bought years ago….I pulled the head and exhaust cover on the second powerhead just to check everything out, all seemed good. Cleaned up the carbon and reassembled. Please note I used the head and exhaust cover pieces from my rebuilt powerhead because they were all cleaned up, just replaced the head and exhaust cover gasket again. I confidently put this project back in Gary’s test tank, only to find it ran exactly the same way it did with my rebuilt powerhead…. Quickly condemned it again, in favor of running a 57 Fleetwin I had brought along as well…
I had never run this engine prior to rebuilding the powerhead, ran the same way with another used powerhead (using original head and exhaust cover with new gaskets.
Lacks power at WOT, even with correct test wheel, doesn’t run rich or lean, or rough, just lacks power (only 3000RPM with correct test wheel)..
Pulled carb apart again, nozzle gasket is in place, has .044″ high speed jet (parts book only lists part number, not size of jet: 315140 (can’t find this part number/doesn’t list opening size)
I had the powerhead and gasket off a few times, sure thought I would have noticed a exhaust obstruction, but saw nothing wrong.
This gearcase does not use the shock absorber, so it is not an issued of this piece binding the gearcase
I was worried that I had installed the wrong flywheel, might have mixed it up with a 9.5hp flywheel I had laying around, but compared the two, magnet location/keyway seemed identical. So, I guess it was a 6hp flywheel I had laying around.
I have researched the carbs for these engines over the years, pretty much the same up to 1975. 1976 was a strange year, used a .052″ high speed jet. 1977 and newer models used a .042″ high speed jet…The high speed nozzles have different part numbers, so am wondering if someone before me messed up this carb with mismatched innards.Don’t know where to look next, have put it aside for awhile hoping that “aha moment” will come to me in a dream sometime. I guess next, I will try a different carb assembly, and recheck the reeds (remember I used the reeds from the original rebuild powerhead, the intake manifold casting was broken on this used powerhead). Perhaps the reeds are partially rusted/stuck closed, but this seems like a long shot, never really tried to push the reeds open, they were not rusted or corroded.
I’m convinced I made some foolish mistake or “assssumption”, need some fresh outside thoughts here….. Was going to attach a video, but it is too large for this website, of course….
Thanks
DonLink and synch is done correctly and compression is right up there? Besides the jet changes, several different cams were used to over the years.
I’ve found when these motors lose power, it’s usually from worn out rings. Something else I’ve noticed is the 5.5 and 6 horse motors like to score pistons more than other models do. Don’t know why but they do.
Link and synch is done correctly and compression is right up there? Besides the jet changes, several different cams were used to over the years.
I’ve found when these motors lose power, it’s usually from worn out rings. Something else I’ve noticed is the 5.5 and 6 horse motors like to score pistons more than other models do. Don’t know why but they do.
Well, I thought I had screwed up the powerhead rebuild, but it runs the same with another powerhead I purchased…But, it is important to note that I reused the head and intake from the original powerhead because I had already cleaned these pieces up and surfaced the head. I suppose it is possible that the old head is porous and leaks water, perhaps I screwed up the reed gaskets or one reed on each cylinder is stuck closed somehow, but that is a stretch. I replaced the worn out plastic cam follower, the carb butterfly is opening fully. The reed gasket mess up seems unlikely, this would affect low speed much more than high speed.
Again, sure wish I knew how this thing ran for the PO, that would answer many questions and rule out some stuff.
So, next I will try a different carb assembly, then pull the reeds back off. I suppose I should just pull the reeds off before changing the carb….A few days later…. Like I said, I did resuse the head off the original powerhead that had taken a bath. I know I resurfaced the head, but perhaps it got distorted somehow if the engine went under while running… I will recheck compression and pull the head again if readings are off….
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