50 hp Merc Siezed

[joblo33]

I was cruising along with my 1973 50 horse merc in the lake today when all hell broke loose. I had the motor at full throttle and it didn't seem to be going very fast (I should've stopped at that, but no, I kept going) and soon it started to quickly jump to a low speed as if a brake was applied and gradually get back up to speed only to do this again. I started to get concerned at this point and idled it down but as it was slowing down there was a bang and it stalled. Now it's siezed. I took off the plugs and found that all but cylinder #3 were wet with fuel, so my theory is that there was no gas, and therefore no oil, getting to the third cylinder, causing it to stick to the cylinder wall. Do you concur..? ..Anyway, my question is: is there anything I should try before I start to dissemble the powerhead? BTW, It's cold now and the flywheel still won't budge.<br />Thanks,<br />Eric<br />(The dumb guy who didn't check why his engine wasn't running on all 4) <br /><br />Edit: Forgot to Mention that the spark plug in cylinder 3 also looks a lot like it's been struck, which seems to disprove my theory...

 

[WillyBWright]

Re: 50 hp Merc Siezed

The piston grenaded. Most likely from carbon build-up. The same carb feeds 3 and 4, so if it was a fuel problem, you'd see it on 4 as well. An ignition problem wouldn't do it unless maybe the timing was too advanced and burned a hole in the piston first. It could also be fatigue or a flaw that survived this long. Age may be a factor, and overrevving could break a piston. Probably not an overheat or all cylinders would be affected and the sparkplugs wouldn't be wet.<br /><br />What happens is Carbon builds-up under the rings and prevents the ring from contracting to the point that the ring sticks to the cylinder. The piston breaks apart almost instantly. The other major possibility is that it broke from fatigue or just plain wear. It's a pretty old motor. But they're good ones.

 

[Clams Canino]

Re: 50 hp Merc Siezed

Yep, sounds like #3 failed pretty hard. It's very like economicly fixable if you can do it yourself. It might be economicly fixable if you can find a small specialty shop.<br /><br />Parts are readily available. And those 44ci motors were one of the best ever.<br /><br />-W

 

[joblo33]

Re: 50 hp Merc Siezed

thanks for the help. How much should I expect as a bill if I bring it to a repair shop vs the parts cost?

 

[700XC]

Re: 50 hp Merc Siezed

Has the water pump impeller been replaced in the few years, after around 10 years the rubber impeller gets hard and fall,s apart, no cooling to the cylinders can cause a heat seizure, I am not sure if the older motors had a overheat buzzer, my 85 40 hp with controls has a buzzer in the remote control shifter. The first thing I replace with any old motor that I buy is replace the water pump kit, points and condencers, plugs and refill the lower unit with gear oil and tear down the carb's and fuel pump and clean out all the old varnish and jellied fuel /oil.<br /> Also I mix my fuel and oil a bit richer for the first tank to make sure all the old bearings and seals are well lubed for the first test runs.<br /> Sorry to hear that your motor went down, i try and shut down any motor at vthe first sign of any problems at least you can minimumize the damage even if a piston goes mabe you can save the cilinder walls from big damage. Hopefully things are not to bad, if you can post some pics of pistons and cylinders mabe we can pinpoint exactly what went wrong so the same problem does not happen again. Good Luck and cross your fingers that damage is minor/

 

[Nos4r2]

Re: 50 hp Merc Siezed

If it's siezed then it'll cost more to fix at a repair shop than it will to buy another motor. The parts are more feasable, but I'd go for a 2nd hand powerhead and swap it over yourself-you can do that in an afternoon and likely it'll be cheaper than the parts. Damn shame you aint in the UK though, I've got a 73 50hp powerhead here that you could have for bits rather than me junking it.

 

[joblo33]

Re: 50 hp Merc Siezed

Thanks, I had just replaced the pump and it was pissing with lots of pressure. I'm not sure why it failed but I'll post pictures of #3 as soon as I get around to spliting the powerhead. For now I'm using one of my other 50 hp's and working on making it into a electric start before my week long fishing trip on tuesday. (See thread Merc 500EL...M)