Seized motor/blown rod

[mstritt]

I have a 1984 Johnson 70hp that was finally working and while out fishing it seized up on me. At first it started hesitating like it was not getting enought fuel(not the problem) but then when I put it in neutral it stopped abruptly. I pulled the top off and found I could not turn the flywheel clockwise but with much effort could counterclockwise. After several rotations counterclockwise(felt like it was unscrewing)I found I could rotate it both ways. Anyway, the engine starts but while its idling there is a "clunking" sound. Is this a blown rod and if it is how hard is it to fix, or even worth it for a 20 year old engine.<br />Thanks in advance<br />Martin in NJ

 

[dmessy]

Re: Seized motor/blown rod

Drop your lower unit and see if it turns over freely by hand(plugs out). This will isolate whether the problem is in the engine or gearcase. Then check your compression on each cylinder. Keep us advised using this post.

 

[mstritt]

Re: Seized motor/blown rod

Thanks for the reply<br />I checked each cylinder and they all go as you turn the flywheel. Also when you put it in gear both forward and reverse as you turn the flywheel the prop turns. Does this help?<br />Thanks again

 

[dmessy]

Re: Seized motor/blown rod

Yeah, prop should spin when in gear. Does the engine turn freely(as in with little effort) by hand with the plugs out? Still need to do a compression check to evaluate.

 

[Steve135]

Re: Seized motor/blown rod

mstritt Hi sorry to hear of the break down. I live here in NJ and if you deside to scrap the engine let me know I have same yhar and model.<br />Nevetsd@aol.com

 

[Beernutz]

Re: Seized motor/blown rod

More likely a piston than a rod.<br /><br />What makes you say fuel starvation wasn't the problem? It certainly could have caused a seizure.

 

[mstritt]

Re: Seized motor/blown rod

The reason I don't think that it was fuel starvation is because I checked the fuel lines and vent as the motor started dying. I also checked the lines after the engine died. I pulled the spark plugs and manually checked the pistons, they each seem to move okay when the flywheel is turned. Everything now seems pretty normal, other then the sound it makes when idling.<br />Thanks for the response<br />Martin

 

[dmessy]

Re: Seized motor/blown rod

So what did the compression check come out as? Probably shouldn't run your motor after a cease without checking.

 

[Beernutz]

Re: Seized motor/blown rod

If your motor had been left unused for an extended period of time, fuel could've evaporated out of the carburetors, leaving residue in the mainjet(s). That'll cause a lean condition that can seize a piston. After it cools, it'll run again, but the scuffed piston(s) can knock, and you'll lose compression on the affected hole(s). Sometimes compression will improve over time, but you've gotta find out why it happened. Otherwise, it'll do it again!<br /><br />If it acted like fuel starvation, it probably was.