johnson engine rattle.

[randyo3629]

1957 johnson 5.5 hp.<br />has an loud engine rattle when rev @ half-throttle and up.<br />i noticed it when running in a water tank-(in neutral).. did not run the motor in gear.<br />also noticed the rectangular cover on throttle control side of engine is discoloring from heat.<br />engine starts fine and runs fine up until 1/2 throttle.does not seem to mis fire.<br />water pump appears fine-(water from exhaust port).<br />I pulled the head off to check for signs of detonation,saw none.spark plugs look fine. one thing i did notice was when the botton piston is fully extended,i can grab the crown of the piston and twist it back an forth a total of about 1/16"...the top piston has no twist movement.<br />(is this unusual and would it cause the rattle?)<br />to me the noise sounds like coming from the flywheel area,but is hard to tell.i checked the recoil for anything loose-none.<br />any insight you all can give would be greatly appreciated..this old motor is like brand new and i hate to give it up.--(if it makes any diff.,the motor has been stored ,laying it on its back cover and prop)

 

[Chinewalker]

Re: johnson engine rattle.

Hi Randy,<br /> DON'T RUN THE MOTOR ANYMORE! From your description I would hazard a guess that the bottom connecting rod is about to let go. At present you might only need a connecting rod. If it lets go, you might need the rod, crankshaft, piston and cylinder block. In other words, far more in parts than the motor would be worth. The noise is probably due to the connecting rod slapping the crankshaft. <br /> That motor is an easy tear-down there are no needle bearings to worry about scattering about your floor, and no spring clips to go flying across the shop. It's about as simple a motor as you'll ever find and quite easy to work on. You're also likely to find a general service manual in your local library that will cover it, or you can order something from iboats (very similar to the early 1960s 5.5hp model, save for cowlings and fuel draw system).<br /> I have lots of parts for those if you need anything...<br />- Scott

 

[randyo3629]

Re: johnson engine rattle.

thanks for the info.i'll tear it down.

 

[Paul Moir]

Re: johnson engine rattle.

By the way, don't ever rev that engine above 1500rpm in neutral or without a load on the prop. There's a danger that the engine could run away when you do that, plus you are not getting enough lubrication for the rpms you're turning.<br /><br />Good luck with it!

 

[randyo3629]

Re: johnson engine rattle.

Originally posted by Chinewalker:<br /> Hi Randy,<br /> DON'T RUN THE MOTOR ANYMORE! From your description I would hazard a guess that the bottom connecting rod is about to let go. At present you might only need a connecting rod. If it lets go, you might need the rod, crankshaft, piston and cylinder block. In other words, far more in parts than the motor would be worth. The noise is probably due to the connecting rod slapping the crankshaft. <br /> That motor is an easy tear-down there are no needle bearings to worry about scattering about your floor, and no spring clips to go flying across the shop. It's about as simple a motor as you'll ever find and quite easy to work on. You're also likely to find a general service manual in your local library that will cover it, or you can order something from iboats (very similar to the early 1960s 5.5hp model, save for cowlings and fuel draw system).<br /> I have lots of parts for those if you need anything...<br />- Scott

 

[randyo3629]

Re: johnson engine rattle.

Hey there Scott.<br /><br />i tore this 57 johnson 5.5hp down-the lower connecting rod is bent and the crankshaft is scored badly in the rod journal.The crank bearings,piston and cylinders look fine.<br />looks like all the damage was confined to the rod and crank.(Looks like one of the rods have been replaced before--the lower conn rod is thicker,in cross-section than the top rod).<br />you mentioned that you may have parts to repair this...what are we talkin' for a crank and one rod.<br />the gaskets look fine--none of them ripped during disassembly.can they be reused? if not, do you have?<br /><br />You were right.it was a very easy engine to tear down.<br />thanks,randy

 

[randyo3629]

Re: johnson engine rattle.

Originally posted by randyo3629:<br /> Hey there Scott.<br /><br />i tore this 57 johnson 5.5hp down-the lower connecting rod is bent and the crankshaft is scored badly in the rod journal.The crank bearings,piston and cylinders look fine.<br />looks like all the damage was confined to the rod and crank.(Looks like one of the rods have been replaced before--the lower conn rod is thicker,in cross-section than the top rod).<br />you mentioned that you may have parts to repair this...what are we talkin' for a crank and one rod.<br />the gaskets look fine--none of them ripped during disassembly.can they be reused? if not, do you have?<br /><br />You were right.it was a very easy engine to tear down.<br />thanks,randy

 

[randyo3629]

Re: johnson engine rattle.

scott,<br />i definitely will need a head gasket.<br />(wasn't thinking straight)<br />thanks.