Diagnose/Starting a rebuild 77 johnson 140

[JWhit]

The motor seized up at the beginning of the summer, just got it home on the trailer. took the piston covers off the back of the motor, one is a little pitted, the other 3 look good. my question is what steps should i take next to find what's causing the motor to seize? If i remove the exhaust port on the back of the power head does that help or show me anything? I guess the only other thing i can think of is flywheel removal to hopefully see something on the crankshaft or bearings? Thanks for any advice

note: flywheel won't budge at all, motor was running up until seizure but did not seem to be overheating at the time

 

[Chinewalker]

Re: Diagnose/Starting a rebuild 77 johnson 140

If you have something pitting the piston then that means something let go inside. Gotta pull the powerhead completely apart to assess and then decide if it's worth dealing with it...

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

Pits/dents on the piston crown are typical when a piston ring lets go. The ring cracks into pieces (usually due to heat or lack of lubrication,) then moves into the intake port and up into the combustion chamber. As the piston moves up and down, the broken ring pcs will get wedged between the piston and the head face, creating the dents. This is a major failure and will require a teardown. Usually at least one new piston is required and 4 new ringsets. I would not re-use a head with the dents in it either. You can pull the heads off, the exhaust covers off as well as the 4 bypass covers on the side of each cylinder in order to get a better look. Have a machine shop check the cylinder bores for wear-that will give you an indication whether boring any/all cylinders is necessary. Once you have an idea what the repairs cost, you can decide whether to repair that engine or spend the money on another one.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

makes sense, thanks. so i should basically start removing anything with bolts around the block to get a better view inside, and will need to remove flywheel and entire power head to get at bearings? Have a feeling this will be more just for fun and not worth rebuilding but should learn some stuff along the way. thanks again

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

You don't need to pull the flywheel to remove most of these covers for inspection purposes. If you decide to split the crankcase, you will need to pull the flywheel.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

just wanted to update, dropped lower unit this morning, no help on seizing issue. also removed exhaust covers and side cover, nothing major of note but can see some light scratches on piston #1. time to remove flywheel i suppose and dig in deep...

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

got the power head open, surprised to find out the slightly pitted/scored #1 was not my problem. Looks like the lower bearing plate broke into 3 pieces, and one was stuck between the crankshaft and block, seizing the motor. also looks like the lower crankcase head got torn up a little and the screws had all fallen out for the most part.

any ideas what the most likely cause of this would be? worth trying to fix and replace all the gaskets and rebuild? Thanks again for any advice, will try to post pics soon

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

pictures attached hopefully, thanks

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

An unusual failure for sure. Certainly not typical. Possible the 4 screws on that bearing plate either lost torque or snapped with age. Visually check those bolts-are they broken or intact? Any signs of water in the block? You may have had some water in the fuel which may have gravitated to that bearing. Also, if there was ever any trace water in the block and it was stored for the winter in that condition, it could affect that bearing. I'd have a good look at the bearing balls-check for pitting and rust on both the bearings and the races. Also, check/count to see that all the bearing balls are intact-perhaps one cracked in half and locked up.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

Makes sense, I'll check the bearing when i get home. the bolts looked good for the most part, there were a number of them sitting upright on the mid-section when i pulled the power head off. i guess they had sheared or something and were just sitting there. only had to pull two out (which were both loose) to get the lower piece off. didn't notice any water issues but always a possibility, although the bolts losing torque is sounding likely since they hadn't snapped. thanks

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

It's unusual for those bolts to loose torque and fail like that. Keep us posted on your findings.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

will do, what should i look for other than water intrusion? how exactly would the water cause such a failure if in the gas? thanks

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

The water will rust surfaces, especially shiny bearing surfaces. If it is stored for a long time between running, (like over the winter) the water can start to work on the internals. Once bearing surfaces get rusty, they can pit. On a bearing surface, it does not take too long for friction to develop, then heat, then a failure. Now that you have it apart, check the large top roller bearing and a couple of rod bearings, too. You may have had this problem for some time...have you noticed any unusual noises from the engine? Water/rust can form shadows/discoloration on bearings. Look for patterns where the bearings may have sat in one position for a long time and a stain was etched in the bearing surface. (and the top of the crank-the upper bearing running surface) You might want to take a fuel sample from the tank and see if there is any water in it.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

no signs of rust or water anywhere in the crankcase, the bearings were dirty and difficult to move, but once cleaned up they spin pretty good. all of the bearing balls appear to be in good shape. leads me to think it was water in the gas, it did have some old gas in the tank but was topped off with fresh and ran fine. i had shut off to switch gas tanks then it was seized when i went to restart.

now the question is whether to clean it up, replace a few parts/gaskets and give it another go or part it out, thanks for any other ideas or advice

 

[emdsapmgr]

Re: Diagnose/Starting a rebuild 77 johnson 140

The 77 140 was a unique (one year) engine. Considered by many as the ultimate OMC 140 crossflow. It was the only year OMC put an exhaust tuner on a V4 engine. Considered by many as a real high performance consumer engine-you may find it easy to part out.

 

[JWhit]

Re: Diagnose/Starting a rebuild 77 johnson 140

thanks for all the help, guess I'll finally part ways with this one since it's for a pontoon application and don't really need all those hp