Seized up twice but still runs smoothly?

[extramile]

I have a 1969 Johnson 55hp super sea horse. I was running at full throttle, heard some clunking and the engine seized tight. After a few hours I was able to start it again. Next day same thing, ran fine then seized while at full throttle for about 10 min. It was on a sandy river and had been through a few sand bars. This time the motor seized solid for 4 days and on day 5 started like nothing ever happened. I've since run it with the rabbit ears on and it runs smooth as ever! I am leary to put it on the water and make it wose. I've been told I must have scored the cylinder, but It wouldn't run smooth then would it? Any advice on where to go from here? [colour=null][/colour]null

 

[tashasdaddy]

Re: Seized up twice but still runs smoothly?

check comperssion,change the impellar and thermostat. then watch it.

 

[Chinewalker]

Re: Seized up twice but still runs smoothly?

Might be the lower unit, too. Check the gear oil for metal shavings...
- Scott

 

[F_R]

Re: Seized up twice but still runs smoothly?

Does the powerhead show any signs of overheating, ie scorched paint? If it does, you need to change the head gasket and exhaust cover gaskets, as well as the water pump. While you have the exhaust covers off you will be able to see if it has scored the pistons. You must have been praying a lot if it hasn't. Pray a lot more if you think you can get away without changing the gaskets. BTW, check the exhaust plate for warpage too.

 

[extramile]

Re: Seized up twice but still runs smoothly?

I see no visible signs of overheating. It litterally looks like it is straight off the showroom floor. Do you still think I need to replace the gaskets? I also plan to replace the Impeller and thermostat as a just in case. Thanks for the help.

 

[ezeke]

Re: Seized up twice but still runs smoothly?

The motor has overheated enough to seize the pistons. Some damage would certainly be possible, but is virtually impossible to estimate without an inspection. The gaskets will have to be replaced if you choose to do the inspection.

If you don't do the inspection, at a minimum, you must re-torque the headbolts and exhaust cover bolts.

The pump impeller and thermostats should be removed for replacement and the cooling circuit flushed.

Try to do a compression test as soon as possible. That will give you some idea of the condition of the cylinders and pistons.

 

[extramile]

Re: Seized up twice but still runs smoothly?

How do I what the proper compression should be? I have the original service manual but I do not believe that is in there.

 

[Pony]

Re: Seized up twice but still runs smoothly?

They usually won't publish compression numbers in the manuals because every compression gauge can be a little different. What you want to look for is the variance between each cylinder. I think 5% variance is great, some will tell you up to 10% is okay too.

If I were you I would take a compression tst, and then post your results here. Someone will be able to tell you if it is acceptable or not. Idealy you probably want to see psi's near 100 or so, but if the numbers are evn it can be run on less. That number is not as important as the difference between the cylinders.

 

[F_R]

Re: Seized up twice but still runs smoothly?

You say the paint looks like it's right off the showroom floor. So I don't think it was overheated. Looks like you need to not assume, but look for some other cause of the seizing. I would suspect a bearing failure someplace. Don't run it till you find the problem, it could get much worse, very quickly. You DO have oil in the gas, right?

 

[ezeke]

Re: Seized up twice but still runs smoothly?

F_R may well be correct.

The problem is that the motor did seize. You did run it in sand bars that could easily have clogged the cooling system.

The possibilities are endless, but based on the symptoms; it could be that you have blown a cylinder head gasket or a exhaust cover gasket which could have allowed water into a cylinder, which could have rusted a ring enough to seize to the cylinder wall.

 

[h_lankford]

Re: Seized up twice but still runs smoothly?

"You DO have oil in the gas, right? "

well, do you?

I once forgot to add oil to the mix of a gas-powered hedge trimmer. It locked up, then ran fine when cooled down. Realized my error. Has done fine since then.

Could you have made the same mistake?

 

[extramile]

Re: Seized up twice but still runs smoothly?

I do have oil and lead in the gas. I will check the compression today and post the numbers.

 

[extramile]

Re: Seized up twice but still runs smoothly?

I just finished checking the compression. 125psi in all 3 cylinders. +/- 2 psi each time. The plugs where also extremely clean Any suggestions as to what this means and where to go from here?

 

[ezeke]

Re: Seized up twice but still runs smoothly?

That sounds very good to me. I would certainly recommend the new water pump impeller and re-torque the head bolts.

Do you have a tell-tale on your motor?

 

[F_R]

Re: Seized up twice but still runs smoothly?

I hate to be a pessimist, but your original post says "I was running at full throttle, heard some clunking and the engine seized tight. " That just is not a normal occurance. The clunking should be a clue. You must find out what happened. The next time you might find a rod sticking through the case or something. As someone said, the possibilities are endless. The next thing I would suggest is drain and refill the lower unit and check the drain oil for metal particles. Use only BRP Premium Blend oil for the refill, from a dealer.

 

[extramile]

Re: Seized up twice but still runs smoothly?

Here's a recap, No outward signs of overheating (have not checked gaskets). Compression is good on all 3 cylindars. I drained the lower unit already and found no shavings.

I will re-torque the head bolts and exhaust cover bolts.
I will replace the impeller and thermostat.
I don't know what a tell tale is, please explain.
I really appreciate all the help I am getting from you all, thanks again.

 

[cobra 3.0]

Re: Seized up twice but still runs smoothly?

Tell tale is a pee hole where a continuous stream of water runs out when the impeller is working. Your engine may not have it was put on in later years.

 

[h_lankford]

Re: Seized up twice but still runs smoothly?

"I do have oil and lead in the gas."

huh?

just curious. lead? you mean lead substitute for octane booster? not needed.

"white gas" (meaning lead-free) is the standard for marine and aviation piston engines, otherwise lead-fouled spark plugs causes dead boat or dead pilot.

 

[iwombat]

Re: Seized up twice but still runs smoothly?

Avgas is the only place you _can_ get lead anymore. But that's beside the point.

"... Avgas has a lower volatility than mogas and does not evaporate as quickly, which is important for high-altitude use. The particular mixtures in use today are the same as when they were first developed in the 1950s and 1960s, and therefore the high-octane ratings are achieved by the addition of tetra-ethyl lead (TEL), a fairly toxic substance that was phased out for car use in most countries in the 1980s..."

 

[Willyclay]

Re: Seized up twice but still runs smoothly?

You might want to take a look at the upper motor mounts inside the lower cowling, not the transom mount. I experienced failure of one on a 1962 Johnson V4 75hp. Heard a loud clanking as power was applied but did not have engine seizing like you. To check, push hard on the powerhead in all directions. Look for excessive movement and metal-to-metal contact between powerhead and lower cowl. If one mount is bad, you should change them all.