Overheated and stalled gt 150

[831Bass]

My fiancé and I just got a new to us boat with a Johnson gt 150 and we had a hard time getting it started but once we did it seemed to be running great and fast (loose plug wire). Then as we were bringing the boat up to speed one time engine cut out and the over heat alarm came on and the motor was smoking a bit. Looked at the the gauge and it was pegged. Let the motor cool for a bit and noticed a clump of weeds and moss caught around the intake area. restarted it and it idled ok so we put into gear pretty quick to try to get back to the dock but it died. We then ran out of battery trying to start it again (battery was already low)
I did a compression check today and 4 cylinders were around 80-90 and one 60 and one under 20. My question is where do I go from here? The plug from the lowest cylinder was pitted and I can see inside that the piston crown thing looks pitted also.
Will I do more damage if I try to run it and limp by while saving for rebuild? Any advice, opinion or input is appreciated
Thanks in advance ,
Brian

 

[racerone]

Time for a complete rebuild ----This will be an expensive lesson !

 

[831Bass]

Ball park how expensive you think?

 

[flyingscott]

If you do it yourself ballpark would be $1500 -2000. If you pay someone to do it $3-4000 ballpark. You may want to look for a different motor.

 

[jbuote]

You have your answer above really.
racerone and flyingscott have probably forgotten more about boats and engines than I will ever know... I'd listen to them.

but just to answer your last question, in case it wasn't clear, Yes....
Trying to run it and get by while saving for a rebuild WILL cause more damage.
That is, if it'll even run at all at this point.
(Pitting on the piston makes me think broken rings)

If it did run, it probably wouldn't run for longer than a few minutes anyway..,
Don't even try..

$0.02

 

[831Bass]

What does a rebuild like this usually consist of? Machine work?

 

[831Bass]

thanks for the replys, I'm torn up about this but just want to move forward and make it a trustworthy boat.

 

[Bosunsmate]

Tear it apart and look at the condition of the other pistons and the piston walls. Ive rebuilt a 90hp with two bad pistons for less than $350 using second hand parts and a new gasket set, id let it be used as a rescue boat its that reliable. You dont need to spend a lot in my opinion to get them good for on going use.
You could get the block pressure tested and bored out but ive gotten by with close visual inspection and a micrometer

 

[831Bass]

Awesome thanks! I'll start pulling it apart and see what it's looking like

 

[831Bass]

Awesome thanks! I'll start pulling it apart and see what it's lookin like.

 

[flyingscott]

A word of warning those motors like to break rings. If you replace one piston you have 5 other old ones that could be ready to break there rings.

 

[jimmbo]

A word of warning those motors like to break rings. If you replace one piston you have 5 other old ones that could be ready to break there rings.

Not a case of 'could', more like a case of 'when'

 

[Faztbullet]

Find a different motor for replacement as you don't want to put $1500 in a motor worth $800

 

[831Bass]

A word of warning those motors like to break rings. If you replace one piston you have 5 other old ones that could be ready to break there rings.

good to know, I might as well just do all of them then

 

[racerone]

They are a simple motor that you can maintain yourself.

 

[Bosunsmate]

good to know, I might as well just do all of them then

Good plan, keep an eye on the chamfers of the ports as rings can snap if these have gotten rough, also check the locating pins a all in solidly, four strokes dont have these

 

[831Bass]

anyone know if I can get a rebuild kit anywhere for this motor? Thanks

 

[flyingscott]

Before you do anything make sure you dont have oversize pistons already. Take the block to a machine shop they will tell you what size pistons you need, and if it can be rebuilt at all. WSM makes a good quality kit that has all the parts you need and a.good price. That was included in the do -it-yourself price I gave you along with machine shop prices.Do not use the old pistons they have all been overheated and damaged. Not to mention they all have ring groove wear.

 

[831Bass]

Before you do anything make sure you dont have oversize pistons already. Take the block to a machine shop they will tell you what size pistons you need, and if it can be rebuilt at all. WSM makes a good quality kit that has all the parts you need and a.good price. That was included in the do -it-yourself price I gave you along with machine shop prices.Do not use the old pistons they have all been overheated and damaged. Not to mention they all have ring groove wear.

Ahh good thinking about checking bore, can't I do it with just a micrometer? Idk Starting to lean towards just having a shop just do most of the work for me so I dont screw it up and I know I'd take forever to get it done. Know of any people or places around central/northern California who would be good to take it to? Thanks again for you help!

 

[flyingscott]

They only way you come out decent on that motor is if you do it yourself. Otherwise sell the motor for parts and buy something else. The pistons will have a size marked on them if no size it is a stock bore. Otherwise it will something like .030 on them.