86 125force low compressin on one cylinder

[BoatsruleGirlsdrool]

First off thanks for taking your time on reading and responding... Well to get right to it I was out going full throtle when i lost about half power and before i could even react it stalled. It wouldn't start back up. Took home peformed compression test from top to bottom first, third, and fourth were all within 5psi of each other 125psi my second one though only had like 14psi so first question would be should i do a tare down see if i need new pistons, rings, gasket or maybe some boring? Also say it is just a piston could i just take a piston from another compatable motor or am i gonna have to buy new ones? Also if i do need that cylinder bored do i have to get all four bored so they're all the same? Model #1251x6b

 

[blackd]

Do the compression again to confirm. If confirmed,if you have a bore scope, scope the cylinder while slowly moving turning over the motor with a wrench. Only remove the head if you can not access the cylinder damage. If damaged you will need to remove head do a more detailed damage assessment. With that your next steps can/will be more clear.

 

[Jiggz]

I've had the same exact problem before except it was on #3 cylinder. This is the steps I took:
-Remove head while saving everything including the head gasket, if you can.
- Remove the piston by dismounting the carb and intake manifold and eventually the reed v-block to access the conn rod.
- Need to make sure you catch all the roller bearings and caps. Do not use magnet to pick up loose roller bearings instead use heavy sticky grease or long handled needle nose pliers.
- Pull the piston out (note orientation of conn rod) and inspect any damage to the #2 cylinder. The most critical is if there is any gouging in the cylinder wall.
Any deep gouges in the cylinder wall will require re-boring. Usually, common test is to run your finger nail across it and if it catches readily, it will require re-boring
If the gouges are very light or are below the ports, then a light honing will probably fix the problem.

Post pic of the cylinder when you can to help in the diagnosis. And yes, you will need a new piston of the proper size if the piston is damaged. However, in some instances only the rings are damaged depending on how bad it is.

 

[BoatsruleGirlsdrool]

Blackd I'll make sure to run test again before tare down...
jiggz when you peformed this operation did you have to take motor off boat? I just finished building a stand thinking that im gonna have to. I'll probably start tare down this weekend I'll make sure to post pic.

 

[jerryjerry05]

Remove the head and check for a bad head gasket, FIRST!!

 

[Jiggz]

Nope do not need to dismount the motor from the boat at all but it'll be nice. But then again that is more work to do. As mentioned, you need to diagnose first to see what action needs to be done to correct the problem. It could just be a blown head gasket for all we know.

 

[Bearmanpaul]

I had the same thing happen. Running wide open, engine slowed and died, couldn't start again no matter what I tried. 20 psi compression in one cyl afterwards. Turned out it was a busted head gasket, replaced and started right up.

 

[Oregonbayliner]

could very well be head gasket if it is dont let the water sit in there. pretty sure thats hoe i lost mine. put it away for winter without knowing i had a bad head gasket pulled it out the next year ran horrible pulled the head #4 had standing water and rust