87 johnson 150 head gasket questions

[js87skeeter]

hello I just bougth a 87 Johnson 150 to replace my motor on my boat that I found has two dropped cylinders couple question got the motor for a steal of a deal the motor has good compression on all cylinders except 1 found water on the plug in that cylinder pulled head found head gasket blow all other cylinders had 115psi of compression this one had 70 with the blown gaskets if you put all the plugs in except that one and check the compression the cylinder will go to 115 what else do I need to check while I have the head off checked the cylinder walls no scoring or pitting so must have blow rite befor he stopped running his boat and what is the tq on the head bolts I know I threw a lot out there hope some one can give me some guidance thanks again

 

[emdsapmgr]

Re: 87 johnson 150 head gasket questions

Torque head bolts to 20-22 ft lbs. Torque in stages, in a circular fashion from the center head bolts to the outside (top/bottom) I'd lightly oil the one piston/rings prior to reassembly. Lay the cyl head on a perfectly flat surface to see if it's flat (not warped.) It's possible that the head gasket failed due to an overheat, so when you restart it, closely monitor/check the head temperatures on the new head gasket side with a laser temp gun.

 

[js87skeeter]

Re: 87 johnson 150 head gasket questions

Thank you for the information should I check the thermostat while I have it off and as far as the cylinder walls I was told I could go over lightly with sand paper then oil them slightly yes or no

 

[HenryB]

Re: 87 johnson 150 head gasket questions

It would be a good idea to check the condition of the gasket sealing surfaces. Look closely for water intrusion paths (like shallow worm holes crossing the path) at each surface. If wormholes are found on the head they can be machined out for relatively short money. If found on the block you might have purchased an anchor.

I would not use sand paper.

 

[js87skeeter]

Re: 87 johnson 150 head gasket questions

Checked the head with straight edge all good there no work. Wholes an Android as far as I just glanced at the eng block did not notice any but will check further when I get home

 

[HenryB]

Re: 87 johnson 150 head gasket questions

The possibility of head warp is strong. Check on a flat surface (the stone counter top if your wife will let you), and check for any rock at all. Again any galling or warp can be machined out of the head. If needed have both heads machined at the same time. Once the machine is set up (that’s where the cost is) the second head can be whipped out in a hurry.

 

[js87skeeter]

Re: 87 johnson 150 head gasket questions

thanks for all the information checked head and block no worm holes in either put flat edge on both aswell both check out good installed new gasket with cooper coat sealer and tq ran it this morning performing like a dream