96 Johnson 30 Head Gasket procedure.

glennkil

Seaman
Joined
Jan 2, 2006
Messages
69
Sorry guys, no manual as yet. Second hand Johnson 30 ELED, starts and idles fine, runs fine at full throttle but takes ages for revs to come up. Compression test is not good with 70 PSI both cylinders which explains a lot. Head is off and bores and pistons look fine. No scratches, gouges and some hone marks still visible in the cylinder. Not much carbon on piston crowns. Head gasket is sus though between both cylinders but I'm not sure. Head gasket on the way but following questions.

1. Gasket goes on dry or needs sealant?
2. Torque specs? I'll start at middle and work out. Bottom ones will be best effort though as no torgue wrench will fit between bolt and cowling.
3. Any sealant on bolts?

Any other reason why compression could be so low? Rings lost tensions due to overheat? I'll start with the head gasket as its easy. If it's anything else I'd reckon it's time for another engine.

Many thanks!
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
36,047
The cylinder head is warped.----Need to make sure it is flat before installing.
 

glennkil

Seaman
Joined
Jan 2, 2006
Messages
69
The cylinder head is warped.----Need to make sure it is flat before installing.

Agree that is one possibility and will be checked before re-fitting. What about the torque settings and sealer on bolts? Other possible causes?
 

glennkil

Seaman
Joined
Jan 2, 2006
Messages
69
The head has a slight warp and there is a gap with a straight edge right under the join between the two cylinders when checking the head :) Removing the cover plate resolved the question of why. The thermostat was stuck half closed! I need to work out how the warning horn works but that's the subject of another post!
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Head gaskets..... If shiny heat actuated sealer is usually incorporated. Use nothing. If dry and plain, use nothing but oil.

Starting at center port side head bolt, torque to factory specs a little at a time (as shown below) in a ever widening clockwise circular design (3 tightening sequences) to whatever the torque is supposed to be,

9....10
5.....6
1.....2
4.....3
8.....7 etc etc..........
 

oldboat1

Fleet Admiral
Joined
Apr 3, 2002
Messages
9,598
can resurface the heads yourself, using a piece of 400-600 grit wet/dry paper, and a flat surface (piece of glass or the steel top of a table saw). Look for uniform shine. On torquing with a box wrench, set one of the bolts with your torque wrench, then go back over it with a box wrench to get the feel of proper torque. Likely will be fine on the bottom bolts.
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Head gaskets..... If shiny heat actuated sealer is usually incorporated. Use nothing. If dry and plain, use nothing but oil.

Starting at center port side head bolt, torque to factory specs a little at a time (as shown below) in a ever widening clockwise circular design (3 tightening sequences) to whatever the torque is supposed to be,

9....10
5.....6
1.....2
4.....3
8.....7 etc etc..........

Ive never heard of oiling a head gasket before but after looking it up seems like you arent the only one to do this Joe
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Ive never heard of oiling a head gasket before but after looking it up seems like you arent the only one to do this Joe

Yeah... That goes back to my day in the trade along with Lew Eppel of OMC. <-- When those guys suggested something, one paid attention.
 

Bosunsmate

Admiral
Joined
Apr 7, 2012
Messages
6,129
Yeah... That goes back to my day in the trade along with Lew Eppel of OMC. <-- When those guys suggested something, one paid attention.

Haha yeah i bet, demonstrations weren't given then by the marketing department
 
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