Johnson Seahorse TN-28

nwcove

nwcove

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May 16, 2011
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6,293
Re: Johnson Seahorse TN-28

a head gasket and a powerhead gasket are two different things, marineengine .com should show how it all goes back together in an exploded view. dont use any sealant on the head gasket.
 
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mindspin

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Feb 15, 2012
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Re: Johnson Seahorse TN-28

nwcove said:
a head gasket and a powerhead gasket are two different things, marineengine .com should show how it all goes back together in an exploded view. dont use any sealant on the head gasket.
Click to expand...

That site only goes to 1955 but looking at a 5.5 CD-12 it seems only a little different. Stupid question but what 5 bolts were you referring to? Sorry, I don't know much (obviously) about this. I've only done minor maintenance before (plugs) and looking around this thing, it looks like I can take another 20 bolts out but want to keep this to a minimum.

Thanks
 
kfa4303

kfa4303

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Sep 17, 2010
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Re: Johnson Seahorse TN-28

A head gasket goes between the "head" (thing the spark plugs screw into) and doesn not use a sealant, whereas a powerhead gasket goes between the two halves of the powerhead and usually does use a sealant along with the gasket. Unless you're going to take the powerhead apart completely, you shouldn't need to open it up to replace the gasket. However, head gaskets are a pretty common/easy fix. When the motor runs hot they can/do blow. The tell tale sign is usually having one cylinder with good compression b/c the gasket is still intact while the other cylinder has much lower compression due to the gasket having blow out in that area. The gasket is only a few bucks and is very easy to install. The only tricky bit can be getting all of the head bolts out in one piece as they have a nasty habit of breaking off in the powerhead. You can do a search here in the forums for tons of threads on replacing and resurfacing head gaskets. Here's a vid that can show you how to remove the 5 bolts in question, if I understand your question correctly.

http://www.youtube.com/watch?v=SVOedhzPP7M
 
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mindspin

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Re: Johnson Seahorse TN-28

Thanks, yeah I have a head gasket replacement handy just in case but the current one seems ok and I have close to even compression in both cylinders. I've already had a couple of bolts stripped (one in the flywheel!) and another that broke around the carb but I was able to replace it so I don't want to touch the head gasket unless needed. I'm eager to start this thing up but now have it in more pieces than I did to begin with.

Thank you for this vid, perfect!
 
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mindspin

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Re: Johnson Seahorse TN-28

OK, one week later and I was finally able to get the powerhead off which makes things a bit easier to see. I think I have the washer, seal and spring stack in order. The problem is getting everything back in place with the water tube being so bent, it literally wraps around the clutch tube. Can this be taken out and straightened or is it supposed to curve? I don't see how it comes off if its supposed to. At the moment it looks like both tubes and the shaft would all rub against each other pretty tightly IF I were able to push it up and through and connect the water tube at the bottom. It also appears that this is how it's been for a long time! I have no idea how I was able to pull it off the first time.
 
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mindspin

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Re: Johnson Seahorse TN-28

OK, I'm FINALLY getting closer to finishing this thing, or at least attempting its first start. The last part was cleaning and replacing the fuel filter however I have three minor roadblocks now.

TN-28-24.jpg



1. The thread in the actual gas tank is strippd pretty bad, I can get the filter in a little more than half way but its really crooked and I don't want to damage the thread any more than it is.

TN-28-25.jpg


2. One of the magneto threads is still pretty loose, not sure if this is a deal breaker or not.

TN-28-26.jpg


3. The top spark plug is stripped, it was like this when I got it as I noticed the spark plug was sitting at a weird angle. I have a threader tool for this but it doesn't work that well.

TN-28-27.jpg



I really don't want to spend a ton of money on those helicoil kits since I would need three of them in this case.

My hats off to mechanics, especially those who worked on these "easy" motors back in the day. I guess most people don't have as many small issues as I did though.
 
HighTrim

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: Johnson Seahorse TN-28

But just think of all the experience you're getting! LOL

Actually, I dont feel that the TNs are easy at all, not one of the more difficult motors to tune like the Old Mercs, but definately more finicky than the standard 55-58 OMC.

What I would reccomend doing is just getting another head. You could get another flywheel, or just re drill/tap for a larger OD bolt.

The tank hole I would try cleaning up with a tap, then using Loc Tite blue on the threads. If that doesnt help more severe measures will need to be taken.

PM me with your email address and Ill see if I can help you out.
 
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mindspin

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Feb 15, 2012
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Re: Johnson Seahorse TN-28

Thanks, PM sent.

I've got a QD-16 coming up next.... there will be a separate thread for that though ;)
 
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