Johnson TN-28, Idle and cooling

[burnt clutch]

I'm back to tinkering with my TN-28 and I'm noticing some things. First, when I run it at a steady speed, I notice that the RPM's surge a little. Is this normal with these engines, or indicative of another problem? Also, when I first start it up, there is a steady stream of cooling water coming out of the elbow for the cooling line under the cylinder. When the engine warms up the stream gets choppy and sometimes turns to steam. Is this normal or should I be checking something out? Thanks in advance for any advice!

-Karl

 

[F_R]

Should not be getting hot and steaming. Are you running it on a boat on the lake, or in a barrel? If the latter, it could be the cause of both problems you are seeing.

Having said all that, I would not suggest you trust any water pump impeller if it is old. They can fail at any time.

 

[burnt clutch]

It actually was in a drum with water in it, I guess I didn't realize the water would heat up that quickly. I went ahead and put the motor on the back of my Jon boat and tested it on the lake. Now come my next questions: the thing will run for about 30 - 45 seconds and then either die suddenly,or let out a big sneeze and then die.. There's no sputter or warning before it dies. And then its really hard to start again, unless I wait for 10-15 minutes but once it starts the motor is only good for another 30 or 40 seconds, and then we start all over again. I did check for water stream out of the elbow and I'm getting a steady flow. It doesnt do any of this when the motor is in neutral, only when it is in gear, so I am stumped! Could there be something else wrong with the motor, like a vacuum leak from a bad intake manifold or head gasket? Also, are all sneezes a symptom of too lean of a fuel mixture? Thanks again for reading and any pointers you could throw my way.
-Karl

 

[HighTrim]

What do you have low speed set at? Little rod with bent tip coming out of bottom of carb? 5/8 is about right out from seated. 3/4 on the high.

Have you rebuilt the carb?

 

[burnt clutch]

I have the low speed needle about 3/4 turns out. I'll tear into the carb and see if there's any crud in it, and then re-run it. Another thing I noticed was water and maybe exhaust squirting out of these holes on the lower unit. Is that normal?

-Karl

 

[burnt clutch]

I have the low speed needle about 3/4 turns out. I'll tear into the carb over the weekend and see if I can find any crud. Another this is that I see water and exhaust squirting out of these holes on the lower unit. Is this normal?

-Karl

 

[nwcove]

are you sure your fuel cap vent is clear and working properly?

 

[burnt clutch]

The vent works, I can hear it hiss when I open it up on a warm day.
-Karl

 

[racerone]

Is the lean sneeze coming from the rotary valve intake ?

 

[burnt clutch]

It sneezes out of the slow speed intake, which I guess is the rotary valve one. I didn't get a chance to tear into the Carb yet, but will post what I find when I do. Would it help to squirt some Seafoam Deep Creep into the cylinders in the meantime?

-Karl

 

[Klink]

re: And then its really hard to start again, unless I wait for 10-15 minutes but once it starts the motor is only good for another 30 or 40 seconds, and then we start all over again.

I'd test the engine head temperatures with an infrared thermometer gun, an excellent tool to have, and only like $17 on Amazon. I got this one: http://www.amazon.com/gp/product/B00837ZGRY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1 .

I've bought 3 1990's Johnson engines and all three peed fine but still didn't get any water to the heads because the water passages were clogged. An engine turning off like yours in my recent experiences is actually good, because it saved the engine from frying.

 

[burnt clutch]

Thanks for the tip and that link - I actually ordered one of those today! I also ordered a Johnson Outboard Master Service Manual & Bonus manual on CD that I found on Ebay so I can get a better idea of what these engines are about and how to fix them. I'm also getting a new head gasket since I see myself digging deeper into this engine before I get it fixed.
-Karl

 

[Klink]

Read the instructions that come with the thermometer. Although the red spot stays the same size always, the place that it takes reading gets wider the further out shoot from. If you want to read exactly where the red dot points you'll have to be like 6 inches away. It's a great tool to pinpoint the hot spots. I placed a temperature gage probe on my 115hp where it was the hottest, so that I could be warned quicker.

 

[burnt clutch]

Here's the latest, I wanted to rule out any intake or exhaust blockage problems with the engine so I treated it with Seafoam deep creep and test ran it again. It acted like usual with sneezing and shutting down. Since I was looking at pulling the head to check for blockages I decided to do a compression check to have a reference point. My compression numbers were 50 and 47 which weren'€™t much better than what I started with when I began to tinker with this engine. Since I just got the master shop manual I decided to do a full teardown and overhaul to see if I could make things better. I plasti- gauged the crankshaft journal and test fitted a piston ring in the cylinder to check for ring gap and everything looks to be within specs. My next question -“ I figger I should replace the pistons and rings if I a€™m going to do a true overhaul on this thing. Where'€™s a good source for these? The shop manual calls for a cement to seal the mating surfaces when putting the crankcase back together? Is there a source or substitute for this too?
-Karl

 

[burnt clutch]

Pictures of last weekends adventures..

-Karl

 

[burnt clutch]

I've had no progress on this lately, as I"m fighting the snapped off head bolts. Easy outs didnt work so I'm going to drill the bolts out and use a dremel tool take the bolt down to the threads and then I'll take a tap to chase out whats left of bolts. I'm trolling Ebay for another powerhead if I screw up the bolt holes.

-Karl

 

[HighTrim]

Yes use 3M 847 on the crank halves.

The pistons may be difficult to find new. Try a wanted ad at aomci.org. If they are not gouged, and measure within spec, I would just re use them.

The rings will be easier. Their original part number was 41-333, superseded to 307575, superseded to 378432. This is for 1 cylinder only, so you will need 2 sets. Sites like ebay will have them, or again try a wanted ad at aomci.org

 

[HighTrim]

The head gasket part number is 41-336, I likely have a few of them around. Checked but don't have any NOS pistons or rings left sorry.

Some other helpful sites:

seaway marine
vintage outboard (they have head gasket in stock 11 bucks)
Dan Gano at ganotech dot com

 

[HighTrim]

Easy Outs aren't so easy are they! lol Never use them, in fact, toss them in the garbage. They are hardened, so when they break, and they will, good luck drilling them out.

Sometimes heat/penetrating oil, and a left hand drill bit work well. Otherwise, drill through, collapse the old bolt in and pick out of threads, then chase with a new tap.

Where are you from? A donor powerhead should be easy enough to find. I have a TN missing recoil that needs a good home!

 

[burnt clutch]

Thanks a bunch for your OMC part #'s, I'll try to search for them later this week. I tried the oil and left handed drill bits but they didnt work the bolts out, but they did cut well. I'm about 30 miles southeast of Kansas City, can I PM you about your TN?
-Karl