June 22, 2015 at 10:00 pm #1830
As you may know, I rebuilt the powerhead on my 1958 Johnson 10hp. The shift handle and upper midsection get hot, the mid hot enough to boil water. I can’t find anything wrong, nothing plugged up, pumps plenty of water. Running it on a hose, you could hold your hand on the cyl. head all day, never checked it on the boat after being up on plane. So my question is, what do you think of removing the plate (#2) in the diagram, to let the exhaust down the mid with less restriction. The plate is right in front of the water discharge hole in the mid and blocks off the exhaust cavity in the mid, directing the exhaust forward as it goes down, into the cavity with the shift linkage.
http://www.marineengine.com/parts/johns … Lower+Unit
Canada Member - 1 Year
Topics: 157June 22, 2015 at 10:28 pm #18711
I believe that plate doesn’t prevent gas from going DOWN, it actually prevents gas from coming back UP>
If you remove it, and look down it, you will notice there is a port a couple inches down, into the chamber that the spent cooling water is diverted on its way out the snout.
The exhaust gas come up the chamber that the plate covers, out through that bypass port, then out the snout with the spent cooling water. If that plate were removed, you would have excess build up of gas there with no where to go.
I don’t totally understand the engineering of it, but I BELIEVE, that there is a siphon type effect that goes on there. Removing that plate would make it worse. Just my 2 cents. Wait till the mechanics chime in.
US Member - 2 Years
Topics: 48June 22, 2015 at 10:48 pm #18713
Still waiting to get home to search around for a midsection/powerhead to look at dissect. But, I don’t think I would remove that plate.
Topics: 8June 22, 2015 at 11:09 pm #18716
Certainly no expert here, but out of curiosity, how do the plugs look? Are there any signs of overheating, what does the mixture ring look like, etc..
Point is, it sounds like you really don’t know what’s going on – as in, is this an issue of excessive heat production (incorrect ignition timing, mix too lean), or an issue of improper heat flow through and out of the engine (improper exhaust flow or weak cooling performance)?
If the plugs are still new or very nearly new, they might not be able to provide enough info. If that’s the case, consider putting in a good, used set and run those for a while, to get a better read.June 23, 2015 at 12:41 am #18726
Plugs are dark, new impeller, wear plate & housing are in good condition. 9 hours of break-in on the motor, runs perfect for all 9 hours, not even one sneeze. Relief hole in the water discharge isn’t plugged up, snout in the gearcase either. 24:1 mixture (1 quart to 6 gals.). If the shift handle wasn’t hot (only at idle) or the upper, starboard mid wasn’t getting discolored, I wouldn’t know or probably even care.
Topics: 31June 23, 2015 at 1:28 am #18732
It seems to me I saw a service bulletin about complaints of the paint turning brown under the powerhead. It seems to me the cure was to remove the powerhead and drill a 3/16" hole at an angle in a specific spot in the water jacket to cool the exhaust under the powerhead.
Now I have to look through 600 service bulletins to find where to put the darn hole.… 🙄June 23, 2015 at 1:45 am #18734
This appeared to be a fairly low hour motor, but froze up from sitting after the top main seal developed a leak, ruining the crank but the conn. rods did have play.
Garry, I’ll be more than than happy to pay you for your time, this DARN thing has me beat. Any way I can help you look for the bulletin from 60 miles away? Not that you would want me on your computer, but do you use "teamviewer"?
Canada Member - 1 Year
Topics: 157June 23, 2015 at 1:47 am #18735
Someone had posted a bunch of the service bulletins somewhere did they not?
I have a few bulletins, but no where near 600!
That is very interesting Garry! Thanks.
Ill look through what I have as well
Topics: 49June 23, 2015 at 2:26 am #18737
Bless you!! I too have been trying to help Robert but as you know I know little about Johnsons. Would a bulletin be in my Johnson service manual? It is a older one with a red cover. As usual you have the correct reply. Does this bulletin appear in the older Evinrude manual as well? The 58 leg was a redesign using the 5/7.5 hp leg correct? Seems the cooling system would be smaller as well too. Thoughts?
Topics: 8June 23, 2015 at 2:48 am #18739quote beerman57:
As you know, that tends to indicate a rich condition – but how dark are they?
In any case, I’d suggest you rule out a rich mixture and/or retarded ignition timing. Not saying these are creating your issue, but IMO it’s imperative that you rule them out before going down any other avenues.
US Member - 2 Years
Topics: 48June 23, 2015 at 9:31 am #18749
OK, finally did find a late model QD midsection. Sorry that I didn’t have time to remove that plate (screws seized) or take pics, another early trip today.
In any event, turn your midsection upside down. You will see a triangular hole almost a foot up against aft side of the housing. Can be kind of tough to see, you may have to clean some of that black glop out of there. In any event, this is where the exhaust relieves into the cooling water outlet. Hopefully, you will be able to remove your SS screws holding that plate, I’m sure you will be able to find where the exhaust is allowed to bleed into the cooling drain on the exhaust housing. I looked up the cooling snout with a light, saw what looked like a slot, but couldn’t really tell. I’m guessing that plate is just there as part of the manufacturing process.
I won’t be home for three days, will try to take pictures then. But, it would seem like if that little triangular hole was carbon plugged, or the other hole into the cooling snout was plugged, that would create more exhaust back pressure inside the housing, forcing some exhaust to sneak out (heat up) through that sloppy shift lever bushing you mentioned.
I will also look for a QD powerhead to see if there is a bleed hole somewhere (in the #2 cooling jacket I’m guessing) that might spray a little water down to help cool the exhaust.
PS- My exhaust housing was pretty clean inside, not all wet goo like yours. But, I’m guessing this is due to you using a heavier break in mix and running the engine extensively in the tank. If our theory is correct, then I’m guessing the shift handle would cool down when underway at high speeds due to less exhaust back pressure.June 23, 2015 at 12:04 pm #18759
I have a Johnson service manual, 10th edition, #302231. I’ll look in it.
I’m not worried about running it too rich, ran 20mph and lost speed if I richened it too much, and I don’t think it would run 20mph if the timing was off enough to make it overheat the mid.
No service bulletins in my manual!!
Topics: 6June 23, 2015 at 12:26 pm #18760quote Jeff Register:
Nope. Only the lower flange of the midsection is shaped to fit the gearcase housing of 5 1/2, but the upper part of midsection is similar to the old one.
The cooling system is exactly the same. The impeller has the exact size and shape of the 18’s one.
Also the gears and shafts are differents from the 5 1/2 ones, with larger diameter…
Topics: 49June 23, 2015 at 12:56 pm #18762
I found in the manual that the powerhead should run no hotter than 150 degrees. Garry thoughts sounds good to drill the 45 degree hole to dump massive amounts of water into the leg for cooling the spent exhaust gasses. Seems others have had the same problems with the 58 J. 10hp too right?I sure would be looking into the drill hole too! ANYONE!!! HELP!!!June 23, 2015 at 1:39 pm #18764
Sounds good, just need to know more specifics before I start drilling holes.
Fleetwin, is that the relief hole? If it is, I already know it isn’t plugged. I hooked up the garden hose to the water tube, stopped the spent water from running out the telltail, had water running out down the inside of the mid.
Here is another "IF" question – when the water leaves the P/H, it goes down the telltail "tube", for about 2" before that removable plate (#2 in the diagram) in the exhaust cavity. So why not drill some "relief" holes in that 2" of tube to let spent water into the exhaust cavity? Or is that the hole Garry is talking about? I don’t see anywhere else to drill a hole.
Look at Mumbles picture of the top of a mid on page 5 of my other post – "QD19 running a little hot?"
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