QD19 Overheat Question – Update

[fleetwin]

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.

[beerman57]

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!!

[enrico-italy]

quote Jeff Register:

Garry,
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?
Thank you!!

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…

[jeff-register]

Robert,
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!!!

[beerman57]

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?"

[Mumbles]

Hey Beer, I found several different year mid sections late yesterday and they all had minor differences in them. When I get back in a few hours, I’ll take some pics and also run up a few motors, including a ’58 QD. 😀

[fleetwin]

OK, I am assuming you had the powerhead on when you plugged the overboard cooling dump, then saw water leaking out of the triangular hole I mentioned. So, if that is the case, I think it is safe to "assume" that the exhaust relief/cooling circuit buried inside that cavity is working as designed. It can’t hurt to pull that plate off and have a look, but only if the screws will come out with no torching involved. Definitely reinstall the SS plate though, don’t leave it off.
I would hesitate to drill the cooling relief holes in that cavity above the SS plate though, that is pretty darn close to the exhaust manifold. Negative exhaust pressures could actually draw water up into the exhaust ports, crazier things have happened!
Hold off on drilling holes into the #2 cylinder water jacket until someone can confirm this is accepted practice with a bulletin or by actually finding a block with a relief hole in that area.
I think Mumbles will be able to provide some good data when he runs several of his QDs looking for a hot midsection/shift handle.

[beerman57]

fleetwin, at this point I’m not going to get in a big hurry to drill any holes. But where about are you saying I might drill into the #2 water Jacket? After looking at the P/H base and top of the mid, I don’t see any likely places to drill a hole. I can send pics of my P/H and mid, but don’t seem able to post them here from my computer.
If I ever get the right base gasket for the ’62’ ten hp. I can play with that one. But with my luck, it will have the same problem.

[phil-b]

Question:

I’m seeing mention of both "tell tale" and "exhaust relief":

To me, a "tell tale" is water tapped from the cooling system and "peed" out to indicate that cooling water is being pumped…. OMCs of this era don’t have those (unless you’ve tapped the cooling system yourself)

To me, "exhaust relief" is the hole on the back of the leg where exhaust and water come out…

[Mumbles]

Today I pulled out both a ’58 QD carcass and a running ’58 QD to see what’s going on. Just like I expected, not much.

The ’58 midsection is designed a bit differently than the earlier ones. The web in the middle separating the two chambres is only 5/8" or so deep while the earlier ones are closer to 5" deep. This allows the hot gases to immediately flow into the shifter area after leaving the cylinder. Some of the exhaust gases travel to the bottom of the housing before coming back up the rear chambre thru a small triangular hole near the bottom. The plate at the top seals off this part of the housing forcing the gases to discharge thru a hole about the size of a nickel into the rear water exit passage and out thru the idle relief port.

After running the motor at both idle and top barrel speed for several minutes, the housing temperature in the shifter area never changed more than ten or fifteen degrees. The shift handle itself never got much more than ninety F which was about the same for everything else in the direct sun today. In other words, the housing and the shift handle were both at good operating temperatures and I wouldn’t have been able to boil water or fry eggs on either of them.

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