QD19 running a little hot?

[orpilot]

…

[orpilot]

Hi Beerman,

I’m curious how many hours you have on the motor? Typically, hot running motors in your situation (right after new rings) stem from the heat generated from the cylinder-ring friction. Having overhauled a few hundred small outboards, I can relate a little of my experiences on how to avoid the problem. First off when honing the cylinders get your hands on a cylinder hone with the little carbide balls instead of stones. They leave what’s called a plateaued finish that creates a better seal with a lot less friction and a much shorter break-in time. I almost always replaced pump arts when doing an overhaul but I can tell you that for your vintage motor the pump housing usually accounts for the most loss of water pressure. If you have any depression in the pump housing surface (where it meets the impeller), replace it.

Back to break-in. First, run a richer mixture of oil during the 1st tank. It’s best to do initial running in a test tank with circulating water, first with lower RPM’s and then once every 30 minutes, bring it up to full throttle for about 30 seconds. Engines that have cylinder walls honed with stone type hones typically take about 6 to 10 hours to break-in and will run hot until the rings seat… usually less than a couple of hours if you’re using carbide ball hones. If your break-in occurs on a boat, run with the lightest possible load, first at the lowest speed that gets the boat on a plane. Avoid running it plowing through the water. Reach back and check water temperature from the exhaust housing. Let it run at a fast idle to cool down if it’s getting too hot. Don’t let it get so hot that you can’t hold your hand in the outgoing water flow.

I’ll assume you resurfaced the cylinder head and you have new gaskets there and on the exhaust cover. Leaks in either place can disrupt water flow.

The ’58 10 HP like you have is a great motor. I’m sure you’ll get it sorted out but I have to say that if you don’t have close to 10 hours of break-in time you may be chasing something around that’s going to go away when it gets some more time on it.

Jim

[beerman57]

The powerhead and exhaust water don’t get hot, the shift handle and upper midsection do. The shift handle cools down after running up on plane, but the mid boils the water that splashes on it when it comes down off plane. You know, after looking at everything yesterday I realized that ALL the cooling water goes right out "telltail" hole on the mid, NONE of it cools the exhaust after after it leaves the P/H. And by the way, the exhaust cover isn’t discolored. To H with this thing, I don’t care if the shift handle gets hot at idle or if the mid is discolored, it runs too good for me to keep wasting so much time on it!!!!!!

[orpilot]

Not having a QD-19 exhaust housing in front of me I can’t say for sure but the typical design back in those days was to have a passage nearby the water outlet where excess water flow found it’s way to the exhaust flow in the exhaust housing. Maybe that passage is blocked with carbon build-up. In any case, having the upper exhaust housing and shift handle getting hot probably means that passage is blocked, for whatever reason. I suspect that eventually the upper part of the exhaust housing is going to start to discolor… get cooked. You might be heating up the area around the pump as well, if it’s not being bathed in water flow. I’d pull the powerhead again and have another look. It’ll be great fun! … good excuse for consuming a couple more beers!

[beerman57]

The P/H is still off, the water leaves the P/H in one spot at the rear – into a separate cavity that is the "telltail", anyway that’s what I call it. The exhaust gases go down the mid in front of that and it’s separate. Here is what I REALLY don’t get – if the P/H isn’t overheating, why should anything else be overly hot? Next time I run it on the boat I’ll take the cowl off and check the head for heat right after coming down off plane, but it runs on a hose OK.
In my original post, I had my flusher turned to the back of the water inlet and it got a little hot, after turning it around and putting water straight into the passage to the pump, no problem.

[retiredoz]

Doesn’t sound to me like you have a cooling problem, you have a ‘dispose-of-the-exhaust’ problem. Silly question time : Did you check the snout for any kind of restriction ?

[beerman57]

I can’t find anything wrong, it’s wide open from the top of the midsection and out the snout. Some people are suggesting there might be a water passage to cool the exhaust gasses that is blocked. Why, why, why would the shift handle cool off from being up on plane but not the upper midsection. Shoot, it’s already discolored, I guess it will probably get a crack in it soon. I probably should have pulled the exhaust cover off before I re-installed the P/H a couple hours ago. But if the exh. cover wasn’t getting enough water flow, wouldn’t it get discolored pretty quick?

[fleetwin]

OK, still a little confused. You have the powerhead off, correct. The engine runs cool, but the shift handle and exhaust housing gets hot, correct?
You mention that all the cooling water is directed out of the cooling upper cooling outlet. Admittedly, I have never looked closely at this area, but guess I should have. Others have mentioned that there is a relief hole that allows some cooling water down into the exhaust housing. I don’t think I have a 10hp exhaust housing apart, but will look. Perhaps someone else has one apart and could post pictures. In any event, I wouldn’t put the engine back together until this issue has been clarified. I’m thinking you could end up with some strange problem/failure letting that exhaust housing/shift handle heat up like that.

[beerman57]

I took a pic of the 1962 ten hp I’m also rebuilding, but I can’t / don’t know how to reduce their size so I could post them. The ’62’ is pretty much identical to the ’58’ at the base of the P/H. I wonder if it’s possible to have a head gasket that isn’t letting in or out of the exhaust cover. But all the water leaving the P/H goes in the cavity in the mid where the telltail hole is, and that’s separate from the exhaust gas cavity. The P/H is back on, but I can put my hose on the water tube and listen for water going through the exhaust cover. Probably will end up pulling the P/H again!!

[fleetwin]

You can email the pictures to me if you want:
dkellogg56@yahoo.com
Again, I want to make sure I understand the issue. The engine/powerhead is not running hot, but the exhaust housing/shift handle does get hot, correct?
If there was a problem with the exhaust cover gaskets, the powerhead would be overheating or leaking water. So, I really don’t think there are any problems with powerhead gaskets.
I understand the water is dumping into the telltale cavity and leaving the exhaust housing. But, I’m thinking there is a relief hole that runs from the telltale cavity back down into the exhaust housing, this is the relief hole that others have reported to get clogged with carbon. Bleeding a little cooling water back down into the exhaust housing probably helps keep it cool, which is the issue I think you are reporting. Look for the bleed hole(s) in the telltale cavity on the 62 10hp you have apart, try to post some close up pictures, maybe we can clarify this issue. I got rid of all my 10hp exhaust housing skeletons, or else I would have a close look also.

[Author]

Posts