Merc 115 Powerhead Question

[calboats]

Earlier today I posted that mt 115 was Blown Out, from overheating. In talking to another club member, he says that if I have low compression, but it starts -- there may be an option to try before I scrap or trade the motor. I'm curious if anybody else has heard of this??

If overheated, but with some compression to start, run it on 30 to 1 oil mix, for an hour if possible to get running, then add brake fluid to free the rings, through the carbs. It is possible that the overheating gummed up the rings without actually damaging the rings or cylinder walls in the process.

Anybody else heard of this fix?? the motor is off the boat, so it is a real job to put it back just for this testing, and probably stops the engine trade till I get it straightened out.

Thanks, cal Drake

 

[Fuzzytbay]

Re: Merc 115 Powerhead Question

Anything is possible. However, if you overheated the motor, yet didn't actually sieze the motor tight, then there maybe little to no damage. I'd first check the compression between all cylinders, (any diffrence of more than 15 lbs between cylinders is trouble). Thats the first step, second, while you have the plugs out, look at them, look for a build up of metal on the electrode. Check to see if they look like they ran really hot. Third, look in the cylinder's themselves (use an LED). Roll the motor over to TDC of each visable cylinder, and look at the piston crowns, and at BDC, the cylinder walls for scoring. If there seems to be no problem signs, then to unstick any pistion rings, I'd just use some deep creep, sprayed directly into each cylinder, tilt motor up, and let sit. Then later rotate the motor through a few revolutions, and redo the deep creep.
As for spraying brake fluid into the carbs(Ford type or ???), well I have never heard of it, seems like a waste of money, even if it does work. Deep creep, (or similar products) DO work, and are less expensive.

 

[Moody Blue]

Re: Merc 115 Powerhead Question

Read your other post and find it strange that all cyls are reading 50-70psi with only 100 hours on a fresh rebuild. Did you do the test or someone else?

So the motor is still running, that's a good thing. Why do you think you overheated it? Ignoring the compression test for a minute, what symptoms were there to think it may have overheated?

 

[ChrisfromVT]

Re: Merc 115 Powerhead Question

If there is a buildup of metal on the plugs (or one of them), is this metal from the cylinder walls, the rings or both? I have the same motor that is blown according to the guy that sold it to me. There is molten metal on the #1 plug, but the the motor turns over fine. Not knowing the history, I feel that a teardown/inspection will make me feel better

 

[Moody Blue]

Re: Merc 115 Powerhead Question

Chris, that metal is part of what used to be a piston. Either has a hole in it or the edge of it is melted off. Chances are that the cyl walls are damaged as well. Will turn over fine but I would bet if you did a compression test, that cyl would read 0.

 

[calboats]

Re: Merc 115 Powerhead Question

Read your other post and find it strange that all cyls are reading 50-70psi with only 100 hours on a fresh rebuild. Did you do the test or someone else?

So the motor is still running, that's a good thing. Why do you think you overheated it? Ignoring the compression test for a minute, what symptoms were there to think it may have overheated?

I borrowed the comp. tester from my mechanic. When shut off the cowling was too hot to touch comfortably. Motor stopped, than ran raggedly in neutral. Piece of metal fused to one plug --- but the compression was 30--130--45--130--130 and I guess I quit at that point. I took the motor off the boatnow, and am thinking about getting a smaller 40 to 70 size. The transom was 8 in. below level at rest. Don't think I need that weight and horsepower to fish our local lakes that are restricted to 10 mph. they all are up here.

Thanks, Cal Drke