Up in smoke...

[shaun77]

89 125 force o/b with a bad exhaust leak that I can't locate. Just swapped mid sections, now when sitting in the water exhaust just pours from forward section under or around powerhead I think (sealed well with high temp rtv). The idle boot is intact and fits snug on the two ports. Any tips on what I should be looking for or what im missing? Also runs like a champ all day on muffs, easy start with top cowling on and no obvious exhaust seen. As soon as it sits in water though forget it.

 

[JAMGO46]

Re: Up in smoke...

Is your exhaust snout in place? Rubber seal below your exhaust tube flange - will allow exhaust up thru midsection - most likely culprit IMO.

 

[JAMGO46]

Re: Up in smoke...

Exhaust seal - #68

http://www.boats.net/parts/search/Merc2/Force/125 H.P. (1986)/1254X6A/MOTOR LEG/parts.html

 

[Frank Acampora]

Re: Up in smoke...

On muffs---no back pressure. Sitting in the water--lots of back pressure. There is the difference. Bet if you got the boat on plane without the cover and then replaced the cover it would continue to run well.

How is the gasket between the match plate and the block? Is the match plate fully seated on the leg in the front? Is there possibly something caught in the relief holes for the front nuts of the match plate? Did you use long studs in the front? The front four studs are about one inch shorter than the rest.

Take a couple of good photos --close and from a couple of angles-- of the block where it joins the leg and post them. Might help photos some if you unbolted the lower cowl and raised it a bit so we can see the joint.

How about the bolts for the upper motor mounts? Heads too high will hold up the match plate too.

 

[shaun77]

Re: Up in smoke...

Thanks for the input...I'll take some pics and post them with the rear cowling off...not sure what the " match plate" plate is though.

 

[Frank Acampora]

Re: Up in smoke...

The Photos are the ones I wanted to see. They do show the match plate to midleg junction. The match plate is the plate between the block and midleg. The six front bolts go through it. It carries the shift linkage and on the exhaust side it has a threaded 1/2 inch pipe plug with a square head. Internally it carries the exhaust downtube. It is called a match plate because it matches the block to the midleg.

Unfortunately, I can not see anything obviously wrong with the installation.

 

[Nordin]

Re: Up in smoke...

Have just rebuild a 1990 50Hp (looks like the same on the 125Hp) and there is one gasket between the powerhead and the spacer plate. This one is a thine gasket. But between the spacer plate and the motorleg there is a thick one (about 3mm).
Maybee RTV gasket can not fillup the space between plate and motorleg.

 

[shaun77]

Re: Up in smoke...

Well i just put it in a tub of water just below the lower cowling so the exhaust wouldn't flood the area of problem. I could see no exhaust leaking around the rtv seal, it's all coming up from the gear shift rod so I guess it must be the exhaust seal itself? Any possible chance of removing the powerhead without a complete disassemble and removal from boat?

 

[MostlyHrmlss]

Re: Up in smoke...

Sure, just did it myself over the weekend. Pulled out about 25 or so bolts, nuts, and screws, dismounted the starter solenoid, disconnected the battery and control wires, shift and throttle cables, and fuel line. Then I just bear hugged it and lifted it right off the back of the boat. Getting the exhaust snout clear can be tricky (be on the starboard side when you hug it), but definitely doable. I'm not a big guy, I'm pretty sure the complete powerhead outweighs me. Putting it back on, well that's going to require some help.

 

[MostlyHrmlss]

Re: Up in smoke...

Oh, and the shift rod comes up through a separate part of the midleg from the exhaust, so in order to get leakage there, it's probably coming from between the midleg and the match plate. The factory put a good ring of black RTV around the exhaust section, I don't know if it would be advisable to just RTV all the mating surfaces or not.

 

[shaun77]

Re: Up in smoke...

Well I've troubleshot all I can with this exhaust issue gonna take it to a shop and get an estimate. Anybody have an exhaust seal replaced lately? If so, what's a reasonable rate? On the other hand is an' 89 125 force with roughly 120-130 on all cylinders, new starter, head gasket, and impellar. Also 2006 trim pump and I just swapped transom brackets, midsection, mounts and kingpin. When to say when?