Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

[dogsdad]

1990 Mercury 135-HP V-6, 2.0 Liter, s/n 0D007523, model no. 1135412LD<br /><br />Sometime back I posted the long sad tale about my 135-horse Mercury overheating. Here's the link to that thread which I cannot bear to look at: <br /><br /> http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=29;t=008684 <br /><br />Anyway, I got around to replacing the impeller and that job was no big deal...getting started was the challenge. So we take the boat out and launch it, thinking everything's hunky-dory, but when we finally get out of the no-wake zone, we find that we have almost NO power! I coulda anchored it with six-pound test fishing line.<br /><br />A compression check reveals three cylinders having NO compression whatsoever---all three on the same bank, oddly enough. The other bank had compression ranging from 40 pounds to about 115.<br /><br />Am I jumping to conclusions when I say that I think I at least need new rings? And, can you get away with just installing new rings, or is that begging for trouble?<br /><br />The cheapest (and ONLY, for that matter) overhaul kit I have found is $1150. OUCH! Who has the best deals on such parts?<br /><br />Thanks in advance for your responses. You all have been very helpful already, and I do appreciate it!<br /><br />-dd-

 

[snapperbait]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

If your absolutely sure about your compression test readings, and you performed the test with the throttles wide open, go ahead and remove the cylinder heads to inspect the damage.. <br /><br /> If the clyinder walls are scored and/or the pistons damaged, a re-ring job would be worthless...

 

[The Marine Doctor]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Yep..sounds like it was overheated too many times.<br /><br />It would be super if you took the heads off and had blown headgasket everywhere <br /><br />But not likely <br /><br />TMD

 

[dogsdad]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Okay...I'll take these answers to mean that it's possible that rings only will be sufficient, but I know better than to hold my breath on this one. But I still haven't removed the heads (I have a job interview this week for which I need to concentrate on preparations and I don't want my feeble mind preoccupied with other stuff). So, who's got the best deals on kits? And, would anyone care to forewarn me of certain pitfalls before I start the process?

 

[y2j]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Look mate don't do a bodgy job<br /><br />Its gonna cost ya $500 or so US but do yourself a favour and bore out the cylinders equally and put new pistons/rings<br /><br />Rebuild the carbys/fuel pumps<br />Clean out the cooling manifolds<br /><br />And re gasket the whole motor<br /><br />And you will have a brand new motor and the motor will outlive you <br /><br />I did everything to my motor except boring it out because they were fine and found out i had 1mm square of area left in the manifold of the water passages for the water to get out the peehole. If i had left it further corrosion woulda blocked it and i would be asking for trouble<br /><br />I thought you'd be fine but it looks like you cooked your motor which means scoring Bad luck mate but think of it as a expensive lesson.

 

[dogsdad]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Today I pulled the head off the motor on the side that showed NO compression when I tested it the other day. The cylinder walls were smooth and nice looking, and the pistons looked fine. When I rotated the engine it sounded as though the rings were sealing, and that got me thinking about the "0" lbs. of compression I had seen. So, I put the head back on and just stuck my finger in the plug holes and turned the engine over by hand, and it seemed like the compression should have read way more than zero. So then I went and bought my own compression tester---lo and behold, every cylinder shows 105-107 pounds of compression! This is one time I am glad I screwed up. I dunno what I did wrong, but that doesn't matter now.<br /><br />So, I put everything back together and cranked up the motor. I am proud of myself because I remembered to use the muffs this time. : ) I have an inductive timing light which I used to see if all six cylinders were getting spark. Another revelation---one bank is entirely dead. That would explain the lack of power, I think! My manual suggests that either a stator or switchbox is bad. Does it not make sense that a switchbox would be subject to heat damage, moreso than the stator?<br /><br />Is there a good easy way to determine which part it would be?<br /><br />Again, thanks in advance!<br /><br />-dd-

 

[y2j]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

looks like you werre lucky as me and didn't need honing of the cylinders awesome<br /><br />You probably blew the gaskets

 

[Trent]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Since that engine has two switchboxes...I think your on the right track.<br /><br /> web page <br /><br /> web page

 

[CU2NITE]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

You can check the stator and trigger with a meter to rule them out, I would also rule out that coil on that cylinder(swap the coils around and see if the problem follows that coil) If all checks out good change the switchboxs(there is no way of checking them) I had the same problem with my 150 and it turned out to be the switchbox. They say to replace both not just one. They're not cheap, but much cheaper than a motor overhaul! Good luck<br />CU<br /><br />-------------------<br />RUNNING THE MOTOR WHILE LISTENING TO THE HORN WILL MAKE YOU MORN!!

 

[kingsbiship]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

The switch boxes must have good grounds or the'll burn out !

 

[dogsdad]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

I'll keep the grounding in mind...<br /><br />Today I swapped switchboxes, and as soon as I started the motor up a bad switchbox was confirmed---I got the oil warning horn. The part I like the most is that the bad switchbox is now the OUTER one. So, I'll see about replacing it tomorrow.<br /><br />I can't help but be skeptical about having to replace both switchboxes---is there any particular reason WHY?<br /><br />Thanks again to all who have been helping!<br /><br />-dd-

 

[Trent]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Always check the bias circuit: Disconnect the jumper between the packs on the white/black posts. Check the resistance from the white/black posts on each pack to engine ground. Standard packs will read from 13-15,000 ohms. Racing boxes will read approximately 9,600 ohms. MAKE SURE THAT THE BIAS READING IS THE SAME ON BOTH PACKS!!! If the bias is out of specification on one pack you must replace both packs to prevent future damage. This circuit effects ignition timing and could cause a powerhead failure.

 

[dogsdad]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Thanks Trent. I went out and checked the good one and the bad one. They both read exactly the same with my DMM. I came up with 14.18 k-ohms on each. I will also check the new one when it arrives.<br /><br />I'm getting close to putting "Blue" back in the water. I've rebuilt the water pump, replaced the head gaskets, replaced a busted thermal switch (does something to air pressure inside the float bowls---if anyone cares to enlighten me on this, I'm all ears!), and now I'm waiting on my switchbox and a pair of thermostats. I think I'll be good to go!<br /><br />My theory on the thermal switch is that it allows or inhibits (which is it??) atmospheric pressure into the float chambers depending on head temperature. Is this a way of keeping the mixture richened up until the motor warms up?

 

[dogsdad]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!

Today, I have success! <br /><br />I received my new switchbox, and the first thing I did was check that resistance which Trent pointed out. The new box reads 14.16 K-Ohms, so it is within 20 Ohms of the other one. So, I installed it and buttoned everything up, then I PUT THE WATERMUFFS ON and cranked the motor, and it sounded very healthy. So the wife and I took ol' Blue out to the lake and tossed him in the water. And today, when we got to the edge of the no-wake zone, we got good, smooth acceleration just like we got in the old days. Top end performance was identical to the way it was before we broke it. <br /><br />We are happy.<br /><br />Thanks to each and everyone of you who helped me out with this. This is a great forum!

 

[Trent]

Re: Thought I Was Hosed, but It's Not THAT Bad---RESOLVED!!!