Is my WOT RPM resonable given the boat, prop and HP?

[deerhuntre]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Some questions:

If I have to replace a piston, wouldn't I want to rebore and replace the other pistons and maybe bearings if I've already gone through the effort to disassemble and later reassemble the powerhead? What parts are best reused if they are ok? Or are certain things generally replaced during a teardown regardless?

And when I look inside, if there is minimal damage, would I be able to use the engine if I don't push the RPM's so I can put off the rebuild until winter? Or is this going to be a hazardous situation to run the motor?

Also, do you guys do your own tear-downs or are you guys generally having the work done at places? I've never done a teardown of an engine, but I've done lots of other work and feel comfortable attempting this work. I'm sure I'll have questions. And I really will have to clean out and organize my work bench and tool boxes before I begin!!

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well with an outboard, it is possible to get away with just replacing the bad pistons and reusing the good ones. Even if you have to rebore a bad hole and go oversize, it is possible because oversize pistons weigh just as much as stock and will keep the engine balanced.
New rings all around is a good idea. Bearing and reeds can usually be reused but should be checked out according to the shop manual.
All cylinders should be deglazed so the new rings can seat in.

If you have damage to a piston crown, the cylinder may still be good, but running the motor will cause that piston to eventually give up the ghost and take the cylinder with it. So you've gone from a cheap fix to a much more expensive project because now you need to completely tear the motor down and send it off to a shop to get rebored.
You should be able to replace a piston without having to do a complete teardown on most models.
It is not the hardest job if you have the right tools and a good manual.

 

[deerhuntre]

Re: Is my WOT RPM resonable given the boat, prop and HP?

OK, but even without a complete teardown, am I still taking out the entire crankshaft and all the pistons? My model is the Mercury 1986 inline 6 115, so could you please describe what I would be doing and which part of the teardown process I could avoid if I just want to replace the piston? When I get home I'm going to review the manual some more to see if I can follow what you are saying.

I have the Mercury service manual with the hard-to-see black and white photo's and I should have most of the tools already. I ordered the after-market manual they sell at iBoats today so I can have two perspectives.

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Unfortunately, that model has no heads and needs to be completely disassembled in order to replace one piston.
It also needs to go to a specialty 2 stroke machine shop that has a single ended boring tool. Automotive shops don't. Very tricky to reassemble as well. You need to install one piston at a time into block and then install crankshaft. Lots of little needle bearings need to stay put.
I hope this is not your first engine rebuild. If it is make sure your order an extra set of rings in case you break some.....

 

[deerhuntre]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Er, uh, um...it would be my first rebuild. I appreciate the advice about the extra parts.

I've been doing all my own auto repairs for about 12 years, so I'm very comfortable working with this stuff. However, this job certainly will be a big one.

 

[jimmbo]

Re: Is my WOT RPM resonable given the boat, prop and HP?

On these inline sixes, the nuts that tighted the caps on the con rods are located on the rod towards the piston not on the cap. That makes it very hard to to align the cap to the rod and torque properly if you try to install each piston in the block and then try to install the crank. I'm not saying it can't be done this way, but it isn't the best way. Normally the rods and pistons are assembled first, then using special ring compressors which will line up the pistons in a single file the entire assembly is lowered into the block.

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

On these inline sixes, the nuts that tighted the caps on the con rods are located on the rod towards the piston not on the cap.

No they are not. There are no nuts at all just bolts that take a 12 point 1/4" wrench. And they do not face the piston.

It is almost impossible to find the 6 specialized valve spring compressors required to do the whole assembly at once and IMHO a real pain in the *****.
Not to mention that they co$t$$$. For a one off it would be way cheaper to take it to a shop and have them do it rather than spend the money on these stupid expensive ring compressors.
I know merc says to do it this way but there is no good reason for doing so.
They F'd up on that. Have you ever tried to put 6 pistons in all at once?
It is a joke. I don't know what they were thinking. The crank weighs enough on its own, never mind the added weight of the con rods, bearings, pistons and rings. Its tough not to break rings that way.
Trust me, 1 at a time with a conventional ring compressor is the easiest way.
I just did my '86 115 last month and it was no sweat. 1 piston at a time, some grease to keep the needles in place. Make sure the rings are properly located in relation to the small pins in the piston grooves. Especially when compressing the rings as they tend to move around a bit.
The hardest thing was trying to find a 12 point 1/4" socket that would clear the bearing cap recesses.

 

[jimmbo]

Re: Is my WOT RPM resonable given the boat, prop and HP?

here are a few shot from the merc service manual. look like 6 point hex nuts towards the pistons

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well, I can see that is what the manual you have shows, but that is not what an 1986 115 inline 6 looks like.

 

[jimmbo]

Re: Is my WOT RPM resonable given the boat, prop and HP?

The manual was current for 85 models, it was ordered in 86

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well I hate to break it to you but the manual is wrong! LOL
Wouldn't be the first time mercury has screwed up.
My 86 # OA974926 does not look like that.
If you look up that serial # at mercurypartsexpress, you will find the a bigger version of this diagram.
I also included a few pics of my finished motor.

 

[jimmbo]

Re: Is my WOT RPM resonable given the boat, prop and HP?

nice motor, can't see the crankshaft though. I said my service manual was current for 85 not 86 motors. I'm sure Mercury made changes to some parts over the years in order to cut costs. Below is a cutaway photos of a 1980 115, look at the con rods

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well I guess enough people bitched at them for making such a hard motor to rebuild that they saw the light and changed the design! LOL

 

[jheron]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Have a look here: http://forums.iboats.com/showthread.php?t=129603
To see my trials and tribulations with rebuilding an inline. Don't let these guys scare ya off with regards to setting the pistons and crank, its a piece of cake if you take your time and pay attention
Note what rodbolt says in the above post about doing it all if you want a reliable motor and not just a fixer upper... wise words
I have 145 trouble free hours on her now
Regards Jon

 

[deerhuntre]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Here's my compression numbers:

Top to bottom: 110, 115, 125, 125, 130, 150

Do you guys think I can limp by until winter or should I begin the overhaul process? Any thoughts on the 150 PSI on the bottom cylinder?

Here are two photo's, one is the paint on the cover. This is how the paint was when I got the motor.

http://the_web_guy.home.comcast.net/cover.jpg

And interestingly, several wires and bolts are labeled as if someone took apart the motor and wanted to make sure they got it back together correctly. So, between the paint and the obvious 'notes' for reassembly, I wonder if this motor was already overboard and what I may find when I measure the bores.

http://the_web_guy.home.comcast.net/coils.jpg

 

[RCSConstruction]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well with an outboard, it is possible to get away with just replacing the bad pistons and reusing the good ones. Even if you have to rebore a bad hole and go oversize, it is possible because oversize pistons weigh just as much as stock and will keep the engine balanced.

Is that really true? Given it has more volume?
Wow! learn something new everyday.

 

[jimmbo]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Paint on the water jacket cover doesn't look too good, probabaly overheated. The silicone around the spark plug hole points to a leak there. When these engines get a little too hot, the water cover warps a bit and the gasket around the spark plug hole shifts and then water leaks there. After replacing the gasket a couple times on my 115 I replaced the cover. put the gasket in without sealer and it never leaked again in the additional 11 years I owned it.

 

[PilotPat24]

Re: Is my WOT RPM resonable given the boat, prop and HP?

General rule of thumb is that you want to wheel a boat so it runs about 20 RPM's over max RPM. You do this so when you load the boat up it'll be at max or a little under max rpm

 

[deerhuntre]

Re: Is my WOT RPM resonable given the boat, prop and HP?

Well redjmp, I really like what you're telling me about the rods and the bolts and about your recent '86 115 rebuild. My SN is a bit lower than yours, but still the 1986 model. I sure hope I find these bolts on mine and not the ones that have the nuts facing the piston!!

 

[redjmp]

Re: Is my WOT RPM resonable given the boat, prop and HP?

You can find out for sure if you go to mercurypartsexpress.com and enter in your s/n#. That way you can be sure of what you are getting into.
The cheapest place I found to order parts has been boats.net.
I got my gaskets, rings and pistons from them.
It has been stated by gurus (clams) of this site to avoid the forged pistons (wiseco) for this particular motor as the expansion due to heat is not good in this application. Go with the cast pistons 2 or 3 ring.
I also read that those pesky con rod bolts should be replaced and not reused.
Oh well too late on mine ...I reused them... wonder if my motor will blow up now! LOL. I also miked all my needle bearings and they were all in spec so I didn't replace any. They all looked fine.
Being a cheap ***, I also didn't replace any reeds or blocks as they were all fine. Still, I took a long time in retentioning those damn reeds 1 by 1 so they all were .001 away from the block. Now I can get my baby to purr right down to 550 rpm in idle if I want, but set it to 750 in neutral so its about 650 in gear. I know the pros frown on this very much but you can't convince me that even if I have reed failure that it will be a catastrophic event. It just means that then I will have to finally break down and shell out for a new one.
I'm sure that I will move up to a verado or etec long before my I6 gives up the ghost. I keep an extra impellor, coil, spark plugs and switch box on hand and the tools to replace them if the need ever arises for all my outboards and though I have on occaision broken down at sea, I have always been able to fix or nurse my way home. Just in case, I also have a good marine radio and a portable one as well along with an epirb....