Can a rookie do a rebuild on a powerhead?

[powrguy]

I'm thinking of picking up a project Merc 150HP, with one blown piston and scored cylinder. Everything else looks good, but am wondering if a "rookie" (never rebuilt an outboard before, but have done mota's on dirtbike 2-strokes, small block Chevy's, etc.), and if it's over my head to do one, or need special tools.

I know that a rebuild gasket set is about $150 or so, and there's the cost of a re-sleeve, for sure, plus the bad piston/rings/etc. Is it worth it to do ALL the cylinders (slightly over-bore) and then have to get all over-size pistons/rings, etc.?

With only one piston replaced, how does that affect balance and longevity?

Inquiring minds want to know.....



thanks

 

[monk-monk]

Re: Can a rookie do a rebuild on a powerhead?

powrguy...yes, a rookie can tackle a rebuild on one of these motors. Im rebuilding my first powerhead right now, and like you, i've worked on and rebuilt almost every type of motor except for one of these, until now! The best thing you can do is buy a Factory Mercury manual and READ it, and READ...you can just bore one cylinder and replace one piston as even the over-sized pistons still weigh the same as a stock piston. Plus, if you will go to one of the websites that supply merc stuff...(crowelymarine.com)...use your engine serial number and you can view all the parts break downs...you don't need a whole master gasket set as you will end up with a lot of gaskets you won't use and its cheaper if you will just buy the gaskets and o-rings that are required for your motor. The exhaust and transfer port cover bolts take a lot of patience to remove and often end up breaking...if you do remove these covers DO NOT attempt to remove the inner exhaust baffle...ALL those bolts will break! It might seem scarey at first, but if you get one open, see what makes it tick, then read, read, read and learn...

 

[saumon]

Re: Can a rookie do a rebuild on a powerhead?

Yes, it can be done with common tools AND an OEM Service Manual. As for the specials tools, the only one that comes to mind is a flywheel puller like this one http://cgi.ebay.ca/Mercury-Mariner-...at_Parts_Accessories_Gear&hash=item483e8c6dc0

Unless it's very badly scored, you usually don't need to resleeve, you only rebore the scored one. IF the others holes are within specs (you'll need to measure them), they can be honed with new rings. But, don't order anything until you've open it. You may also need, for example, new crankshaft bearings and seals.

While there, with any engine of unknown history, it's standard practice to also service at least the fuel pump, the carbs, and the water pump impeller.

 

[powrguy]

Re: Can a rookie do a rebuild on a powerhead?

powrguy...yes, a rookie can tackle a rebuild on one of these motors. Im rebuilding my first powerhead right now, and like you, i've worked on and rebuilt almost every type of motor except for one of these, until now! The best thing you can do is buy a Factory Mercury manual and READ it, and READ...you can just bore one cylinder and replace one piston as even the over-sized pistons still weigh the same as a stock piston. Plus, if you will go to one of the websites that supply merc stuff...(crowelymarine.com)...use your engine serial number and you can view all the parts break downs...you don't need a whole master gasket set as you will end up with a lot of gaskets you won't use and its cheaper if you will just buy the gaskets and o-rings that are required for your motor. The exhaust and transfer port cover bolts take a lot of patience to remove and often end up breaking...if you do remove these covers DO NOT attempt to remove the inner exhaust baffle...ALL those bolts will break! It might seem scarey at first, but if you get one open, see what makes it tick, then read, read, read and learn...

Yeah; I use the Crowley Marine parts displays all the time when I need parts for my current motor, or see what parts for different motors are interchangeable.

I also have learned (from my limited experience with used parts) that a freshwater motor seems to be WAY easier to do disassembly on than a saltwater motor. I kinda stay away from saltwater motors if I can, as the corrosion tends to be a nightmare on bolt removals. The other part of a rebuild that's a bit spooky for me is to do the carbs (rebuild). I have done cleanup and re-gasketing, but never a full-blown carb "rebuilding".

I have the lift ring/flywheel removal gadget already, as when I remove the motor from my boat, I needed the lift ring anyway.

Thanks for the input (from you and monk monk), and I think I just may jump into a rebuild and see what happens.

 

[skeeter16]

Re: Can a rookie do a rebuild on a powerhead?

Get a manual. Carbs are easy and very simple. The rebuild may require mercury ring compressors.

 

[powrguy]

Re: Can a rookie do a rebuild on a powerhead?

I have the factory manual for the motor. I think I have a ring compressor from the old small block Chevy days, too. I just didn't know if I needed any special tools, other than the screwdriver with a ground down tip I made to remove the retaining cap screws in the carb. The one tool I probably will get is a micrometer set (inside/outside) for the pistons and bores, I guess.

thanks

 

[monk-monk]

Re: Can a rookie do a rebuild on a powerhead?

Im not sure you want to use the ring compressor that you would use on a small block chevy...if you will notice the pistons on these merc motors have a pin in the ring landing...when you squeeze these rings down, you need to be able to see the ring end gap and make sure it centers over that pin...if you attempt to compress the rings with a "full circular" compressor, you will not be able to verify the ring is centered over the pin, plus it can break the tip of the ring if it is compressed into that pin...

 

[powrguy]

Re: Can a rookie do a rebuild on a powerhead?

Im not sure you want to use the ring compressor that you would use on a small block chevy...if you will notice the pistons on these merc motors have a pin in the ring landing...when you squeeze these rings down, you need to be able to see the ring end gap and make sure it centers over that pin...if you attempt to compress the rings with a "full circular" compressor, you will not be able to verify the ring is centered over the pin, plus it can break the tip of the ring if it is compressed into that pin...

That's a good point. A standard wrap-type ring compressor would not be real easy to use, then, to see the alignments of the rings/pins. Might have to get a compressor that allows for the locating pins in the assembly process.


thanks

 

[monk-monk]

Re: Can a rookie do a rebuild on a powerhead?

Are you familiar with what the Factory ring compressors look like? The reason i ask is because when the Factory compressors are installed they squeeze the rings at a point 90 degrees from the ring end gap...two reasons for this, #1 you can see how the rings are being compressed in relation to that locating pin...#2 if you look down in the block at the bottom of the cylinders you will see two relief cuts, one on each side of the cylinder,...this is the guide slots for the ring compressors...this enables the compressors to "lead" the rings into place...The pros actually load the pistons in the block, position the crank just above the rods and lift or lower the crank to the rods and then torque...im not sure how im going to approach mine...i have the compressors, but still not sure about loading the whole assembly at one time...LOL..!!

 

[powrguy]

Re: Can a rookie do a rebuild on a powerhead?

I have no idea what they look like, or how that technique you're talking about is done. I am, of course, going to go through the process in the manual a few times to get an idea what to do, and will try to get the correct tools that I'll need when the time comes.

I don't think the rebulding is going to require a surgeon's skill, but I do want to have an idea what I'm doing before I start.

 

[jheron]

Re: Can a rookie do a rebuild on a powerhead?

Set the pistons one at a time and use a beer can, a tyrap and lots of 2-stroke oil for lube, as your ring compressor, works very slick. I described my process in this old thread HERE post #35, I used this method a few times now and it works great.
To get your jugs bored you will need a machine shop that can do blind holes, make sure you mention that when you call around as they need a special boring bar to do it.
Good luck!
Cheers,
Jon

 

[powrguy]

Re: Can a rookie do a rebuild on a powerhead?

Set the pistons one at a time and use a beer can, a tyrap and lots of 2-stroke oil for lube, as your ring compressor, works very slick. I described my process in this old thread HERE post #35, I used this method a few times now and it works great.
To get your jugs bored you will need a machine shop that can do blind holes, make sure you mention that when you call around as they need a special boring bar to do it.
Good luck!
Cheers,
Jon

LOL

I love it; I can drink the beer and proceed to use the empties for "ring compressors". Works for me !