just out of curiosity

[gafaling]

I hear them term blown powerhead all the time, what exactly is considered a powerhead? if a 1 out of 4 cylinders has no compression does that mean a complete rebuild is needed or can a new piston and rings be installed if the wall looks good?

[gafaling]

guess I should have asked about sunglasses if I wanted to get any replies, great forum lol..

[Ludicrous]

I hear them term blown powerhead all the time, what exactly is considered a powerhead? if a 1 out of 4 cylinders has no compression does that mean a complete rebuild is needed or can a new piston and rings be installed if the wall looks good?

Powerhead is the power producing part of an outboard engine. Like a small block chevy with the transmission and engine accessories removed.

You can do a 1 cylinder rebuild in some cases. Should you in my opinion? No. All four pistons and rings are not a bank account buster.

Throwing four new pistons in a 2-stroke without determining what caused the problem is foolish. What causes most 2-stroke problems you ask? Lean burn condition. Neglect that fuel system and you'll toast the newly rebuilt powerhead in short order.

Check the oiling system as well...

LOL...Here's a video of a powerhead doing it's stuff (wow...videos, not all boating forums have this nice little feature)

[Ludicrous]

The mechanic in me needs to post this:

Motor (electric):

Engine (combustion):

[emudryj]

And here you can see the power head in action...

http://auto.howstuffworks.com/engine1.htm

[wiley]

guess I should have asked about sunglasses if I wanted to get any replies, great forum lol..

With all due respect you asked the question at 11pm at night. Plus a more descriptive title would have helped.

"Blown Powerhead" as the title would have received quicker replies.

[165Striper]

Disclaimer: I am not even a good shade-tree mechanic..... I can troubleshoot a bit, though.

There are a number of things that can keep you from having compression on one cylinder, including but not limited to:

1) stuck ring(s)

2) heavily scored cylinder wall

3) blown (seriously blown) head gasket

4) hole in side of cylinder

I would think that the second two would be easy enough to determine without tearing much down. The first two may take a look inside the engine with a scope or head removal. I would definitely look at all possibilities and engine history before removing important pieces.

I would would call a hole or mangled large metal pieces a "blown power head". I don't know what a mechanic would consider a blown power head. It is a fairly loose term on the boat forums.

If you have 0psi compression on one cylinder, I would be suspect of other issues (carbs for one). I would find out why there is no compression before deciding on my course of action. If it is a stuck ring, you MAY be able to free them without opening the engine. If you have to take the motor apart, I would go over it with a fine tooth comb and replace anything that I felt could be a weak link. There is no point in tearing a motor down and not replacing a few dollars worth of parts while you have the chance to maybe save some effort later.

Ludicrous:

While any of those motors should work fine in my boat, I think that I NEED that 3.3L!!! I love the sound of a well built motor (before it breaks!)

[Ludicrous]

Can I reuse these???

[epanzella]

The mechanic in me needs to post this:

Motor (electric):

Engine (combustion):

I always wondered why outboards are called motors instead of engines.

[165Striper]

Can I reuse these???

Again, I'm not a mechanic. However, I think with a little emory cloth that piston will be almost like new. I doubt that you were seeing much compression loss before you pulled that one out. It looks like one of those new asymetric multi-hemi pistons that use partial rings to keep the compression from getting too high.

If I'm wrong on that guess, then I am certainly glad that didn't come out of any motor I've ever operated