Frequently Asked Powerhead Questions
A few common questions about maintaining, troubleshooting, and rebuilding outboard powerheads. I'll continue to update the FAQ section as often as possible. Feel free to suggest a question that you feel should be covered here.
How do I break-in a new/rebuilt powerhead?
Is rebuilding a powerhead much different than a car engine?
Do I have to bore all cylinders, or just the ones that need it?
Can I have an automotive machine shop bore my block?
Do I really need to use a special grease on needle bearings?
Uh-oh, I stripped the spark plug threads. Do I need a new head?
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How do I break-in a new/rebuilt powerhead?
It varies--check your manual for model-specific details. It usually breaks down to varying RPM's and running
double-oil for the first tank or two of gas. In most cases, this means run 25:1 in pre-mix applications and 50:1
in oil-injected models, which works out to be 25:1. Avoid sustained full-throttle and heavy loads for a while,
too.
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Is rebuilding a powerhead much different than a car engine?
Yes. For one, a two-stroke powerhead is much more sensitive to mistakes. A clean working environment is critical.
One of the first things you should notice, if you're only familiar with 4-stokes, is the difference in bearings.
The soft, flat metal bearings in automotive engines have a surface that often allows dirt particles to embed, without
harm. Roller and needle bearings on the other hand, can be destroyed by one piece of debris--including a piece
of hair, falling from your head. A needle bearing only has to slide instead of roll, for one crank
revolution, to cause trouble.
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Do I have to bore all cylinders, or just the ones that need it?
It's fine to only bore the cylinders that require it. Try that with your car engine and you'll definitely run
into problems. A two-stroke's cylinders are sealed off from each other, and have equal crank case pressure on the
other side of the piston. Since a four-stroke doesn't have crankcase pressure, you would end up with one high-compression
cylinder fighting the others.
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Can I have an automotive machine shop bore my block?
Sure, if they're equipped and qualified to do the job. Some of them might not be equipped to do outboard V-blocks,
though. Inlines shouldn't be a problem for most of them, unless there's a clearance problem with their tool at
the bottom of the cylinder.
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Do I really need to use a special grease on needle bearings?
Yes. It's a special grease that pretty much dissolves as soon as gasoline hits it. That's very important because
it's what keeps the needles from sliding instead of rolling. As far as required lubrication goes,
you could just use two-stroke oil, but the grease holds the needles in place, making the job a lot easier. I believe
Mercury simply calls theirs needle bearing grease and OMC calls theirs Sealube.
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Uh-oh, I stripped the spark plug threads. Do I need a new head?
Nope, the threads can easily be repaired. Just go to your local auto-parts store and pick up a spark plug thread
repair kit. There are a few different ones available, but I prefer the one that reams and re-taps the hole with
the same tool. It comes with everything you need to do the job. The inserts are stainless steel and if the job
is properly done, the repair is actually an improvement. The kit should probably cost somewhere in the $15-20 range.
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Disclaimer: Use this information at your own risk. Seiler Marine is not responsible for
the mechanical ability of others. Never attempt a repair without the proper tools and service manual.
When it doubt... take it to a shop.
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