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Lately I am seeing a lot of late 90's and early 2000's 4 cylinder four stroke motors for sale at fair prices. I have learned a bit in the last couple of weeks. First these motors have a lot of parts in them. Second the parts are not cheap. Third avoid the parts or blown up motors. Their too costly to rebuild. Fourth you cannot make one good one out of two. They seem to blow up the same way.
Questions:
How many hours do these power heads normally last?
Can you renew these as good as new with a proper rebuild like you can a car motor?
Do they have good resale once refreshed?
Lastly, when you rebuild one can you make it more powerful and more durable than it was originally with better parts, machine work and programming?

Hi Don,
I think you could rebuild a 4 stroke and get better power by cutting the heads, then re flashing the ECU with greater fuel delivery, and modified advance curve. However the gains would be marginal at best. Somewhat improved acceleration with minimal top end gains.

To do a real noticeable improvement would require the above, along with flow work on heads, with larger intake and exhaust valves and more agressive cam timing. Unfortunately, the valves and cams are not available. That creates a big negative, unless the stock cam can be welded and reground to a more agressive profile. Similar problem with obtaining larger intake and exhaust valves, nothing available. Also a larger throttle body on the fuel injaction would be required. As of yet, I don't think anyone is making hi perf. parts for 4 stroke outboards. That wouldn't be a bad idea for a new business?

They can be rebuilt with great success...cranks can be reground like an automotive crank. We've done a few bigger 4cyl and ran them for years. Most get sunk or hydraulic locked...those you can deal with. The valve drops are usually catastrophic....It's not as cheap as a 2-stroke but you can get parts.

You're going to struggle getting power out of the little motors because there is zero support for such an endeavour...like Todd said there's no one making hot rod parts AND the small stuff is pretty light duty to keep weight down.

Since there is no support from OEM or aftermarket a better idea would be to look at the motorcycle industry and motors in the 500 to 1000 cc range. You then focus on adapting the motor to the mid section. The internal motor stuff Is already there. You may luck out and be able to modify a 40 or 50 hp 4 stroke 15 inch mid to work or build your own mid.

They are always thinking ahead of us over there. They don't seem to worry about the cost. Here people want to see return on their investment and there is not enough demand for the product to make it profitable.

The cool thing with a bike/Sled/PWC HP 4-stroke is they have an external oil tank which gives you more options rather than having to deal with the sump in the mid. I've been saying this for years...if Yamaha or Honda ever got it in their head to make an HP 4-stroke the outboard industry would be turned on it's head. Yamaha's new 3 cylinder 998cc sled motor pushes 204hp....glue 2 of those bastards together...deadly.

They make their own islands over there....they carry this kinda R&D money around in their wallets

The sled guys do spend some serious $ on some of those drag sleds thou

We would have to start doing dock starts so I could use the 2-step....nothing like setting the boat next to you on fire getting the boost up