Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

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SeaRayder4

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Sorry about the long post, but it's winter here in Ohio - what else is there to do....(boating wise...)

I'm in the middle of a rebuild project of a 90hp Mercury Sportjet (3 cylinder) Powerhead.

The motor was purchased on Ebay (rebuilt by a Merc certified tech) and I only got 8 hours out of it after a proper breakin. Needless to say, I've got way to much money in this engine, but I'm trying to save it and make it a reliable engine for fishing and some tubing with the kids.

The machine shop bored my block 0.030 over top and bottom cylinders and the middle at 0.020 over. Several folks have said that it's OK today (maybe not not 20 years ago) to have different sized holes in a 2 stroke. I'm far from the expert and the machine shop didn't want to take off good metal that might be needed for future rebuilds. I can still do all 0.030 over as the final bore hasn't been done yet, I still have to match pistons. Thoughts anyone on the best approach for cylinder size (all the same or odd hole OK)?? Which brings me to my question about type of piston.

I'm debating about Wiseco pistons (forged from what I understand) and a hyper-eutectic cast piston (Vertex) or others from what I understand.

My cost to replace the pistons with Wiseco and the gaskets I need is around $350. The freshly rebuilt engine had a whine sound to it immediately upon starting it - (but it wasn't too bad and I've never broken in a new engine) so I thought all was OK . Upon disassembly, my bottom piston was melted and rings were crushed. Fortunately, I could save the block and the carbs will be totally rebuilt as well since I've heard this is most like a lean fuel condition that lead to this problem.

Because of the whine, I concerned there may be other parts that should be replaced (maybe all the crank bearings). I want this engine to BE RELIABLE, not for racing, just back and forth to the fishing hole and occasional tubing with the kids.

A company on Ebay Tri-State Marine makes a TOTAL REBUILD KIT (minus carb kits which I will do also) for $750.00. Here's the link, if it doesn't work search Ebay for item 380027276464.

http://cgi.ebay.com/ebaymotors/ws/eB...K:MEWAX:IT

I wrestling with how to get the best benefit for the time and money since I was so dissappointed in the last rebuild done by someone who should know what's up. For $400 more, it seems like I'm getting alot of valuable new parts that should lead to reliability??

I asked Tri-State Marine (Ebay seller) some honest questions about their kit (they have 1200+ positive feedbacks ) to compare it to factory parts and Wiseco or Vertex. Here's what they said:

In our opinion Wiseco, being a forged piston is more suited for race applications. A forged piston has a greater expansion rate than a hyper-eutectic cast piston. This expansion rate is so much more that if not fitted properly it can lead to seizure. therefore you should fit the piston with more clearance than the factory outlines in the service manual. In some cases the piston must be 'looser' in the bore than even Wiseco recommends. The added clearance can promote greater cylinder, piston and bearing wear not to mention piston noise. The Vertex piston is a good choice as this is a hyper-eutectic cast alloy, although we are not a fan of the piston ring manufacture Vertex chose as a vendor. Our pistons are hyper-eutectic cast alloy and our piston ring vendor is RIK, a Japanese manufacture who supplies Yamaha. This is the best ring made hands down. The piston is manufactured in Italy to our specifications.

We are in agreement with your machine shops good advice and (1) odd-sized 0.020 piston is OK with (2) 0.030 pistons.

Lastly, most engine failures are related to cooling or fuel supply. Be sure to rebuild the fuel system and pay very close attention to jetting for restrictions and double check float levels. Check for intake leaks as well as good constant fuel supply to the engine. Lean air to fuel ratio will cause high combustion temperatures which will cause failure. Be sure to set carb linkage and adjust the ignition timing as outline in the FACTORY service manual. Renew the water pump complete and not just the impeller. Thermostats should also be replaced. Please keep in mind most outboards when run at 3/4 throttle or around 4000 RPM is actually peak load for the motor. These motors are made to run at full throttle as there is less load on the engine. There are a lot of Marine Technicians out there that do not address the cause of failure when making the repair. If you do address the cause the repair should give you years of service.

Can anyone share some thoughts or opinions about the best approach for me?

Again, I'm not racing, just wanting reliability from this engine.

Thanks in advance for everyone's 0.02.

George
 

Jeff Walkowiak

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

different size holes are just fine,, been doing that for many years with no issues,, be sure the bottom crank seal is good those can cause the engine to run lean and hatch the lower piston especially since it was the bottom piston,that failed on you, that one usually runs the coolest,, also check the reed valves ,, forged pistons are heavy and idle smoother,, but as they said expansion from heat can get a bit dangerous,, you will do better with cast pistons. also forged pistons must be measured and each hole has to be cut for the exact piston and the piston marked so you put it in the hole that was cut for it because none are the exact same size.
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Jeff,

Thanks so much for the quick reply. My machine shop wants to wait to do the final bore until I have the pistons. Then he says he will do the final shave to make sure it's the perfect fit. He's a Wiseco dealer, but says I don't have to buy them from him.

From your advice it sounds like the cast pistons are the way to go. Ever see these kits on Ebay I mentioned? They seem like a good deal but I don't want this story to have another unhappy ending.

A company on Ebay Tri-State Marine makes a TOTAL REBUILD KIT (minus carb kits which I will do also) for $750.00. Here's the link, if it doesn't work search Ebay for item 380027276464.

http://cgi.ebay.com/ebaymotors/ws/eB...K:MEWAX:IT


You mentioned crank seals could be the problem? It was interesting (I'm new to this) but when I disassembled the block and was about to remove the crank - I noticed the open part of the ring seal (metal ring) was facing up (I thought they were broken). The service manual says to rotate them 180 degrees after you install them and the crank is seated...aaahhh - could be the smoking gun so to speak here??:eek:

Just want to get a few good seasons out of this engine. That would take me to a happy place for sure.:D

Thanks again. If anyone else wants to chime in thoughts that would be great.

George
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Jeff is right as usual , Forged pistons can be very pickey , I used them for years building race engines for stock cars , I used to buy 3 sets the same size just so I had 8 that would have identical specs in the motor . My short track late model motors turned about 8500 to 8700 rpm . Your SJ 90 like mine should only turn 5500 max , rev limiter is set at 5800 if i remember correctly . Cast Hyper pistons are fine and getting the complete kit is the way to go .. You are into it this far do it right . I could not pull up the e-bay page but if you post who the seller is I will search and find it and let you know . But looking at what they sent you I believe everything they have said in their response. I just want to see what is in the kit before I would recommend it with a clear mind .

By the way the few "street sport " short track motors I did build I used cast Hyper pistons as these motors rarely turned over 7300 rpm and I NEVER had a piston failure .
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

OK tooooooo much beer , I just noticed your ebay info in red , Looked at the Kit and found some specs on it ... GET IT ... When I go through my motor in feburary I will get the same kit if they are still available !!
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Thanks so much. A couple more questions if you don't mind. I'm getting ready to order the complete rebuild kit and I'll post all my progress on here to help everyone. I still have some warranty questions for Tri-State I'm waiting to hear back on. I also have a second powerhead (exact same one) that I want to rebuild also - so I have a spare on the shelf (if this one turns out OK):eek:.

My 2 questions for now are regarding special tools:

1) Mercury says to use a special "pillow block" and pin tool to drive out the piston pins without damaging anything. It's ~$125.00. I'll spend the money if necessary, but I was wondering if something like would work?

http://cgi.ebay.com/ebaymotors/UNIV...738093QQptZMotorsQ5fATVQ5fPartsQ5fAccessories

If the link doesn't work it's Ebay.com item number 250394738093

2) The complete rebuild kit includes lower (output shaft) and upper (flywheel side) crankshaft bearings that I would like to replace since I have them and am looking for reliability. The lower slides off (wow...it really did), BUT the upper must be pulled off with a speciality tool (again $100+). Should this be a machine shop job or would a tool like this work?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=8832

There is no play in the upper bearing and it doesn't rock at all so I'm guessing I probably don't need to replace it....just asking for thoughts.

Again, thanks so much everyone. :cool:

BTW - kend301, what boat do you have with a SportJet 90 - and has your engine been good to you?
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Had a chance to look at the tools as well as take a look in my shop manual .

First of all I have to let you know that I have never done the crank assy rebuild in a boat , So all I can tell you is from what I can read , see from parts diagrams and my experience with engines .
The tools look like they should work but I am kinda suspect of the bearing puller . It may not have enough "claw" on it to properly remove the bearing. Also the installation looks like it requires a "HOT" installation , The bearing must be heated to get it in place , If you miss the first time you could ruin the bearing trying to get it off.
As far as the piston pin tool goes , I am weary about the fact you have a roller bearing to press through in the rod , Bend or score one roller and the bearing is done .
Based on what I see it would be well worth the money to let a machine shop perform these tasks , Most shops would charge about $ 10.00 per piston and $15.00 for the press operation to change the bearing . So for 50 bucks you will have no worries , Worth every penny in my book .
This is my OPINION , As I said I am not speaking from experience here .. Great time for Jeff W to chime in and give some guidance based on experience !!

PS ... I have a 1994 Bayliner Reflexx , It was swamped and I bought it for a project , I have replaced the entire eletrical system to be safe , Went throught the carbs and fuel system and it runs everytime I fire it up . Even today when it was 31 deg outside .
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Thanks for the reply and thoughts. I'm getting closer to ordering the kit, but it seems like the only question they won't answer is what the warranty means. :confused: Still waiting on that one.

I'll ask the machine shop about that stuff...just trying to think that if I'm rebuilding 2 engines...somehow the special tools would be worth the money...but maybe not.

Wow a 1994 Bayliner Reflexx. I sure know that boat well as someone on JetBoat14 (now shut down) expertly installed a SportJet 175 in it. It worked great, but there was more involved in it then he thought. It would run about 50 mph though and got there fast.

My boat is a SeaRayder 14 converted to a bassboat. Works great for fishing when the engine is running properly. (rare lately).

You say you are probably rebuilding your engine in February? Why?
 

Jeff Walkowiak

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

I made my own wrist pin tool it is pretty simple to do,,
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Thanks Jeff - can you elaborate or would this Ebay tool be a good start (in your opinion)?

My machine shop said they can do it for $18 per piston, but I love to learn...

http://cgi.ebay.com/ebaymotors/UNIVE...Q5fAccessories

If the link doesn't work it's Ebay.com item number 250394738093
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Wow a 1994 Bayliner Reflexx. I sure know that boat well as someone on JetBoat14 (now shut down) expertly installed a SportJet 175 in it. It worked great, but there was more involved in it then he thought. It would run about 50 mph though and got there fast.

WOW you just made me ... well lets not go there , That is what I want for my boat but given that I am in the automotive industry my income sucks right now , It will be some time before I can do it but it will happen . I am going to go through my motor for the hell of it , I know the boat spent at least 2 hrs swamped at a ramp in about 2-3 feet of water , I almost swamped it again the first time out .. see my post in " Stupid Human Boating Tricks " under "did you forget the plug" .
My motor runs great but I am a speed demon ( raced for 14 years ) and need something faster then 37 mph .. But I am restricted to how big a boat can be as I live on a canal that has an entrance under the bridge that can be as low as 36 inches at high tide .. I have already broken a windshield going through it .
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Yep - I'm restricted by income and like the fact that the SeaRayder will fit easily in the garage and not be a pain to tow somewhere. And it really is a great fishing boat for 2 people.

I have the compete PDF of the 90 to 175 Reflexx conversion just to put in your dream file if you'd like. It was copied just before the site shut down. I would need an email address to send it to (just checked - it is 11 files each about 500K in size)
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

See your PM for my e mail address .. and THANK YOU !!!
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Sent the files. Happy reading.
 

kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Got it ... Thanks , I can't believe he got less than 5k for that boat .. Kinda scares me about the conversion . But if I do it I will buy a 175 jet boat that has an open front and swap both engines and resell the one I bought with my 90 in it as a fishing boat to try to keep actual cost down to mostly my labor .
 

SeaRayder4

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

Bill is a very meticulous boat owner and the buyer got a great deal for sure. If you love the Reflexx hull - it would be a fun project - but I don't think a boat that had a 175 in it would get much in selling price (unless the purchaser was somewhat ignorant - like I was of the reliability of the 90hp design).

I love my hull, as long as there are no problems, I plan on converting it to a 60-90 outboard. I've seen it done and a fellow did it to a 90hp Sportjet Boston Whaler and it performs great. He too documented the who thing and it can be viewed at.

http://smg.photobucket.com/albums/v472/sraab928/Rage Conversion/

The guy who did it is a iboats member sraab928 and details are on this thread.

http://www.boatdesign.net/forums/bo...-jetboat-into-outboard-engine-boat-15567.html

My SeaRayer is a fishing machine. I know that look is not for everyone, but it works well here in Ohio. It even has a microwave - great for the spring and fall fishing trips.
 

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kend301

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Re: Sportjet 90 Powerhead Rebuild questions - Piston Type Choice

George ,
Awesome conversion to a fishing boat !!! The 90 is very dependable if everything is right and the engine / carbs have a proper tune , Should be all you need as long as you are OK with the performance .
 
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