2001 Merc 90 blown motor

[peter94]

Hello everyone,

I just picked up a 2001 Mercury 90HP to put on my 2000 Tracker Targa.

I bought the motor for $400, with a hole in the piston.

Now, the next question...What did I just get myself into?

I am an ASE certified technician, and going into an engine or transmission is nothing new to me. However I just want to know if there are any do's and don'ts in the marine world that I need to watch out for while rebuilding this thing.

Also I need to figure out what the root cause of the failure was.

Top CYL is completely toasted, middle cylinder is very scored up, and bottom cylinder appears to be OK.

Since the oil tank was still 1/2 full, and the bottom cylinder is ok, can I assume that this was not due to a lack of oil? Possibly a carb problem or cooling problem?

I just dont want to put big $$$ into fixing this thing only to have it burn again.


Other questions...As far as gauges go, are they fairly universal? or do you have to get a mercury only gauge because of the sending units?

Thanks
Peter

 

[kmarine]

Re: 2001 Merc 90 blown motor

These engines are not as complicated as a 4 stroke, however thing like this happen for usially three reasons. The most common is a lean condition in the carb resulting in piston burning and scoring because fuel and oil cool and lubricate the engine. second would be oil pump related. I like to pre mix fuel after engine rebuild and map oil injection system to make sure it is working properly. The other is using the wrong oil make sure it has the proper rating especially with fuel injected engines.

 

[Faztbullet]

Re: 2001 Merc 90 blown motor

Shoulds like a overheat to me. Check block sleeve to make sure they havent shifted and bore all 3 cylinder to oversize,Check bearings for "bluing" and if so discard and install new, Replace upper and lower crankshaft seals,Inspect oil pump gear for warpage,and replace impeller...

 

[Chris1956]

Re: 2001 Merc 90 blown motor

Outboard oil injection systems mix oil in the fuel pump, or in the fuel line to the carbs. There is no way (on a carb motor), that one cylinder would not receive oil with it's gasoline/air mix. If the oil injection failed, all cylinders would be affected.

You need to fix the source of the problem. I would recommend you clean and rebuild all carbs, replace waterpump impeller, test or replace thermostat, and check timing and carb synchronization.

 

[peter94]

Re: 2001 Merc 90 blown motor

Ok, so it sounds like we will rebuild all carbs, replace the impeller and thermostat, check the carb sync and ignition timing. After rebuild run motor with premix AND oil injection to verify oil injection is working.


Chris 1956, I agree with you in that if it was an oil related problem, I would expect to see all cylinders with even wear.

Keep in mind this has not been disassembled yet, just simply looked through the exhaust ports.

Also when I bring the block in to have it machined, Are there certain specs I should follow to make sure I can get a piston for it? I know i've seen .015, .020, and .030 over pistons.

Thanks alot so far everyone!

Also are the factory mercury manuals pretty good? I was thinking about dropping the 85 bucks for one...

 

[Silvertip]

Re: 2001 Merc 90 blown motor

Gauges for two stroke motors are very generic. Voltmeters don't care what engine alternator they monitor. Fuel gauges are boat related, not engine related. Water pressure gauges montitor water pressure and again, don't care what engine they are monitoring. Temperature gauges for outboards typically require a sender with 33-240 ohms resistance. Again, very generic. Tachometers read pulses from the charging system stator and therefore don't care how many cylinders the engine has. Your engine has a 12 pole alternator which generates 6 pulses so the tach gets to 6P.

 

[peter94]

Re: 2001 Merc 90 blown motor

Silvertip,

That info was very helpful! Exactly what I was looking for!

I cant remember exactly what my boat has in it for gauges (Just bought it, and just tarped it up), but I want to make sure I have water pressure, and water temp. I didn't know what the difference was in the sending units.

Also I want the visual alarm kit and everything for it so I dont wind up melting the motor.

 

[Faztbullet]

Re: 2001 Merc 90 blown motor

You can get a .010,.015,.020,.030,.040 for that engine. If you need more info pm me....
(and these are not Wisco pistons)

 

[peter94]

Re: 2001 Merc 90 blown motor

What is the deal with wisco pistons? I thought they were a good brand?

 

[daveswaves]

Re: 2001 Merc 90 blown motor

What is the deal with wisco pistons? I thought they were a good brand?

There is nothing wrong per se with Wiseco, they just tend to expand quicker during the initial warm up than the cyl does, leading to sticking. If you warm up properly there is no issue. The problem is most people don,t warm up, they just go. It is common to bore an extra .001 when using wiseco pistons in an outboard operation. Other opinions may differ. I use persan pistons in my inlines.

 

[Faztbullet]

Re: 2001 Merc 90 blown motor

Wiseco's when new are like "butter" soft and need to go thru several heat cycles to "temper". They need extra clearance as posted but the newer one are a different formula casting which stops this I heard.(I aint using a customers engine as a test bed!!!) You are better using a cast piston as new, I sell several brands of cast pistons including them Argentina pistons as well as Vertex and both are getting harder to get imported. I dont know this as a fact but rumors going around that JE pistons owns or part owns Wiseco that reason of the piston change

 

[daveswaves]

Re: 2001 Merc 90 blown motor

Pappy is correct, Wiseco,s are a forged piston which is ductile when finished. Repeated heat cool cycles temper the piston. The traditional if I can use that term, forged piston has lower silicon content and as such it expands more. The cast pistons have higher silicon content reaching close to saturation percentage (12% give or take). That results in a harder piston out of the box and less expansion. Technology has advanced with work done by BMW, mercedes etc to develop a forged piston that acts like a cast piston by using more silicon. I suspect that the new wisecos use a similar technology.
Just an opinion, no facts to confuse the issue.

 

[peter94]

Re: 2001 Merc 90 blown motor

Alrighty....

Motor is in teardown process.

Impeller is 100% in great shape

Oil injection pump appears to be operating correctly (gears are all intact).

So what gives? I have no idea what killed this thing.... There IS a hole in the top piston. It looks like bad detonation to me. Middle is not so bad, and bottom is ok (still showing signs of damage though).

Any ideas?

 

[CharlieB]

Re: 2001 Merc 90 blown motor

Impellers are cheap enough, don't guess as to servicability of the old one.

Look closely at the stainless parts of the pump, the upper cup and lower plate that mate with the impeller. They are originally flat surfaces against the side of the impeller.

The impeller has a raised 'ring' around the center hole that is the side 'seal'. This seal causes wear on both matching surfaces of the cup and plate causing a groove to appear in the metal. This groove is an indicator of a poor impeller seal to the pump.

Replace the impeller and stainless parts.

The upper plastic housing MUST be flat AND seal with the lower housing or the pump will suck air at speed, as when on 'plane' the gearcase elevation leaves the pump above the waterline.

 

[peter94]

Re: 2001 Merc 90 blown motor

The point of my impeller comment was to point out that it was not the cause of failure. Not to point out I'm too cheap to replace it. Trust me that is one of many components that will be replaced during the rebuild. I'm just trying to figure out the source of the original failure. So far I have come up with nothing. Impeller is in good shape, oil pump works, thermostat opens at about 120-130 degrees F. Maybe it was an isolated incident, like a clogged water intake.

 

[Faztbullet]

Re: 2001 Merc 90 blown motor

Post a picture of the piston. A hole in center of piston is usually preignition due to a ignition problem.

 

[peter94]

Re: 2001 Merc 90 blown motor

I would say it looks very much like detonation to me. I only have the exhaust cover plate off so I will try and snap a picture of that.

The flywheel does spin.

Are there any known problems with these and preignition?