2001 Mercury jet20 2 stroke

[MarineVet2004]

I have a 2001 Mercury jet20. "ran last spring" says the guy I got it from. Came with a service tag that read. Won't start. I pulled the plugs and they are getting good spark. Fuel is getting to the carburator and the Pistons have heavy scoring on the exhaust side. I know it needs new pistons and to be honed/bored the cylinders. From what others have said in post's. My question is. Can the starting problems and it not starting be all because of the heavy piston scoring, and due to the lack of compression? Or other problems? I enjoy projects like this. So any input would be great.

 

[GA_Boater]

Welcome aboard. Follow the Forum Help link in my sig for photo posting help.

Do a free auto parts store rental of a compression tester and check the compression first before tearing the motor apart.

 

[racerone]

If pistons are " heavily scored " the motor will need to come apart.----Not going to heal itself !-----I assume you looked through the covers on the side to see the scoring.

 

[MarineVet2004]

I'm trying to post pictures. But it's saying "you are not authorized to create or remove attachments.

 

[MarineVet2004]

Yes. I removed the exhaust cover and instantly saw the scoring. It's mainly on the exhaust side, from the looks of the cylinder on the other side. having hardly any scoring.

 

[hardwater fisherman]

After three posts you should be able to post photos. So try again. And there is a tutorial for posting photos in the forum rules and guidelines section.

 

[RCO]

Those pistons are trashed. That is not typical worn out from use wear. Appears overheated. I would be very surprised if it could build up enough compression to fire I would think the bore is going to be just as bad, and a good possibility of the crankshaft too. Your best bet would be to replace the entire power head.

 

[flyingscott]

Looks overheated. Tear it down and see what the crank looks like I would bet it is OK. If you rebuild it you need to find a good machine shop that has experience in blind bores and the Mercosil block.

 

[MarineVet2004]

Thanks guys for the input. I'm going to pick up a compression gauge and flywheel puller. Test it. Then start disassembling it. Definitely needs new pistons. Will post pictures.

 

[MarineVet2004]

I checked the compression today. Top cylinder 80 PSI and bottom 40 PSI. Shouldn't it be in the hundreds?

 

[GA_Boater]

Whatever the number is supposed to be, they should be with 10%. Those numbers are 50%.

Without having the motor in front of me, I'd say it needs an oversize rebore if the scoring isn't too deep.

 

[flyingscott]

Those are very bad #s. You should be over 100 psi with a healthy motor around 120. You need to tear that motor down.

 

[MarineVet2004]

Removed the pistons. Top piston has very little scoring. Bottom piston has pitting and heavy scoring. Both on the exhaust side. Now on the other side of the pistons, no scoring. The cylinders match everything above exactly in duplicate.

 

[racerone]

Cast iron cylinders or something else.-----Look for O/S pistons first.

 

[MarineVet2004]

Taking the pistons and cylinder to a buddies shop today to have it looked at for a estimate. When I buy new pistons. I need to get .030 OS ones correct? Also, does that mean that the cylinders will have to be rebored to .030?

 

[RCO]

The amount of oversize depends on how much material the machine shop has to remove. These are plated bores, not sleeved correct? If that is the case they need to be bored out and replated, most shops send them out for that. Most machine shops will want the new pistons to fit them to the bores also.

 

[racerone]

Cheaper to find a parts motor.-----Your location ?

 

[flyingscott]

That is a mercosil block. Can be bored out it the machine shop is capable. Kits are available to rebuild it

 

[Dirk Diggler]

Subbed. I want to see this come back to life if it's possible.

 

[MarineVet2004]

The machine shop said that they can do it. But also said that I could get away with just buying new ring's for the top piston and a whole new bottom piston. What places sell the cheapest parts? I have looked on one website and the pistons go from standard to os $120- $145. Which is fine. But you guy's may know cheaper places.