Any 2 stroke experts?

[4x15mph]

Low compression on cylinder #2 after last weeks debacle and overheat on the Delaware. 15 PSI lower and I saw slight scoring in the cylinder through an inspection cam. Started the tear down today and will rebuild the top end which I have been itching to do for a couple of years now.

Please respond if you have any experience with the 2 strokes in case I have questions.

Here is the piston from the exhaust port view.... seems like the heat glazed it although the top of the piston looks fine and it didn't melt. I am in too far already though and will do the rebuild

 

[—Яiвs>]

What was your debacle? I had an overheat issue a few years ago with my 2stroke. Ended up being sediment deposits in the cylinder cooling passage. Must have scooped out a bucket of silt.

 

[4x15mph]

I had a tree limb(s) jam between the impeller and the duct but the real root of the issue was there was a portion of tree that was completely clogging my water intake/inlet in the impeller duct = engine had not cooling. Although the rpm's were limited, I was still able to keep it under 3500 and after letting it sit, I tried to run it again not knowing the real problem. Smoke was coming out of the pee holes and the engine was HOTTTTT..... That said, one of the pistons was reading lower compression so I tore it down.

 

[Bruce]

@Speedling, has rebuilt these engines.

 

[—Яiвs>]

You could probably get away with a set of pistons, rings and a fresh hone. Unless you wanted a full rebuild.

 

[boudin]

@4x15mph you'll find a good deal of information in the 2-stroke Yamaha forums on greenhulk.net. I've rebuilt at least a dozen of the 1200NPVs, but stopped a few years ago when I switched to all 4-strokes. What are your questions?

-Greg

 

[4x15mph]

Thanks all - I have posted to Green hulk as well. I will just be doing pistons, rings, and a honing/bore for now. No questions at this point since many have been answered and I am well on my way.

 

[Speedling]

Thanks all - I have posted to Green hulk as well. I will just be doing pistons, rings, and a honing/bore for now. No questions at this point since many have been answered and I am well on my way.

Awesome!
Subscribing to this in case you have questions. Been a good while since i rebuilt.
I remember it being surprisingly easy to get apart.
I think we had to bake a part to get the sleeves out?
I did oversized pistons i found on ebay.
Had a local shop bore out for me.
Had a hot rods crank that i believe was just a bit better quality same stroke.
Had some minor marring on the head piece and had it cleaned up (slightly less than "milled".
I just know that when all said and done i did hit 60+ mph on super smooth water!
Was perfect for chasing the bil baja at the time.

 

[Yamatuf]

SBT has a complete exchange kit, new cylinder bored out to your liking with pistons n rings. just need a core. You may have additional issues if you warped the head.

 

[boudin]

He'll want to check the cylinder walls for aluminum fragments. Sometimes small ones can be chipped off with a razor blade, or a bit of muriatic acid and then the cylinder honed. Often not and it will need to be bored with oversized pistons. The 65U has steel cylinders and are not nearly as resilient as the 66V power valve motor, which are Nikasil coated from the factory.

Really should also check for aluminum fragments in the crank, but given the piston did not break up, crank is probably okay. If you do end up getting into the bottom end, use sealant around the crank seals--the 65U is known for blowing crank seals.

If it's been more than 2-3 years, a good time to rebuild the carbs with genuine Mikuni kits. The SBT kits used to leak--not sure if they have corrected that.

Blah, blah... I can go on and on. Trying to forget my 2-stroke knowledge.

-Greg

 

[4x15mph]

I think the crank will be fine since there was not a lot of scoring. Fullbore will provide the whole kit and use my cylinders (honed) which is what I want. I will not use SBT for these engine components....

@boudin - definitely understand what you mean about genuine Mikuni carb kits. I learned the hard way when I started with SBT and had a leak the season after. Redid the carbs with Mikuni and all has been good.

Once I get started, you can bet I will be back @Speedling , @boudin , @Yamatuf. Thank you!

 

[boudin]

Sounds like you are on top of it @4x15mph!

I always thought it would be fun to do a 4-stroke MR1 conversion of an LS2000. I have done five Yamaha SUV MR1 conversions... it should be pretty much the same just 2x (the stock SUVs use 65U motors). Once you move the motor mounts, it's pretty straight forward. This is from last year, but I've done three since then: http://www.greenhulk.net/forums/showthread.php?t=260189

-Greg

 

[Yamatuf]

I agree with the Makuni carb kits only.
I replaced my 701 superjet cylinder with an exchange unit from SBT with specific bore size( I had a crack/waterleak just below the piston line) . I had no problems to date - 2 years old.

Converting my LS2000 to a 4stroke has got my attention @boudin. Has anyone done this to a LS2000?

 

[the MfM]

Sounds like you are on top of it @4x15mph!

I always thought it would be fun to do a 4-stroke MR1 conversion of an LS2000. I have done five Yamaha SUV MR1 conversions... it should be pretty much the same just 2x (the stock SUVs use 65U motors). Once you move the motor mounts, it's pretty straight forward. This is from last year, but I've done three since then: http://www.greenhulk.net/forums/showthread.php?t=260189

-Greg

Been done in an exciter. Be easier with the extra space in an ls/lx/ar

But I don’t know why anyone would want to give up the simplicity and great smell of the two strokes.

 

[boudin]

This is the thread here. Impressive.
http://www.greenhulk.net/forums/showthread.php?t=231543

He even used the pre-2010 VX bearing housings. There must have been fiberglass work involved. If you use the 2010+ VX pump setup, it's a bolt on, except for moving the motor mounts. I say that, but don't know the driveshaft length on the LS--would need to know that first.

He also did a nice job on the fuel tank.

-Greg

 

[the MfM]

He did a nice job but it’s a lot of work and money to save a little gas and go slower...

If I was going through the trouble of a swap it’d be something a little moar exciting.

 

[4x15mph]

I got the pistons off using a makeshift puller

I also pullled the impeller liner and it was in bad shape. My boat is going to be so much faster with a new top end and impeller liner. I learned a lot today and had fun doing it.