Top end rebuild

[piper84]

I pulled the cyl head off and found damage on aft piston that I could not see otherwise also elongated Cyl wall in spots. This is the cyl at 90 psi comp ck even lower when wormed up. I am replacing all three pistons and ordered a remanufactured cyl head. Was recommended by supplier to also rebuild the carbarators. Dammage to piston side was on the exhaust side most likely due to a lean running carb. So I’m going to rebuild all six carbs and replace oil lines.

 

[boudin]

Yes, dirty carbs and oil lines coming off are the #1 killer of 2-stroke Yamaha's. Carbs should be rebuilt every 2-3 years. Try to use Mikuni or WSM kits. Go back with stock high/low mixture screw settings--check greenhulk.net for stock values, but also make note of the # of turns when disassembling the carb body. If you add aftermarket flame arrestors, that will also lean out the mixture--there are formulas on greenhulk.

You might also want to pickup an impact screwdriver for stuck screws.

-Greg

 

[piper84]

Has enyone ever tried to use an infored digital hand held thermometer to detect a lean our hot running cylinder?

 

[M@__]

Ohh man. This is getting deep. I’ve done it on my motorcycle. Chambers are flat black. it worked.

Not sure where to point, or how much hotter middle cylinder is, but I’m interested in what you come up with.

 

[the MfM]

I’d use one of these handheld (wired) thermocouple readers

https://www.amazon.com/Leaton-Therm...&keywords=type-k+thermocouple+4+channel&psc=1

 

[4x15mph]

Has anyone ever tried to use an infored digital hand held thermometer to detect a lean our hot running cylinder?

I have been using an IR thermometer to check the temperature of the exhaust and the cylinders/head. I don't do it frequently enough though since when I have the storage tray in, it is a pain to take it out for a quick measurement. I started this when my exhaust was clogged and my overheat sensor was tripping and limiting the engine RPM's. I think you can do a lot of preventative checks with one of these IR's especially on a 2 stroke

 

[M@__]

Would you point it at the cylinder/chamber connection?

Spark plugs?

I almost put something about thermo couples and a digital readout and started imagine an airplane cockpit... decided to keep that to myself, but those sensors aren’t too expensive.

My understanding is head temps drop on both sides of a perfect mix, but EGT continues to climb as you lean.

What are they doing on greenhulk? That’s really the best tuning source.

 

[the MfM]

Would you point it at the cylinder/chamber connection?

Spark plugs?

I almost put something about thermo couples and a digital readout and started imagine an airplane cockpit... decided to keep that to myself, but those sensors aren’t too expensive.

My understanding is head temps drop on both sides of a perfect mix, but EGT continues to climb as you lean.

What are they doing on greenhulk? That’s really the best tuning source.

I thought of those too. I have a bunch of them wired to a panel for my boiler.


https://www.ebay.com/itm/Red-LED-Di...468580?hash=item488abfc3a4:g:-nAAAOSwTM5YwSHS

eBay search “ds18b20” ... could do the arduiono thing and have a touch screen at the helm to monitor cylinder temps

 

[M@__]

I need to slowly step away from this thread....

 

[4x15mph]

I point it at the cylinder and the spark plug area. I used this mostly for the exhaust though but I will get in there and measure "normal" temps on the engine head in hopes that I can be more proactive.

I like @M@__ idea on using sensors and they do look very inexpensive.

 

[piper84]

Well did it got the top cyl. Block installed with eng. In the boat. I used an SBT top end rebuild kit, the trick i used is to use dryer vent hose clamps to hold the rings in place and slide the cyl. Assy. On to all three pistons at one time. Was a good sound when the rings clicked in to place. Carbs are all rebuilt will see what happens when fired up.

 

[M@__]

Good job!

 

[piper84]

Well finely in the water this past weekend. Top end rebuild went well eng. response is realey good in port eng. Found that the starboard eng. was sluggish but matched rpm with split throttles. Checked and found # 1 plug not firing. Changed plug with no fix. Suspect #1 coil may be bad since the other two cyl. Are firing. Anyone have something simmer happen?

 

[DCB-270]

If you need coils and wiring check out http://www.jetskisolutions.com/index.html

 

[4x15mph]

I am replacing all three pistons and ordered a remanufactured cyl head.

Where did you get the remanuf. cylinder head and pistons? You did this while it was in the boat, right?

 

[boudin]

Try https://www.shopsbt.com/

-Greg

 

[piper84]

Where did you get the remanuf. cylinder head and pistons? You did this while it was in the boat, right?

Top end kit was from SBT in Florida. Round about $850.00, I did do the rebuild in the boat with the help of another person when sliding the cyl. Head on to the pistons, very easy with a little pashionts, took a few hrs. total. Had to use a small merrior for the piston shims and rist pin Locks to insure thay where seated and in the Wright place. All in all thay are great little motors!

 

[bluejetvt]

How did you come to the conclusion your exhaust was plugged? I ask because i am having an rpm cut out as well. No water coming out my pisser. How’d you check into your exhaust?

I have been using an IR thermometer to check the temperature of the exhaust and the cylinders/head. I don't do it frequently enough though since when I have the storage tray in, it is a pain to take it out for a quick measurement. I started this when my exhaust was clogged and my overheat sensor was tripping and limiting the engine RPM's. I think you can do a lot of preventative checks with one of these IR's especially on a 2 stroke