Super Jet Ring replacement time?

[johnwkerns]

I bought a 2009 Superjet (701) new from a dealer and have ridden it regularly (maybe 20-25 hours per season) for 15 years. I've done a little ocean riding but always rinsed it well. Always used good quality oil and run 40 or 45-to-1. I was planning to do a ring replacement this winter thinking it is probably way past due, but I did a compression test yesterday and got 150psi on both cylinders (+/- 2psi).

Should I put a new top end in this thing or leave it alone?

 

[schicks]

Run it. Prolly last another 15 years.

 

[JC-SuperJet]

For the Rings to have such low wear, you probably didn't have as many actual Engine-Hours as you estimate. According to your guess, that Top End has more than 300 hours which would definitely wear the Piston Rings down, and a Compression reading and loss of performance would reflect that.

Hanging out at the Water for two hours with the Jetski is not the same as running the Jetski for two hours total.

The Crank Seals are a bigger concern after 15 years, since the Seals are a wear Item also. The Crank spinning inside the Seal will eventually wear the Seal inside-hole enough to allow Air Leaks.

If the Ski idles well and the Throttle responds as usual, keep on riding.

If not, do an Engine Air Leak-down test to confirm that the Seals are holding pressure (Crankcase Compression aka Primary Compression). Find any and all Leaks, and fix accordingly.

 

[johnwkerns]

For the Rings to have such low wear, you probably didn't have as many actual Engine-Hours as you estimate. According to your guess, that Top End has more than 300 hours which would definitely wear the Piston Rings down, and a Compression reading and loss of performance would reflect that.

Hanging out at the Water for two hours with the Jetski is not the same as running the Jetski for two hours total.

The Crank Seals are a bigger concern after 15 years, since the Seals are a wear Item also. The Crank spinning inside the Seal will eventually wear the Seal inside-hole enough to allow Air Leaks.

If the Ski idles well and the Throttle responds as usual, keep on riding.

If not, do an Engine Air Leak-down test to confirm that the Seals are holding pressure (Crankcase Compression aka Primary Compression). Find any and all Leaks, and fix accordingly.

Is this a cylinder leak-down test? Or do I pressurize the crankcase somehow and do a leak-down test on that?

 

[schicks]

You get results from both case and cylinder in leak down test. Like jc said, if it runs good, idles good, its prolly good. To do a thorough leak test, you need to pull motor, flywheel, stator, carbs, exhaust, make sealing plates for intake and exhaust, then pressurize 7psi thru pulse nipple. Worth doing on a fresh rebuild, but not on a good running motor imo. I stand by my statement of run it. They last a long time if your not sucking water in and dry out bilge and start engine to blow out excess wster in exhaust after riding and vent the engine bay.

 

[kevbo]

Piston rings aren’t an issue with a stock exhaust port. I’m sure the ski could use a good inspection and maintenance. Leave it alone if you are not prepared to make everything perfect. Disassembling and cleaning everything is a lot of work. You will make it worse otherwise.

 

[WFO Speedracer]

Is this a cylinder leak-down test? Or do I pressurize the crankcase somehow and do a leak-down test on that?

Complete engine fully assembled except for the carbs and the exhaust , block off plates go on the intake manifold and on the exhaust ports , air is injected at 10 PSI then a gauge is installed to measure how much pressure it holds over a 10 -15 minute time span , worst case it needs to be less than 1 PSI per minute hopefully it is much less than that and preferably zero pressure loss is what you are looking for.

 

[brapperdoodle]

I think air leaks are a very commonly overlooked failure point. Harry did a great write up on this, could be helpful to folks!

Air Leaks – Group K

groupk.com

 

[johnmarchetta34]

Complete engine fully assembled except for the carbs and the exhaust , block off plates go on the intake manifold and on the exhaust ports , air is injected at 10 PSI then a gauge is installed to measure how much pressure it holds over a 10 -15 minute time span , worst case it needs to be less than 1 PSI per minute hopefully it is much less than that and preferably zero pressure loss is what you are looking for.

I would say take the flywheel cover off to, that way if the front crank seal is leaking, you will know. If you leave the flywheel cover on, it could seal up the leaky crank seal.

 

[kevbo]

Air leaks are 10x more of a problem for motorcycles than for PWCs. Watercraft engines never operate in high vacuum except when out of the water. Motorcycles do anytime they’re not wide open. Skis with leaks will have idle runaway problems out of the water before it causes a piston to mysteriously stick.

 

[WFO Speedracer]

I would say take the flywheel cover off to, that way if the front crank seal is leaking, you will know. If you leave the flywheel cover on, it could seal up the leaky crank seal.

Probably not a bad idea on a Yamaha

 

[Quinc]