Posted on 11/09/2014 4:23:52 PM PST by Blueflag
We are looking for advice regarding Yamaha 2-stroke engine for their (older) line of personal watercraft- say 2002 - 2007; pre-four-stroke motors. We want to buy two used ones (the full watercraft, not just the motors), and don't know how to gauge the hours of use on the Hobb's meter. How many hours is too many? What if the cost of a rebuild? How do you know it needs a rebuild? IF this was about chainsaw motors, I could answer my own questions. Looking for FReepers with experience with Yamaha PWC.
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Two strokes have problems with sitting. If they sat too long, the seals that separate the working chamber from the outside of the case harden and leak.
Check for how much play the main rod bearing has, the manual will tell you what is acceptable. The little end of the rod usually has a roller bearing which is easily replaced.
Check for cylinder scuffing from people who think the less amount of 2cycle oil you use the better it’ll run which is B.S. Use what they recommend and carry a spare plug or two with you, better a fouled plug than grenaded engine.
Hopefully the engines have never had cox fuel run through them, they’ll run like a bat outta hell, for a while and smell like a model engine running.
You can take the cylinder off easily or look through the exhaust port to see if there’s any scuffing on the piston. I think Yamies use a reed valve which can crack and cause problems or break sending the pieces into the engine but they’re easy to replace and not expensive.
If the price is right, they fire up and run well, who cares about the engines? Every running two stroke failure I’ve had was due to scuffing of the pistons and cylinders and it’s easy to bore the cylinder and get an oversize piston, just make sure the machine shop bevels the transfer ports in the cylinder.
The other failure I’ve had was an Rd350 that sat and its crank seals dried up and cracked. It ran (after being towed) but it sucked in the regular gear oil which is a good indicator you need to get the crank rebuilt which was easy to get done in the 70s. Since yours are from around 2002, I wouldn’t worry about parts and if you’ve never rebuilt an engine, a two stroke is easy, just make sure you put the piston ring gap in the pin in the ring land or you’ll have a bad day.
How many hours are on them now ?
The most effective and accurate way to tell if an engine needs a rebuild is a compression test. Hour meters are good for preventive maintenance, but actual wear and tear can happen at differing rates to identical machines doing identical service, even if they are running the same fuel mix.
Compression tests and overall cleanliness/condition of the engine, engine space and entire machine will tell you better than an hours meter.
JMHO, YMMV. I was a small engine mechanic for 20 odd years.
LX in #2 has a better detailed reply than I. He’s quite correct in what is said there.
One motor has 156 hours, and the other has 352.
These are both 2002 Yamaha Waverunners that have seen light yearly use in Lake Lanier Georgia. No salt water exposure.
Hulls are in good shape; reverse works well on the three seater; fuel lines looked good. Bilges looked like 12 year old bilges, but no oil accumulation. Bit of glazing on the dash gauge, but otherwise good. Fired up and ran just fine. No particular smoke when running (water running through the bypass) either at idle or throttle-up or throttle-down. Seemed sound.
Since the price was right for the pair (well under $6K) they are very tempting. Just a bit concerned about the 352 hours on the three-seater.
One motor has 156 hours, and the other has 352.
These are both 2002 Yamaha Waverunners that have seen light yearly use in Lake Lanier Georgia. No salt water exposure.
Hulls are in good shape; reverse works well on the three seater; fuel lines looked good. Bilges looked like 12 year old bilges, but no oil accumulation. Bit of glazing on the dash gauge, but otherwise good. Fired up and ran just fine. No particular smoke when running (water running through the bypass) either at idle or throttle-up or throttle-down. Seemed sound.
Since the price was right for the pair (well under $6K) they are very tempting. Just a bit concerned about the 352 hours on the three-seater.
True. I used to make beer money in college as a British Leyland mechanic. A leak-down was one of my first tests, after watching the tailpipe on throttle up, then throttle-lift ... rings or valve guides - which would it be? ;-)
Engines looked leak free. Exhaust systems were sound. wiring good. *IF* the bilge had been pressure-washed, you’d be hard-pressed to know these were 12 year-old motors.
Never done a compression test on a small displacement 2-stroke; only 4-stroke automotive - mostly 4 cyl.
Is it as simple as removing one plug, cranking the engine for 5 seconds and timing the leak down? (then repeating fore other cylinders)
I don’t know the proper leak curve ;-)
Also as Lx says, do not take this too seriously. These things soldier and smoke on forever. Rebuild. Enjoy. Buy more.
I put 1200 hours on a Rotax using Redline synthetic oil. Normally half that time would be excellent.
Because 2 strokes open the both the intake and exhaust ports as they approach BDC, you have to accept only the peak compression reading. Leakdown tests are difficult, to say the least.
Do one test “dry”, then squirt some light (sae20) oil into the plug hole and test again. A significant difference is obvious and telling.
HTH.
This is a non-invasive, pre-purchase inquiry.
I recognize it’ll need a rebuild again, and maybe again. So do aircraft engines. Used to that.
Just looking for guidance.
If the dang thing seems to run real good right now, with that many hours (~150/350) should I *normally* expect a rebuild RIGHT NOW, SOON, or after 200 more hours?
Fir instance, I have NEVER had to have my Stihl chainsaw motors rebuilt. Ever. Many a bar, chain, pull cord and spark plug, but NEVER the engines.
Just don’t know jack about these Yamaha waverunner motors.
Makes sense. That implies wear around the rings/sleeve are the primary concern?
BTW, this is a pre-purchase question. A “what am I getting myself into?” question.
Won’t have the chance to get into the motor.
Pretty much. While they are not the peak of technology anymore, they were becoming very well engineered and sophisticated towards the end of the 2 stroke era. Advanced metallurgy, oil and fuel injection, etc.
A piston and pot with gasket set are usually reasonably priced if you need it, but I would just run ‘em ‘til they quit, then worry about repairs.
yep, about $180 for a 2-cylinder kit / $260 for a three cylinder.
Reasonable.
I was looking at one to convert to electric, but the more I researched it the less practical it was, because everyone I found with a bad engine had a bad pump too.
The Yamahas run as required, and when they don't, which is rare, well it is a sailboat and the prevailing wind is a westerly that blows me home, so all I really need is power to get out, as long as Wave-Runners don't wake-blast me in narrow channels!
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