Yamaha Gp1300r lost a cylinder

[haddles]

I was riding my ski and it was performing perfectly. I was sitting on around 5000 rpm on half throttle when it suddenly stopped. I tried starting it again and it turned over as if the battery was flat. After a couple of attempts it started and ran for about a minute before dying again. It did this all the way back to the boat ramp but I could tell it had lost a cylinder. I took it out of the water and looked at the engine bay. I noticed the powervalves were not cycling properly as they usually do at shutdown. After manually turning the cable a few times they freed up. I then took each plug out and noticed that the rear plug had been hit by the piston as there was no gap and a light mark on the top of the piston. I regapped it and the engine fired up but still on 2 cylinders. I took the rear plug out and it was ok gap wise but had obviously not been firing as it was covered in fuel. There was spark to all plugs. I stuck my thumb over the spark plug holes and the first 2 pistons had good compression at crank over but the rear one had nothing. What could have gone wrong, the ski has about 70 hours, always get's the correct oil and is rarely thrashed. Could it have something to do with the powervalves or am I looking at a rebuild which I won't be happy about as this is supposed to be a performance engine and has had a pretty easy life. How could the piston hit it then not hit it again? Please help

 

[haddles]

Re: Yamaha Gp1300r lost a cylinder

By the way, it turns over well now, just like normal and starts easily, just run's on 2 cylinders now. It's a 2003 EFI powervalve model. I was told these motors are good for 400 hours of normal use. I did put it back in the water and it would pull around 5000 rpm but from the exhaust note it was obvious that it was running on 2 cylinders and there have been no more issues of the piston hitting the plug. The engine does not make any bad noises but obviously shakes a bit now as it isn't running properly. There were no warning alarms.

 

[Jeff Walkowiak]

Re: Yamaha Gp1300r lost a cylinder

check to see if the oil line fell off the back cylinder// very common problem with all yamaha 2 stroke engines

 

[haddles]

Re: Yamaha Gp1300r lost a cylinder

Curiosity got the better of me and I pulled the head off it to find a holed piston. The bore is ok except for one deep groove down one side. Hopefully I haven't done the crankshaft or I'll be taking it out and sinking it. I haven't checked the oil line to the rear cylinder yet but that may be what caused the problem. You'd think something as critical as an oil line would not be a 'common' problem given the 40 odd years that Yamaha has been making oil injected 2 stroke motors. I would have thought that would have been addressed 39 1/2 years ago. Thanks Jeff, i'll check it out and let you know.

 

[haddles]

Re: Yamaha Gp1300r lost a cylinder

Ok, oil line looks to be intact, how then did it hole one piston? It has throttle body fuel injection so if i'm not mistaken, each cylinder would be getting the same mixture. I was running 10% ethanol in the fuel but the other two pistons look fine. I looked more closely at the bore on the rear cylinder and it is badly scored which would indicate a seizure but it might also be from bits of piston grating up and down. The stuck powervalves may have been caused by debris exiting the exhaust port. The cylinder seems fairly oily. Any ideas what happened? I'm going to fix it myself. Should I assume the crank is ok? I don't want to fix it and have it happen again.

 

[Rob454]

Re: Yamaha Gp1300r lost a cylinder

It leaned out and/or detonated and burned a hole in the piston. you probably got some debris in the fuel line and the cylinder wasnt gettign the proper amount of fuel. Especially at 5-6000 RPMs.
If youre gonna rebuild it might as well go and do the whole motor. reseal the crank case. clean the carbs etc. The crank should be ok but I woudl still have it checked out. you need to check the bearings and make sure shavings from the piston and cylinder wall didnt get in the bearings

 

[haddles]

Re: Yamaha Gp1300r lost a cylinder

Explained the problem to a mechanic and he seems to think i've done a crankcase seal and water has entered and the crank bearing has disintegrated and the debris from that has entered the top of the motor and holed the piston. I hadn't used the thing for 5 months. I don't want to get ripped off but i'm not really up on this stuff. He's down the Gold Coast which is an hours drive from me. He reckons he can weld up the old barrel and re nikasil it. The head has pitting which he says he will grind out. I don't want some slapped together piece of junk so was wondering if this is the way to go or just replace what I can see and hope for the best. Maybe a quick fix and a fire sale is in order.

 

[Jeff Walkowiak]

Re: Yamaha Gp1300r lost a cylinder

if the oil line is ok then it ran lean as someone stated and the rear seal could have caused the problem.. allowing air to get in the crank case section for that cylinder and leaning out the fuel mix.

 

[haddles]

Re: Yamaha Gp1300r lost a cylinder

I'm sure you are all waiting with baited breath as to the outcome of my dilemma. After shopping around for a good mechanic I found one who pulled the engine down and we discovered all the bores were scuffed and therefore I bit the bullet and went for the full rebuild. All crank bearings, new pistons and rebore with new Nikasil plating as well as all new seals and reconditioned head. 3 grand later and the ski is running beautifully. No real explanation as to what made it let go but he seemed to think it may have taken in water at some stage. Under 80 hours is not normal for these engines. There was some evidence also of air entering the base gasket of the rear barrel as well which had been happening since new he thought. Most Australian skis are used almost exclusively in salt water and the salt air going into the engine probably doesn't extend their service life either. The guy I bought it off used it for wave jumping in the surf so the chance of it being capsized was probably high. So what I initially thought was a loose spark plug wire turned into a full rebuild. I'll probably post again in another 80 hours.........