gp800 cyl exchange problems

[silvercrxsir]

Just bought a cyl exchange kit a month ago and have been having prob ever since.had some scoring in both cyl,front was a little worse so I called tech support and talked to warranty and they insisted I had a lean condition and my crank seals were most likely bad so I ended up dropping another $150 on another new piston and base gaskets and crank seals changed it all out and vac tested it and had no leaks and after running it with new piston and still had a noise at idle after running only a few min in water and only at idle so I pulled the plugs and they were getting plenty of fuel which is 24:1 premix and also checked compression which was even and hadn't fallen at 146 psi which is fairly high on this motor for some reason but swish is at .05" which is correct so I proceded to tear it back down to inspect the bearings on the rods and noticed that the new piston is again starting to lightly score in the same areas around the ports so I paid a machine shop this time to measure everything and the piston clearance that the manual calls for that should be .0035-.0045" is actually at .009" in both cylinders which is way off meaning the cylinders weren't properly fit to my pistons.I called warranty and they say that they don't have these problems with their cylinder exchanges and don't have a warranty just on the pistons for defects and expect me to bring them there which is a 2be drive or pay to ship them which i already dumped $175 that I shouldn't have had to and I'm really getting tired of this thing sitting in my garage apart and don't want to wait forever and now its gonna need all new base and head gaskets again and getting tired waiting on parts so I asked if they could warranty just the pistons and gaskets and just send me the next size up and I would just pay someone locally to do the machine work so I can get this stupid thing done but still insist that I send everything back so it can be inspected which i can respect but its cost me almost $200 now and I'm sick of waiting and the damage on the pistons is obvious that they aren't fit right and now I just don't know what to do

[Technical Support]

Re: gp800 cyl exchange problems

First off the 24:1 fuel oil mix is way to rich it will create more heat and a lean condition in the combustion chamber. Yamaha recommends 50:1 and I will tell customers that ask 40:1 is as rich as you should go on a Yamaha engine. You are mixing extremely rich and the fuel does not burn as it should so your air to fuel ratio is way off, 2 strokes rely on the correct fuel ratio to keep the cylinder temps in a safe zone, the water cooling to the engine cools the block and stabilizes temps, if you run too little fuel and have plenty of water flow you will still score cylinders, always keep in mind the fuel keeps the cylinders cool on 2 strokes. Your carb stock settings are set to run with a 50:1 mix not 24:1 and if you’re running 87 octane fuel then things are even worse off. Two strokes rely on the exact correct fuel air mix to survive, make the mix too thick and it will not burn correctly and result in an overheated cylinder. I have seen the pictures you have sent and must say you are seizing most of the way around the piston, if we had machined as large as you say you would have broke the skirts off the pistons due to excessive piston slap. To correct the issues you are having you should mix to the correct fuel oil ratio, adjust the carbs properly, check pop-off pressure and make sure the fuel lines, fuel filter and on/off/reserve valve is working properly.

[Technical Support]

Re: gp800 cyl exchange problems

One other thing to do to help prevent future failures is to perform spark plug checks before running wide open, spend a little time and research different methods of reading plugs.

[silvercrxsir]

Re: gp800 cyl exchange problems

I ran the 24:1 on the first run never made it past the 30% throttle stage of the break in period when I notices an issue and brought it home the fuel in it now is sunoco 93 even though the ski is rated for 87 as per the decal on the the hull mixed at 32:1 which is the recommended ratio for a powervalve motor and the fuel lines are the blue hose that I purchased when I was there picking up the top end which I can ensure are routed properly the popoff is at 70psi in both carbs and they do not leak and were rebuilt with new mikuni kits.I do understand that there might have been a slight issue with a lean condition but I did pay for the parts because I understood their explanation of the prob and it was believable but I do ensure the issue on that end is fixed that and I'm just worried about the current prob with the excessive piston clearance.the back cyl never had an issue and its scoring around the exhaust and intake ports and same with the front cyl.a machine shop measured the clearance at .009" I did email lynne pics of this issue last night.the new piston has under 10 min of run time at idle speed only

[silvercrxsir]

Re: gp800 cyl exchange problems

Pretty much what happened was either the pistons were made out of spec or the machinists finished the cyl to the improper size.judging how everything went when I arrived was I got a call saying the order was ready and when I got there the next morning I waited around while the put it all together and packaged it up and it seems like they just grabbed the parts off the shelf and threw them in a box without making sure everything was sized properly and especially sounds true considering how when I placed the order they stated how they would set the ring gap and the rings were never opened or touched this is b.s. and becoming a pain in my butt and my prob is being ignored

[Technical Support]

Re: gp800 cyl exchange problems

Trying to summarize a response to your issues:

1) You are not being ignored. but you're asking for new parts without evidence that there was a manufacturing issue. Cylinder exchanges are less expensive than engines, but they don't come with warranty since someone else is doing the work. We will certainly look at if they were bored incorrectly as your implying (the pistons vary by tenths of a thousandths piece to piece, so it is not likely to be the piston), but we have to measure it as that would be a rare case.



2) The original pictures you sent of your piston showed all the signs of running lean or hot, not piston slap, as you were first told. A bore that is sized incorrectly and results in a loose fit would end up with piston slap, which would be visible on the pistons rim and skirts as contact marks. It would not result in an overheat, which your pistons pictures seem to show.



3) You bought another piston, had your machinist hone the cylinder, then appear to have piston slap. If during honing he took out 2-4 thousands, you're now at 7-9 thousands and may truly be having a piston slap issue (from the piston pictures you sent, there seems to be contact at the top of the piston and on the skirts). But as we understand it this is the same hole that was machined by an outside machine shop. So we unfortunately have no idea how much they took away when they honed it.



We are in a difficult position. You first had a piston showing 4-corner seizing from either fuel to air ratio or overheat. It damaged the cylinder, which you had machined by an outside shop. You put another piston in of the same diameter as the original, and are now getting what seems to be piston slap on the same cylinder that you had machined. Warranty had offered to have it looked at if you had brought it by or sent it in, but if it has been machined by someone else we couldn't warrant clearance concerns done by another shop anyway. We are not sure how you are holding SBT at fault at this point for a cylinder that has been modified.

[Ericka-SBT]

Re: gp800 cyl exchange problems

Amended for pictures

Trying to summarize a response to your issues:

1) You are not being ignored. but you're asking for new parts without evidence that there was a manufacturing issue. Cylinder exchanges are less expensive than engines, but they don't come with warranty since someone else is doing the work. We will certainly look at if they were bored incorrectly as your implying (the pistons vary by tenths of a thousandths piece to piece, so it is not likely to be the piston), but we have to measure it as that would be a rare case.



2) The original pictures you sent of your piston showed all the signs of running lean or hot, not piston slap, as you were first told. A bore that is sized incorrectly and results in a loose fit would end up with piston slap, which would be visible on the pistons rim and skirts as contact marks. It would not result in an overheat, which your pistons pictures seem to show.



3) You bought another piston, had your machinist hone the cylinder, then appear to have piston slap. If during honing he took out 2-4 thousands, you're now at 7-9 thousands and may truly be having a piston slap issue (from the piston pictures you sent, there seems to be contact at the top of the piston and on the skirts). But as we understand it this is the same hole that was machined by an outside machine shop. So we unfortunately have no idea how much they took away when they honed it.



We are in a difficult position. You first had a piston showing 4-corner seizing from either fuel to air ratio or overheat. It damaged the cylinder, which you had machined by an outside shop. You put another piston in of the same diameter as the original, and are now getting what seems to be piston slap on the same cylinder that you had machined. Warranty had offered to have it looked at if you had brought it by or sent it in, but if it has been machined by someone else we couldn't warrant clearance concerns done by another shop anyway. We are not sure how you are holding SBT at fault at this point for a cylinder that has been modified.

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