07 yz450f stall then hard to start when hot

Yamaha YZ450F 2007

56 replies to this topic
  • Family Man

Posted December 19, 2012 - 10:08 PM


The smoke contains oil. Doesnt smoke at Idle but when reved it puffs.

  • Family Man

Posted December 19, 2012 - 11:30 PM


Tore it back apart and the piston dome and valves are covered in oil. The piston rings look good. The piston I have in there uses one compression ring and the normal 3 oil rings. All Im thinking is maybe the oil rings wernt staggerd enough, could that be the cause?

  • grayracer513

Posted December 20, 2012 - 07:46 AM


The two most common mistakes made with oil rings are rolling one of the rails out of the groove during assembly, which folds it over and usually jams the piston, or overlapping the ends of the expander ring (the center element of the oil ring). If the ends are overlapped, the rails of the oil rings will have almost no tension against the bore, and can't effectively seal.

How much a bike smokes after a rebuild should depend entirely on how much oil you slopped it up with when you assembled it. Once that's gone, it should quit. In extreme cases, or where there was a lot of oil or coolant in the exhaust before the work was done, the muffler packing can become coated with it, and that can take a long time to clear.

  • Family Man

Posted December 20, 2012 - 08:53 AM


Im guessing " overlapping the ends of the expander ring (the center element of the oil ring." Should be ok to install. Eric Gore says a metal gasket can be reused a few times if coated with Permatex Copper Spray-A-Gasket Hi Temp. What do you think? Im thinking I should spend another 50 on new gaskets

  • grayracer513

Posted December 20, 2012 - 08:57 AM


The base gasket can "probably" be reused. I wouldn't try the head gasket, though. Why invite trouble? Otherwise you shouldn't need any of the others.

  • Family Man

Posted December 27, 2012 - 02:32 PM


Got it back together, rode it around the yard. Its still smoking. Has tons of power and is super fun. Im missing my 450. Do you think the oil rings are bad? They have around four rides on them, maybe they wore when the cams seized? On a long shot I'm gonna try a differant pipe to see if it still smokes. If it does Im gonna order another head and base gasket and new rings and or piston.

  • Family Man

Posted December 27, 2012 - 05:08 PM


The cylinder is smooth no scratches but the cross hatching is pretty much gone. Thinking about ordering a flex hone and flex hone oil to insure the new rings seat. Is there anything else that could be cause the smoke. There is wet oil comming out the exhaust with the smoke. Could the valve seals be bad? Does the Athena std bore piston use oem rings?

Edited by Family Man, December 27, 2012 - 05:09 PM.

  • Family Man

Posted December 28, 2012 - 01:38 PM


Im thinking of ordering a valve spring compessor so I can change the valve seals too. Im thinking new valve seals and new rings along with the cylinder hone and it should be good to go this time?

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  • grayracer513

Posted December 28, 2012 - 02:08 PM


Read the post in Common Threads about honing Nikasil bores. After the hone, you should have the cylinder measured to be sure it's not past spec already. They only allow .002" wear.

  • Family Man

Posted December 28, 2012 - 03:12 PM


can the oil rings, the ones on each side of the expander ring be installed up side down, does it matter?

  • grayracer513

Posted December 28, 2012 - 03:43 PM


There's normally no difference between the upper or lower oil ring or between the top and bottom side of either ring, so, no you can't install any of it upside down. The position of the ring gaps is shown in the manual, and that is reasonably important, so be sure to check that.

The important thing with the oil ring is that the ends of the expander are butted together, and that both rail rings are correctly seated above and below it. The whole thing needs to float in the ring groove as a unit.

  • Family Man

Posted December 28, 2012 - 04:01 PM


I spaced all the ring end gaps as per the manual. except the Athena piston only has one compression ring. I made sure all the rings were installed as per manual. Thats the reason I took it apart this time. Checked once they were installed in the bottom of the cylinder. Expander ring was butted not overlapped. compression ring mark face up. I ordered up a valve spring compressor, a flex hone, flex hone oil, new gaskets, new oem rings, new circlips and wristpin. I allready have an unused set of valve seals. Do you know if the oem Rings fit an Athena Standard bore piston? If they dont I have a low hours pro-X 13 to 1 piston Im going to reinstall with the new rings. The bike wasnt smoking before the cams seized which is making me think the valve seals got cooked?

  • grayracer513

Posted December 28, 2012 - 06:32 PM


Regarding the ring interchange between OEM and the Athena single ring, I wouldn't think so. Might, but I'd want the piston maker to tell me that.

  • Family Man

Posted December 28, 2012 - 10:18 PM


I'll just put the new oem rings in the Pro-X piston. Allready order new circlips and wristpin so Im good. I'll probley use the Athena piston on the next rebuild, after getting new athena rings, wrist pin and circlips for it, its only got about 4 rides on it. It would be cool to swap the oil seals and try the athena piston and rings that are in there. Have a hunch thats it. But Im going to hone the cylinder and change the rings/piston as well so I hopefully dont have to open it up for a while.

  • grayracer513

Posted December 28, 2012 - 10:25 PM


Allready order new circlips and wristpin so Im good.

Be certain that the circlips are the correct type and size for the piston you're using. Failing that is another common error. The consequences are ugly.

  • Family Man

Posted December 28, 2012 - 10:32 PM


I ordered oem circlips so they should be good with the pro-x piston. But thanks for the heads up, that for sure could be an easy thing to over look, and be a big mistake. I'll keep it in mind when I buy Pistons and circlips in the future.

  • Family Man

Posted January 02, 2013 - 07:20 PM


I honed the cylinder and installed the new rings and pro x 13:1 piston. The piston with new rings is alot tighter in the bore than the other piston and rings I had in there. I installed the rings as close to the manual as I could. Im thinking that was it. I also changed the valve stem seals too. Havent fired it yet becasue I mucked up one of the valve stem seals a little bit and am going to get another one before I put it together. Let you know how it goes.

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