Red hot pipe, almost melting and engine noise

4 replies to this topic
  • RRmike

Posted August 15, 2005 - 03:14 PM


Im working on a YFZ426 and got a new motor for it, since the crank, head and valves were wasted on the old one from a skipping timing chain.

The engine I got used is out of an ATV conversion, put it back into the bike. It had a wetsump conversion so I converted that back by putting the oil pump from the original in the new motor and putting the lines back where they should be including the Y line from the side cover, case and head.

The motor starts, runs relatively good but makes alot of racket, almost rattling like a cam chain hitting a cover on down revs mostly but is usually present most of the time.

The header pipe is scary hot, to the point its sparking (there is a little rust on the header pipe right outside the cylinder) and the rust is sparking off.

I have to check the fuel/air screw but I am worried there is something else going on, do these engines make a fair amount of noise is it common for a rattle hear and there?

  • biznet1

Posted August 15, 2005 - 03:42 PM


You might get beat up about the red hot pipe. This is normal. The sparking is probably something on the pipe burning off. I believe you've already figured out the most likely cause of the noise (yet they are noisy to some extent), but no way to know for sure til you pull the valve cover and look.

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  • RRmike

Posted August 15, 2005 - 05:08 PM


It definitely sounds like cam chain noise but the cam chain is primo, the wear strip at the top of the valve cover is not even touched and the cam chain is tight with no slop. I did find a couple posts that on the 4th page or so found the primary drive gear was slapping on the keyway. I will have to check on this.

Im familiar with glowing headpipes, this is a little extreme.

  • yamahazinger

Posted August 15, 2005 - 05:30 PM


as for the red hot pipe you are extremely to lean. Id clean the carb and if its still runs that hot , id richen up the jetting. Id wouldnt recommend running the bike if the pipe is glowing red. As for the noise it may be the lifters or valves. On a 4stroke i have there is a little clicking from the valves but nothing loud.

  • RRmike

Posted August 15, 2005 - 06:27 PM


It was the straight key on the primary drive gear (crank). I was a little shocked when I opened the side cover and found splines on the crank. They are apparently only for the clutch drive gear, the balancer gear (at the crank) was moving atleast 1/4 inch back and forth, I turned the key over and it fits snug now, tightened the crank nut (which was loose) and used all 3 sides on the lock washer to reinforce.

I found the inner clutch hub severally beat too, its inner slug which is cast into the aluminum part allowed it movement as well.

Luckily this is a 2001 bike, the original motor has a good part to swap in. Too bad the crank was toast or I would swap that in too.

Now to button it up and get the idle circuit jetted a little richer.

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