How far on cam timing before valves bend


3 replies to this topic
  • myoung

Posted December 30, 2006 - 02:05 PM

#1

I have a guy's '01 426 at my place right now that he wanted me to put in a new set of Hotcams in. He brought me the bike not running but said it had been running. He told me it was running ok, but they were having a lot of trouble keeping plugs alive and it was gradually getting harder to start. By the time I got it he said they couldn't get it to start anymore, but said another plug would get it to fire.

He had taken it to a shop to have the top end rebuilt complete with a valve job so I know someone had their hands in it. After it started acting up, someone he knows checked the cam timing and said something didn't look right and he speculated the gears had spun on the cams, this is where the new cams came in. He brought it to me because he didn't trust the shop anymore and didn't want to pay the high cost of the dealer. I told him it was unlikely the cam gears spun, but he told me he just wanted to go ahead and replace the cams so I figured fine, whatever, easy enough.

I went ahead and ordered the cams and was finally able to get some time to toss them in last night. When I took the valve cover off I found out what the guy meant when he said it didn't look right. The exhaust cam was advanced a tooth and the intake advanced by two teeth. I had a hard time believing a shop could screw up that bad so I assumed the tenioner gave up or the chain was so streched it jumped, but the tensioner looks fine and still looks like it has quite a bit adjustment left to keep the chain tight. Besides, it sounds like it wasn't running right from the time he got it back from the shop so I guess it's possible they just screwed up.

Anyway, I went ahead and put the new cams in since he wanted the upgrade of the Hotcams regardless. However, I hadn't put in a new plug yet since I figured the starting problem was probably the cam timimng. Sure enough it still wouldn't start as of last night. I went and picked up a new plug today, but I'm starting to wonder if I should do a compression check first in case the valves got damaged.

So ultimately after all this rambling my question is, is it possible to bend the valves with the cams off as far as they were? Any chance the shop would have advanced the cams on purpose for performance? Seemed a bit too far for that, but I don't know if this is common. Anybody else have this issue before?

Just looking for a little feedback before I proceed.

  • mxis4me

Posted December 30, 2006 - 05:09 PM

#2

you could do a compression test on it if u have a comp gauge. also if the valves were bent from cams being out of time the valve clearance will be xtra loose on the valve that was hit by the piston, but thats with the original cams though. did u have to make any major changes to your shim pads to adjust the valves? if so u prob got a bent 1.

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  • myoung

Posted December 30, 2006 - 05:53 PM

#3

Yeah, good point, only minor pad adjustment for new cam. Probably a good sign.:lol:

  • Yamahafan

Posted December 30, 2006 - 07:27 PM

#4

He should have replaced the timing chain when doing all this work. If not, there is a good chance that it is worn out (stretched) which allowed the chain to slip forward. I have seen numerous posts about this recently.





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