Defective Hot Cam?


6 replies to this topic
  • G-BRO

Posted March 14, 2014 - 03:07 PM

#1

Has anybody had a negative experience with installing a Hot Cam exhaust on any of these thumpers? Specifically the auto decompression on the YZ 426? I've heard that once in a while somebody will install the cam correctly to later learn after troubleshooting it was somehow a "dud" from the factory. Signs? Symptoms? Experience?

  • grayracer513

Posted March 14, 2014 - 03:32 PM

#2

The only issues I'm aware of cam up when they started making stage one (and beyond) cams for the WR450F.  The trouble was confined to the ability to use the electric starter.  No trouble with 426's that I'm aware of.



  • travisn

Posted March 19, 2014 - 12:25 PM

#3

Can you elaborate on the ability to use the electric starter part? 

 

We use a wr450 engine with yz top end in our race car and have always had starting issues. http://www.rit.edu/kgcoe/formula/



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  • jojo1224

Posted March 19, 2014 - 02:36 PM

#4

Can you elaborate on the ability to use the electric starter part?

We use a wr450 engine with yz top end in our race car and have always had starting issues. http://www.rit.edu/kgcoe/formula/

Are you stating issues related to the starter not being able to crank it over? From what I have seen here the YZ and WR decomp pins in the exhaust cam are shaped different allowing the stater to turn over the WR engine. If I am remembering this correctly the WR decomp pin has more of a square profile.

  • travisn

Posted March 19, 2014 - 02:50 PM

#5

Yes, we had to go to a 24v starting system to spin it fast enough. I guess we didn't use a yz head last year, but still had difficulty starting. I think it was because we have a very large plenum volume among other things most likely. I believe we went through 5+ starters, probably more, at $250 a pop. 



  • grayracer513

Posted March 19, 2014 - 03:06 PM

#6

The length of the decompression pin (not its shape) controls the timing of the closing of the left exhaust valve, which the decompression system holds off the seat beyond its normal closing point to reduce cranking compression. The timing of that event has a pronounced effect on cranking compression, as it normally closes at around 20-25 degrees BTDC. A very small variance in length will change the compression significantly, owing to the narrow range of crank rotation between too much to start, and not enough to start.

The early Hot Cams had trouble getting the length right, but that's been pretty much worked out now.

  • NitrousR1

Posted March 20, 2014 - 02:50 AM

#7

I had the estart issue with my wr450. Would not fire up on the button. I called and complained and they sent me one of the updated exhaust cams. It then worked





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