Another blown head gasket.

12 replies to this topic
  • Chase Goodling

Posted September 15, 2013 - 01:26 PM


Alright... I jad replaced the headgasket on my 450. Here we are not even 6 months later... blown yet again... rode motocross all summer every weekend with no problems. know its the headgasket... cause coolant is coming out the overflow tube. Exact symtom as last time. Which is leading me to a warped head... could this be possible and what the most accurate way to check it? Thanks!!

  • NitrousR1

Posted September 16, 2013 - 03:48 PM


You can use a flat piece of glass and then use feeler gauges between the glass and head. Ideally you would use a machinists square edge but glass works. Here Machining the head is only $20. You can also take off your cylinder and measure that for warpage as well.
You want to machine as little as possible since the tensioner will need to take up the extra slack in the timing chain as you are moving the head closer to the crank sprocket
Out of curiosity Did you use a OEM head gasket?

  • grayracer513

Posted September 16, 2013 - 04:12 PM


Moving the head closer to the piston is a much bigger concern.  The chain tensioner will have no trouble dealing with a head cut to reasonable limits.

  • Chase Goodling

Posted September 16, 2013 - 04:30 PM


No I did not.... I used tusk gaskets.

  • NitrousR1

Posted September 19, 2013 - 01:30 PM


That's the problem. I had a 06 yz450 come in with a blown tusk gasket recently too. There's a reason the whole tusk kit is $18 and the oem gasket is $25, stick with the oem head gasket and measure the head for flatness and you should be good to go
You must Measure piston to valve clearance anytime the head or cylinder is machined. The machine shop will want to measure that before machining anything

  • Chase Goodling

Posted September 19, 2013 - 01:36 PM


@NitrousR1 ok.. whats the easiest way to measure clearence... and how much to machine it.

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  • Geoffit

Posted September 19, 2013 - 03:07 PM


You can cut up to .020" from the head with no valve clearance issues ( stock cams) . Normally the cylinders are no issues just run it across a surface plate on some 600 grit paper. Normally 004" will clean up the head fine .

  • superretard

Posted September 20, 2013 - 05:14 PM


Most of the time OEM gaskets is the only way to go.

  • NitrousR1

Posted September 21, 2013 - 01:03 PM


We always measure piston to cylinder clearance with a piece of clay and rotating the engine by hand. Based off of experience with this motor with the stock cams and stock compression ratio piston .005" will be fine.
take the head to a machine shop to be decked. They will get it dead flat with the right surface finish for the head gasket. It could be done at home, but for how little $ it costs, just go to a machine shop and know its done right the first time.
Are you running the stock cams and a stock compression ratio piston?

  • Chase Goodling

Posted September 21, 2013 - 03:28 PM


Stock cams and not a stock compression... 13:1

  • NitrousR1

Posted September 23, 2013 - 08:31 AM


You should be ok but it doesn't hurt to measure the piston to cyl clearance.

  • grayracer513

Posted September 23, 2013 - 11:16 AM


You mean piston to cylinder HEAD clearance, do you not?  Can't measure piston/cylinder clearance with clay

  • NitrousR1

Posted September 23, 2013 - 02:10 PM


Sorry gray Piston to valve clearance. I'm in a similar thread about piston to cyl clearance in another forum.
You should be fine though in using a athena 478 big bore kit with a vertex high comp piston and stage 2 hotcams with the head milled .004 and still have good piston to valve clearance with well over 150 hours on each bike

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