warped yz426 head


5 replies to this topic
  • yammyz426

Posted March 13, 2013 - 05:11 PM

#1

I bought a 2000 yz426 with a blown head gasket. I was finally able to get it resurfaced. The sad part is that .012'' had to be taken off before it was level again. The gasket had vibrated quite a bit and put a lip on the exhaust side of the head so that didn't help either. So it is now correct but my question is will it still have enough clearance between the valves and piston with the stock gasket? Or is there some type of shim I can put on the bottom of the jug or add to the head gasket? I was told I should clay it to make sure but I want to see what options are available so im prepared when I put it together. I had polished the intake and exhaust ports so im gonna do a valve job as well which will help my clearance a little. Any advice would be greatly appreciated. Thanks

  • marv02

Posted March 13, 2013 - 05:50 PM

#2

You want the intake ports ruff so there turbulence keeps the fuel air atomized better and keeps it from puddling in the intake you want the exhaust polished to a mirror finish.

Others will chime in but if you can remove the casting flaws on both intake and exhaust don't change the shape of the ports you can do more damage than making better I had High velocity type porting done to my head the bike is very fun bike to ride now.

(High velocity porting makes the intake smaller to keep the higher rate of intake flow yes it sound nuts but to big will kill the air flow charge velocity that's go for to small of port also think of a garden hose with adjustable nozzle it will flow water wide open but kind of just flows out at low rates of speed if you start closing the nozzle to a fine stream it comes out in a high velocity stream).

As for the head gasket if you need a custom one to gain more clearance give Cosmetic gaskets a call they can make you a custom one I had to have them make a custom on for my 3mm big bore piston for my 426 now it a 450.5

I would use the clay to find out you valve to piston clearance and piston to head make sure nothing hits.

  • yammyz426

Posted March 13, 2013 - 06:17 PM

#3

Well I cleaned up everything. I didn't want to go too big because of the reasons that you (marv02) had mentioned. I took some off of the walls on the intake side so the air wouldn't deflect off them. Just made all transitions as smooth as I could and removing the big casting marks. Hopefully I didn't do any damage. I delt with 2 different engine shops and both had seen it before and told me what I needed without hogging it out. Both said the ending result turned out very well but I have read it is easy to harm the power by port and polishing too much. Im on my phone and don't think I can upload pics so ill try tomorrow. Thank you for the response as well. I didn't know that cometic would just make custom gaskets like that. Ill be contacting them tomorrow!

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  • grayracer513

Posted March 14, 2013 - 07:10 AM

#4

If you are concerned about piston to head & valve clearance, "clay" the engine. To start, bolt down the cylinder on a used base gasket and measure the distance between the top of the piston at TDC and the top of the cylinder ("deck clearance"). There should be around .005 - .010" at least. Then put a thin layer of modeling clay onto the parts of the piston likely to make contact with anything, smear a light coat of oil on the valves and head to keep the clay from sticking, bolt the head on with a used gasket, assemble the cams in time, and rotate the engine through a few times.

Remove the head, identify the areas where the clay was compressed the most. Cut across those areas and remove the clay from one side so as to be able to measure the thickness of the clay. That will be your clearance.

  • yammyz426

Posted March 14, 2013 - 08:01 AM

#5

Gray, how much clearance would be ideal or "safe"? Iknow that since it is cut down so much it will slightly increase the compression, which I don't want too much because of possibly burning holes and having to run race gas. Not sure if that would be a result but it doesn't hurt to ask an opinion

  • grayracer513

Posted March 14, 2013 - 08:29 AM

#6

The head should clear the piston by at least .035". Valves are safe at about .020".





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