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Mk3 R4 Head

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Mk3 R4 Head

Posted by mike_steer at September 21. 2017

About to re new the valve guides in the R4 Cyl Head I have.  Have I read that these heads are prone to cracking around the inlet guide area when removing or installing guides.  If so is there a recommended way to go about safe removal or is it basically: oven, guide removal tool, freezer for new guides, insert, hope for the best!!!  I have replaced several sets of valve guides in the past on Tridents and R3's using the 'traditional method mentioned above.


Re: Mk3 R4 Head

Posted by David Comeau at September 21. 2017

The RH4 heads were probably cracked, from new, from the factory.

I found this around 2000, on several heads with incredibly low mileage and had never been disassembled from new.

Without proof of course, I believe the big  3/4" guide AND the 32mm ports and a ham fisted factory assembly guy busted the very thin port wall. about 50% of the heads I've inspected have one or two intakes cracked. I've never found a RH10 cracked!

Upon valve removal, clean the intake ports real good, then 3 part die penatrant test them before going any farther. The crack will go from the guide toward the intake port (not the valve seat).

good luck

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