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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.

regards

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

http://atlanticgreen.com/nhth.htm

Re: Mk3 R4 Head

Posted by alec_stevens at October 28. 2017

Previously David Comeau wrote:

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

http://atlanticgreen.com/nhth.htm

Re: Mk3 R4 Head

Posted by alec_stevens at October 28. 2017

Bye the bye ,leaky RH4 heads,  I"ve  got a" 74 850 Mk2a , and ,yes there is oil leaking mysteriously from the Head area." Yes Sir they all do that" but I was interested enough to read the Atlantic Green  link. This seemed to say that RH10 heads were superior in this respect. It also went on to say that the RH10 head had 30mm  rather than the usual 32 mm ports. As it turns out,  I have  an RH10 head , after years of not bothering to look. Can someone explain why  please.

Re: Mk3 R4 Head

Posted by john_holmes at October 29. 2017

Because MK2a's came with RH10 heads as does mine. RH4 was on 73 and 75's, RH10 on 74. Dave Comeau's site says that.

Re: Mk3 R4 Head

Posted by richard_payne at October 29. 2017

My RH4 head has had guides two or three times over the last thirty-five years and the head is as dry as a bone. Perhaps I've just been lucky ?

I've seen a lot of people troubled by third fin up oil stains who haven't sealed the inlet rocker cover properly though.

Re: Mk3 R4 Head

Posted by james_fanning at October 30. 2017

Also have RH4 heads on both my '73 Mk 1A and '76 Mk 3 without sign of leakage or cracks for their entire lives.

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