Going soft in the head

[MickG]

When I rebuilt my engine about 3 years ago I was a little concerned when I torqued the head that several of the head bolt washers on the exhaust side were pulling into the head. I managed to obtain the correct torque and left it at that. Just recently I noticed water dripping from under the air intake box, not a good sign. I removed the oil filler cap and found the unwanted mayonnaise forming around the cap. I drained the oil and Gordon Ramsey would be proud of the mayo that came out.
With no visible signs of any leaks I concluded it must be the head gasket. It may have been the water pump/housing but I was very careful when assembling with RTV sealant so I discounted that as the cause of the leak. I replaced the head gasket, renewed the head bolts reassembled everything fired up to running temp and left it to cool down. Still losing water and making emulsified oil big time. The only way I could think of locating the leak was to pressurise the cooling system and look internally. I purchased one of those endoscope things of ebay and checked all around the water pump, no leaks. I then checked the bores and found that I had Niagra falls inside number two cylinder. I checked the torque settings and found that the bolt adjacent to number two cylinder was not holding the pressure. I tried to re-torque the bolt but all it seems to do is pull the washers further into the head.
I concluded from this that although I can initially obtain the correct torque the softness in the head releases the pressure. I am also assuming that as this sinking washer phenomenon has only affected the exhaust side of the head that its due to the heat softening the ally casting. I think the head is now past redemption as it's been skimmed to its limit and I cannot tighten it down successfully.
I don't really want to buy a new head but I feel its the only solution. I know some of you have replaced you cylinder heads and would be grateful of any recommendations as to the best supplier. Or even a cheeper alternative.

Sorry to have rambled on and thanks for reading if you got this far.

Regards MickG

[rgh0]

Hi Mick

Yes it sure sounds like the head alloy has gone soft with age and heat. You could get it hardness tested to confirm if you wanted but its pretty clear what the issue is. It is theorectically possible to reheat treat the heads but it will be expensive as you really need to renew all the guides and seats and it may need straigtening if it bends in the process and you should insert press fit washers in the head to compensate for the sinkage of the head bolts.

Given the head has been heavily machined already then time for a new head or a good second hand one. SAS make good heads from the couple of examples I have looked at in detail but not cheap. You can buy a complete used twin cam for about the same price I think but at least you know you have a good sound starting point if you get a new head.

What is the engine number or head number for the soft head? I am trying to see if any particualr period of manufacture relates to heads going soft or whether they occur at random.

cheers
Rohan