Used cylinder heads, beware!!

[Chris Wilson]

I have had at least 3 people with MKIV's bring used heads to me for use in rebuilds, only for me to have to tell the owners they are scrap. What's reminded me of this is a poor sod who has bought an expensive secondhand, ported and big valve Skyline head for me to use in a rebuild, and when i checked it I found it had been overheated and had gone soft. Alloy heads, if run with low or no coolant will change their crystalline structure and go "soft" meaning valve seats can come out, and head gaskets fail to seal. Skimming them to regain head to block surface flatness, if they have warped with the heat makes no difference to the hardness of the material. There's also a 90% plus chance the cam bearings are no longer in a straight line, but banana shaped, giving cams a hard time, causing dramatic bearing wear and low oil pressure. The only true check is a Brinnel hardness tester that tests the surface hardness of the alloy. I have the required kit and only charge £10 to test a head, so if you are buying a used one stipulate it must be of OE hardness and not overheated to the point of going soft. I can also check head to block face trueness, and cam bearing saddle trueness. The Skyline guy is £2K down now with an expensive boat anchor....

[bradleyh_15]

a very expensive lesson learnt by the poor skyline owner!

[bignum]

Good to know chris.

[Swampy442]

Sound info as ever Chris

[supra dan]

can you tell me what figure the hardness should be chris?

[jagman]

I would have thought that any big power rebuild would use a new head , but those without budget available -well worth getting the used heads checked ,they also suffer with heat cycle defects as well as material changes with age

[Ark]

It always surprises me that people buy used engine parts and just expect them to be good as new, or handle 600 BHP, especially given the comparatively low cost of a new part in many cases.

 

Mind you, hearing about testing a soft head makes me think Chris is going to hit it with a hammer and listen for a Rolf Harris-esque "woing" noise!

[hiten55]

Good to know, thanks Chris

[JamieP]

I would have thought that any big power rebuild would use a new head , but those without budget available -well worth getting the used heads checked ,they also suffer with heat cycle defects as well as material changes with age

 

Worked out better for me to go new with the prices i was getting quoted here, i bought a brand new fully built head, all uprated supertech parts for something like £1600 from mvp, i was getting quoted more here for building up a used head.