Soft in the head??
Soft in the head??
(OP)
I keep hearing people with aluminium heads claiming that their heads have gone soft after overheating and gasket failure. Does this phenomenon really occur and if so what temperature causes it and what problems does it cause (I imagine valve seat movement could be an issue).
How can you test if a head has gone soft and if it has is it then scrap....??
Thanks in advance guys....
How can you test if a head has gone soft and if it has is it then scrap....??
Thanks in advance guys....





RE: Soft in the head??
------------------------------
seat inserts will move around
headgasket "imprints" much too far into alum surface
also many times the "imprint" depth is uneven
as hardness varies
dull looking finish when resurfacing/milling heads
valve guides move around , loss of valve seal
the exact temperature ?? there are more qualified here in this Forum to answer that question than i am .
Larry Meaux (maxracesoftware@yahoo.com)
Meaux Racing Heads - MaxRace Software
ET_Analyst for DragRacers
Support Israel - Genesis 12:3
RE: Soft in the head??
Many high performance engine manufacturers keep the exact alloy specifications that they use somewhat "confidential" for obvious reasons.
Remember that there are temperature gradients in all materials under thermal stress. The temperature at the surface of the head in the combustion chamber can and will vary substantially compared to the temperature of the surface at the water jacket. The same for the valve guides, especially the exhaust valve.
Without helping at all, or answering your question, I hope this helps!
Chumley
RE: Soft in the head??
The main concern for high performance engine cylinder head is the exhaust valve bridge in case for 4 valves and 5 valves engines. We would like to keep the exhaust temperature below 250 celcius if possible. Above this temperature, the Al may not be back to its normal shape. Once it deforms, it really affects other components.
As for the valve seat, once it is deformed, you will see some compression loss. So make sure you get your compression reading for every cylinders before you torture the engine on dyno. Later, it is a good practice to measure the compression reading using the hydraulic pump.
RE: Soft in the head??
An unexplained change in tappet clearance also indicates that the valve seat might be receding into the head.
Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Soft in the head??
I think my main point is: if you were given a head for porting or skimming, or even if you wanted a replacement stock head for your car, how would you know whether the head was "soft" or not.
So far I have gleamed that an exaggerated gasket imprint, radically moved seats and loose guides are indicators - as is the mull finish after skimming.
Is there a more fool proof way of knowing whether a used head is worth using?
If a head has gone soft, is it scrap or is there anyway to re-use?
RE: Soft in the head??
Rod
RE: Soft in the head??
Rod
RE: Soft in the head??
RE: Soft in the head??
RE: Soft in the head??
I most cases with cast iron or properly hardened aluminum cylinder heads, this may not become bothersome or cause failures (at least not right away), but with 'soft' heads it can be disastrous. Overtorquing can distort gaskets to the point of failure and, of course, break bolts/studs---even on cast iron. I bring this up as I had to remove a broken bolt just yesterday!
Rod
RE: Soft in the head??
Obviously in an ideal world we would all use new castings, however there are clearly many occasions where this will not happen (non-availablity, cost etc). What I guess I am really asking is what people look for on 2nd hand castings before they carry out head work. Clearly no one wants to spend time and money installing guides, seats, porting and skimming, only to find the head has been overheated and softened previously. How do you guys avoid this scenario?
RE: Soft in the head??
RE: Soft in the head??