Is this a dead head, or a bargain?

[reb53]

My son picked this head up the other day.
It was removed, and replaced, during an extensive, and expensive...., engine rebuild.
The engine was a runner, and as far as I know no particular problem brought about the rebuild just a general dissatisfaction with the car and a desire to get it right at all costs.

I suspect the cracks are not unusual and probably exist on a few running, fitted, heads.
Thoughts ?

I'd be interested on thoughts also about the depressed areas under the head bolt heads.
I know this is usually indicative of a softened head but I have a feeling they're not much different from the head in my car and it has no problems.
Does anyone know what the actual hardness of a good head should be ? No point in doing any work until it's been tested.
The broken off carb flange is courtesy of the local courier but is a small problem compared with the potential others.

Ralph.

[el-saturn]

.....even if it was a freebee...... I?d not waste too much time on this head and I?d say this IS soft: the headbolt surface (not the crack) shows either completely wrong torque settings, on and off 2 mio. times OR soft. then there?s the plug cracks, probably others, nothing left for skimming, prob. crooked etc.!! I wouldn?t get too exited in this case - alpine greetings sandy

[rgh0]

Hi Ralph

The cracks from the spark plug are normally not a problem, most heads have some, but you need to pressure test it to be sure. The cracks you have at the worse end of most I have seen

The head bolt recession is on the high side and it would be desirable to fit hardened washers in the head to limit it in the future and return the bolt to the level surface. However doing this can cause misalignment in the cam bores (if you don't have it already from the bolt seat recession)

The desired hardness is above 60 Brinell minimum. My engine machinist will work on a head down to around 50 at your risk. Below 50 he will not do it. The risk is the valve seat inserts or guides will move or the head bolts loose tension and the head gaskets blow. Are the numbers written on your head the Brinell hardness? If so it is at the bottom end which I would expect from the degree of bolt recessing

cheers
Rohan

[Chancer]

Were the soft heads incorrectly heat treated, indeed was heat treatment dont at all in manufacture? Or do they soften in service?

I know all (or knew all to be precise) about hardening, tempering and annealing of carbon steels but little as regards cast aluminium, I know that rolled strip and sheet alu according to its composition can be various grades of hardness but cast?

[rgh0]

Yes exposure over long periods to temperatures about 135C ( 10,000 hours) or shorter periods at higher temperatures can return the heads to softness like the as cast condition in the <50 brinell range. So they will soften with use especially if overheated. Theorectically possible to reheat treat a head but I know of no one who has done it successfully in practice.

I have attached some details on the LM25 alloy that is used in at least the later heads after around 1969 as i have a Stromberg head with this casting mark on it, My other earlier heads dont have any alloy identification. . Somewhere I have read they used LM8 alloy but i cant find the reference now. This is similar to LM25 but slightly different alloy components and is not really used these days.

LM25.pdf

(531.09 KiB) Downloaded 1356 times

cheers
Rohan

[Chancer]

Brilliant!

Told me all I wanted to know and more