Cylinder Head Metal Hardness

[Westfaling]

While I had a cylinder head in for a skim the machine shop hardness tested the head and found it to be at about 56 brinnell hardness. They stated that "Absolute minimum should still be above 80, so head is to soft and will continue to move, loose loading on bolts and head gasket".

I didn't know that the alloy "softened" over time.Can anyone shed any further light on this? Or know the original spec? I'm hoping it just means more frequent re-torquing will be required!

Nick

[DJT]

Nick,

The heads are cast with LM25 on them. My brother-in-law lives in Michigan and is an engine designer. When I showed him a spare pair of Stag heads a few years ago he noted the LM25 and told me that this alloy is still widely used in the manufacture of heads. Whether the foundries that made heads for Triumph/BL stuck rigidly to the alchemy required to produce this alloy is something we'll probably never know.

[Mark Shutt]

they're probably all like that! from what I've read in the past Triumph didn't use the best quality aluminium available..

[flying farmer]

IIRC Rover K series heads have a particular problem with the heads going soft, particularly on the exhaust manifold side of Land Rover discoveries.

I believe it is the result of the head being overheated, a particular problem on the 1.8 Disco as the engine had to work so hard to drag a vehicle that size around, and the heat soak from the red hot exhaust manifold is the problem. The head gasket fire ring tends to cut into the face of the head when it has gone soft on the K series, but from what I remember doing the head gasket on SWMBO's Rover 75, the head gasket has a very narrow fire ring.

Neil

[Ian Durrant]

One of the solutions to the softness on the K series engine was to fit a stainless steel shim to the head. Similar "Saver shims" are available for the stag, so if it it really is too soft (maybe we are all driving around OK on 56 Brinnell hardness), maybe that solution would work on your heads. Tony Hart and Gosnays engineering in Romford sell stag saver shims.

[Westfaling]

I'm not sure that a saver shim would be the complete solution as a bit of googling under "cylinder head hardness" indicates that the studs/bolts can recess themselves into the head causing loss of pressure on the head gasket. There is an outfit down under (in Australia) that says they can re-harden heads (All Head Services) but I dread to think what the cost would be. I don't have much choice but to re-use the heads but it pretty depressing if I'm facing premature gasket failures. A new pair of heads from SOCTF look like they'll cost much more than a repower package so if the heads do perform poorly that'll be the end of the Triumph motor.
Nick

[Ian Durrant]

Hi Nick,

As I understand it the heads were quenched to increase hardness. I suspect redoing that would result in some level of warpage which might be costly to put right. I doubt softness of the aluminium would affect location of the head and cause it to float around. Think about the clamp area of the gasket, it's really quite large. It's more likely a soft head may get indented by the head gasket fire ring causing the head gasket to fail. This is what I understand happens to the K series engine.

[jakesmig]

I've had K series engines in my Midget for 14 years, firstly a 1.4, then a 1.6 and ultimately a 1.8 and all showed indention to some degree when stripped for initial refurbishment. Generally I treated them all to porting, valve seat cutting, skimming and cleaning water journals which tended to be unfinished castings, extremely rough and very small in section. I drilled all these out using a 10mm drill and rounded off the edges.
I never had any trouble with overheating with the K series after that work even though the engines were well thrashed, using 8500 rpm on track days.
The 1.8 was stripped a couple of years ago, having done about 40K miles, to recut the valves and generally clean the ports & chambers, and the head face showed no sign of further indentation.
Have to say I haven't retorqued a head in years.

John

[GTJones]

Hi Nick

I would not despair to much as you will see below the Brinell for LM25-M is between 55-65 for Sand Castings & as far as i am aware the heads were sand cast.

If you did want to Heat Treat it you could do it in a domestic oven and increase the Brinell to LM25-TE

LM25-TE (Precipitation treated) - Heat for 8-12 hours at 155- 175oC and allow to cool in air


MECHANICAL PROPERTIES
Sand Cast LM25-M LM25-TE LM25-TB7 LM25-TF
Brinell Hardness Number 55-65 70-75 65-75 90-110

LM25 Alloy Detail.pdf

Gary

[Westfaling]

Gary
That sounds much more encouraging if the heads were sand cast and had no other treatment as standard. I wonder if the SOCTFL guys would know this as they're working on having the heads re-cast.
Nick

[jleyton]

Nick,

Wasn't it your machine shop that described Helicoils as rubbish ?

Cheers

Julian

[Westfaling]

Julian
yes it was! But I do think the Wurth versions are better.Although at the moment I'm using another brand. Every time I pull the motor apart and it seems to be often, I end up replacing a thread or two.
Nick