Thread: Td5 Head Work

I would say the difference would be so absoloutely negligible in effect it would make no difference.

Imo you really should get he head skimmed anyway however, as the head gasket cuts into the surface slightly, so the new one will work better when it has a totally smooth surface to bite into.

ETA if you do get it skimmed get the absoloute minimm taken off, and I mean the absoloute minimum. It really needs to be less than about 6or7thou from memory.

Originally Posted by Psimpson7

I would say the difference would be so absoloutely negligible in effect it would make no difference.

l thought that too until did some rough calculators.
Setting the valves 0.25 mm higher in the head reduces compression ratio from 19.5 to 19.1 to 1.

Being an alloy head, I would have thought the valve seats get replaced, rather than re-cut? I thought re-cutting was in cast iron heads.
I could be wrong...

you can regrind seats in the head if you need to.

19.5:1 vs 19.1:1 with a turbo diesel that makes over 1atm of boost is next to nothing. infact you'll find that if you up your boost and fuel you can run the engine a little harder than a spec engine due to the extra air capacity of the combustion chamber when its at full "squish".

its only once you drop below about 17ish:1 that diesels start having problems.

My main concern here is that if too much is removed from the face of head the "surface hardening" will be removed ...

Which got me thinking ...

What is the process that is used to harden the face of the head? I don't know of any process that is able to tolerate the temperatures (>1500C) of combustion in a turbo diesel. (But I'm no expert)

So is the face of the head hardened or is it stress relieved?? (or neither)

And the final question, has anyone had a head/head gasket fail after having too much removed from the face of the head??

same chemical process they use on the turbine blades of he donk in the f111.

Since I just happen to have a fully accredited TAE/Boeing approved engine building facility with some mates in it nearby I was never concerned about getting too brave with Tombies Big map.

its quite impressive watching a pre and post treatment point hardness test getting conducted.

and yes I have a first hand experience of a head that was completely butchered and reassembled. It did not have a long life after reassembly.

Yeah dropping half a point in compression is good, you can now put in more boost for the same peak cylinder pressure.

Check the comp ratio on the new high performance diesels. I think BMW's 3 litre diesel (the 600Nm, 200kw one) runs around 15:1.

Originally Posted by Blknight.aus

same chemical process they use on the turbine blades of he donk in the f111.

But they are a nickel/titanium alloy not aluminium alloy...

Originally Posted by Blknight.aus

and yes I have a first hand experience of a head that was completely butchered and reassembled. It did not have a long life after reassembly.

How was it butchered and how did it fail?