Thread: Td5 Head Work

Originally Posted by awabbit6

But they are a steel alloy not aluminium alloy...

actually they are an ally type alloy, the main disc is the steel part the blades just slot in quick change style.

Originally Posted by awabbit6

How was it butchered and how did it fail?

press straightened after cooking warped it, shaved extensively and not re-hardened In the areas where it hadnt been scoured there was evidence of some of the worst machining I've ever seen on an engine component, Without exagerating I could have quite probably done a better job with a set of long hand files

It's second failure method was either melting of the head between the 2,3,+4 pots or massive head rewarping allowing the hot gasses to do the damage after the gasket failed.

it was bad enough that the cam journal and face were visible distorted.

Originally Posted by awabbit6

To test the theory of surface hardened Td5 heads, the engineer that has my head at the moment did a couple of hardness tests for me. He compared the hardness of the face to other areas of the head ... and he discovered ... that all parts of the head have the same hardness!!!

My head has not been subjected to excessive overheating so it is unlikely that it has softened ...

... So what is the reason that Td5 heads shouldn't be skimmed if it isn't to prevent removing the hardened surface??

More investigating to be done ...

When my TD5 head was machined the machine shop stated that TD5 heads were no more or less machineable than any other model Diesel Alloy head. But in all cases a component has its limits. According to them 6 to 8 thou skim (not warpage) was no problem and that taking less than 2 to 4 was not realistic in most cases to remove suface imperfections from gasket fire rings even on an undamaged head.

I am not arguing the level of hardness here and for the record, agree that flattening in a special press and heat treatment is indeed the correct way to do a technicaly correct job. But even these need to be machined regardless and will have a few thou taken off where the fire rings from the gasket sit to ensure a good surface.
IMO, in the majority of cases if the head is so warped as to require this treatment it is most likely to be cheaper to get another. (Alice doesnt have this facility available) When these become rare and collectors items, maybe this will be an option. Also IMO, a head requiring this kind of work has an associated bottom end with the same horrible effects of heat.

Ignoring hardness, it is not the alloy head which poses problems, but rather that all modern heads now have 1 or more camshafts in them. When these are subjected to too much warpage, ie from a warped head machined flat, they stress and break camshafts, often after they have damaged bearing jounals and spread the mayhem around the motor. Years ago the old pushrod motor heads could be machined until you ran out of metal around the water jackets or valve clearance became too small, because the camsgaft journals were in the block.

The other major issue with machining too much from the head is that, because the distance between the centre of the camshaft and centre of the crankshaft has now been reduced, the timing chain (or belts on other motors) being a fixed pitch, will now place the timing out.
It will be retarded and the amount will obviously vary by the amount machined. This is one reason why o/head cam race motors and boyracer types have adjustable timing gears.
TD5s have a slotted camshaft sprocket to counter this and fitment of the 3 size thickness head gaskets available. ie 1, 2, or 3 hole.

This isnt a post to justify either method of repairing your head but give a few reasons why LR have said dont machine, yet many including LR do and why some who have machined have ended up failing while others have trouble free motoring. It isnt a decision to be made by tinkerers or based around saving a few hundred dollars.

Cheers