Td5 Head Work

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Originally Posted by awabbit6

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

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

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Originally Posted by awabbit6

How was it butchered and how did it fail?

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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.

Thanks Dave. I appreciate your responses.

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Originally Posted by Blknight.aus

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

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Superalloys

Gas turbine engine blades and nozzle guide vanes are exposed to very demanding conditions. Some of the most advanced materials and processes have been developed for such applications, which are now a major outlet for vacuum cast nickel-base superalloys.
Taken from Investment Casting - History, Materials and The Future

And this indicates that aluminium is a minor component of the alloys used in modern gas turbines.

https://www.aulro.com/afvb/images/im...010/03/901.jpg

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Originally Posted by Blknight.aus

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.

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OK. That one was destined to fail.

How about a failure of a head that had simply had 0.010" or more machined off the face?

While I am firmly in the "do not machine the td5 head without having its face hardness checked and rehardened as required" camp.

from my rough guestitistices based on only accounts on the forum, cases where I have been able to establish from the vehicle owner or the mechanic that has done the reassembley work and the few jobs where I've seen the reports from the machinist.

heads that get 4-5 thou off of them to get it back to within tolerance and to redo the surface finish about 3/4s maybe more make it. It's worth noting though that most of these ones are also done by places and people that are "oldschool" type mechanics and machine shops. Most times these heads had had a harness check done on them and pass the hardness testing
(I know of about 8 or 9 heads in this group)

heads that go 10 thou + have about a 50/50 success rate with the rest doing the "shoulda listened, and paid for the hardening tests and rehardening" thing. However thats not necessarily conclusive as

1. I dont have a split on how many of these heads were hardness tested post machining.
2. a fair portion of the heads got done "backyard" style and further failure could have been a result of some other missed cause (the thermostat)
3. some had evidence of poor assembly work (no costing for new head bolts on the paperwork)

(I know of say 25 or so heads in this group and includes the previously mentioned butchered head)

If you want to count 3rd party reports on machining the head then shaving about 10 thou goes up to around the 70% mark a net search on UK rover forums as well as AULRO should back this up.

OR why not run a poll?

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!!! :o

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 ...

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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!!! :o

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 ...

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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