alloy cylinder head repair - possible on a diesel?

[mark_in_manchester]

Hi All
I've made a Ural-Daihatsu, and have 2 spare cylinder heads, both of which display a common problem with the 993cc Charade engine - heads crack between the valve seats. Length of crack is about 1/4" (visible - probably continues underneath both valve seat inserts), all 3 pots on both heads. Cracks presumably link combustion chamber to water jacket.

Does anyone have any idea whether a high-compression diesel engine will tolerate the alloy welding / skimming / new valve seat inserts which a repair looks likely to entail? Better still, can anyone recommend a UK firm for this kind of work? I imagine I could get the valve seats out and get the alloy welded at work, but I'm unsure as to the grade of filler rod / quality of work necessary to withstand the fairly extreme conditions this will operate under...

cheers
Mark, Manchester

[albertaphil]

Mark, I don't know anything about the Dihatsu, but I've seen many VW 1.6 diesel aluminum cylinder heads, and every one of them had cracks running between the intake and exhaust valves on most, if not all cylinders, and none of them ever leaked combustion gases into the water jacket, or water into the cylinders.

I don't know if this expertise is tranferrable, but that's how it is with VW's.

Cheers,
Phil

[mark_in_manchester]

Thanks for that encouragement Phil. I know one of the spare engines lost compression, and the other showed heavy pitting / erosion of alloy in combustion chamber and even the top of the cast-iron cylinder liner on one pot, presumably where water was being drawn in - neither of which sounds too hopeful. I have spoken to someone who belted his cracks with a punch (or should I say, who carefully peened the cracks closed) and ran OK...perhaps worth a go for the cost of the rebuild time and a head gasket.

It struck me that although the compression ratio is high in a diesel engine, diesel burns slowly and with less heat than petrol. So - peak combustion temperatures and pressures are probably lower than those in a petrol engine, where I know head welding has been used sucessfully. Again - any opinions, gents?

[smokyjoe]

Hi mark,

Does any of these engines shoe lots of soot in the water jacket? That would be a sure sign of either head gasket failure or head cracking. I have had the same experience with VW engines like albertaphil- cracking between valve seats- no worry. You could pressure test the block/head assembly, that may show water leak, but I'd think that you'd show combustion gases in water before the other. The other thought with the cylinder/head corrosion could be head gasket failure. Both should show soot and bubbling in the coolant before all heck breaks loose. Usually failure of this type is pretty dramatic with lots of steam, blown radiators, etc.

Good luck

[Stuart]

A friend of mine who runs his own car repair business used to swear by that stick adhesive for sealing cracks. Apparently the better branded stuff was developed for deep water use where the pressures an conditions are harsh. Perhaps some of the more runny, metal based, two part glues could be warmed with a heat gun and forced into these cracks? This stuff is being pressed inward by the pressures and may last a lot longer than you think. No guarantees though!
My 106 diesel car had some glue type stuff to help build up the surfaces between the pots. Didn't think it would last but it was still there last time I looked. And I didn't put it there in the first place either

[buckles]

Hi Mark, try, mkengieering.co.uk. I've seen those blokes weld alloy heads. Speak to Martin.

[chevy43]

Nissan Diesels usually have cracks between the valves and it doesn't seem to matter. I've heard the same about the invinceable Cummins B series too...

[Stuart]

I did my car head gasket Saturday and there are some tiny holes appearing at one end that I think are responsible for eventual waaters leaks there. I used a little liquid metal Araldite gues to fill these before torquing that head down. Fingers crossed it's still running