Kubota Engines & Indirect Injection

   / Kubota Engines & Indirect Injection #31  
Re: Kubota Engines & Indirect Injection

VW IDI were usually not decked because the head is warped. Decking it does not unwarp it, but leaves it warped. The problem is on the other side of the head, where the camshaft now must try to run in misaligned journals.

Decking of an unwarped head could be accomplished, but no reason to, and clearances are close, set by head gasket thickness.

I am not a diesel expert....just fairly sharp on non-TDI VW diesels.

Edit: Overheating failure modes of non-tdi were warped head, and piston smear on the cylinder wall. It's nasty.
I'm not a machining expert, but, isn't the purpose of decking a head to get it flat again? That's what I have done on many motors to make sure I did not blow a head gasket again.
 
   / Kubota Engines & Indirect Injection #32  
Re: Kubota Engines & Indirect Injection

I'm not a machining expert, but, isn't the purpose of decking a head to get it flat again? That's what I have done on many motors to make sure I did not blow a head gasket again.

You can make the mating surface flat again but the head will still be warped. You can't just consider the mating surface, you also have to consider that with the overhead cam, the cam journal bores need to remain in their proper plane. When the head warps it also distorts the cam journal alignment. Sure that can be align-bored, but now you have to make spacers or get an oversized cam machined. It is no longer worth the expense.

Brian
 
   / Kubota Engines & Indirect Injection #33  
Re: Kubota Engines & Indirect Injection

You can make the mating surface flat again but the head will still be warped. You can't just consider the mating surface, you also have to consider that with the overhead cam, the cam journal bores need to remain in their proper plane. When the head warps it also distorts the cam journal alignment. Sure that can be align-bored, but now you have to make spacers or get an oversized cam machined. It is no longer worth the expense.

Brian

+1 Agree.

Some remanufacturers claim to be able to heat the head and make it flat again, but only if it is not cracked.
 
   / Kubota Engines & Indirect Injection #34  
Re: Kubota Engines & Indirect Injection

I do not know for sure, but believe that cost is more expensive for IDI than DI. In a DI engine, the combustion chamber is the circular bowl that makes up the top portion of the piston. It is as easy to cast or forge this shape as a flat top, dome top, or any other shape. An IDI pre-combustion chamber is very often a separately cast and machine piece that then has to be integrated as part of the cylinder head. These inserts were typically made out of much harder and more heat resistant metals as they would get much hotter. Think about it, the fuel would be injected in the pre-combustion chamber to initiate combustion, but these pre-combustion chambers would not have the benefit of being cooled by air moving in & out like the rest of the piston/cylinder. I remember that most machine shops would refuse to 'deck' VW diesel cylinder heads because they would not stay flat. They would not stay flat because the precombustion chamber was made out of some hard alloy, and not soft as the rest of the cast iron cylinder head.




The Duetz Air cooled engines have pistons that have a clover leaf depression cast into them to allow fuel and air to enter to be consumed during the power phase of the four cycle combustion process.

The Diesel Volvo Pentas are also the same way from what I remember.
 

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