4 replies to this topic

[nikollou]

Hello people,

 

I have a few questions about my cyl head and I was wondering if people could help me.

 

 

1) is my cylinder head unleaded or not?

 

Unfortunately I haven't figured it based on the casting number, it's a 12G940 but next to the thermostat it says 22K6 so I haven't found any info based on that. It only popped up in a dutch forum but no info there.

 

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I also read on a post here that a fair indication is whether the oil gallery plug near the thermostat housing is brass or riveted and in my case it is brass (you can see it in the photo). Does that mean it is leaded?

 

 

 

2) Is it normal for exhaust guides to be recessed in the boss?

 

I am attaching a picture for reference.

 

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This definitely doesn't look normal to me. I did check the installed height and it seems within specs.

 

 IMG_6514.jpg   50.83K   0 downloads

 

 

 

3) What is the best time to do modifications?

 

I will be taking the head to a machine shop to change out the valve guide (got the manganese bronze ones), install unleaded seats if necessary and skim the head to get the desired CR.

 

At what point is it best to modify the head? Would it make sense to punch out the current valve guides myself and work on the head (which would give me more space as well and make it easier to form the boss) and maybe once it is back from the machine shop I could do some touch up work?

 

 

 

Thanks,

Nik

[Spider]

It doesn't look like your head is an unleaded type. There's no numbers or external reference for this, though if fitted to the original cylinder block, it is indicated as part of the engine number. I have made my comment based on the photo of the exhaust valve guide and what I can see of the seat.

 

The exhaust Valve guide looks normal for one of these castings, well hidden away and chocking the port,,,,,,

 

In regards to head modifications and sequence of work, what modifications do you have in mind?

[Turbo Phil]

The exhaust guides are fine fitted like that. The only way to see if it's unleaded is to look for the exhaust seat insert, if you look down into the port throat it's usually quite obvious as it often overhangs into the throat a bit. Unless you're planning on using the stainless valves stick with iron guides they wear just as well and are less than half the price.
I've had heads with the brass rivet that weren't unleaded so don't rely on that.

Phil.

[russo]

If all else fails your local engine reconditioner will be able to tell you.

[nikollou]

Thanks everyone!

 

The only way to see if it's unleaded is to look for the exhaust seat insert, if you look down into the port throat it's usually quite obvious as it often overhangs into the throat a bit.

 

Are you saying that the factory unleaded heads used an insert? I assumed that the entire head was a different material. If that is the case, then yes my head is def leaded because there are no signs of an insert whatsoever.

 

 

In regards to head modifications and sequence of work, what modifications do you have in mind?

 

 

I have purchased David Vizard's book so I plan to follow the book in modifying the head in all its main areas (combustion chamber, short and long side radius and the port throat). I think it would make sense to remove the current guides, then work on the head using the book as reference and then send it off to have the new seats pressed in. Does that make sense? 

This would allow me to better form the boss area since the guide will not be in the way. 

 

Which does bring me to a further question:

Given I am developing a forced induction engine, Vizard mentions in the Forced Induction chapter ("Freer Breathing" section) that one should not take away too much metal from the guide boss because it is needed to conduct heat from the valve to the head. Is there a guideline as to how much I should take away? Should I make the boss at least level with the end of the bullet guide? Maybe even a photo to help me out? :)

 

Other than this, for the intake and combustion chamber areas I will follow the diagrams that are referenced in the N/A section.

 

Cheers,

Nik