15 replies to this topic

[Flaming Skull 57]

Hi All

 

I am thinking of having the head Port and Polished, with the valves reseated/refaced, and also shaved 30 thou.

Is 30 thou too much. Will the valves hit the crown of the piston.

How much can be shaved off the head without the valves hitting the piston or blowing the arse out of the engine?

 

Cheers

John

[Bruiser]

If it’s not been shaved before, .030” isn’t much.
Would pay to be sure about what compression you end up with, though
The mob who does the work can advise on this, and check the cc of the chambers for you
to match the comp to the cam you are using, you don’t want too much or it will
ping it’s head off
I don’t think the inlet valve can catch up with the piston on it’s way down,
Or the piston can catch up with the exhaust valve on it’s way up.
Someone please tell us if I am wrong

[grumpy xu1]

You'd be better off doing the work to a small chamber head like 161 or something.

[yel327]

173 head (high comp 173) is the same chamber as a high comp 161.

[Flaming Skull 57]

It's a 173 High Comp engine. Sounds like 30 thou isn't too extreme.  I'm happy with 30 thou.

Out of interest how far can you shave the head without damage?

[grumpy xu1]

I haven't had a 173 since i was 18 or so. So I've just learnt something. Are the cd 173 in the lj high comp or low comp then Bryon ?

30 thou, is only .75 of a mm. Or 3/4 of a mm, so stuff all, with a small cam.

[S pack]

I haven't had a 173 since i was 18 or so. So I've just learnt something. Are the cd 173 in the lj high comp or low comp then Bryon ?

30 thou, is only .75 of a mm. Or 3/4 of a mm, so stuff all, with a small cam.

Gary, CD prefix is high comp, CE prefix is low comp.
 

[S pack]

173 and 138 high and low comp engines use the same cyl heads. 202 high and low compression engines use the same cyl head as low comp 138 and 173.

[yel327]

As Dave says, there was only ever really two red heads with minor tweaks along the way (such as rocker arm change and other such things):

 

The big engine head - as used on 179, 186 and 202. To create the low comp 186 and 202 they dished the pistons (larger dishes on 202).

 

The small engine head - as used on 130, 138, 149, 161 and 173. To create the low comp small engine (138 to 173) they used the big engine head, plus dished pistons on 173 only.

 

Most of you all know that in general the rocker gear changed on the 161-173 and 186-202 transition although from memory the 130 and 138 spanned that change.

 

XU1 aside of course as those heads were not standard production red heads. 

[Bruiser]

It's a 173 High Comp engine. Sounds like 30 thou isn't too extreme.  I'm happy with 30 thou.
Out of interest how far can you shave the head without damage?

I think most would say once the thumbprints on the head face are gone, there’s not much further you can safely go

[grumpy xu1]

Maybe someone can put up a photo of the thumb prints, so the original poster can see what is meant.

[grumpy xu1]

Thanks Dave and Byron, apart from xu1, I've mainly just played with V8's apart from just a rebuild on the 6's, since my younger days.

[claysummers]

Basically distinguished as closed or small chamber and open or large chamber, and Byron didn't mention that the closed chamber heads were also used on 186 and 202 xu1 motors with the big cams. I know most people know this but obviously not all.

Here is a closed chamber head showing thumb print centre.

Sent from my SM-G781B using Tapatalk

[yel327]

Yes I did Clay! Last sentence. You’re right I didn’t mention the chamber though.

[Bruiser]

 IMG_0662.jpeg   94.43K   5 downloads

I always thought one of these was the thumbprint
Not actually certain which one

[I'm a Red Motor fiend]

I've had at least .100" taken off my head. No thumbprint left....

Attached Files

•  Resized_20230812_145427.jpeg   208.37K   3 downloads