OST-013: Massaging a virgin ;)

[oldeskewltoy]

As far as I know.... the OEM guides are bronze... in fact you can see them for yourself!

There are 2 reasons to change guides in an "A" head... wear, or changing valves to a narrower stem. In ALL the heads I've done to this point I've had to change 2 guides.... only 2. The 4AG head has quite a remarkable bit of engineering in it, largeport and smallport


A very useful 2 panel, there is a lot of information in that view. On top is the untouched port, below is the same port after getting it to the new size.



The red lines indicate 2 things:
1) they show the flash along the port walls (horizontal lines) which has now been removed and blended,

2) they also show, along with the veritical line running parallel with the valve guides, the area of the intake port that get major attention.

Note in the lower view, the outer channels along the outer edge of the guide bosses, are fully visible. In the top view these channels are NOT visible, and the arrows are pointing at these areas. The port top/roof has been "opened" up to allow the airflow an easier path past this restriction. Finally, the port floors (top of view) has remained untouched, retaining the larger radius it had before


Also note the valve seats have been blended into the bowl walls, all the flash has been blended, and the machining mark in the right hand port near the valve seat has been blended away.