boggla500 said:
Ok I have a pontaic 455 heads 6x the machine shop says I need to reseat the valves with new guides I never heard of this but I don't know every thing and wondering how true is this or are they trying to take advantage. My machanic mentor says it bs. The bill to due this is enough to buy used bare pontaic aluminum heads soooo Iam not realy buying it. Oh and its Car Quest. any help would be great!
The valve seats are machined with reference to the guide. Typical guide repairs don't take into consideration the location nor angle the original guide had with the seat. The typical guide repair starts with the guide in what-ever shape its in and either:
1) reams it oversize for a larger stem valve
2) reams it oversize and presses a tubular guide into the hole to restore the original valve stem size.
3) runs a knurler thru the original guide to expand the material, then a reamer is passed thru to size the hole for the valve stem.
You will note that all of these processes never use anything other than the original guide hole to locate the rebuild or repair of the guide. Since the tools used are not guided in 3 dimensional space, especially with small, fast and dirty shops. So these set ups take the path of least resistance thru a worn guide, thus there is no way to assure the guide is located either in the center of the existing seat nor aligned to the seat at a 90 degree angle. This requires that the seats be re-shot to insure that they are concentric and at right angles to the guide.
Bogie