We've had some interesting things happen to vclearances in my brother's 18rg heads too, but not this problem.
When a head is rebuilt, it is common to expect the clearances to become smaller by by a couple of hundreths of a mm.
This happened with the 88253 head that we had on first.
After we replaced that head with an 88270 head, the clearances went the other way, they got bigger, and have continued to get bigger since.
These changes in clearance weren't restricted to one side as you found, but were almost uniform across all valves.
every mechanic I've asked about this problem has been stumped as to why the clearances grew on the second head.
We checked the uniformity of the grinding done on the shims and found that none of them were tapered.
About all we could come up with was, as this head appeared to be almost unused (could still see original machining marks where buckets go) that the machining ridges on both the buckets and the shims had receeded.
It is interesting that you've had this trouble using springs that have caused float.
We have "Performance Springs" heavy duty springs and have not had trouble like yours.
Wear and tear info is always good to know, thanks for posting it.
Sat, 08 May 2004 13:57
