Valve stem seals

[david premo]

Well if it turns out that over sized guides have already been installed, it’s unlikely that you would be able to put in the correct size guides as the holes the guides are in are most likely has been opened too much to go back to the standard guide. This problem can be approached in a couple of ways. A machine shop could machine the top of the guides that are in the head a use standard seals for a Chevy or other domestic car with the same size valve stems. When I built Steve Allen’s 3 main R16 stroker I did that because the early heads just use O-rings as the valve seals. You would need to have early style valve spring metal shims to go against the aluminum head to protect it from spring damage. You could also use the bad seals you have and cut off the seal portion and leave the washer section that rests on the head to protect the head from the valve springs wearing down the head.
Dave

[JT68]

Dave is exactly right.

Anyone that has actually installed guides or works on cylinder heads knows you would not go with oversized guides unless the head press fit was compromised. It is 3x the work.

Also if we are splitting hairs, the OEM guides measured .5625-.5635 with a micrometer-(not 10$ calipers). The SI guides are slightly oversized at .5645 for additional press fit which is fine. We have 100's of SI guides in stock and they are excellent.

Stock sized guides won't work if there are already oversized guides in place.

A few thousandths oversize is a non-issue for the stock seals. As I recall the oversized Nissan guides were .010" over, but probably were machined for stock seals since I don't remember Nissan offering an oversized seal.

It is a fairly simple operation to machine the top of the guide for a later style seal, but does require a special piloted tool. That is probably the best answer in this case. We also have later style teflon/viton seals in stock, but there is no issue with the factory type seal if it fits properly.