I have a 1 piece rear main seal block and I bought a 1 piece oil pan gasket ( Fel-pro 1886) that I thought would work. However, when I went to install it tonight the oil pan wouldn't fit down on the timing cover section. I thought something else was interfering with the pan, but I doubled checked my clearances with the pickup and it was fine. The gasket seems to be too thick? I belive the front and rear thicknesses on the old style is 1/4" and the newer ones are 3/8" (someone please correct me if I'm wrong). So I measure the rear portion and it checked out 3/8" thick and then I measured the front part 5/8" thick. I don't believe this right. Aren't the gasket's supposed to be 3/8" thick on both ends? Thanks.

The "thick" and "thin" front seals are for the pans on 2 piece RMS blocks. The 1886 is supposed to be the gasket for all 1 piece RMS pans.

Thomas, Fel-pro makes two different one piece gaskets for the small chevy. One with a thick front seal and one with a thin front seal. The thick front seal is commonly used with the aftermarket front covers. It sounds like you got the thick and need the thin. I don't remember the part numbers, but if you check the Fel-pro catalog I'm sure it would clarify it for you.

Well, then something isn't right. Possibly the oil pan? Its just not fitting over the seal. The oil pan is supposedly for a 1 rms, could it actually be for a 2 rms? I mean would any other dimensions be different except for the seal depths? It seems to fit fine (another great ebay purchase). I started to think it might be for a 2 rms after awhile.

What side is the dipstick on?

Dipstick is on the passenger side.

Its either the pan or the gasket that isn't right.

Doing a little more research and I found out that Fel-pro does have 2 different part numbers for the 1pc rms blocks. #1886 (which I have) and #OS34500R.

For the 1886 description: (taken right from their site) "1986-97 w/ 1-piece rear main bearing seal, GM Bowtie short deck block, Non-cnc bow tie block w/2 piece seal adapter. Thick front seal, R.H side dipstick."

The OS34500R seems to be more for stock replacement, but it is a 1 piece rubber gasket, I can't find much on a description.

So I can't rule out that the gasket is wrong. I'm going to try to get the OS34500R gasket and see if that works. If it works great, if not, I'm out $30, but I know the pan is wrong. Process of elimination...

OS34500R is a kit that comes with a couple of other things. The actual pan gasket itself is probably the same, but you never know.