S-10 Forum banner

small journal 2.8 to large journal

542 Views 9 Replies 5 Participants Last post by  jimmykicker
I understand the early 2.8 engins like in my 85 had small journals and had a tendency to break like mine did. Later engines I think starting in 87 or 88 had large journals and this problem was corrected. I still have the block of the original 2.8 can it be converted to a large journal? I could keep my mechanical fuel pump then as 3.4 does not have a place for a mechanical pump.
1 - 3 of 10 Posts
The switch to large journal was in 1985.5. But as above if yours is small journal, it's just much cheaper and easier to add in an electric pump near the fuel tank.

The switch between external balance and internal balance was in 1987 or 1988, depending on what source you use.

Any block that doesn't have provision for a mechanical fuel pump will be large journal, since that change happened after the switch to large journal.

I'm not sure what the 3.4 has to do with the conversation, but if you were thinking you could swap 3.4 internals into a 2.8 block and have a 3.4, that won't work. The crank itself will swap into a large journal block, since the crank is shared with the 3.1 (3.31" stroke). But the bore of the 3.4 is larger.
The 2.8 and 3.1 share the same bore, 3.503"
The 2.8 stroke is 2.99"
The 3.1 and 3.4 stroke is 3.31"
The bore of the 3.4 is 3.62"

So you can swap a 3.1/3.4 crank into a 2.8 block, along with 3.1 pistons and have a 3.1, if you wanted. I did this many years ago, when I built my "Franken60" that also utilized FWD aluminum heads and intake.

Timing chains are interchangeable between small and large journal cranks. Rod journal sizing didn't change until the 3500 (LX9) was introduced in 2006. The large and small journal reference is to the main journal size.
See less See more
  • Love
Reactions: 1
1986 was the first year of EFI and the block mounted fuel pump provision also went away.

I don't know for sure, but the 1985.5 block used up to the introduction of the 1986 model year should be large journal with mechanical fuel pump provisions, however, finding one of these blocks will likely be difficult, and running an electric pump is easy to do.
Ok thanks. Is there a way to identify a 1985.5 2.8? without tearing it open and measuring the journals?
Not that I'm aware of.
1 - 3 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.