I have a 26 block that is good other than a crack between a valve seat and the cylinder. Would just a seat insert fix it or would it also need a sleeve? Just trying to salvage it for possible future use.
Sleeved, pinned and seat installed. Start with pinning then install seat. Some blocks were cast with a very thin web over the port. If all that goes ok, sleeve. But before doing any thing ask yourself if you really want to lay out the cash for a block to use "someday"? There are other blocks in better shape. As these cracks are fixable and at some point maybe you will need the block, coat it with grease an store for now.
I would also suggest checking the whole block for passable other cracks.
What Mark says about checking for other cracks also is good advice.
I had a block with a crack from the exhaust valve seat to the cylinder on #1 cylinder and was going to have it fixed. After it was hot tanked, etc., another crack showed up at the same exhaust valve seat. At that point I opted for a replacement good used block and saved a good chunk of $.
Jim, I quit buying 26-7 blocks at auctions unless the head is off of them, sent to many to the junk pile.
Then again, the block in my 25' Touring is cracked the same way. Been like that for at least 20 years. No leaks & no valve seat troubles. As they say, your mileage may vary.
(It's a very late 25' block, with the 26/27 style mounting pad on the back for hog's head attachment, but undrilled.)
If your cracks look like this it can be repaired.
Unfortunately the people who attempted this repair thought that bigger seats would beat the crack.
It just made the crack worse by installing bigger seats. We sleeved this and installed seats with the crack repair that stopped this from opening again.
I would strongly suggest you check block carefully as there may be other cracks.
I think you add a sleeve to that cylinder.
I have one of those cracks from the exhaust seat to outside, it's been like that for many years and miles.
Some people make a drama of those cracks, Throwing away otherwise perfectly good engines.. but i've never actually found a problem with them as long as the valve seat doesn't fall out.
You can keep the seat in place if it is a couple of though shorter than the hole you drive it in and put a few center punch marks around the outside in the deck surface.
Someone will tell me that's a terrible thing to do because they've owned a workshop for umpteen years and blah blah blah but i don't care. Do i own a shop? No i don't. i do what works for me.