what can go wrong with an engine rebuild?

Wrong parts, inaccurate measurements, improper alignment and installation of parts - or leaving some out, improper tightening, inadequate cleaning, poor inspection of all of the components. If you really don't give a shit about the outcome, go for it. Otherwise, you are looking for problems.

What is the reason for a rebuild? Do you have all the tools and equipment required to do the job? Do you have the abilities to use those tools? IE: read mics, bore gauges and such? Who will be doing the machine work (cylinder boring, crank turning, rod resizing, align hone, head surfacing, valve seats and valves)

Will the end result cost more than a factory replacement engine, which is very likely if you do the rebuild properly?

Current price for a 3.4 GM - $1,900.00 Accurate - $1,500.00

As for what can go wrong - all the above. Plus you might have other issues that you haven't even seen till you open the engine up.

Putting things in backwards or the wrong way and using the wrong parts.

I rebuilt the 352 on my F-100 way back. Took the block to a speed shop and they gave it a bath, miked the bores and sold me the correct oversized rings. Also had them mike the crank and bought the bearings they recommended, also a couple thousandths oversize. They also installed the cam bearings. Total cost for the bath, miking and cam bearing install, and parts was less about 2 bills, but this was in 1975. I remember the cam was 30 bucks. I checked the crankshaft bearing with Plastiguage, for the hell of it. When I put it back together it spun the cam bearings and knocked pieces of the cam lobes off. I had put in a new cast iron timing gear, replacing the old fiber gear. But I also reinstalled the spacer, whereas the new gear had the spacer as part of the casting. This allowed the cam lobs to be hit by the crank throws. I had tossed the timing gear, and the trashmen had picked up the garbage. So I had to pull it apart and put it together twice. The shop apologized for not warning me about the new timing gear, and gave me another cam gratis. But I paid for another block bath in install of new cam bearings. Wasn't much. But it was a big time loss. You'll need a cylinder hone and ring groove cleaner, and maybe a ridge reamer. I needed a ridge reamer on mine. I farmed the heads to a head shop. It ran perfect, but was burning about a quart of oil every two gas fills because the head shop had screwed up the valve stem seals. Only burned oil under high vacuum, which is common in city driving. I made a 3000 mile round trip to Yellowstone and only used 1/2 quart. I decided to live with it. Total cost was near Though I don't regret doing it, I wouldn't do it again. You can get a brand new 3.4 for less than 2g's. I wouldn't trust a rebuilt. Had a 350 that was rebuilt by a major rebuilder, and shortly after I had to do the heads, the bottom end failed.

All kinds of stuff can go wrong! You name it... errors caused by machinists who don't know the specifics of a particular head (some heads, for example you want to skim, but others you definitely don't). Errors caused by machinists not paying attention and taking off a little too much or too little metal. Errors in assembly. Errors caused by bad replacement parts, or slightly different replacement parts. Errors caused by trying to reuse parts that should have been replaced.

Do not let this scare you, though. Do the rebuild. It might be perfect, it might be horribly wrong, but either way it is thousands of dollars worth of education about engines for $800.

--scott

Are you really sure you want to rely on the advice of these spuriously skilled, albeit highly opinionated knuckleheads? To help you decide, take a gander at the replies to this thread commencing on Oct 6: