340 Rebuild/Freshen up

**BigRivy** · 02-01-2010, 12:12 AM

Another thing I would suggest if you are going to try and hone the cylinders and reuse the pistons. Check the side clearance on the top ring groove. Read up on it if you are not familiar with it. Basically take one of the pistons with the rings still on it, or reinstall one in the top groove if you've already removed them and see how much clearance you have between the ring and the top land. Use feeler gauges and go around the groove checking it in several places and see how much clearance you have. Check several of the pistons. All ring manufacturers list the maximum side clearance in their instructions that come with the rings. Some repair manuals do also. If you have more than about .002 clearance you will need to replace the pistons, even if they look brand new. I have run into this several times in the last few years on vintage engines that the customer just wants to "freshen up", the bores look decent the pistons look to be in good shape but the top ring groove is shot. You will never get satisfactory service from an engine that has shot ring grooves. The wear is usually not even all around the piston and if the ring is moving all over in the groove it will never seal like it is supposed to. Your basically going to be trying to hold compression with the second ring, and that never works very long. At this point you are better off to bore the block and buy new pistons. Although there is a way to fix a shot ring groove if you can find someone that still has the tool and has the knowledge to machine the grooves properly to except a spacer. Of course you still have to find the right sized spacers too. This was a common procedure when these cars were new and a couple of the major ring manufacturers sold the tools and spacers. Replacement pistons got pretty cheap in the 70's and 80's and this procedure kinda went by the wayside. I've got a buddy in another shop that still has one of these set ups and I have had him do a couple of sets of expensive hard to get pistons and they work really well, although his supply of spacers is rapidly dwindling and he is having a tough time finding any new ones. Anyway I hope your grooves are okay but you definitely need to check this as nothing will ruin your day worse than an engine deal with a buddy that goes south because the job doesn't turn out well or live up to expectations. Good luck.

**Lennox** · 02-02-2010, 03:21 PM

Yes, you are right and thanks for the reply. Do they make .030 over bearings for the 340 Buick?

**DaveWalls** · 04-06-2010, 06:53 PM

You should give paw performance's website a good look over they still carry complete kits for this engine, and they have stellar prices, and as posted before you can get an awesome crower cam straight out of summit. I still have not found a source for the valve train parts so if you run into anything let me know. My 340 is going to a local machine shop as I am working my behind off on my chassis atm.

**exfarmer** · 04-08-2010, 09:45 AM

EGGE Machine should have oversize bearings. egge.com

**Lennox** · 06-01-2010, 09:11 PM

Thanks to all for the advice with the 340. The block cleaned up with a 0.030 overbore and the crank cleaned up with a .010 and .010. Got most of the parts for reassembly, just waiting on rings. Wow, what a different(for me) set up for the rear seal what with the metal pins and all. Also, I think my supplier supplied the wrong crank bearings as the rear main will not fit the block. Even the "tang" on the bearing shell is incorrect. All in all its coming together! What is the best scenario for the rocker shafts......dismantle and clean?? What have you all done rocker/rocker shaft wise in your rebuilds?? Thanks....Lennox.

**Lennox** · 06-27-2010, 09:28 PM

Hello to all! Very excited about the 340. Turns out the main bearings were correct from the supplier.......it was me who was wrong!! Installed the crankshaft tonight and then ran out of steam......spent the majority of the day assembling the front end and suspension. Probably have the short block done this week depending on my regular job. I'll keep you all posted!!

**Aaron65** · 06-28-2010, 05:06 AM

Congratulations! Did you get the rocker shafts cleaned and inspected? I believe a few vendors sell new shafts if they are worn...

**matt_lyons** · 07-14-2010, 08:50 PM

company called performance suspension technology website www.p-s-t.com i ordered a rebuild kit from them and it is simply amazing. good shipping time as well and lifetime guaruntee on all parts as long as the car ownership doesn't change.