Dauntless trouble update

yeah, .017 is way too much clearance. I would think the clearance would be greater on the thrust axis than where you're measuring unless I'm seeing the picture wrong. I'd be interested to know how much of a ridge is at the top of the cylinders. May have been bored too much initially.

 

I had a SBC 350 that had a similar issue. When I tore it apart I found that whoever rebuilt it before I got it had put the wrong rods on the pistons. ie: #1 rod in #2 hole. Lower part of the cylinders were almost all over .030 out and the top was fine.

 

Wow. It's hard sometimes to figure out what happened. The only way to be sure is to remove the pistons, and measure them against the bore size to see. Could be whoever bored it out ran the machine poorly and the top is the only place that is correct. I'd be curious to know the size at the bottom in both axis.

 

So, remove the crank and put it back on the stand. You NEED to remove the pistons and check the bore. Your rings cant seat with that much of a gap. Actually with that much gap the piston may gouge into the side of the cylinder wall quickly making your block useless. Assembling the engine without fixing this makes no sense.

I am guessing you have a over bored block caused by someone screwing up. Dissemble the engine and check the bore you may need to order larger pistons. I don't know the max bore but just from looking at service manuals .30 seems close. You may be able to re-sleeve this engine as another option. Some of the experts on here can tell you how far you can go with the bore.

 

3.790 is .040 overbore not .030 overbore, 3.800 would be a .050 overbore, plenty of room for a .017 feeler gauge. A.030 overbore cylinder would indicate a 3.780 bore plus maybe .002" for clearance giving you a final size of 3.782. This engine should have had .040 or .050 over pistons in it.

 

.120 over? wow. I'm at .060 over and that was the largest piston I could find. At least that I could find advertised for the 225. Thought about using a different piston if the block would've had to go much further.

I've seen some pretty sloppy clearances that would run fine. You never can tell. I remember reading an old TSB from the 50s regarding the then new SBC. There was a problem with clearances and Chevy's recommendation was to allow ??? clearance. Don't remember the exact figure but it was a large number comparatively speaking.

 

I think I checked the pin height and I was looking at boring .009 over something and using a 231 piston. This was only 11 years ago so the specific sizes I don't remember but it was an option IIRC. It may have been .069 over and using a .010 over231 piston. Just don't remember and don't have the sizes in front of me.

If wall thickness isn't compromised, then you can find something that'll work.

 

That is a mess Patrick and why I haven't bought a rebuilt engine for better than 25 years. Even if they do replace it, you are usually out a couple days work.

I purchased a rebuilt Dodge 230 for my 53 1T and it maybe went 1500 miles (very poor valve job) and the oil pump o-ring was not installed in the block groove-just pinched under the pump cover. It blew out about 400 miles from home (caught it quick so no bearing damage) with less than 500 miles on it. Just pure sloppy work. At least when you put them together yourself, you know who to blame when something is amiss.

AFAIK, all sbc rods are the same for any given motor and can be installed on any journal-assuming they are all sized the same. Yes, it is best to mark them and reinstall in the bore the came in, but that should not have caused any cylinder damage if it was otherwise correctly installed. Where you could get into problems would be having a piston facing the wrong direction so the valve reliefs were no longer matching the valve positions-bent/broken valves and/or pistons, which could indeed have happened swapping #1 & #2 if the pistons were correctly installed on the marked rods.