Big-End Bore size of 263 Connecting rod??

**ebbsspeed** · 07-14-2010, 12:37 PM

I have my 263 connecting rods in the machine shop to get reconditioned, and none of their reference manuals have the information they need, regarding the finished size of the big-end bore of the connecting rod. Is there any info on a Buick site somewhere that has this info, or might any of you be able to provide some documentation?

Thanks!

**ebbsspeed** · 07-16-2010, 09:51 AM

Anybody got rebuild manuals with this info? I've searched all over the internet, and found nothing regarding this particular measurement. I've found 1042 sites with crankshaft journal dimensions, 1359 sites with torque specifications, 833 with piston-to-wall clearance info, and even found one site that says the length of the 263 dipstick, from the stop on the stick to the bottom, is 12.5 inches long. But nowhere am I able to find the minimum and maximum bore size for the big end of the connecting rod.

**alleycat** · 07-16-2010, 07:42 PM

ebbsspeed, don't let anybody touch those rods untill you check a few things! Do not believe the old storys like; " well, they've been in there for 50+ years, how good do you think they are?" or "it's just a good idea to rodo them as part of the rebuild" or whatever story you've heard. It's baloney. Buick put a very good rod in all the str8s and they were very particular about them. They were actually very much better than the power levels of the engine needed. It is way easyer to make them worse than it is to make them better. And, once that metal is off, it does not go back on. I have hi-perfed a lot of rods and every time I sent them out for resizing or peening, they came back worse. I had to put them in anyhow. Did they work? Yeah. But it was'ent exactly what I had in mind. And I do my own peening now.

This is what you do: Look inside the big end, the bearing shell will have the manufacturer logo and a part number stamped on it, if there is a "shadow" imprint of the logo etc, on the rod, then the bearing crush is perfect, it can't be improved. Next: Take the rod apart, knock out the bolts with a brass drift, they are not a press fit. Clean everything up. Run the part line flats across some emery paper to knock off any high spots. Bolt back togather, snug up the nuts. Get a inside mike, dial calipers won't do it. Measure the inside of the big end side to side, back to front, about every 20 degrees, every rod. You are not looking for any particular size as much as every measurement the same. You will likely find every rod within 1/2 thou, or .0005. Possiably even less. I've measured a LOT of str8 rods and never found a bad one. Obviously, if you are getting .002-.003 out measurments, they may be candidates for resizing. Have someone else double check. Lastly, with a good dial caliper or such, measure the closest point between the big & small end. It should be within .001 on all 8 rods. Thats what I've found. If they all fall within these specs, you could spend money and get them back no better and possiably worse. It's tough to beat Buick at this job. I would leave them alone. And, if you have 1950 rods, they are gold, the best. I'd be REALLY particular. All this may seem like a lot of overkill but loosing a rod bearing or rod can cause much unhappyness. alleycat

**ebbsspeed** · 07-16-2010, 07:54 PM

alleycat, thanks for the reply. I am replacing the rod bolts with ARP bolts, and I've always understood that if the bolts are replaced, then the rods should be resized. True? I really never understood why, because the the bolts fit tight in the rod, and a portion of the thicker part of the rod bolt also goes into the cap, so the cap should center perfectly on the new bolt.

I'd be interested in the theory behind this/

By the way, they are 1950 rods, going into a 1953 motor, and all of that is going into a 1937 Special.

**BigRivy** · 07-17-2010, 01:30 AM

Yes, but when the rod was originally sized, at the time of it's manufacture, the cap was centered on the old bolts. Rolling a knurl on a bolt shank is not a super high precision process. When you pound or press an old bolt out and install a new one there is a fair chance that the new bolt center line is not exactly where the old bolt center line was, and that can cause the cap to fit different. The rod bolt is an interference fit in the rod. Meaning that the knurl on the bolt has to smash down a little to fit in the hole in the rod or the rod has to expand a little to let the bolt in. It's probably a combination of both. The knurl is never going to crush the same on each bolt, making it a one shot deal. And you can bet that whatever space age material that ARP is using is not going to crush the same as the stock bolts. Especially if it is one of their Wave Lock bolts. In an old Babbitt pounder it may not be a big deal. Most aftermarket rod bolts are put in high performance engines where a rod cap that is offset a couple thousandths will be a big deal. I've installed bolts in and re-sized a ton of rods in my years in the machine shop business and yes new bolts will often make the caps fit different. Have the machine shop torque up a rod with the old bolts and measure it on their AG 300 gauge on their rod hone and see what size it is and how far out of round it is. If it's not out of round, and it was working fine before you can bet that if they re-size the rod back to that size it will work again. They could also measure them, install the new bolts and measure them again, and if they don't go out of round, which is unlikely but could happen, run them. Stock rod bolts get a bad rap which is really a shame because in my 20 years in the machine business I have never seen an engine failure caused by a broken stock rod bolt. I've seen a few broken bolts, but they were a result of some other failure, like running it out of oil and spinning a bearing at high rpm that caused a catastrophic cascade of things coming apart in the crank case. In most cases the stock bolt will take anything the stock rod will take.

**ebbsspeed** · 07-17-2010, 05:46 PM

There is no knurling on the stock or the new ARP bolts, totally smooth, so I expect the bolt center of the new ones won't be off much at all. The ARP's aren't wave locs either. I've had one rod bolt failure way back when I was spinning a small block chevy 327 faster than I probably should have. Since that catastrophic failure way back in my young years, I've always replaced rod bolts in any engine I build, with good bolts. I imagine in most all cases it was unnecessary, just something I've done for my own peace of mind.

**saltracer** · 07-18-2010, 09:04 AM

check with the bearing manufracture on the finished opening size for their bearings..........as far as rod bolts also talk to ARP, they will recomend a size for their bolts.

I do not know anything about this size engine........but there are no direct replacment bolts for the 320's........I use a 7/16 Hemi bolt, but ream the hole to .452. That gives me a .0005 interference fit on the bolt in the rod and the cap and about a .003 press on the top of the bolt into the rod itself..................then YES have the rod resized.

Make sure the rod caps are tourqed to ARP spec before sizing (it is a hell of a lot more than stock spec)

**alleycat** · 07-19-2010, 10:07 AM

Yes, I've heard the "if you replace the rod bolts, then the rod must be resized" story as well. When I got into racing back in the 80's (sounds like a long time ago, don't it?), I was doing a set of rods for our sbc. I was kinda up in the air about the fit. The bolts went in snug-ish but diffinatly not .002-3 thou or tighter fit. I could not see how that light of fit could distort the rod end enough to require a resize. I had a buddy that worked at a place called Rocket Recearch, this place had what they called a "qualifing table". It was a granite slab about 8'' thick with a laser measuring system on it. It also had a hand held wand for inside measuring. At the time this thing was so cutting edge it was almost secret. We put a stock rod on it, measured everything. I then worked over the rod, put bolts in it, torqued it up and back over to the table, a few days later. The only difference we could find was that where the bolt went through the hole, the inside of big end where the metal is thinest, was slightly convex, to the tune of about .0002. 2 tenths of a thou is just not enough to worry about. Thermal expansion will produce more. We put the rod in and ran them for 2 or so years. I then put them into a somewhat built 327 I did for another buddy's car, and they may still be going around in there!

So, the jist of this is; it depends upon the fit. If the bolt is really tight, that is, a lot of interferance, the rod will likely need to be resized. Since the buick bolt is a drop-in in the rod, and is a smooth ground shank, and the ARP bolt has the same smooth shank, and ARP bolts are deadly accurate, the only thing you need to be concerned with here is: the bolt fit in the bolt bore. Does it drop in? Is it a light fit? Or really tight? Another thing, since you have the 1950 rod and all the rods in all the engines prior to 1950 are the good ones, they will rockwell about 26, which indicates that they are made of something like 4130, this stuff won't strech much. A light press fit is likely to not move much. I would'ent just cram the bolts in...So, I'm with BigRivy here, put one togather, check for cap align, etc, measure it to death! And, don't toss the stock bolts, they are actually not bad at all.

On a slighty different vein, how do you plan to mount the engine in the 37? Can you use the 263 side mounts? Will the pylons fit and everything & stuff fit? alleycat