On Ray’s engine I'll try to go more into the depth of what goes into prepping a connecting rod for a rebuild. Now some of you may think what we're doing here to be taking it to the hilt, but the procedure you see me doing to Ray's rods, would be what I consider the norm that should be done during a rebuild. Now in this build the assembly will be balanced, and that is considered above the normal; the factory does balance the rotating mass, we'll just do it to a tighter tolerance. Everything outside the balancing, I consider to be the absolute minimum of what you need to do in a rebuild of a high mileage street engine. What I find the most in high mileage street engine connecting rods is that that the rod's "housing bore" (housing bore is the size of the rod's big end with the bolt torqued) has became somewhat egg shaped; the rod doesn't holds the bearing shell correctly, and while most of the time this isn't the end of the world, in extreme cases this could cause a turned bearing, and a engine failure. Rod bolts are an interesting deal on a 1275, as the factory chose to use nylock nuts as a rod fastener. This was an iffy choice at best; I think it's a good idea to replace rod bolts when doing a rebuild and sizing the rods. Now if you go to any of your favorite Spridget parts vendors you are going to get a quick education in replacement rod bolts. The factory replacements are ungodly expensive, so much so that it's cheaper to use the far superior ARP rod bolt set. Now over the years, a few clever folks have discovered that a ARP big block Chevy rod bolt will fit a 1275, however this is not a wise choice. Even though the cost is much less, the head of the bolt is different and the nut is too large. The only reason some vendors chose to go this route is for larger profits. I use the correct ARP A-series 1275 rod bolt kit (ARP # 206-6001). I once let a very well known race engine builder talk me into using the big block Chevy rod bolts, he even prepped them for me at my shop in front of me. Wouldn't you know it, one failed and took out the bottom end of the race engine. While many have successfully used the big block Chevy rod bolts, sorry, I’m not staking the life of a engine on making another 50 bucks profit. So it's nothing but ARP 206-6001 rod bolt for my rods…period.

Ok first step on Ray’s rods is to degrease them. I did this in the parts washer, and then air blew them dry. I then split the rods and removed the rod bolts. 1275 rod bolts are tap in, not press in, so a couple taps of the hammer and they are out of our way. The rods then go to the bead blast cabinet for a blasting. After the rods are blasted and cleaned again in the part washer, they go to the Sunnen cap grinder. To size the big end of a connecting rod, you must first make the housing bore smaller so you can hone it back out to the desired size. The Sunnen cap grinder use a stone to face the parting line of the rod top and cap to put a new face on it. Normally you take very little off the rod and the cap, a couple of thousands of an inch.

Here's a photo of a rod top in the Sunnen cap grinder. You level up the rod or cap on a mounting pad, then clamp it in place. The cap grinder has a stone that you can move upward towards the rod or cap's parting line, until it touches, then with the clamp handle you can swing the rod or cap across the rotating stone, and continue to feed the stone higher in 1/1000s of an inch increments to complete this portion of the job.

Once the cap and rod parting line are freshly refaced on the Sunnen cap grinder, next, deburr the parting line. This is done with a simple hand file, the only thing you are doing here is getting the burr off the parting line. If you ignore this you can get a false reading later in the job. After the rods have been deburred and cleaned yet again, you can now install the new ARP rod bolts. ARP suggest that you use their assembly lube on the threads, or 30wt oil, and torque the bolts three time to cycle them in. After the third torque you are ready to size the rod's big ends on the Sunnen rod hone. There are different size mandrels for different connecting rods. I own two big rod mandrels, one for MG A-series rods and one I use for MGB and Triumph rods. Sunnen CR mandrels are pretty expensive, the two I own cost well over a $1000 dollars. When you go to your local machine shop and see a dozen or more CR big end mandrels, this could easily equate to $7500 worth of mandrels. That is why I don't have any more mandrels than the ones I use to build the engines I usually rebuild; tooling can be big time expensive.

Here's how the Sunnen hone works; then I'll go into the Sunnen AG 300 rod gauge. First thing you do is get the correct mandrel for the rod you are sizing; for 1275 rods it is a CR-1750. Then you set up the AG 300 rod gauge to the desired size you want. In the case of Ray's rods, I went to the small size of the spec of the housing bore which is 1.7005". The AG-300 gauge reads in tenths of one thousandths of an inch. By sizing Ray's rods to 1.7705", with the size of his rod crank journal, this will net us a rod journal clearance of .0015" - .0017". If this was a race engine this clearance would be a bit bigger, depending on the engine, somewhere around .002" - .0025".

Here's a photo of one of Rays rods being measured on the AG-300 rod gauge. This is a $2000 tool, but one I deemed necessary to have. There is no better tool on the planet to measure connecting rod big ends. You set the tool up using a micrometer and lock it in place. Here you can see me measuring one of Ray’s rods; notice the dial indicator is zeroed out, meaning we're good to go.

Ok, now that we have the rods sized where we want them, the next move is to balance them. We start off by weighing. I was taught many yeas ago, how to balance rods by a very smart race engine builder I worked with. He sank the procedure into my head; made me do it different ways, so in the end I fully understood what I was doing. You'll notice that I take two weights, total, small end and big end. I equalize my total weight by removing material only from the small end side of the rods. What this does is match small end and total end weight at the same time; all bottom end weight will be removed from the cap of the rod. Here is a look at a matched set of factory 1275 rods (Ray's rods) that are, in fact, matched balanced by the MG factory. My job will be to get all these weights to within a single gram.

Here are the big end weights.

Here's a picture of one of Ray's rod having the big end weighed.

Ok, next move now is to actually do the balance job on the rods. Here's a photo of the Ray's after the sizing was finished.

I do a lot of prepping of stock connecting rods for SCCA racer. In SCCA production class they have an engine prep level called "limited or restricted prep". This level of prep requires that you use stock connecting rods in most engines, but you are allowed to lighten them, polish them, even convert them from press fit to floating pins. Needless to say a lot goes into those rods, and if you get all the bell and whistles you can put almost as much money into a set of stock rods as you can a set of some aftermarket rods. Racing rules are always designed with the intention of making racing cheaper, but rarely does it ever work out that way. Anyway in my SCCA race prepped stock rods, when it came doing all the polishing and then taking the rod caps to the grinder to match big end weight, it seemed like a crime to take a grinding wheel to a work of art. I developed a way to take weight off the bottom end with an end mill on the Bridgeport mill. It turned out to be a pretty easy way to do it. Now on most rods sets I use this method to remove weight from the rod cap. It looks cooler than grinding marks on the cap and that was my initial reason for doing it. It is no better way than the using the grinder, just easier and better looking. If your builder use the bench grinding to balance your rods its A-Ok. You'll see I do my small ends with the grinder.

Here's a photo of a rod cap getting milled.

Here's a look at all the big ends with their big end weight within a gram.

Here's a look at the small ends. By limiting my total weight reduction to the small end, I effectively accomplish both small end and total weight balancing together. When I first learned how to do rods my mentor wanted to get me out of his hair for a week or so. He gave me a box full of 2300 Ford rods that had been mismatched as far as caps and rods. He had me match everything back up, grind the parting lines of the rods and caps, hone the big ends, then balance them. There must have been 50-60 of those rods. During the balancing stage of this project he first had me match total, small end and big end weights. Then he taught me the trick of getting total and small end at the same time and proved to me that it was, in effect, the same method, just a time saver. Needless to say, I never did it the other way ever again. At the time of the Ford 2300 rod ordeal, I felt like my mentor was just giving me a big ole chore to do, to get rid of me, and I think he thought that too. What it did was make me own that job; I had I had to do the job, a set of rods at a time. Over time, it would have taken me much longer to learn this, so what seemed like punishment, really was a great learning tool. Notice, on the small ends, two are untouched as they both worked out to be the same. They were the lightest two (you don't always get so lucky); one was a just a single gram over, and the worse of the bunch was like 8 grams off the target. You can see the two small ends that needed grinding and how much the two rods got ground on to achieve the target weight. So, next time you have a machinist do this job for you, you know have a idea of what the job entails and where your money is going.

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E-mail Ray at ray@raysmg.com about MG interests you may share.