Inliners International Forums General Discussion Hi Performance 7 inch conrods

I am building a 6 cylinder engine and would like to use a modern pistons to do this the rods would need to be 7 inches center to center .990 wide to suit a 2.100 crank pin Thanks in advance

What engine are you building? A 292 has a rod journal of 2.100", but has not other rod that can interchange with it, so custom is going to be your only choice for getting a rod to match the specs you are requiring.

Here are some topics from here where this was discussed. Sorry I don't know how to make a link here but I think you can copy and paste it into the search box.
rod length question for 292's, Forged pistons from LS1 in 292, Re: Piston & Rod Specs?.
As you ca see this is not a settled issue. As you did not tell us which engine from the specs I assume it is a 292.

gentlemen,
there does exist a conrod whose configuration needs only very simple machining operations to replace the stock 292 rod.
the C2C length is 7.0", the weight is 28oz, the material is SAE1145. the design and finish are both superior to the 292.
the problem is the rod is of 50's vintage and last saw very limited use in the 60's.
with prices being driven by supply and demand (a set of 6 was $150 the first time I found them but a year later the price had
"dropped" to $60 for the set), I want to finish the machining on mine, build my 292 and test their merit before possibly
increasing the demand for an item of known limited supply and unknown performance.
if they "connect" as well as they look we should all be able to find and purchase sets without "disturbing the market" and
driving the price beyond their true value. a 60% price cut is not hard to bear as it will pay for some of the machine work.
kalklein

Are you referring to the Jag rods or the GMC?

CNC Dude, Sir;
I have been off the Internet for almost a full year. At my age that puts a serious dent in my understanding of whats going on.
My comments have been aimed at finding a better rod for 292's.
I agree with Beater that a lighter, cheaper piston must be supported which means 7.0" or more rod length is mandatory. The 283 SBC is a good match as its compression height gives a longish thrust face to bridge the long and "flexible" cylinder wall.
I've got the hardware, now it's time for me to put up or shut up; "judging a book by its cover" is fraught with risk and
error but I don't have too much invested this far.
hopefully, kalklein

I think we are all in agreement that an "off the shelf" performance piston of another engine can provide some added benefits, many lower costs. But I was referring to which rods you had found to swap into the 292. I was asking if the Jag rods or the 302 GMC rods were what you are meaning you found to be potential candidates, as they have both been discussed as likely swaps for this in the past.

gentlemen,
the "rod core" to which I have been referring was once called the MF rod. some investigation on my part at that time (about 2yrs ago) ran me into six possible applications with eight forging numbers. I turned up three or four possible bearing widths and then two different big end diameters.
I currently have two examples with the same forging # but one has an underside piston oil squirter above the head of the rod bolt. now that is something I don't need in a higher winding 292 so how do I isolate these "features" in advance when making a purchase on eBay halfway across the country? with eight forging numbers and at least six "applications" I am hesitant to make any kind of recommendation for this rod in 292 use.
on paper I have a candidate but how good and how many of the "others" are as good I do not yet know.
sincerely, kalklein

Well, if they follow the same logic as Ford and others that had rods with a spit hole, I have found that the same forging # could go either way. At least with ebay, you get a picture of what your buying in advance, and can at least ask the seller to show a close up of the rod if in doubt.

yes, you are correct. but what I fear is things that are unwritten like changes in alloy, different production techniques, etc.

take for example SBC oil pumps. they have been made by GM and outside vendors both and supposedly meet the same nominal requirements. on the outside they appear virtually identical but inside they can be significantly different. if I am going to "modify" a pump it must be in a configuration that is compatible with my mods.

I would also like to know I am starting with the "best possible" piece in other respects. how many were made, to what specs, selection for "special duty" like "pink rods" for SBC HP use. if I Brinell/Rockwell test them does that prove anything?

if I sound too cautious it's my engineering background that's partially to blame, that and years of flight hardware experience in the "military/industrial complex".

doing it right the first time is usually faster and cheaper in the long run. kalklein

M/F? Does the "M" stand for Massey or Mother? When we were talking about this a few years ago I was amazed that there seems to be no list of connecting rods by specs. Almost every other engine component can be referenced by it's measurements. It would seem that a chart of rods by center to center length, big end bore and width, small end bore and width, and weight would be available in the computer age. Every rod from a 048 Cox to an ocean going freighter would fit on a single CD. Much of this information is actually becoming harder to find as stingy old Hot Rodders take their secrets to the grave. You can not race in Hell ,or if you do you can't quite win.

BotP,
as hard as these rods are to find I would vote for "M" standing for Mother. but it's Massey as in Massey/Ferguson.

I have in my possession two "old" TRW parts interchange books that I regard as priceless. they list rods, bearings, pistons, valves, retainers, rings, sleeves, and more by size, part number, or some systematic identifier. hardly anyone ever used them because you're reengineering the motor when you go that deep to find parts.

(I'm helping build an Edsel drag car that started out with a 410 MEL motor. when it gets to the strip it will be a 467 MEL motor courtesy of the 440 Mopar rods, offset ground crank, and custom Arias pistons. 4.400" x 4.000", thanks TRW)

back in the 80's I was building Chevy II 4 bangers and came across a Pontiac OHC 6 rod. it is still the best factory HP rod I've ever seen. but, try to find a set. the last six I got out of a boneyard Tempest in Shreveport, LA. the early demand for them was for SBC's; all you did was narrow the big end and go racing. they were the next best thing to Carillo's. but the high demand and the brutal use drove the price almost to Carillo's.

as far as the loss of information is concerned, I am too dumb to understand how the proliferation of demand for something does anyone any good when it's not even known if the item meets the requirements. rather than find the solution to a problem in a junkyard, which requires work, patience and understanding, too many modern Hot Rodders just turn to a vendor and order the latest "billet, bolt on" replacement.

like the man says, "Speed (custom) costs, how fast (trick) do you want to go (look)". banning competition would go a long way towards minimizing the influence of greedy, "stingy old Hot Rodders". penitently, kalklein

I'm always on the look out for a few of those Pontiac rods. I'm not making a ton of HP in the Chevy 4 I'm building but the safety factor would be nice. I don't really need them.
I've got a couple of old books that have some rod specs but don't give enough other information to nail down the application. I guess that is what makes it fun.
The Edsel sounds interesting.

BotP,
what fascinates me is the fact that Chevrolet and Ford both had big "flat head wedge" motors at the same time, the "W" 348/409 and the "MEL" 410/430/462 respectively. they appeared and disappeared at virtually the same times. what was the cause for their demise?

back on the 292 rod subject, my TRW books have a "Weatherly" number as they a part of a larger system. do you know what system this is? given same we could communicate far more "fluently" with car book types and run down the "sibling" publications. that is something I have wanted to do for decades.
kalklein

The demise for the 348/409 Chevy, it was the BBC came out (396). Much lighter engine than a 348/409, much better flowing cylinder heads.

Not sure about the Fords.

MBHD

I think Ford's problem was a focusing issue. They had too many different car divisions(Lincoln, Mercury, Ford) and too many different V8 engines at the same time(FE, MEL, Y-Block, 385 Series, SBF)and just couldn't figure out what engine they wanted to tag as being the hot rod.

Maybe I`m being dense but I don`t see any info on this miracle 292 replacement rod. Is this a jag or gmc or ? and what makes it a better piece than the stock forged unit ? Not trying to be critical, just looking for info.

The reason you haven't been able to find any info on a "miracle" rod for the 292 is because so far, there hasn't been one found. Not that one would be a true "miracle" rod, short of a custom billet rod, but one that will bridge the gap for where the stock rods falls short. The stock 292 rod is very undesirable for the elevated power levels and RPM that can be easily obtained using todays modern performance components. The Jag and GMC rods have been discussed before as being likely candidates for swapping into the 292 engine, but different issues prevent each of them from being used successfully to do this.
The aftermarket has provided solutions for the 250 engine with making available several different inexpensive race quality I-beam and H-beam rods at a cheaper cost than custom billet rods, but for the 292, there hasn't been any such aftermarket parts made for the 292, only custom $1000+ rods, making it very expensive to build a 292 for high performance use compared to a 250 engine.

sparks,
when a rod "goes" in a inline engine it usually takes out the whole block, crank, cam, etc. rod failures are catastrophic. I want the best rod I can get for the money I've got.

rod failure can be attributed to many causes but there is usually not enough clear evidence left to isolate the real cause.
the best general guess is structural distortion of the big end followed by lubrication failure and then seizing on the throw.
wimpy, poorly designed big ends probably cause more than their share of rod failures.

the stock 292 rod weighs 24oz. the "mystery" rod weighs 28oz all the additional material is on the big end, just where it's needed.

the stock 292 rod is forged of SAE1015 steel. the M rod is made of SAE1145 steel. this results in a better finish and stronger rod.

both rods have 3/8" thru bolts so the bolt pad design will be a more important factor in the fastener strength. again the nod
goes to the M rod.

the use of 283 pistons is of major importance as a balance needs to be struck between skirt length and piston weight; the 1/4" longer rod is a good compromise. forgings exist weighing less than 500gm. the stock 292 scales in at 700 to 800gm.

a friend here is town is starting a new 292. I am going to bend his arms and see if he will use my M rods in his motor. "the proof of the pudding is in the tasting". kalklein

Just one point of curiosity and thinking ahead. If you can modify this rod to work, what are you going to be using for rod bearings. Since the whole purpose is to create a better rod for performance applications, there isn't a performance or race quality bearing for the MF, and you will definately need one for any performance usage.

CNC Dude,
there is a Clevite77 bearing available that is just short of 1" in length. most of the bearings for Chevy/GMC sixes are 3/4" or less in length so the 1/4" addition should suffice to raise the load capacity of the rods.

doesn't sleeve bearing capacity increase as the square of the length? that's why grooved lower main bearing halves are frowned upon by bearing experts. (and why Chevy cross drilled cranks for decades.)
kalklein

The stock Chevy bearing is .842 wide, and still often needs to be chamfered to clear the crank radius. 1" is going to be too wide and cause problems. Are you planning on using a MF rod bearing or a Chevy rod bearing?

CNCD,
I suspect that I will be going to the Mopar dealer for my bearings.

the 0.842" bearings you mention must be the ones for the 2.10" big journal 292. I was confusing them with the 2.00" small journal 194, 215, 230, 250 sixes. didn't some of them use V-8 bearings?

it has been said that "crush" is what keeps bearings in their places. so I'm not going to worry too much about tang location except for longitudinal location in the rod when the rod is first torqued.
kalklein

All these inline 6's used V8 rod bearings, and they are all .842 in width for the I6's and V8's. The 194-250's uses the small journal V8 rod bearings(CB745), and the 292 uses the large journal V8 rod bearings(CB663). Yes, bearing crush is important in keeping the bearings in place, and the tangs keep the bearings from spinning in the housing bores, but of course you will need to use the right bearing for the correct housing bore size to obtain it also.

There has also been another thread posted recently about machining rods and bearings to fit into an engine other than what they were intended for that has many pics and details that can help you out if you have never done this before.

CNC-D,
my apologies for spreading erroneous information. the small and large journal bearings share the 0.842" length. however one book I have calls the 0.842" as HD for the sixes. and somewhere I have a book that indicates narrower V-8 bearings were used for LoPo apps.

I think I might be confusing the 151 Iron Duke rod bearings with 153 and thus 194-250 sixes. I must quit trying to remember everything and use the books I have for giving me the correct info. Mia Culpa.
kalklein

In modern times, there has always only been the one bearing width of .842 as the recognized standard for all the 6's and 8's made by the more premium top shelf brands, could have been a misprint or outdated source of info you found that indicated otherwise. Some generic brands might have offered something different if there was a different width.

Older books are neat as a reference, but often are found to be irrelevant on some issues pertinent in todays mainstream, as many companies update and change procedures with time and advances in technology requires them to, and many parts are superceded or replaced by newer designs and thinking.