dibbons
Well-Known Member
Enjoy the video:
To Resize Connecting Rods or Not?
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PRH
Well-Known Member
The only way to know for sure if a particular rod(or set of rods) will need resizing after new bolts are installed is to swap out the bolts, torque to spec, and check the sizing.
They either need it or they don’t.
They either need it or they don’t.
Yeah and it's better to do it regardless. Although, I've replaced many a rod bolt right here at home and not resized the rods. I did it like that in the Ford 400 in Gladys and she's been fine for about three years now. It wasn't a money decision, at the time there was nobody around that would do it. Machine shops around here at that time were non existent.
It's been a while since I've seen that one, I love the quote at 5:40 in about the difference between a micrometer and a C clamp! But anytime you put in a fastener that requires more torque it's going to be a pretty safe bet that it's going to distort the bore from what the stock bolts did. Like with cylinder heads in particular, with the price of aftermarket chromoly rods being what they are compared to cost of new bolts and reconditioning the stock 5140 steel pieces (and having seen the outright repeated abuse they can take in a stroker!), it makes me second guess wanting to go that route when you can upgrade for not much more...
Newbomb Turk
Well-Known Member
I only made it to the angel/devil point but in my opinion it’s not the clamping load that distorts the rod. It’s the criminal press fit of the bolts.
The first time I used the much loved and worshipped ARP wave lock bolts I was stunned by the amount of press fit that bolt had.
Being the prick I am, I called ARP and was told that’s what makes the bolts better. The extra press fit makes the rod/cap interface stronger.
I didn’t buy that so I called a couple of engineer guys I know and they didn’t buy that either.
If the bolts you are replacing have more or less press fit the rod will distort.
I sized every rod that came through the shop. It wasn’t an option.
The first time I used the much loved and worshipped ARP wave lock bolts I was stunned by the amount of press fit that bolt had.
Being the prick I am, I called ARP and was told that’s what makes the bolts better. The extra press fit makes the rod/cap interface stronger.
I didn’t buy that so I called a couple of engineer guys I know and they didn’t buy that either.
If the bolts you are replacing have more or less press fit the rod will distort.
I sized every rod that came through the shop. It wasn’t an option.
dano
Evil Handy Man
That's the conclusion I came to when my rods were all over the place for length and some were trash so new Scat I-Beams became the more cost affective route, even with the small fee of checking them.
That's the flat out best way. Make it a requirement for a build or don't do the build. You cannot warranty someone's stupidity.
Remember to, there's more than just the size and roundness of the big end ID. There's the LOCATION. If the big end ID isn't in the right place, it will affect the rod's center to center length.
Yeah, no doubt the greater factor involved.
I'd call B.S. on that too... Only with the addition of ring dowells around the bolts or cap screws or (in the case of Gene Fulton, at least) register grooves machined in the cap to rod interfaces.
dano
Evil Handy Man
This is what I found out when I finally decided to totally go through my 340, again. Some too short so junk.
Which sucks because I originally paid to have them resized and balanced with the rotating assembly. Basically I got a Friday afternoon job.
It's unfortunate, because a lot of shops don't even check length. They just get the hole round.
Scody21
Just send it
For the race engines my bother builds, having the rods spin 6K to 10k rpm for 15-20 hours of life span, the 75 dollar cost difference of a new Carrillo rod vs having them reconditioned it’s a no brainer to buy new every rebuild. Every single rod, piston, ring, pin etc has to be checked. The run out (out of round) of new valves is way more common than that of new rods…
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Plus, as to the mismatched rod lengths;
it took me the better part of a day to assemble just the pistons, rods, and crank, into my 367 to get the deck heights to a tight average; cuz
The milled decks were not level front to back, no two rods were the same length, and, it seemed to me that my reground crank, did not have the rod journals all at the same distance to the crank centers. But, kudus to the KB107s which, if there was a difference in compression heights, I couldn't measure it.
Imagine what that assembly job would have cost, at the local engine shop.
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Later, after the rear main seal had to be changed twice, I discovered that the real problem was that during the line-hone that the engine shop had highly recommended, they actually bored it crooked, one end was way to high, and it was impossible for the rear main seal not to leak.
I took the engine out and down, then took the block back to the shop, who confirmed that they botched the job, and that the decks were now out to lunch as well. So, of course, I wanted compensation. which they were willing to give. But I had to supply a different core cuz this one was fubarred.
So I asked the guy, if I bring you a stock block on my dime; you will bore it, and deck it, and line-hone it for free, right.
Hyup was the answer.
and so, I dug deeper and said; What assurance can you give me that you won't muck the second one up, same as the first? or worse?
crickets.
I said no thanks.
I'm not rich; so that hurt. I went home and adapted a rope-seal from a 383. But it ain't perfect either. that crossed up 367 still went 93 in the Eighth, so, I'm not crying about it anymore.
In my case; 8 different-length rods actually worked out for me, as the deck heights came in pretty tight. and the engine now has over 100,000 miles on her. But, it was not a bolt-together deal.
And yes, I re-marked the rods, lol.
it took me the better part of a day to assemble just the pistons, rods, and crank, into my 367 to get the deck heights to a tight average; cuz
The milled decks were not level front to back, no two rods were the same length, and, it seemed to me that my reground crank, did not have the rod journals all at the same distance to the crank centers. But, kudus to the KB107s which, if there was a difference in compression heights, I couldn't measure it.
Imagine what that assembly job would have cost, at the local engine shop.
------------------------------------------------
Later, after the rear main seal had to be changed twice, I discovered that the real problem was that during the line-hone that the engine shop had highly recommended, they actually bored it crooked, one end was way to high, and it was impossible for the rear main seal not to leak.
I took the engine out and down, then took the block back to the shop, who confirmed that they botched the job, and that the decks were now out to lunch as well. So, of course, I wanted compensation. which they were willing to give. But I had to supply a different core cuz this one was fubarred.
So I asked the guy, if I bring you a stock block on my dime; you will bore it, and deck it, and line-hone it for free, right.
Hyup was the answer.
and so, I dug deeper and said; What assurance can you give me that you won't muck the second one up, same as the first? or worse?
crickets.
I said no thanks.
I'm not rich; so that hurt. I went home and adapted a rope-seal from a 383. But it ain't perfect either. that crossed up 367 still went 93 in the Eighth, so, I'm not crying about it anymore.
In my case; 8 different-length rods actually worked out for me, as the deck heights came in pretty tight. and the engine now has over 100,000 miles on her. But, it was not a bolt-together deal.
And yes, I re-marked the rods, lol.
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harrisonm
Well-Known Member
I was told by a guy who owned one of the best machine shops in Little Rock about 35 years ago that any time you buy new CR bolts, you need to resize. I am NOT saying anything against anyone, I am just repeating what he told me. BTW, he did an AMAZING job doing the machine work on my block and crank and balancing my 340.
I tend to agree. Only reason I didn't on my 400 was because I measured before and after and there was very, very negligible difference.
I'm willing to bet that a lot worse than the precision wer'e talking about came out of the factory back in the day...
In my opinion, the factory 'precision' is a lot better than people give credit for.....
And when I hear, comments like my deck was out 0.015"......yeah right.
Two simple examples bear this out:
- Mopar main brg caps are indented to the block on V8s. A snug fit, might need a tap to insert. Half a thou too tight, doesn't fit; half a thous too loose, drops into place.
- cyl head dowels. Half a thou out, & head needs 'help' to fit over dowels.
Using the 'common sense' derivative, why would other machining operations that are less obvious than the above be less accurate?
And when I hear, comments like my deck was out 0.015"......yeah right.
Two simple examples bear this out:
- Mopar main brg caps are indented to the block on V8s. A snug fit, might need a tap to insert. Half a thou too tight, doesn't fit; half a thous too loose, drops into place.
- cyl head dowels. Half a thou out, & head needs 'help' to fit over dowels.
Using the 'common sense' derivative, why would other machining operations that are less obvious than the above be less accurate?
Newbomb Turk
Well-Known Member
I'm absolutely certain. Just look at all the other tolerances. Deck height and such.
harrisonm
Well-Known Member
But keep in mind we are talking about mass produced parts, mass assembled engines. I wonder how much time was actually spent on checking tolerances during casting, machining and assembly. I have read stories about how engines were checked and when oversized pistons or bearings were installed a special symbol was stamped. So I know there was some level of checking, but how much? As fast as the engines were being manufactured, could everything on every engine be checked?
Oh yeah. I've had a few engines over the years marked with the Maltese Cross. That means non standard size "somewhere".
Here's some Magnum rod caps getting ready for a resize last week, take note of the **** factory surface finish of the mating surface, picture 4, picture 1/3 is a light pass with the cap cutter, helps to show the irregular surface condition.
33IMP
Well-Known Member
Glad somebody brought that up. Resizing is only a good idea IF you have at least a competent machinist to do the work.
A hack can do much more harm than good.
Frankly, I prefer quality new rods with good bolts, to risking a resize job expense, plus additional good bolts.
And remember, even a great machinist can't do decent work on a garbage machine.
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