New Rod Bolts

[Captainkirk]

Just weighed my stock 340 forged rods...they weigh in at 753g.
With the pistons I had before (660g) we had a piston/rod combined weight of 1413g (not including pin and clips)
Using stock rods, I would have a combined of 1418g, a stock 340 piston and rod would weigh approx. 1472g
Using the new pistons with the Eagle SRI rods gives a combined P/R weight of 1333g, considerably lighter than any of the above combos.
Not sure if this will make a difference. I'm not wanting to have to have Mallory metal added to the crank.

 

[70aarcuda]

H Beam 6.123 2.125 .927 Bronze Bush 4340 Connecting Rods Chrysler 318 340 360

these weight in around 680 grams..

those are less expensive then rebuilding 40 year stock rods.....yeah..I was turning stock rods 6500 to 7500 for years to until one broke...after 3 broken sets..
no more.....Stock rod in street car.. a ok...

the rods listed above scat...eagle....k1....modnar are all made in china...how many foundries are making mopar rods in china?...one two three?,,,

just my opinion...as said...do what ever makes you sleep the best at night...LOL

 

[NC Engine Builder]

With a lighter piston/rod combo you shouldn't need heavy metal in your crank

 

[nm9stheham]

Just weighed my stock 340 forged rods...they weigh in at 753g.
With the pistons I had before (660g) we had a piston/rod combined weight of 1413g (not including pin and clips)
Using stock rods, I would have a combined of 1418g, a stock 340 piston and rod would weigh approx. 1472g
Using the new pistons with the Eagle SRI rods gives a combined P/R weight of 1333g, considerably lighter than any of the above combos.
Not sure if this will make a difference. I'm not wanting to have to have Mallory metal added to the crank.

Just as an FYI on crank balance, it is not just the total rod + piston/pin/ring/lock weight etc. It is somewhat dependent on how much of the rod weight is at the little end (piston end) vs the big end. The big versus little end rod weights factor differently into the bobweight computations: the big end is part of the purely rotating weight component and the little end is is part of the purely reciprocating weight component.

Having said all of that, with the SIR or SCAT rods, the big and little end weights will both be smaller, and the bobweight used in the crank balance process will be smaller and so weight will be taken off of the crank. I quickly ran some complete bobweight numbers (with a few assumptions so these numbers are not guaranteed): For your old TRW's + stock rods, I got 2267 grams; with the new pistons and SIR or SCAT rods, I got 2068 grams. So yes, weight will be removed.

FWIW, my son and I went with the SCAT I beam rods purely based on comments. Engine is a street engine, near 400 HP, and with emphasis on a wide torque band. Paid just over $300 for a set a year ago.

IMHO, if I was changing rods and rebalancing, then I'd go with even lighter hyper pistons....unless you already have the new pistons. Gets more weight off of that crank.

 

[MOPAROFFICIAL]

A lot a good points, but watch out for this build turning expensive with others experiences steering you into spending on parts you simply do not need. If its cheaper and doent compromise the longevity or reliability.....do it...but what are you really going to do with it? Because you have a two drag racers telling you what you need.lol

 

[70aarcuda]

A lot a good points, but watch out for this build turning expensive with others experiences steering you into spending on parts you simply do not need. If its cheaper and doent compromise the longevity or reliability.....do it...but what are you really going to do with it? Because you have a two drag racers telling you what you need.lol

Not telling him what he needs ...point out that those rods are cheaper then rebuilding the stock rods...Just pointing out options...believe me...I dont buy anything I dont need....well almost..lol

just use the stock rods and rod bolts...cost nothing...

 

[MOPAROFFICIAL]

Not telling him what he needs ...point out that those rods are cheaper then rebuilding the stock rods...Just pointing out options...believe me...I dont buy anything I dont need....well almost..lol

just use the stock rods and rod bolts...cost nothing...

It's all just advice till it becomes repeated posts on the same recommendation, then It seems high pressure sale.
Though Im in agreement with the rod idea ,given the same price or close , why not, but who I'm I anyways ??...and this just the internet, We know to actually verify what gets posted, right??

 

[Captainkirk]

IMHO, if I was changing rods and rebalancing, then I'd go with even lighter hyper pistons....unless you already have the new pistons. Gets more weight off of that crank.

Pistons are a done deal. I purchased the Speed Pro L2316F's and have them in-hand.

 

[Captainkirk]

Guys, I would like nothing more than to use the same ol' original forged rods and hardware and save myself 300+ dollars! This is a street machine, will probably never see strip time unless just for kicks one or twice. More than likely not. I am simply questioning the wisdom of going through all this monkey-motion with overbore, new pistons, etc and then putting in 45 year old rod bolts. The machining of the rods, etc is collateral damage from installing new ARP bolts...one necessarily must follow the other. The though of heaving a rod through the side of an irreplaceable 340 block has me asking, "Why would you even risk it?" I really have no issues with the stock 340 rods; they are factory forged pieces, they were shot-peened at the factory, and again at the first build. I probably didn't put 2500 miles on that motor after the first build and it's been sitting, so chances are those rods are fine. It's the 45 year old bolts that have me spooked.
But if it's gonna cost 225 to recondition and new forged rods can be had for under 300, well..you see the dilemma.

 

[Captainkirk]

H Beam 6.123 2.125 .927 Bronze Bush 4340 Connecting Rods Chrysler 318 340 360

these weight in around 680 grams..

those are less expensive then rebuilding 40 year stock rods.....yeah..I was turning stock rods 6500 to 7500 for years to until one broke...after 3 broken sets..
no more.....Stock rod in street car.. a ok...

the rods listed above scat...eagle....k1....modnar are all made in china...how many foundries are making mopar rods in china?...one two three?,,,

just my opinion...as said...do what ever makes you sleep the best at night...LOL

Have you used those rods you linked?
Are they forged in America or China.
Price is almost too good to be true! Noted that the bolts are not ARP, though.

 

[fishmens67]

China

 

[nm9stheham]

Just to throw this out there FWIW:
- I ran stock American V8 rods for years in performance street cars, when 350 HP was pretty good power. Stock bolts, stock rods, just inspect and put them in. Rev to 6500 over and over.
- I raced several sets of stock Opels con rods for 1000's of miles. Rallying, so revving to 7500-8000 10's of thousands of times. Retorqued some of the factory rods bolt sets probably 8-10-12 times, maybe more. Never worried over it.
- Ditto for stock Mitsu 1.6 and 2.6 rods.
I was never pushing more than around 1 HP per CI N/A, or 1.6 HP per CI turbo'd.

So the rods are fine for what you are doing IMHO... 'specially if you already shot peened them; I missed that before. The thing about not re-torquing bolts more than 5 times? I dunno..... I never fretted over that. 5 may be a good conservative limit, but isn't it just a number pulled out of the air to use as a limit? What is it based on? Perhaps a safe limit on rod bolt reuse for a high class of drag engines or something similar? That stress is well beyond what this is.

If the $300 was not readily available, and no hard running anticipated, then I am sure I would inspect, and then use them as is, and take my chances; based on my prior experience, I would feel it is a good call.

As for the price delta: If I really fretted over protecting the block and other parts, then $300+ is really a cheap investment, and I would spend that (if I had it, which I do today) in a trice. But, then again, it would be spending $300+ to protect a $400-$500 block.... that's a a bad insurance return unless the failure probability of the stock rods is above 50%....

Like I said... FWIW. And like 70aarcuda sed: Whatever makes you sleep well at night. One reason I put the SCAT rods in the son's 340 was just to make things a bit more bulletproof for him; the $$ were spent as a precaution.... And the new rods were a better deal on the whole, especially since I did my own bobweight work and saved over 50% on the balance work that way.

 

[MOPAROFFICIAL]

Pistons are a done deal. I purchased the Speed Pro L2316F's and have them in-hand.

Have you used those rods you linked?
Are they forged in America or China.
Price is almost too good to be true! Noted that the bolts are not ARP, though.

My advice to anyone who if only is wanting to re ring a motor, recon the rods. Do what makes you feel good, this is a fun hobby, it costs money....but its all about fun.
If the rods are to be considered junk based on age....then as is the whole motor.lol JK.
Chinese rods don't scare me dependent upon who machined and checked them..but I myself would insist on arp bolts.

 

[Captainkirk]

If the rods are to be considered junk based on age....then as is the whole motor.lol JK.
.

The rods don't scare me at all. Like I said, they've been peened twice now and have had plenty of romps into the 6K range in my misspent youth. I was only concerned with the bolts due to their age. But maybe I'm making it all up in my mind...

 

[MOPAROFFICIAL]

The rods don't scare me at all. Like I said, they've been peened twice now and have had plenty of romps into the 6K range in my misspent youth. I was only concerned with the bolts due to their age. But maybe I'm making it all up in my mind...

It would be nice to know the brand, if they are sps or arp...reuse them

 

[Captainkirk]

It would be nice to know the brand, if they are sps or arp...reuse them

They are the stock Mopar forged 340 rods,,,

 

[nm9stheham]

I am not aware that there is any weakening of rod bolts with just age (assuming no rust or other corrosion), torqued in place or not. If there is, that would be good to know.....but I am doubtful.

 

[toolmanmike]

Reconditioning your rods? Put in new bolts. Once you take them out new ones should go back in. If you're just installing new bearings, use the old ones for your build.

 

[MOPAROFFICIAL]

I am not aware that there is any weakening of rod bolts with just age (assuming no rust or other corrosion), torqued in place or not. If there is, that would be good to know.....but I am doubtful.

I agree. I think the opening post sent a little confusion through the wire and had most of us thinking to start from scratch, if the bolts are of quality and have only 2000 miles of cruising around the street, reuse them.
That's why I asked the Captain if he knew the brand. I have resized the same set of rods 3 times and left the arp's I installed from the 1st round...motor is still turns 6800 frequently.

 

[Captainkirk]

OK, to blow away some of the clouds of confusion:
The rods are original Mopar 340 forged rods circa 1972
The bolts are OEM, what were in the rods when I got the car. They have never been replaced even at the last build. While I put roughly 2K on the car since last build, I have no idea how many miles were put on the engine from the time it left Mr. Norm's in 1972 until I got it in 1975. So, there are number of unknowns here, which is why I thought it would be a 'good idea' to replace the rod bolts with ARP's.
I have no issue re-using the factory forged rods, but am being told that replacing the bolts with new ARP's required reconditioning and align honing the factory rods...at a price very near buying new forged rods with fasteners installed.
Make sense?

 

[MOPAROFFICIAL]

OK, to blow away some of the clouds of confusion:
The rods are original Mopar 340 forged rods circa 1972
The bolts are OEM, what were in the rods when I got the car. They have never been replaced even at the last build. While I put roughly 2K on the car since last build, I have no idea how many miles were put on the engine from the time it left Mr. Norm's in 1972 until I got it in 1975. So, there are number of unknowns here, which is why I thought it would be a 'good idea' to replace the rod bolts with ARP's.
I have no issue re-using the factory forged rods, but am being told that replacing the bolts with new ARP's required reconditioning and align honing the factory rods...at a price very near buying new forged rods with fasteners installed.
Make sense?

10-4, It's all understood now. The choice is yours and yours alone. Have fun!

 

[furyus2]

When I build an engine, i usually have the rod bolts changed and rods resized. The old rods might have a nice round bore, and the old bolts might be good. Might not .Doing it makes me feel better. If it breaks because I didn’t spend the money, I'll be kicking myself in the ***. Changing to different rods has to include balancing the engine. Why replace rods for peace of mind, then possibly introducing bad harmonics that might cause a number of issues by not balancing the assembly? So i think you need to include new ARP bolts, and balancing to the new rods to compare fairly. Even if i bought new rods, I would still use ARP bolts. I've seen too many issues with Chinese bolts. I had a rocker arm adjuster snap off at the hex, without any torque put on it. The grain of the metal looked like sand. I replaced them with ARP. This is just my opinion.

 

[Captainkirk]

When I build an engine, i usually have the rod bolts changed and rods resized. The old rods might have a nice round bore, and the old bolts might be good. Might not .Doing it makes me feel better. If it breaks because I didn’t spend the money, I'll be kicking myself in the ***. Changing to different rods has to include balancing the engine. Why replace rods for peace of mind, then possibly introducing bad harmonics that might cause a number of issues by not balancing the assembly? So i think you need to include new ARP bolts, and balancing to the new rods to compare fairly. Even if i bought new rods, I would still use ARP bolts. I've seen too many issues with Chinese bolts. I had a rocker arm adjuster snap off at the hex, without any torque put on it. The grain of the metal looked like sand. I replaced them with ARP. This is just my opinion.

Well...just 'cuz I hate spending money twice.
When I first tore this beast down, I sent the rotating assembly to Tony for balancing. Rods were reconditioned using the old bolts. Paid for balancing. All good.
Then I found a forged crank in my other donor motor. Oops! Sent everything back to him with the forged crank. Balancing was checked again (and paid for). All good.
Now I wanna change the rod bolts. Guess what I may have to pay for again?
It's getting monotonous. But what choice do I have?

 

[Marcohotrod]

maybe Norm changed the bolts, look at the top of the bolt heads, any markings or a dimple in the center? the advice of rod bolts should only be torqued 5 times is from a company that sells bolts. the bolts can be changed and the big ends measured, may be O K. good bolts also available from Mopar and Pioneer. I prefer rods made in USA

 

[moper]

I've run the same number of factory rods as aftermarket over the years. IMO you don't need new rods. You do need new rod bolts and the rods resized. I also have the pin bushings replaced but that might not be required. You need a dial-bore gage to measure the bores properly.
The "might as wells" will add up. Any change in rods or pistons means rebalancing. So with the new pistons, it needs to be balanced. Budget and choces are up to you.