Rod Bolts Weights During Bearings replacement

[bigsurge]

So most engine builders balance the crank when installing any new setup. When you guys install ARP rod bolts which as far as I've heard are heavier then the stock BMW rod bolts how do you sleep knowing your engine is out of balance ? Or do you think because each rod has the same bolts it cancels out ? Not trolling, just couldn't find anything on this subject.

On rods they weigh the big end and small end to make sure all rods match then they put the respective bob weights on the crank to make sure its balanced. Wouldn't introducing heavier rod bolts throw this out of balance ? Or is the general thought process that since some pistons will be top dead center some middle some down etc etc... it balances out ? All this talk about clearances and measurements but I couldn't find any information on the weights effects on the balance(weight differences in bearings and bolts)

I'm curious because I plan on doing my rod bearings and dont really want to go through the ridicolous bmw torque procedure

[DukeofAlexandria]

Cranks are balanced based on rod and piston setup.

Where have you read that ARP bolts are heavier? Not saying they aren’t, but you’ve made the statement, now where is the documentation for that vs OEM bolts? And by how much? 100ths of a gram….1000ths of a gram….it matters.

And that “ridiculous torque procedure” is 100% needed in order to ensure you’ve torqued to spec and your caps have been set properly.

Half of this reads like conjecture and the other half reads like you’re trolling. I know you say you aren’t but it’s just odd how you’ve made a lot of generalized statements.

I would suggest following SYT_Shadow builds or deansbimmer builds on specifics regarding S65 internals.

-Duke

[bigsurge]

At 27:32 they compare weights and say the aftermarket rod bolt is heavier than the stock one.

Again I'm not trolling I coudnt find either rod bolts weights online whether stock or ARP best I could find was a shipping weight of .5kg

And yes I understand the torque procedure with BMW oem rod bolts which is what I plan to use unless someone can verify that they either weigh the same or its a non issue as I would MUCH rather use ARP. Engine are balanced to the gram rods big end and small end all balanced to a gram

I mean half the literature here you guys are arguing about 1/10000" and no one thought to weigh The bearings and rod bolts oem vs BE and ARP?????

[DukeofAlexandria]

Originally Posted by bigsurge

https://www.youtube.com/watch?v=qqlD3iBC8cc

At 27:32 they compare weights and say the aftermarket rod bolt is heavier than the stock one.

Again I'm not trolling I coudnt find either rod bolts weights online whether stock or ARP best I could find was a shipping weight of .5kg

And yes I understand the torque procedure with BMW oem rod bolts which is what I plan to use unless someone can verify that they either weigh the same or its a non issue as I would MUCH rather use ARP. Engine are balanced to the gram rods big end and small end all balanced to a gram

I mean half the literature here you guys are arguing about 1/10000" and no one thought to weigh The bearings and rod bolts oem vs BE and ARP?????

He put it in his hand and said “see how it weighs more?” That’s a very scientific way of measuring weight.

Now I KNOW you are trolling us lol.

-Duke

[bigsurge]

Hahaha no dude hand to heart Im not all these years I thought the arps were weight matched to the bmw rod bolts

but if these youtubers can feel a difference now Im concerned can you tag greeneggs or Bert to either verify the weights or to tell us why its a non issue lol I dont want to freaking torque each bmw bolt 3 times

Ive watched a lot of steve morris he says of oil weights and windage a gram here or there on the bobweights doesnt matter but if its 5 grams per bolt 20 grams per journal aat 8k rpm I think we got a problem

I havent been on the forum in years so i dont know how to tag people

[rantarM3]

I just weighed my BE-ARP bolts and got 26.7 grams per bolt. Now you just need someone to weigh a stock bolt for you as I don't have any laying around.

[bigsurge]

https://www.hubauer-shop.de/en/conne...247834522.html

according to this site the new oems are heavier at 28grams per bolt so when installing the arps if I put plenty of lube on the threads should just about even out...

I was hoping the balance issue would explain why supercharged guys are blowing out the mains but I guess not

[Scharbag]

I would argue that the bolt mass should not really matter that much given the changed mass in 1/5 will be offset by 4/8 and 2/6 will offset 3/7. Basically, the center of mass will not change (as long as the bolts are all the same mass).

Perhaps I am out to lunch on this but it makes sense in my mind based on simple physics. That said, engines are not always required to follow simple physics it seems…

[Green-Eggs]

I don't have any ARP-625's at the moment to compare. But here's the others.

OEM: 28.65 grams
BE-ARP: 26.61 grams (ARP-2000, bespoke custom made)
VAC: 25.54 grams (ARP-2000, modified Chevrolet bolts)

[spammysammich]

Originally Posted by bigsurge

https://www.hubauer-shop.de/en/conne...247834522.html

according to this site the new oems are heavier at 28grams per bolt so when installing the arps if I put plenty of lube on the threads should just about even out...

I was hoping the balance issue would explain why supercharged guys are blowing out the mains but I guess not

I would guess that the extra load or vibration transmitted to the long crank snout would have more to do with it than rod bolts.

[bigsurge]

thanks for the replies guys , if its 28.6 vs 26.6 were looking at 4 grams per journal at that point I would rather use oem bmw bolts or find a way to make the arp's heavier v8's aren't as naturally balanced as inline 6's

does anyone have weights on the rod bearings themselves ? if be's are heavier by two grams it could be a non issue but i doubt it, I would guess they'd be lighter due to less material

[Green-Eggs]

Originally Posted by bigsurge

thanks for the replies guys , if its 28.6 vs 26.6 were looking at 4 grams per journal at that point I would rather use oem bmw bolts or find a way to make the arp's heavier v8's aren't as naturally balanced as inline 6's

does anyone have weights on the rod bearings themselves ? if be's are heavier by two grams it could be a non issue but i doubt it, I would guess they'd be lighter due to less material

I think you're overanalyzing it, and searching for a non-existent problem. Entire sets were measured below.

BMW 088/089: 21.08-21.37 grams
BMW 702/703: 21.07-21.19 grams
BE V1 Shells: 21.11-21.46 grams
BE V2 Shells: 21.18-21.58 grams
VAC SP1512HX: 21.38-21.53 grams
ACL 1580-H STD: 21.13-21.26 grams
King CR 224SV/CP 20.96-21.44 grams

Now that we're measuring sets, here's the rod bolts:
OEM: 28.59-28.90
BE-ARP: 26.54-26.70 (ARP-2000, bespoke custom made)
VAC: 25.44-25.54 (ARP-2000, modified Chevrolet bolts)

[tdott]

Originally Posted by Green-Eggs

I think you're overanalyzing it, and searching for a non-existent problem. Entire sets were measured below.

BMW 088/089: 21.08-21.37 grams
BMW 702/703: 21.07-21.19 grams
BE V1 Shells: 21.11-21.46 grams
BE V2 Shells: 21.18-21.58 grams
VAC SP1512HX: 21.38-21.53 grams
ACL 1580-H STD: 21.13-21.26 grams
King CR 224SV/CP 20.96-21.44 grams

Now that we're measuring sets, here's the rod bolts:
OEM: 28.59-28.90
BE-ARP: 26.54-26.70 (ARP-2000, bespoke custom made)
VAC: 25.44-25.54 (ARP-2000, modified Chevrolet bolts)

Another great source of data, thank you for always sharing.

[charliev68]

I think this raises a very valid and interesting point! This is a variance on the rotating assembly. A true engine builder would take the weight difference into account and balance the whole thing accordingly!

[Redd]

While it is ideal to rebalance the entire rotating assembly, I think the small weight difference so close to the crankshaft's rotational axis will have negligible impact on the balance of the rotating assembly. That weight difference in a piston will have a much larger impact on the balance of the engine due to its distance from the rotational axis.

[tsk94]

I wouldn't worry about it, lol.
How many motors at this point have rod bearings done using aftermarket bolts -thousands, tens of thousands? No issues yet, so I don't see such a small difference in weight being problematic.

This would be the next level of what already is the rod bearing hysteria for these cars.

[charliev68]

Does anyone have the weight of ARP625+ they can share? I would like to know before I consider ordering it for my refresh build.