Rod Caps, balance, weight confusion. Need help

[93dakman!]

Long story short. I took my 360 magnum rods and pistons and a scat cast 408 crank to my balancer. I Started to assemble my engine and like an idiot took all of the rod caps off and placed them in a pile on the bench and started putting the bearing halves in both the rods and caps. It wasn't until i had the pistons in the block that I realized the rod caps had been machined by my balancer and each one had been ground differently. I guess I was just used to assembling a stock engine and not worrying about switching up the caps.

So now im not sure what to do.

Do I take the rods/pistons and caps back to the balancer?
Do I run it and not worry about it?
Do I get a digital gram scale and weigh them?

I figured if did the weighing my self I would couple the heaviest rod/piston with the lightest cap, then the second heaviest rod/piston with the second lightest cap, and so on until the lightest rod/piston had the heaviest cap.

This is not above my ability but definatly outside of my normal area of operation.

My set up is a balanced scat cast 4 inch crank, magnum stock rods, mopar stroker pistons.
My intended use is in a non race vehicle that will never go past 6000 rpm.

I need help figuring this out.

 

[DDodger]

you cannot switch rod caps, or for that matter, main caps, whether they are balanced or not

 

[93dakman!]

I knew the mains could not be swapped, infact they are numbered. The rod caps just got me in a pickle

 

[toolmanmike]

The rod caps aren't numbered too? They should be. tmm

 

[moturbopar]

Rods and caps are machined to go back to each other! Need to match the caps back to the correct rod. No numbers on the caps and rods?

 

[toolmanmike]

Each cap is usually stamped on the parting line for which cylinder it came from.

 

[toolmanmike]

Here's a sample.

 

[93dakman!]

[/url]IMG_20141122_201253_493 by gpz900r.93dakman, on Flickr[/IMG]

IMG_20141122_201309_760 by gpz900r.93dakman, on Flickr

IMG_20141122_201324_314 by gpz900r.93dakman, on Flickr

 

[93dakman!]

I didnt stamp them prior to taking them apart.....and my balancer didn't either.........I just simply screwed this up. I don't know what to do now.

 

[OldmanRick]

With no numbers, a trip back to the machine shop is mandatory as far as I'm concerned, especially if the've been reconditioned. My concern is more about a round hole then the weight at this point.

The caps would have been milled in the process, and not necessarily the same amount, then mated to a rod for machining a "round" hole. As alluded to earlier, the mix and match could lead to bearing failure without the right crush even if the clearance was in a decent range.

I personally would try and put it back on the shop for not numbering them, meaning this should cost you little to none to correct the problem.

Good luck!

 

[krazykuda]

Did your balancer machine the caps and rods at all?


You have to match the proper rod and cap that they were machined to. If you mix them, it can cause drag on the crank, or even make the crank so tight that it cannot turn from the mis-match.


On some rods and caps they chamfer the sides of the rod for the crank bore. If they are, sometimes you can look at the chamfer and match the chamfer on the cap to the rod from side to side. It's like doing a puzzle.


If there are no chamfers to help judge by, then you have to rely on the stamped numbers on the rod and cap from the factory.


ALWAYS KEEP THE MATING CAPS AND RODS/MAINS TOGETHER - NEVER MIX AND MATCH THEM.

 

[93dakman!]

Also, there is a good chance that when I took the caps off the rods while dissembling the engine last year that I didn't put the caps on the respective rod that they came from.

 

[GeorgeH]

not really sure even resizing them again is even a good idea, misaligned bolt holes, caps etc. I'd call the machinist and see what he says. Try to put it together and you'll probably need more crank work before its over.

 

[OldmanRick]

Also, there is a good chance that when I took the caps off the rods while dissembling the engine last year that I didn't put the caps on the respective rod that they came from.

Shouldn't matter now if the've been machined.

 

[93dakman!]

I gave him the crank, the new mopar pistons and the old rods/pistons. I just simply told him do to it what needed to be done for 6000 rpm. All 8 rod caps do indeed have machine marks on the bottoms just for balance.

 

[OldmanRick]

"F" the balance right now dakman.....you need round holes.

 

[93dakman!]

Ok, I took the caps off and pulled the new bearings out. There are (for lack of a better word), symbols from the lettering/symbols of the old bearing halves "stained" inside the caps. These rods must not have been machined.

 

[93dakman!]

I dont know if I am at blame for being an idiot and not stamping or keeping track of the rods/caps and not having the shop machine the big end bores, or if the shop is to blame for not stamping the pieces or machining the big ends.

 

[OldmanRick]

My shops always numbered the caps during recon. I not surprised they didn't mark them since they probably never took them apart. I guess this means you we're going to reuse the existing bolts also?

 

[OldmanRick]

And don't call yourself a idiot.....Even if you didn't ask the right questions, a competent shop should have taken the time to explain things to you. That's my opinion!

 

[93dakman!]

I was (and still am) under the impression that the rod bolts are not TTY and can be reused. Its no big deal to get new rod bolts now, especially if I have to send the rotating assembly back to the balancer.

Im just a little distraught now. I am assuming that crank was balanced to use what I have right now, if I take it back to him and we use ARP rod bolts that will surely throw off the balance, if he runs a hone through the big end that seems to me that it will also affect the balance.


Also, since my rods also do not have any numbering for what cylinder they came from, it shouldnt be of any concern to which cylinder I put them in during assembly should it? They were all balanced to the same weight + or - a fixed amount...

 

[OldmanRick]

The reason I asked about the rod bolts is, once the've been pressed in and out, a big end resize/cleanup is mandatory in my opinion. Since yours are still stock, that's not a issue. As far as a quick hone to the big end to make them right, it will have a miniscule difference as far as weight is concerned.

One thing that hasn't been addressed is, were the rod/main journals on the crank just polished or have they been turned undersized? I only bring this up so you can make sure you end up with the right bearing shells.

Again, round journals, round rod big ends, and the proper bearing clearance with whatever machining was done is most important.

 

[93dakman!]

Ok, so heres my plan.

Pull all 8 rods/pistons from the block and clean up all the assembly oil, etc. off of them.

Take them to the shop and have him deal with finding out which cap goes to which rod based on weight. Also have him hone them for roundness. Use the original rod bolts. I have not torqued them to spec since installing them.

My crank was brand new from scat so I did not specifically ask to have the rod or mains touched. If he did anything it was on his own accord and did not tell me. The main bearings that I was recommended to were Celevite .001 larger than stock (for more oil clearance) h series bearings.

I have not built performance v8's internally before. This is all new to me. I have rebuilt engines in the past but they were all stock, or just replacing the mains, or the rear seal or a quick freshening up. So I left the rotating assembly with the shop with the instructions to just get it ready for no more than 6000 rpms. I did not know what to ask, so I left it up to him. I felt confident in my ability to build it once the machine work was performed.

 

[OldmanRick]

That sounds like a good plan.

Sorry I forgot about the new 4" crank. :banghead:

And yes, I have no doubt of your ability. That's gonna be solid build when it's right. Big torque is always fun. :thumbrig:

 

[toolmanmike]

I would suggest a new set of ARP rod bolts, resize the rods, and mark the caps properly. It wouldn't hurt to recheck the balance either. Lesson learned. tmm