Rod Caps, balance, weight confusion. Need help
- Thread starter 93dakman!
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Ironmike
Well-Known Member
Don't know what kind of rods you're using, but if it's a Scat rotating assembly the rods are marked. At least mine are...
This is how I've been told rods are manufactured. First forged rods.
Take a hunk of metal and heat it red hot and hammer it into a shape on a big press usually between more than one set of dies. Then the rod gets machined for the thickness and small end .the big end is drilled for bolts then cut in half then bolted together and finish machined.
Do you see now why each cap must be kept with its original beam?
Powdered metal rods the cap is cracked off making them even more unique to their matching beam.
Take a hunk of metal and heat it red hot and hammer it into a shape on a big press usually between more than one set of dies. Then the rod gets machined for the thickness and small end .the big end is drilled for bolts then cut in half then bolted together and finish machined.
Do you see now why each cap must be kept with its original beam?
Powdered metal rods the cap is cracked off making them even more unique to their matching beam.
GeorgeH
Well-Known Member
This is my understanding also and my concern with the cap alignment. I know on a typical parts house recon rod they chamfer both sides so they can go in any hole and they look as though the sides have been surfaced. Not sure if the sides could be surfaced with the pistons hung so the rods don't eat each other because of a misaligned cap.
How is this going to work with a 4" arm?
The stock 360 mag pistons?
Inertia
Well-Known Member
I think you'll find the machine shop'll figure em out without machining., a buncha them will obviously be wrong when you try to mate them,, they'll have visible mismatch in the surfaces and edges,,
Mating up the cross-hatch patterns with a magnifying glass will finish the job.. then they'll mic 'em..
Mating up the cross-hatch patterns with a magnifying glass will finish the job.. then they'll mic 'em..
64 Possible Combinations
Ain't no big deal here.
It only takes time to match the Caps to the Rods.
Ain't no big deal here.
It only takes time to match the Caps to the Rods.
fishy68
Tyr Fryr's Inc.
If you do end up having to have them resized there's no way I'd use old stock rod bolts for something that your obviously going to run hard. If you have to pay to have them resized spend the extra money and put in some ARP bolts
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moper
Well-Known Member
Give the rods and pistons back to the shop. (assuming pressed pin so pistons are pressed on?) Tell them what happened, and have them match them and number them for you. You might owe them an hour of work but you need them matched for weight and roundness.
Normally rods are not stamped when done. I've had places remove the original numbers with the expectation that the builder will re-stamp once position is determined, and others who leave the sides alone and you get back whatever you had, numbered or not. I always number prior to final cleaning if there's nothing there - even on new rods.
Normally rods are not stamped when done. I've had places remove the original numbers with the expectation that the builder will re-stamp once position is determined, and others who leave the sides alone and you get back whatever you had, numbered or not. I always number prior to final cleaning if there's nothing there - even on new rods.
Well......
Thank you all for the help. I got all of the pistons/rods apart and took them to the balancer today. He said, after I told him the story, that he was sorry if he ever mislead me into thinking he was resizing or honing any of the rods. He told me that there was a good machine shop in Evansville that would be able to fix me right up as far as getting the caps back on the right rod, and once the machine shop sorted that out, all i would need to do is bring back the rods/pistons to him and he would take care of the rebalance of the bid end. He went on about weights and percentages of bob weights and quite alot of technical lingo that I didn't understand along the lines of being smoother at higher rpms if he has to take 3-4 grams off each rod to get them back to equal balance.
So I left there and went to the machine shop and spoke with Bill. He seemed like this was something they do more often than I figured they would. He said they start by eye and try to match them up, then they move to looking at the chamfer on the outsides of the inner big end hole, then use a magnifying glass to match crosshatching from the original honing. He was going to hone them afterwords (with the pistons on). On a worst case note and I have to get the rods resized or buy one or even all new rods, he told me that he has a jig that cradles the rod that will press out the wrist pin without destroying the piston.
So, I may have fouled this up but it just looks like its a minor setback in time and possibly $100-200. Much better than wasting the crank and all 8 rods.....
Im going to stamp them with numbers first thing after I get them.......
Thanks to everyone of you all. I should have this fixed in 3-4 weeks, depending on how busy the machinist and then the balancer get. Holiday season sets everybody back too.
Thank you all for the help. I got all of the pistons/rods apart and took them to the balancer today. He said, after I told him the story, that he was sorry if he ever mislead me into thinking he was resizing or honing any of the rods. He told me that there was a good machine shop in Evansville that would be able to fix me right up as far as getting the caps back on the right rod, and once the machine shop sorted that out, all i would need to do is bring back the rods/pistons to him and he would take care of the rebalance of the bid end. He went on about weights and percentages of bob weights and quite alot of technical lingo that I didn't understand along the lines of being smoother at higher rpms if he has to take 3-4 grams off each rod to get them back to equal balance.
So I left there and went to the machine shop and spoke with Bill. He seemed like this was something they do more often than I figured they would. He said they start by eye and try to match them up, then they move to looking at the chamfer on the outsides of the inner big end hole, then use a magnifying glass to match crosshatching from the original honing. He was going to hone them afterwords (with the pistons on). On a worst case note and I have to get the rods resized or buy one or even all new rods, he told me that he has a jig that cradles the rod that will press out the wrist pin without destroying the piston.
So, I may have fouled this up but it just looks like its a minor setback in time and possibly $100-200. Much better than wasting the crank and all 8 rods.....
Im going to stamp them with numbers first thing after I get them.......
Thanks to everyone of you all. I should have this fixed in 3-4 weeks, depending on how busy the machinist and then the balancer get. Holiday season sets everybody back too.
Inertia
Well-Known Member
Glad you got it sorted out,, sounds like you're talking to the right people,
moper
Well-Known Member
A couple things - if he's rebuilding the rods (new bolts and honing the big ends round again) the matching doesn't matter. He'll only need 8 caps, and 8 rods.
I would advise adding better bolts.
He should NOT be honing the big ends with the pistons mounted. Honing stone material and iron material can get washed into the piston pin bores and ring lands during the work and cleaning after. You are much better served to have the rods redone, the assembly balanced (does not require parts to be assembled beyond the caps on the rods), and then have it all washed and the pistons hung.
I would advise adding better bolts.
He should NOT be honing the big ends with the pistons mounted. Honing stone material and iron material can get washed into the piston pin bores and ring lands during the work and cleaning after. You are much better served to have the rods redone, the assembly balanced (does not require parts to be assembled beyond the caps on the rods), and then have it all washed and the pistons hung.
n.y.340 dart
Well-Known Member
a good machinest would of stamped them. take them back or do a lot of work for nothing. my 2 cents.
sst3193
Well-Known Member
Please don't stamp on those rods without them installed on the crankshaft, or something suitably solid inside them. Be a shame to egg shape them, even a little, after all the worry.
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