When a rod gets re-sized does it change the length?

How is it re-sized anyway??

I THINK??, I think that 1st, the little end is size honed, then the Machinist removes a bit of metal off the cap parting lines and maybe the rod too?

Then he install's new bolts and hones the big end by holding the rod by the little end to hold length right. Rod might be the bit removed off the cap and maybe off the rod shorter, but not by much!

And if you want them dead-nuts stock length blueprinted, then he will bore the little ends out and bush them undersize and then offset rehone them for blueprint length!!

Where's our Machinist Guys??

pdq67

They are measured, and if need be, any material would be taken off the unbolted portion of the cap. The big end is rehoned to the correct journal size, and measured again. If too much material needs to be removed, the rod won't be used. Then its balanced.

Yes, but the difference is miniscule

The change in length is on the order of 1/2 a thou to a thou. In length you'd barely note it when checking piston to deck height.

Usually just the cap gets cut a bit and the process of rehoning the big end bore back to proper size will cut into the actuall rod a bit.

The reference PDQ67 made to rebushing and reboring the small end on a machine like a Tobin Arp ( they were great tools ) is from the past before inexpensive blueprinted rods like Scats became so easy to get.

I recall decades ago ( ya I'm older. Todays my brithday and I'm older still ;-) I would get a pile of 40-50 350 Chev rods and use the Tobin Arp just to measure them. It was easier to find 8 matching rods in a pile than go thru the trouble of actually making them the same length.

Today you just can't touch the aftermarket rods and price. Its rarely worth reworking the stock 5.7" long GMs.

Happy birthday Tom!!!!

Happy birthday Tom!!!!

Thanks Doug! Hope you and gregh are havin fun with his latest powerplant!

merry Christmas to you as well.

Tom

they hit it pretty much on the money. it's really best to cut the cap "and" the rod,, so that the thrust flanges of the 2 halves stay square to each other. you line up the locating tang to the same direction (but the rod is inverted in the machine for cutting,, so to speak) for the cap and the rod (say for instance,, both tangs to the rear) and it will make the 2 halves line back up where the thrust flanges will be square to each other when you invert the cap over onto the rod (the parting line angles will be equal and opposite each other),, and not cocked over like if you just cut one or the other,, meaning either the cap or the rod only.

if you just cut either the cap or just the rod,, some cap cutters aren't perfectly square,, and some rods aren't cut perfectly square from the factory at the parting lines,, with them being exactly 90* to the thrust flange. so best to cut both the cap and rod sections.

if you cut .002 off each,, the cap and the rod,, the rod will be shortened by .002 after honing on the big end. as mentioned,, that can be corrected for with a tobin-arp when boring out the pin "bushings" on the small end.

if not,, then you'll have to measure each rod,, and do some math to figure out how much to cut from each rod and cap on all the other rods to "match them back up". alot of work with non bushed small end type rods,, but easier with bushed small ends.

i'd much rather one rod be .002-.003 shorter than the others than have it the other way arround. it's not enough material removal to effect balance enough to worry about though. size it up and run it!!!
andy