Tips for prepping rods?

[andrew_mx83]

well its coming to the time in my build where i will be getting the rods shotpeened soon.

was just after any tips in the prepping/polishing process as ive never done it before or seen it done.


i assume you start on the belt sander to take the ridge off the outside of the beams, use finer and finer grit wet&dry by hand then hit it with the buffing wheel? is there anything to be done on the inside or is it all just the outside of the beams?


thanks in advance

[andrew_mx83]

also, at what point do they get sent out for balancing? after polishing but before peening?

[Sam_Q]

I didn't use a linisher to do mine as it would of taken too much material off. So instead I used something akin to a large electric die grinder with a stone in it to run down it. If you look closely at the second picture they still have a curved shape to the main beam. This is probably un-necessary and overdoing it a bit but I wanted to have the maximum strength at the time.





When mine where done the mistake was made that the plugs in the end fell out damaging the little end bearings. So when you make some plugs out of nylon or something for both ends make sure they slide right through and are firmly in place.

Are aftermarket rods not readily available for your engine?

[oldcorollas]

the idea of linishing/polishing, is to remove any potential crack starters.
the idea of the shot peening is to put a layer of compressive stress on the surface, to help hold any crack starters closed (or... increase the critical size a crack starter needs to be before propogation occurs...)
also, by linishing you make any crack starters run along the length, not across.. and it is the across ones that are more dangerous.

you need to be careful you are not removing too much material, and accidentally weaken the rods, especially in the big end area.
the forging flash on the bean of the rods increases their width (slightly) as well..

are you trying to lighten the rods? or trying to reduce susceptibility to fatigue failure?

polishing may be good to reduce the amount of oil sticking on there, but have you considered a oil-phobic coating instead of polishing? if so, that would determine what fnish you use prior to the coating.

re: balancing, the weights shoudl realy be checked while you are doing the linishing and grinding, so that you don't take too much material off. you need to check total and end-to-end weights.
shot peening should not remove any material, so balancing should be done before, but checked after anyway to be sure.
you can probably make up your own rig, with the availability of kitchen scales that can do 0.1g resolution, or even 1g might be ok. lots of images on the net of how to do end-to-edn measurements properly.

so basically, remove minimum material possible, unless you are trying to lighten. remove any scratches or cracks or defects running across the width. balance during and after grinding. think abotu coating to stop oil sticking, instead of mirror finish polishing.

[mick08]

Beam polishing like above can be done alone without shotpeening its up to you, its all about stress riser removeal, certain sports car manuf just do the polishing only, you must do these steps tho before they are sent out for balancing, you don't want to be removing material after their weights have all been matched, i had a 400 smallblock which are not known for high RPMs with short conrods, I beam polished the rods and the assy was properly balanced, with good heads and big cam that engine went 7500RPM all day long no probs,well no rod probs anyway.

[oldcorollas]

and if hasn't been said.. now is the time to get good rod bolts.. it is possibly more likely to have a rod failure from bolts than the rod itself...

[mick08]

and if hasn't been said.. now is the time to get good rod bolts.. it is possibly more likely to have a rod failure from bolts than the rod itself...

Yep second that notion, i have had exp with ARP they are the shit! If your bottom end needs this kind of 'Special' attention you'd better fit some ARP head studs as well, maybe stud the main caps too.

[mookschank]

If you're taking any material off, I would think end to end weight balance is important as well, not just overall weight.

Just putting it out there that taking material off the surface of a forged part will reduce the depth of compressive grain structure on the surface from the stamping process, something to consider in weighing up doing this kind of work...only applies if your rods are forged...

[oldeskewltoy]

good recommendations all...

may I add one.... lighter wrist pins



I saved over 23 grams per pin.....

[dangdang]

And also don't forget to have the big ends of the rods honed with the new bolts fitted and torqued up, as fitment of the ARP bolts can change the rod cap alignment slightly.

I didn't polish my rods, I just honestly don't see the need unless you wish to remove material to lessen weight in which case your actually weakening the rod or your prepping for big revs, in which case aftermarket would then be the go and probably work out cheaper than having someone polish (I know most here would polish themselves but) and then shot peen or cryo the surface.

All the 4age's I've ever seen with a leg out of bed have broken the bolts not the rod itself so ARP fasteners is a big must IMO.

[andrew_mx83]

thanks for the replies guys. im just trying to make them stronger, although any weight lost is a bonus (have been losing it everywhere else!)

i will investigate coating as i want to get the inside of the block done as well to help oil drain


arp bolts are definately on the table, as well as flywheel bolts and main/head studs.


sam q it has been decided that polished/peened rods are strong enough for this high rpm NA build.... they are already forged and M series rods are supposed to be pretty tough. i am using 5m rods so are a little harder to find aftermarket, i could get them made when the pistons are done but meh...



are the lighter gudgeon pins same material just smaller or something stronger? i may as well knock a set of light ones up while im playing on the lathe. mmmm titanium anyone?

[mick08]

good recommendations all...

may I add one.... lighter wrist pins



I saved over 23 grams per pin.....

Are these pins tapered? I know of the tapered pin design for V8s but haven't seen them for a four cylinder.

[andrew_mx83]

tapered pin design

please elaborate. ive heard of this before but no idea what its about?

[mick08]

please elaborate. ive heard of this before but no idea what its about?

Basically its tapered on the inside being thicker in the middle and thinner at each end, i think its pretty high end stuff when your chasing appsolute tenths, i guess they worked out where you need the extra bulk and where you can trim it a bit,its nothing new i don't know who first came up with it but the books i've read it in are from the 70's, Probly good on a race engine that gets pulled down every so often and checked for cracks.

[andrew_mx83]

hmm ok will have a think about it. realistically they would only need to be 1/2 as thick going through the piston as through the rod. although with correct choice of material it probably wont matter (i think i actually have titanium bar stock in the right size already and its bloody light!!)