Shotpeening advice

[KARNAGE]

and a small tip if you are doing this your self wear some nice thick gloves as those rods are going to get f*&cking hot as all hell when buffing them

[oldcorollas]

Now shot peening actually induceses stress back into the rod as the peening process changes the rods surface structure.

i thougth the point of shot peening was to compress the surface, to induce a compressive stress, so that it is harder for cracks to form from any defects (since cracks only form from tension, not from compression)..
I am not 100% sure on the sonic relieving, but if you can induce enough stress into a rod by vibration to change the internal structure.. then the rod won't be strong enough to be used in an engine?

[jeffro ra28]

Isn't he going to need to weigh the rods as he linishes them in order they maintain some kind weight tolerance? And, what sort of tolerance would be required?

Saliba engines (Clayton?) quoted me $275 to race prep (linish and shot-peen) 4 rods. They do excellent work. Maybe it's worth going pro on this one?

To balance rods properly the small ends and big ends must be weigh. There isnt going to be any great improvements unless this is done. There are a few ways people do this. Do a google for "rod balancing jig". Weighing just the total mass of the rod isnt good enough if doing the job properly. I use my own jig that i made and some scales that measure down to .1 gram. I usually try and get the rods to atleast within half a gram of each other, sometimes better depending on the engine. The small ends must way the same, the big ends must way the same, and the total mass must be the same.
Usually the rods are recoed first, then polish beams, then weight and end for end balancing, then shotpeening. Also, it helps if the pistons are all the same aswell. Often, even good qaulity forged pistons are 1-2 grams out!

Joey, be carefull using a die grinder mate, i can see the beams of your rod turning out wavey! You are honestly better of with a linishing belt! Its much easier to acheive a long flat surface with that then a 1-2cm diameter grinding burr!

There really isnt anything that "pro" about the task. Attention to detail, accuracy and surface finish. Joey is still able to linish the rods himself to save on labour, perhaps get them balanced in a good shop, and then send them away for shotpeening or whatever. Or maybe the expense of the tooling outweighs the expense for sending out the work!

[oldcorollas]

when i did my engine, i did rods total and end to end within 1gram, but Tosco manual for K motors said 1gram is ok.... closer is better tho.
one of my end caps weighed (iirc) 7grams more than the others! it did make for noticable vibration and harmonics...
so.. 7 grams at one end is not good
i think difference in weight is mor eimportant at the big end than little end tho, and the big end swings around, and the little end is kinda combined with piston weight.

check the weight of the piston pins too.

[jeffro ra28]

Iv seen some discraceful weights, generally from holden/ford/chev engines. Some 18r's and 2tg's iv done werent bad. But the 1uz i did was pretty good for balance standard!

If getting the crank balanced, the balancing shop like to have this information:
1. Rod weight
2. Piston weight
3. Bearing shell weight
4. Piston pin weight
5. Piston rings weight.

But there are always differences to how particular people get.

[af300e]

Always more to it than just a clean 'n' peen.

How does the resilience of a prepped oem rod compare to that of a good aftermarket rod?

[30psi 4agte]

i thougth the point of shot peening was to compress the surface, to induce a compressive stress, so that it is harder for cracks to form from any defects (since cracks only form from tension, not from compression)..
I am not 100% sure on the sonic relieving, but if you can induce enough stress into a rod by vibration to change the internal structure.. then the rod won't be strong enough to be used in an engine?

I dont believe it is to alter the internal structure of the rod. I believe it is more aimed at testing the rods new fatigue level after it is put through the stress of shot peening. This is done on a bed rather than in a high dollar engine.

I know some of the guys that build the sprint car engines use a oil bathing process after shot peening to relieve stress from the process also....... I know even less about this though.

To be totally honest stu i dont know enough to answer the question fully how id like to. -- I will find out more as you know have stumped.

[oldcorollas]

i just know some things that engine builders do, don't have any practical method, but they hear someone else did it, so they had to keep up or lose customers..
or, what they did was right for the wrong reasons

i had a look and can't find much, but i am not an expert in ultrasonic stress relief of metal parts
i will check in scientific journals tomorrow (if i can remember )
there may be some fact to it, but i am not sure if it is worth doing after shotpeening, as the point of that is to:
http://www.metalimprovement.com/shot_peening.php

[allencr]

i just know some things that engine builders do, don't have any practical method, but they hear someone else did it, so they had to keep up or lose customers..
or, what they did was right for the wrong reasons
http://www.metalimprovement.com/shot_peening.php

That's beautiful, thanks!
The link's illustration http://www.metalimprovement.com/shot_peening.php shows gear teeth, something that can use more surface hardening then a rod can, but every little bit may help.

[joey]

If i'm only polishing the shaft to remove the casting mark and small imperfections, i won't be messing with the small weights on the end of the rods and its not like im taking large chunks of the rod out, does it still need to weighed? Is it more of a safety thing to make sure they are all still weighed correctly from factory or is it something everyone has to do when polishing/peening?
I had a chat to a guy at a machine shop (who is going to be doing the resizing) about what i intend to do and he reckons to only bother polishing the main part of the shaft and not to bother covering the big and small ends of the rod if they are going to get resized.... does this sound right or could it potentially cause any problems with the bearing -> rod mating surface?
I've sorta followed along this write up here which is pretty usefull. http://www.chevyhiperformance.com/te...ods/index.html

[oldcorollas]

That's beautiful, thanks!
The link's illustration http://www.metalimprovement.com/shot_peening.php shows gear teeth, something that can use more surface hardening then a rod can, but every little bit may help.

i didn't notice that
i would be reluctant to use it on gear teeth.
1. shotpeening is not dimensionally accurate
2. it leaves an undulating surface (maybe this is good? less points of contact?)
3. the surface of the teeth should be hard enough that they don't need shotpeening
4. gear teeth are usually hardened in such a way as to create compressive stress at the surface anyway.....
but.. removing machining marks and peening the base of the teeth i think could be worthwhile, since most fatigue failues of teeth begin there, rather than halfway up a tooth.

for rods, the material is soft, and usually has a lot of imperfections. linishing removes them, but introduces it's own crack starters, but they run lengthways = not as likely to start a crack as scratches running sideways, or point defects.
shotpeening squashes the material to effectively remove the scratches, and compresses the surface 0.xmm to stop any cracks opening.


joey, it is always good to weigh them. if you have access to a 0.1gram balance (i got one that is accurate enough for about 3000yen from hardware store here.. is a cooking scale but when i did my rods, i used a 0.01gbalance to be pedantic) it is easy to rig up a jig to weigh them. if they are significantly out, you will get vibrations in the motor, but it has to be a few grams out to make a difference. you can work out how much weight needs to be removed etc, as 1cubic cm of steel is about 8grams.
toyota parts are usually pretty good weights from factory, but it is better to check.
peening shouldn't remove weight (or then it is sandblasting ), but linishing will remove some weight. it is better to check before and after, both total and end to end weights.

i think it is better to cover the surfaces anyway. then it gives you the option NOT to resize.
if you resize, then you will need to check weights again, as material is removed.

article is not bad but doesn't really go into specifics.
it is better to use the sanding belt thingy Jeffro mentioned, so you can keep the surface flat and smooth.
you onyl want to grind off enough material to remove the dags and potential failure points. any more than that will reduce strength of rod, by reducing it's dimensions.
don't reduce size of rod above or to the sides of the pin too much, as it is thin enough already

hmm, if the rods are resized... and then you need to rebalance... then it is probably better to peen the areas where weight was taken off to balance also.

then again, polishing those areas to very fine finish might be enough (can peen with a hammer if you really need to )

random analysis http://members.ozemail.com.au/~mtce/peenreport.htm (0.1mm depth)
can't find any good guides in my 2 mins search.. will look later

[jeffro ra28]

I was always of the understanding that polishing the rods removed the hard surface the rod already had. In order to get this hardness back, it needs to be shot peened. Hence, do not polish rods without shot peening as it will actually make it weaker!

[oldcorollas]

rods shouldn't have a hard surface layer... unless they were diecast or something strange?

if you polish rods, you put lots of nice crack starting scratches in them.
if you polish across the beam, you make perfect crack starters (hence polishing along the beam).
by peening, you squash those scratches together, to stop them opening into cracks.

if you peen without linishing/polishing, then you may still have crack starters that go below the depth of the peening.. ie the peening has no effect at all. since peening is only 0.1mm (100 microns), small surface defects from forging/casting are bigger than that, so you have to remove them first.

[jeffro ra28]

I havent got the book with me so cant quote. but that theory came from "four stroke performance tuning" by grahame bell or somthing like that.

[joey]

No turning back now. Partially done linishing one of the rods:




So how far up should i go? Should that suffice or should i go over the outer parts of the caps where the bolts sit in aswell as around the pin? Also should i linish the rods to be flat or to have a slight curve in them?