so what are stress risers??

points on metal that are perfect starting points for mechanical failure, that's what....!

you can think of them as the small tear in a phone book that allows you to tear all the pages in half... without the initial weak point it wouldn't happen with normal human pressure.... but WITH the initial week point it tears easily.... same thing goes for fabric....

metal structures can have several sources of weak points...whether they arise from impurities, voids, or geometric weakness.....

a stress riser is commonly a sharp point or edge.... a thin point where a crack can begin...and once a metal has a crack in it, it's the beginning of the end... the crack will eventually propagate through the entire piece ...

2 methods of surface stress relief that apply to stress risers are :

1) peening ... or impact ... something like small area forging... where impact hammers the surface and not only changes the small scale surface shape of the material...but shallowly changes it's strength porperties as well..... shot peening would be the type used here...like sand blasting , only with small steel shot instead of sand

2) polishing... pretty simple really.... a smoothly polished and radiused surface wont have any sharp\ thin edges...so there wont be a stress riser ...or raised portion of the material to begin with....

those who have been following know that i made a small run of one off pistons for making the yfz into a long rod stroker 501.....

98mm bore + Hot Rods stroker makes for 501cc's in the yfz...... yamaha has 3 different lengths of oem rods :

shortest = 06 & up yfz.... yamaha shortened the rod when they lengthened the stroke, keeping the same installed assy height

middle= 04 7 05 yfz

longest= WR or dirt bike rod.... smaller wrist pin & longest rod length

so...not from necessity...but rather just because i prefer the long rod stroker setups.... i'm putting together a WR \ long rod stroker 501 engine....

today the box with the Venom WR501 piston.... the polished oem WR rod...and the Hot Rods Stroker Crank ....is on its way to Crank Works of Arizona for rod swapping, clearancing, and balancing...

i called a freind of mine...sweetwilliam... who does gunsmithing "melt down" & polish work.... to see if i could get him to do the polishing and radiusing of the WR rod for me....instead, he brought over his bench polishing wheel setup and started the work with my porting tools.... the next day i continued the work & finished up with his bench polisher..... i should have taken "before" pics...but all i have is the "after"

Click to view attachment

That looks good!

wow looks sweet too bad you'll never see it...lol what about plexy cases

can't wat for the results good luck

NICE!
I think I can see myself in the shine!

man there is some time into that... looks great. i guess that would be a great way to find any imperfections in the metal to, at least on the out side of it..

i have seen the same polishing done on v8's. question is i thought i heard you should do that unless you are going to have the rotating assembly balanced? not sure if this is true...just thought i'd ask

Nice work!

Good info!

Thanks John

Looks very pretty Johnny!

Now how much grams would you guesstimate came off the rod? I talked to Crank Works yesterday and asked about balancing the crank to the piston and if they had to add metal the cost my go up another $20. Not bad I thought. I was thinking now they might have to add more to get it to balance. Where I am going with this is... The HR +3 is "supposed" to be balanced to the OEM piston. What is the weight of OEM vs. a Venom piston? Now, if you balance the crank to a 98mm or bigger piston, what happens when you (may) decided to go back to stock? I have heard of vibration with the BB and +3, due to it not being balanced. Now, I wonder about the logivity of a balanced crank to a 98mm or bigger piston and returning back to stock. As I sit I would rather have a balanced 501 or bigger motor then a un balanced 471.

Back to stress risers... did you round off any of the crank weights or are they pretty good to begin with?

Once the crank is balanced for a set piston weight, then thats it, obviously you will be dealing with a inbalance issue if you increase/decrease piston mass. The HR+3 crank and WR rod work well with 3-4oz's removed from the total mass of the crank assy.

Yes, that is why I am wondering about the balance of the crank to 95mm OEM piston weight vs. a 98mm (or larger) CP Venom piston weight. Maybe a compromise between the two will keep both the 95mm and 98mm combos with in a gram or so of balance of each combo?

eric...when i weighed my stockbore and bigbore pistons side by side i dont recall the weights but they were VERY VERY CLOSe...far closer than you would think...i think within a half ounce of each other...but i cant remember so dont take what i say to the grave LOL

good question

it is more critical on a multi cylinder engine .... you don't want different amounts of metal removal on different rods to create an imbalance from the weights being too different....

so that usually means getting all the similar lightened parts the same weight before the final polishing...

but this assy will be balanced @ crank works for the best setup with the piston that will be used

when stroker cranks are clearanced for the piston skirt clearance @ BDC.... quite a bit of weight is taken form the crank weights.. a lot really...

the rod lost maybe a couple grams ...spread out over the entire length... with the raduis & polish job...

i'll check the stock piston VS the oem piston assembly weights today....

if there is ever an imbalance in an assy... lighter is naturally less stress than heavier.....

I am looking for piston weights now. Both CP 95mm, Venom 95mm and 98mm as well as OEM 95mm. So your saying by lighter being better... do you mean a lighter piston then what the crank is weighted (balanced) for? Like balancing the crank for a 98mm and then later having a 95mm on the end, would be better then a balanced crank to 95 and then adding a 98mm weight?

I hope that makes sense.

lighter piston and\ or rod.... the crank weights keep their intetail direction always in the same rotation .... the stuff that has to stop and change directions (piston & rod) is always better if it has less weight that has to start & stop and change direction several hundred times per second....

Gotcha.

Any plans to try out a lighter fly wheel on the yfz?

nope, not really... i have tried all sorts of flywheels on the trx's... and i wouldn't bother doing any of it again...

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