Author Topic: Major Hot Rods Stroker Crank Issue (Read 21778 times)

rsss396 · « **Reply #45 on:** January 16, 2015, 09:30:57 AM »

Sorry but IMO you have created a disservice to yourself and the 250r community by wanting a crank rod with less material around the bigend bearing so it is a true drop in.
Someone with a engineering background at HotRod probably made the rod changes for increased strength and durability but did not make it known to the sales division.

I hope like hell they do not make the changes so they are drop in, Engine builders (not assemblers) should be assembling a motor with a stroked crank because of the porting and head changes that come along with it.

If you have ever looked at a typical snowmobile rod you would realize how small ATV/MC rods are, this is because of durability needs of a snowmobile engine, they run at higher rpms for extended periods of time.
But if you already take a rod designed to be lightweight and remove even more material what do you think happens to its durability? stroker cranks have always been notorious of high failure rates maybe its because of poor workmanship or maybe like JerryHall said its because the bigend of the rod is thinned out and the rod actually deforms and now the rollers bunchup together and can not freely turn.

rablack21 · « **Reply #46 on:** January 16, 2015, 09:58:34 AM »

Quote from: rsss396;48787

Sorry but IMO you have created a disservice to yourself and the 250r community by wanting a crank rod with less material around the bigend bearing so it is a true drop in.
Someone with a engineering background at HotRod probably made the rod changes for increased strength and durability but did not make it known to the sales division.

I hope like hell they do not make the changes so they are drop in, Engine builders (not assemblers) should be assembling a motor with a stroked crank because of the porting and head changes that come along with it.

If you have ever looked at a typical snowmobile rod you would realize how small ATV/MC rods are, this is because of durability needs of a snowmobile engine, they run at higher rpms for extended periods of time.
But if you already take a rod designed to be lightweight and remove even more material what do you think happens to its durability? stroker cranks have always been notorious of high failure rates maybe its because of poor workmanship or maybe like JerryHall said its because the bigend of the rod is thinned out and the rod actually deforms and now the rollers bunchup together and can not freely turn.

First of all, I agree with you that machining down the rod can weaken the design. Yes, it is a better design to have lots of material around the bearing. Being an engineer myself, this is not difficult to understand. Again, this thread was NOT to discuss design theory and maximizing durability. It was to discuss a defective batch of cranks that got out. And how they dealt with it. It's as simple as that. It was a product that got out the door with a defect, just like any other part you would buy from a parts store or retail store. I inquired about the issue, recorded it, and made a thread about it in case someone else might have ended up with one as well.
Also, I never said that I wanted a crank rod with less material over one with more material. You did. I went with this particular crank because of the budget I had to work with. And there are alot of people running them, not just in 250r's but many other 2 strokes and 4 strokes for that matter.
I spoke with the engineering department. This was NOT an engineering change for them. It was a mistake in the cnc programming. Their crank rod was DESIGNED to have smooth transitions on both sides. My crank did not work because it was not machined to THEIR DESIGN INTENTION. And yes, like you said, I hope someone put in the time and did the FEA on this design to make sure it wasn't detrimental.

JesseA420 · « **Reply #47 on:** January 16, 2015, 10:14:29 AM »

Quote from: rsss396;48787

you have created a disservice to yourself and the 250r community by wanting a crank rod with less material around the bigend bearing so it is a true drop in.

sorry but you must have misread somewhere. how does having a smoother transition from the machining to the forging in this spot to clear the top area of the cases have to do with having less material around the big end bearing?

C-Leigh Racing · « **Reply #48 on:** January 16, 2015, 11:13:28 AM »

Might be, Hot Rods just needs to change the wording for their stroker cranks, to no say drop in replacement.
Things are strange how they work, just like that 6 mil ESR stroker Wayne Walker has, I wouldnt have trusted that crank to run across the road & stay together, but it has proved me wrong with as long as hes been running it.
Maybe he'll chime in & let us know the hours on it.
Neil

mrtwidster1 · « **Reply #49 on:** January 16, 2015, 07:42:55 PM »

I have one of these cranks. New in the box, but I will clearance my cases. (ESR offered to modify the rod but that was not Mr. Sanders recommendation.) Since my engine is not together then I will machine my cases. Once the Pics are posted of what Hot Rods is doing to fix the problem then I will decide if I want the exchange.
Just a question here also, are cranks balanced and if so are they balanced with the rod or without??

udontknowme · « **Reply #50 on:** January 16, 2015, 08:15:55 PM »

im with rsss. i dont like the idea of reducing the the strength of the rod at all and i simply refuse to alter rods if it might compromise its integrity. heres a story from some years ago when i was much less knowledgable. my problem was similar to you guys. i installed a heavier duty rod which snagged right at the top and pretty much rubbed through the full circumference of the stroke. i had this brilliant idea to machine down the the rod completly around the big end circumference so it could make a full swing unobstructed. hell i even had to make a stepped crank pin so i could fit this new heavier duty rod.

well i almost got the engine assembled when somehow i came to my senses and realized i had a train wreck waiting to happen. so i pulled the crank back apart, installed a new unmolested rod, trenched and grinded the cases where needed, bored the hole of the crank wheels for the larger pin. i sleep much better knowing theres almost zero chance this crank assembly will fail. still got the machined down rod and step pin on the garage shelf as a reminded what a bad idea it was

Jerry Hall · « **Reply #51 on:** January 16, 2015, 09:39:38 PM »

This post was moved to:

http://trx250r.org/threads/5107-Stroker-Cranks-and-Con-Rods-vs-OEM-Cranks-and-Con-rods

rablack21 · « **Reply #52 on:** January 16, 2015, 10:12:28 PM »

Guys, neither of the last 2 posts are relevant to this thread. Please stay on topic. Again, this thread is NOT to talk about crank and rod design. If you want to talk about that topic, start another thread.

mrtwidster1 · « **Reply #53 on:** January 17, 2015, 05:39:57 AM »

Thanks rablack21 for bringing up this topic. I would also like to add this.
I am a novice at all this, but I am learning. This site has helped me tremendously. That being said, of almost 60 years of lifes experiences I have learned that for me to accomplish my goals, I must listen, gather information, and trust others in their experiences. We all started this "R' journey somewhere. Some have more experience at it than others. Some have more passion. Sometimes it is best to "AGREE to DIS-AGREE". At the end of the day I alone am accountable for my decisions and their consequences. Respect and consideration are some of the things that make this site a "GREAT" R forum. I thank you all for your contribution to my world!

Pumashine · « **Reply #54 on:** January 17, 2015, 04:49:20 PM »

Quote from: mrtwidster1;48834

I would also like to add this.

The drop in crank vs the make it work attitude is easy to work out. But the motor builders tend to lean against taking too much off the big end of the rod. There is good reason for this and think it matters to everyone concerned. Thanks to those that add to our understanding why taking too much off the rod will lead to failure later on. Its too bad they cannot pour the rod without having to machine the much needed material here. I guess its just cost effective.

udontknowme · « **Reply #55 on:** January 17, 2015, 08:02:33 PM »

Quote from: rablack21;48790

First of all, I agree with you that machining down the rod can weaken the design. Yes, it is a better design to have lots of material around the bearing. Being an engineer myself, this is not difficult to understand. Again, this thread was NOT to discuss design theory and maximizing durability. It was to discuss a defective batch of cranks that got out. And how they dealt with it. It's as simple as that. It was a product that got out the door with a defect, just like any other part you would buy from a parts store or retail store. I inquired about the issue, recorded it, and made a thread about it in case someone else might have ended up with one as well.
Also, I never said that I wanted a crank rod with less material over one with more material. You did. I went with this particular crank because of the budget I had to work with. And there are alot of people running them, not just in 250r's but many other 2 strokes and 4 strokes for that matter.
I spoke with the engineering department. This was NOT an engineering change for them. It was a mistake in the cnc programming. Their crank rod was DESIGNED to have smooth transitions on both sides. My crank did not work because it was not machined to THEIR DESIGN INTENTION. And yes, like you said, I hope someone put in the time and did the FEA on this design to make sure it wasn't detrimental.

im sure you know now, or maybe you dont, theres nothing defective about that crank assembly. it simply has a standard unmolested rod on it, like what you would see on any standard stroke crankshaft.

alot of rods dont have a smooth transition at the sides, contrary to what you might think. got several rods from several engines sitting around and they dont have the smooth transition. some rods may very well be a smooth transition, depends on the design, manufacturer, etc. but to say its defective simply because its not a smooth transition is nonsense. you might be misinterpreting whats going on here. the rod you have is typicall of what you would see on a standard stroke crank. hotrods had failed to machine it down even further, in order for it to be considered a 'drop in' deal, but by no meens is it defective in design

if you dont mind me asking, what engineering field are you in ?

rablack21 · « **Reply #56 on:** January 17, 2015, 09:05:41 PM »

Quote from: udontknowme;48873

im sure you know now, or maybe you dont, theres nothing defective about that crank assembly. it simply has a standard unmolested rod on it, like what you would see on any standard stroke crankshaft.

alot of rods dont have a smooth transition at the sides, contrary to what you might think. got several rods from several engines sitting around and they dont have the smooth transition. some rods may very well be a smooth transition, depends on the design, manufacturer, etc. but to say its defective simply because its not a smooth transition is nonsense. you might be misinterpreting whats going on here. the rod you have is typicall of what you would see on a standard stroke crank. hotrods had failed to machine it down even further, in order for it to be considered a 'drop in' deal, but by no meens is it defective in design

if you dont mind me asking, what engineering field are you in ?

you call it what you want to, but if a part in any manufacturing plant gets out the door without meeting its design intention and without all the proper machining to meet that design, then it is defective. And hot rods indicates this as well. Call it a manufacturing errors if it makes you feel better about the terminology. The bottom of this rod is purposely machined down to be a stroker crank. Otherwise it would be as cast. As would be expected with normal design. And just fyi, if something doesn't meet it's design intention, then yes it is defective. That is obvious. No, I don't mind you asking at all. I am a design engineer with emphasis on structural analysis.

Pumashine · « **Reply #57 on:** January 17, 2015, 09:53:13 PM »

Quote from: rablack21;48875

I am a design engineer with emphasis on structural analysis.

So when your rod fails you will understand why!

rablack21 · « **Reply #58 on:** January 17, 2015, 09:59:10 PM »

Quote from: Pumashine;48881

So when your rod fails you will understand why!

Lol!

udontknowme · « **Reply #59 on:** January 17, 2015, 10:03:55 PM »

since your not a engine builder or in a engineering field that deals with engines im just trying to help you understand whats going on here. many rods are machined on the bottom, whether their final destination is on a standard oem stroke crank or some after market longer stroke.

does the 250r hotrods 72 stroke crank not use the same rod as the +4 crank, 130.3mm ? hotrods only shows one rod available which suggests both cranks use the same rod. this is where i was trying to tell you the rod you have is what would be used on the 72 stroke crank, they simply take that rod and machine it further to be used on the +4, in order for it to be classified as "drop in". theres nothing defective about its design.

with some weird combination of 250r parts it seems like the piston skirt can contact the crank wheels at bdc. is the piston defective ? of course not.

but you insist on calling the crank defective. defective is a crack, or egg shape bearing hole, atleast in my book.

this is a rod intended for a oem stroke, as i recieved it from the manufacturer. its not a smooth transition and has been machined, no different than your defective rod :lol: