Predator stock max RPM

Filidog

Filidog

Member
#1
#1
Ok, I’m not trying to start stuff between members. I just torn between all these posts on these sites. Why do they have stock predator racing classes that have 5500 rpm max? If the people on OldMiniBikes have said stock flywheel can’t go over 4500 RPM. I’d really like to know if I ran 4700rpm (+/-200)on stock flywheel. Would it in your opinion!! Last a season? I’m just really cufused on this. I understand that going too high in RPM’s can cause major failure. I understand that with any RPM above what the motor was intended Is not recommended. But really, why do they have racing classes that have an RPM max ? And yes, at some point maybe in the fall or in the spring of next year I will buy a rod and flywheel but for now. Really, what’s considered pushing it, and what considered reasonable ? Also, does the gearing/load have an affect on this equation. Again I understand this is just you all’s opinion and not trying to start an argument with anyone or any group of people. That being said I’m adding these pictures that I screenshot BCAFA5C2-7612-4995-83C3-C0EA838D50AF.png 61805588-235B-401F-BD51-5C36DBC312E9.jpeg
 
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TheDullCarbide

TheDullCarbide

Active Member
#2
#2
Filidog said:
Ok, I’m not trying to start stuff between members. I just torn between all these posts on these sites. Why do they have stock predator racing classes that have 5500 rpm max? If the people on OldMiniBikes have said stock flywheel can’t go over 4500 RPM. I’d really like to know if I ran 4700rpm (+/-200)on stock flywheel. Would it in your opinion!! Last a season? I’m just really cufused on this. I understand that going too high in RPM’s can cause major failure. I understand that with any RPM above what the motor was intended Is not recommended. But really, why do they have racing classes that have an RPM max ? And yes, at some point maybe in the fall or in the spring of next year I will buy a rod and flywheel but for now. Really, what’s considered pushing it, and what considered reasonable ? Also, does the gearing/load have an affect on this equation. Again I understand this is just you all’s opinion and not trying to start an argument with anyone or any group of people. That being said I’m adding these pictures that I screenshot View attachment 106293 View attachment 106294
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It's all personal preference. And because we're on a site that gives advice, we have to error on the safe side.

Say cars are meant to do 75mph. We could tell you it can do 85, even though you could probably do 100 safely.
 
DeadPixel

DeadPixel

Member
#3
#3
On a racing kart the flywheel is sitting away from you and very unlikely to hit you if it exploded. On a mini bike your sitting above it and have a much greater chance of getting hurt in a flywheel explosion.

I have seen that a mud boat company called mud skipper is going to be selling a 208cc clone that uses a factory honda flywheel with a charging coil ( the hondas are supposed to be stronger than clone flywheels ) and there selling the motor with the governor adjusted to 4,700K. Makes me also question a little but I also don't want any one to get hurt based on my opinion. I have not broke one so don't 100% know for sure what RPM they explode at. We try to keep people safe when we give advice. I also believe new flywheels are stronger than old flywheels and racers tare there motors apart a lot to inspect there parts. You tell a guy he can spin his stock flywheel to 5,500 and it will probably hold together for a while. It might also slowly develop stress cracks and later explode on him a few days, weeks months or a year down the road.

My honest opinion though is I have spun my motor to 5K and was not too worried about any thing braking. I was surprised though when I pulled the rod and it was marked up pretty bad from lack of lubrication due to the high RPM. I pulled 2 rods that were damaged from that motor cuz I replaced the stock rod with a hardened BSP rod before installing the billet. I think as long as the stock springs and cam are in that the flywheel is fairly safe but would rather not have some kid pull his governor and get injured. The rod should be replaced though if the governor is tampered with for sure. It will not last long at high RPM. You also have to under stand though when we give advice that some of us know the risk of things and are willing to take the risk but we also give advice knowing that the person we are talking to dose not want to take that risk, has kids that ride or are a child them self.

The parts in these motors have poor quality control and are all over the place. When you start to push parts to the limit one person might have the motor last and another might brake his with the same set up. Our goal when we give advice is to give solid good advice and to help a person build a quality motor that will last them years with out the risk or fear that they will get injured or damage the motor and cost them money.
 
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DeadPixel

DeadPixel

Member
#4
#4
If your in a racing kart I would not be so worried and honestly think 4,700 will last. Like said in post above I would be worried about the rod long term and think as long as the stock springs are in to keep the motor from being able to spin too high and your governor is limiting your RPMs and not your valve springs floating I would think it would be OK.
 
Filidog

Filidog

Member
#6
#6
Thank you all for your insight on things. This will not be on a cart, but rather a mini. From the looks of things. I building from the frame up. I do not in any means plan on removing the governor. I am only going to slightly adjust the tension spring on the governor and keep a tach on it. I wanted maybe for the Govenor to kicking around 5000k and bring the revs down to 4600-4700 cruising speed. If I can find a discount code that will work for me in a month or two then I will definitely buy a rod and new flywheel. Because right now it’s looking at $180 for the both of them with shipping. And literally building a bike From just the frame has gotten really expensive on me.
 
EVOL Tweety Bird

EVOL Tweety Bird

Active Member
#8
#8
Is this a sanctioned race event? If so I would think there would be some rules/tech on what can and can't be done to the engines.
Is there any such thing(s) in your event?

Also along with the info on the rod and flywheel chance of failure at the higher rpms, you need to look at oiling, all you have is that little slinger to keep the rod bearing happy. Don't keep it happy and it's not going to be pretty.
 
Filidog

Filidog

Member
#9
#9
EVOL Tweety Bird said:
Is this a sanctioned race event? If so I would think there would be some rules/tech on what can and can't be done to the engines.
Is there any such thing(s) in your event?

Also along with the info on the rod and flywheel chance of failure at the higher rpms, you need to look at oiling, all you have is that little slinger to keep the rod bearing happy. Don't keep it happy and it's not going to be pretty.
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It’s not an event. Just trying to get a few more RPMs out of the bike without killing anything. Just for the summer.
 
65ShelbyClone

65ShelbyClone

Well-Known Member
#10
#10
Filidog said:
Why do they have stock predator racing classes that have 5500 rpm max? If the people on OldMiniBikes have said stock flywheel can’t go over 4500 RPM.
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It's not that the parts "can't" do it for a while. They can, but what happens when they can't anymore? And when is when?

Kart tracks and sanctioning bodies have insurance, attorneys, and waivers for people to sign before they run in those classes. Even the spectators probably have to sign waivers.

On a privately-owned forum where a lot of the users are minors and young people who may not be completely aware of the risk, it's simply prudent to discourage modifications that increase the potential for serious harm. It's like telling them to ride only with a proper helmet; you can't make them do it, but you've done your part by pointing it out.

Flywheel explosions are not to be taken lightly. Although it's pertaining to cars, there are lots of horror stories here:
https://www.jalopyjournal.com/forum...eel-explosions-lets-hear-some-stories.185297/
 
DeadPixel

DeadPixel

Member
#11
#11
^ Well said.

Just be careful Filidog don't want to see ya get hurt. A lot of us have done things we would not suggest on this sight so just be safe.
 
Filidog

Filidog

Member
#12
#12
DeadPixel said:
^ Well said.

Just be careful Filidog don't want to see ya get hurt. A lot of us have done things we would not suggest on this sight so just be safe.
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When I first posted this. I didn’t even have the bike road
Worthy. I’ve actually put the governor down after messing with it. I believe it only tops out at 4K, maybe 4.2k. I really only wanted st first a short burst of 5.5kand keep it at or under 5k. This thing at 4,000 gets up to 40mph ridiculously fast. I need a different front tire because at or approaching 50 miles an hour I start getting front wheel wobble up and down. I’ll try and upload some videos. My son loves the bike too. We had fun with it yesterday before it rained. 39F725D9-2DC0-4888-B796-27AF122ABC10.jpeg
 
Filidog

Filidog

Member
#13
#13
DeadPixel said:
^ Well said.

Just be careful Filidog don't want to see ya get hurt. A lot of us have done things we would not suggest on this sight so just be safe.
Click to expand...
When I first posted this. I didn’t even have the bike road
Worthy. I’ve actually put the governor down after messing with it. I believe it only tops out at 4K, maybe 4.2k. I really only wanted st first a short burst of 5.5kand keep it at or under 5k. This thing at 4,000 gets up to 40mph ridiculously fast. I need a different front tire because at or approaching 50 miles an hour I start getting front wheel wobble up and down. I’ll try and upload some videos. My son loves the bike too. We had fun with it yesterday before it rained. View attachment 106724
 
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