Resolution for broken KW C38 blower pulley bolt that breaks?
Joined: Jan 2015
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Joined: Sep 2005
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From: Baraboo, WI
Hi guys...just my thoughts... If we put a stronger bolt in to replace the one that keeps breaking, what's to say that we won't damage the main shaft that the pulley is bolted to (I believe this is called the sun shaft). In doing this we will transfer more torque to this shaft by increasing the breaking point of the screw. Just a thought...
Joined: Dec 2007
Posts: 2,274
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From: Midwest
First question to rotrex is do they use the same bolt for all superchargers?
How many serpentine drive bolts have failed? Personally I have not heard of any.
Why has one person had 3 bolts snap with the Kraftwerks kit?
Kraftwerk's need to do some investigating.
How many serpentine drive bolts have failed? Personally I have not heard of any.
Why has one person had 3 bolts snap with the Kraftwerks kit?
Kraftwerk's need to do some investigating.
Thread Starter
Joined: Dec 2007
Posts: 4,757
Likes: 120
From: Waukesha, WI
hi rain H&R i Brake 3 bolts in 5 month... now i have the car in the shop we are working on a cnc port head , custom intake manifold and cams.... and also we are building a new custom Billet forged bolt .. i will upload pics in a few days of the bolt and the other parts in my topic. since this bolts brake when you hit the rev limiter a lot and oversping the blower... i look for the arp bolts but they dont have the head alem that use the pulley from KW. 
Why even risk hitting the limiter seriously. If your max rpm is 8500 then set limiter at 8600. If you have an ap1 then set it at 9400 if you want to absolutely push the maximum revs. Mine is set at 8600 but honestly if I want to push it I will go to 4 blinks 8400 and shift. It's just not worth risking damaging the blower bouncing off the rev limiter IMO. We have been told that the rotrex blowers don't like it.
Is there any real evidence that hitting the rev limit has any effect on the bolt or the supercharger? It seems that there is some speculation that this may be a contributing factor and that this is getting repeated to the point that it is assumed to be true.
The picture of the broken bolt indicates the bolt broke due to bending forces. This bending force comes from two sources. One source is the torque required to drive the supercharger. It is the torque to drive the supercharger divided by the radius of the pulley. Bouncing off the rev limiter produces a rapid acceleration and deceleration which causes a varying torque and therefore varying bending force on this bolt.
The other source of bending force comes from the belt tension pulling on the pulley. Of course, the tighter the belt, the more the bending force. The design of the belt tensioning system makes it very easy to over tighten the belt.
Another contributing factor could be that if the bolt starts to loosen and back out, then the bending moment on the bolt at the point where it enters the supercharger increases as the bolt backs out. Bouncing off the rev limiter can cause vibrations that may cause the bolt to loosen if it is not tightened properly (lock-tight helps with this). However, I don't see a key way or splines that connect the adapter to the input shaft. If there are none, then torque is transferred from the adapter to the input shaft by friction and that friction is provided by the clamping force of the bolt. If this is true, when the bolt starts to back out, the adapter would slip and the car would loose boost.
The stock S2000 has a rev limiter that cuts fuel at the limit then keeps it off as the engine coasts down for a several hundred RPM to the "recover speed" then puts the fuel back in. This is what causes the stock engine to feel like it is "bouncing" off of the limit. The FlashPro sets the limit and the recover speed independently. Hondata recommends that they be set within 300 rpm of each other, which is less than the factory difference. I have mine both set to 8200.
The picture of the broken bolt indicates the bolt broke due to bending forces. This bending force comes from two sources. One source is the torque required to drive the supercharger. It is the torque to drive the supercharger divided by the radius of the pulley. Bouncing off the rev limiter produces a rapid acceleration and deceleration which causes a varying torque and therefore varying bending force on this bolt.
The other source of bending force comes from the belt tension pulling on the pulley. Of course, the tighter the belt, the more the bending force. The design of the belt tensioning system makes it very easy to over tighten the belt.
Another contributing factor could be that if the bolt starts to loosen and back out, then the bending moment on the bolt at the point where it enters the supercharger increases as the bolt backs out. Bouncing off the rev limiter can cause vibrations that may cause the bolt to loosen if it is not tightened properly (lock-tight helps with this). However, I don't see a key way or splines that connect the adapter to the input shaft. If there are none, then torque is transferred from the adapter to the input shaft by friction and that friction is provided by the clamping force of the bolt. If this is true, when the bolt starts to back out, the adapter would slip and the car would loose boost.
The stock S2000 has a rev limiter that cuts fuel at the limit then keeps it off as the engine coasts down for a several hundred RPM to the "recover speed" then puts the fuel back in. This is what causes the stock engine to feel like it is "bouncing" off of the limit. The FlashPro sets the limit and the recover speed independently. Hondata recommends that they be set within 300 rpm of each other, which is less than the factory difference. I have mine both set to 8200.
Waiting game is right, with KW at least! I prefer this popcorn gif, for obvious reasons!
Originally Posted by Memo6453' timestamp='1435302055' post='23661099
KW emailed me that they are still looking into these failures and mentioned it could be from improper supercharger pulley torque or tightening sequence, faulty hub adapter, etc... but a super tight belt would not do this as you would damage your belt or pulleys before damaging the center bolt... but that they have not confirmed exactly why this happened.
hopefully they have a response on this one ASAP...
im curious how many -81 kits had this happen vs. -91 kits...
-Mike
hopefully they have a response on this one ASAP...
im curious how many -81 kits had this happen vs. -91 kits...
-Mike
Please check out thishttp://rotrex.com/Ho..._Technical_Data
These are my opinions based on 7 yrs of refining our kit and seeing other kits fail and retract from the market. This development has given you something that works, we see more boost at the engine then others and that creates power. We have now catered for the 2.2 litre motor as well with revised pulley ratio's to give the most power available. I don't know which motor you have be either make awesome power. The Supersport kit is £3900, shipping is expensive at about £250. I will do you a deal of £3600 shipped. We are looking at 21 days lead time as we have had such a run on kits since the beginning of the year. I would like 50% deposit, you pay the rest when we are ready to ship. The Race kit is £4600, same shipping. I can do you this kit for £4100. shipped. same lead time. The exchange rate is around 1.65 to the Pound so your right about your cost. Sorry you will have to have a word with Barack see what he can do for you . If you want more info its best to email me richard@tts-performance.co.uk
All the best
Richard
quote from reichard @ tts.
All independent replies aside, KW loves to play the innocent game. They generally do not take the blame when something goes wrong. They even accuse reputable vendors that "they are the only ones who have problems with their KW products." I do not expect them to do much more for the kit. Although they have made changes since the first kit which does surprise me. Unless we increase the pulley bolt size, I do not see how this issue will be resolved. 12.9 is a very hard bolt, and as mentioned by Brian (07S2k06Si), I do not think making the bolt un-breakable will help the large C38 blowers live very long, especially when people abuse their car and bounce the engine off the rev limiter.
I will say this though, I just do not think the KW kit is worth the money. I have said since day 1 of this kit coming out it would be an issue. The ONLY system you should consider when you want a rotrex is the TTS. However, as I have also always said, buy the bracket and blower from TTS, have a local shop fabricate the rest. (Cough, King Motorsports, couch. Ohh bless you. thank you!)
All of this aside, the car I helped put together is my close friends car and we will be tracking this S2000 a lot, so I will have a lot of thoughts and opinions on how this kit can handle the abuse, heat, and durability needed to perform in the harsh elements of road courses. We are going to remove the bolt today, do measuring, and order spares so if it happens, especially at the track, we can replace it on the spot.
Thread Starter
Joined: Dec 2007
Posts: 4,757
Likes: 120
From: Waukesha, WI
Originally Posted by Habitforming' timestamp='1435359547' post='23662093
Originally Posted by Habitforming' timestamp='1435215185' post='23659863
It would be great if someone could get a good pic of the head of the bolt, one of you that has a kit you haven't installed yet... we should be able to determine what grade it is.
Registered User
Joined: Mar 2013
Posts: 436
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From: Cordoba
rain, sorry if you dont understund my worlds... im from argentina... my english its not good.. hope i can help .
im going to upload the custom bolt we are doing more stronger.-
no offense at all what you are saying. i drive my car only weekends... no hit the rev limiter in 1st and 2 gear .. my kit has 900k milles used , im very carefully when i race my car never launch etc .- here is a little video some revs..
[media]https://www.youtube.com/watch?v=yc13xwxJ4WI[/media]
im going to upload the custom bolt we are doing more stronger.-
no offense at all what you are saying. i drive my car only weekends... no hit the rev limiter in 1st and 2 gear .. my kit has 900k milles used , im very carefully when i race my car never launch etc .- here is a little video some revs..
[media]https://www.youtube.com/watch?v=yc13xwxJ4WI[/media]
Thread Starter
Joined: Dec 2007
Posts: 4,757
Likes: 120
From: Waukesha, WI
Thanks for the update guys.
We took the bolt out today, we needed to anyway so we can make sure we have the tools we need when we are at the track to replace the bolt if it breaks.
My frustrations with KW continues. What a joke they are. The contitech application to measure belt tension via frequency is a joke. The install directions for the kit simply say to use the app. It does not give step by step for how to do the test. Smh.
As I decided to press on and "wing it," I come to find out you cannot even use the app because the test area is 139.5mm long, the app only can preform the test if it is between 200mm and 800mm long. Their is not a single spot on this kit where the distance between two pulleys is longer than 200mm. What a JOKE!
Yet again KW, you suck! (YES, I said joke 3, now 4 times!)
We took the bolt out today, we needed to anyway so we can make sure we have the tools we need when we are at the track to replace the bolt if it breaks.
My frustrations with KW continues. What a joke they are. The contitech application to measure belt tension via frequency is a joke. The install directions for the kit simply say to use the app. It does not give step by step for how to do the test. Smh.
As I decided to press on and "wing it," I come to find out you cannot even use the app because the test area is 139.5mm long, the app only can preform the test if it is between 200mm and 800mm long. Their is not a single spot on this kit where the distance between two pulleys is longer than 200mm. What a JOKE!
Yet again KW, you suck! (YES, I said joke 3, now 4 times!)