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Old 03-11-2013, 02:35 PM   #70
BaylorCamaro
Track > 1/4 Mile
 
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Drives: 2013 ZL1
Join Date: Sep 2009
Location: Kemah, TX
Posts: 5,275
I haven't updated this in a LONG time. Been posting in my FI V6 thread, since I think that's where most people that follow my build look...

Sooo here's what has happened over the past month:

UPDATE 2/5/13
I heard a weird rattle coming from the engine bay earlier today. Once I got home I used an automotive stethoscope to pin the location of the sound down to the tensioner bracket and found this.

My guess is a stress fracture, just like what happened to the bolt that snapped off the tensioner a few months ago. The real salt in the wound is I haven't even been to the drag strip since I got my car back from RX. Even worse, aside from two Saturdays ago I haven't even taken my car past 4,000 RPMs (drive to work is only 5.5 miles in the city). Tensioner is hardly holding any tension on the belt.





Just spoke with Tracy, looks like he has a different bracket (1/2 billet). Stay tuned.


UPDATE 2/6/13

Well here is the one silver lining. My current plan is to remove the tensioner bracket and bring it to my work. One aspect of our company is metallurgical testing, so I am going to have the bracket tested for hardness and try to determine the exact type of metal we are dealing with (unless Tracy knows). From that I'll be able to see if this type of metal is strong enough for the application. The next step (based on our metallurgist suggestions) is to buy an appropriate strength metal, I'm thinking Aluminum 7075. I will then have our machinist replace or build a new bracket out of the upgraded material. The end result will hopefully be something way stronger than is necessary but hopefully will never fail.

Over my lunch break I removed the tensioner and brought into work. Our Ph D who is head of the lab along with our metallurgist looked at it and determined the failure was a result from stress and fatigue.

This picture shows where it started. If you look at the bottom right corner, rings extend out from bottom right to upper left like a radar ping which explains the origin point of the failure.



However if you look at the below picture you can see the the bracket was cut to accommodate the shape of the tensioner. It appears it wasn't machined in this shape and because of that there is a possibility it introduced a defect. Which makes sense since the fatigue originates right at the center of the cut.



In conclusion the break resulted from fatigue / stress fracture. However whether or not that was because of the quality of the metal isn't determinable unless a full failure analysis is performed. It IS possible that the way the bracket piece was cut rather than being machined introduced a defect, such as a hair line fracture.


So after work I took another look and found that one of the screws stripped in two. This is the second time that this has happened now.





Also here are more pictures. As you can see the bracket has VERY crude cuts.





You guys like the hearts in that last picture? I just noticed that..... lol


UPDATE 2/8/13

So here is the full piece of the tensioner bracket that catastrophicly failed.





As you can see it looks like it was just placed in a blender. Machined very poorly

Also I just ordered 316 stainless steel to make these new brackets. Should be much much stronger than necessary but I am sick of this. Lol.


UPDATE 2/24/13

Shop at work has been backed up for the past two weeks. Good for business not good for my situation. Here are the pictures of my new bracket with the old broken one. It is made out of 316 stainless steel 1:1 scale as the broken bracket that came with the system. To ensure there are no stress risers anywhere in the piece, it was smoothed out with a grinder and then machine polished. The pictures do not do it justice, it has a mirrored finished almost. The guy that has been doing our polishing and grinding has been doing it over a decade. Only took him about 15 mins to polish it like that.


















I have however run into yet another issue. The metal pulley on the tensioner is eating up the belt. I noticed this a couple months ago but it wasnt anything major, I could just tell one side of the belt was fraying and being eaten. Well today I talked to J-Rod6410 (Jamie) who did the install for v6owner and KMAGRIZZ apparently he saw the same issue with KMAGRIZZ's set up and had to switch to a plastic pulley rather than metal. However v6owner never had this issue. Very strange. Stay tuned for more details.


UPDATE 3/4/13

So I have a new situation, who's really surprised at this point though? lol

I installed the new bracket on the system, however for whatever reason it started eating the outside edge of the belt (side farthest from the engine). I thought maybe I installed something wrong, didn't tighten something, operator error etc. So I got a new belt put it on, seemed like it might be ok, took it for a test drive and heard the belt making some awful noise less than 15 miles into the drive. I poped the hood and it turned out the backside of the belt (smooth side, not ribbed side) was getting worn down really fast. I got back to my house and it looked like the pulley wasn't aligned perfectly and was a couple millimeters off, the outside edge of the pulley started to ride the belt and acted like a pizza cutter slicing pieces of belt off.

I talked to Tracy and he sent me the old version of the pulley (made of plastic not metal) we thought maybe this would fix it, unfortunately same exact issue. I tried buying a slightly narrower belt (5 ribs vs 6 ribs) thinking this may help the issue. As soon as you turn the engine over the belt rides to the side of the tensioner pulley that was eating the original belt.

I cannot shim the pulley because it would shim it the wrong direction. However the tensioner has a slight lip where it bolts to the new bracket I made. I took a dremel and filed down that lip and took a steel file to smooth the edge. I installed the tensioner Sunday and so far so good.

HOWEVER it looks like the backside of the belt (side opposite of the ribbed side) appears to be wearing. This is the side that the tensioner rides on, so could it be the tensioner is too tight? Maybe this is normal wear on a new belt for the set up? I don't know as I never paid this close attention to it the first time I got the car set up.

I've always had an issue with the outside edge (1 rib) being eaten. However once that edge was worn down it was OK.

Anyways here's a quick video I took to test the tensioner. As you can see my AFR goes rich in 3rd-6th gear. Something I'll have to adjust later.




UPDATE 3/9/13

I think the belt is fine, I took some measuring calipers and measured the belt and then compared the measurements to a brand new belt and they are within .01" of each other.

I changed the gape in my spark plugs, going down from .037 to .035. The engine still seems to break up around 6,100 rpms in 3-6 gear, as seen in the video below. AFR goes rich in 3-6 gear as well. Looks like I just need to work out the tune.

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