The MMS pulley actually wants to sit still but, the friction from the bolt holding it against the crank pulley makes it move with the crank pulley. The pins are there to help get the MMS pulley moving and take some of the burden of keeping it from spinning off the crank bolt. If you turn the MMS pulley clockwise the pins will not be able to do the there job.

Also, if for whatever reason there is slip between the pulleys the crank pulley "spokes" will have that much more momentum when they come around and smack those pins.

Is there any way to drill and pin both pulleys to the crank? That would be your best bet.

 

I have a pin kit coming but this will pin only the LS1 CP to the crank.
But I understand the dynamics of the situation. I see exactly where you are coming from and I know what the pins are there for. But the S/C belt is always pulling the S/C CP clockwise and the headunit probably has quite a bit of momentum causing the S/C CP to spin into the "sharkfin" side of the spokes causing the pin shear and the big divots on the clockwise side. The Counterclock wise side shows only a little divot, so this leads me to be it rebounds with less energy on that side. Check the pics, you will see what I mean. This is my theory and if it doesn't work I will post it.
But, I have done the counterclockwise thing before and it led to this point. So I have to try something else. But I thank you for making sure I know what I am getting into first.
I just wish the MMS pulley and the ATI pulley were pinned on both sides of all three spokes. This way it wouldn't go anywhere. I like how the Vortech LT1 kits s/c crank pulleys bolt directly to the LT1 crank hub. That sucker goes no where (if you have your crank keyed). I wanted to drill into the center of the spokes and through the MMS CP and use the same pins or longer but I am not that enterprising or brave.
J

 

Ok, so you have divots on both edges of the crank spokes? I've never really payed that much attention to what the stock pulley looks like so I didn't notice it.

So I guess when you take off it slips one way and then when you stop it gets pulled the other way.

I bet a competent machine shop could take and fix you up with a way to pin the MMS pulley better to the stock crank pulley. They could do just like your saying with the pins into the stock crank pulley. Once that was done you could pin the crank pulley to the crank and then fit your pinned MMS pulley on. Then tighten the bolt and dare it to move with about 15psi.

Good luck with your testing.

John

 

Are you snapping the belts on accel or when you let off?

If it's when you let off maybe you need a bigger blowoff valve?

I think Bos' issue might be tensioner or alignment related. In his case he might need to check the runout on his pulleys.

 

XLR8NSS, Yep both sides of all 3 spokes have nice little pin divots. I followed up on your advice about the machine shop doing some pin work on both pulleys. The machinist was freaked out on the pics that I showed him. He said for me to bring him a new LS1 CP and the MMS CP and he will pin it to the spokes. I will use this set up on the new Forged 348 9.1-1 beastie sitting in the garage.

PSJ I snap the belts right at the 1/8 mi mark at the track, pretty funny both belts decided to go to crap at that point. So its under pretty hard acceleration at that point. I am also launching with the spray on so that probably doesn't help things. lol one day it will go
J
PS car is back on the road and we will head to the track tomorrow to see what happens.

 

TRACK UPDATE, nothing new, broke the f@#king belt on the 2nd F@#king pass AGAIN. This is getting old. I am taking the MMS pulley off and going back to the stock ATI CP. I will be digging into the car now to see if the dowels were sheared off again.
I launched soft at 1800rpm with crappy 1.80s and still managed to snap the belt. At least with the ATI CP I was in the mid 11s. With the MMS pulley I can't break out of the 12s
Anyone want to trade their turbo kit for my S/C kit lol.
J

 

I think clockwise on the pulley is not the way you want to turn it. The pulley doesn't want to spin b/c of the sc not wanting to spin, but the cp turns clockwise, so you'll want to seat the mms pulley counter. I have recently had this same problem stepping up cp's, my first one came loose and was throwing the belt and sheared the pins. I have another on now, more locktite, more tq on the bolt, and a better belt alignment(still working on the exact spacing), and testing in baby steps. Plus, slow testing slows belt consumption and saves $$ . Note to self:turbo's don't have belt problems...

 

Oh and try cleaning the hole out so the locktite has good contact w/ the crank. I used brake cleaner, and a pack of those pipe cleaners kids use in school projects with the bristles on them, like $.70 a pack at walmart in crafts. Got a good bit of black dust crap out.

 

Thanks Azzhauler, going through this really sucks. Yeah I figured that clockwise was not the way to go, after much thought on what XLR8NSS had to say. But this is what I found out upon disassembly.
MMS Pulley still had all three pins intact and still on the clockwise fins. So I got real confused right here. I figured that I would find sheared pins but that wasn't the case. Checked and rechecked the alignment of the pulleys and it is dead on with a metal straight edge= more confusion and starting to get frustrated. Ran a bit of threaded rod down the crank too clean it out. Then hit it with brake cleaner. Cleaned the crank bolt, checked the end of it to see if the red paint that I put on there was scratched or nicked(would indicated bolt bottoming out) paint was A O.K. Bolt length is fine. Started banging head on the ground as it began to sprinkle. Thanks God Put everything back together clocked the MMS pulley, as I am giving it another chance.... to the counterclock wise side spokes. Torqued it down and thats where I am at now. I was throwing ideas at my Dad and he is thinking my belt might be too long even though I am not close to bottoming out on the tensioner. Sounds like it might be as I listened to him. He figures that with the belt being a tad bit too long it is slacking up at upper RPMS on the topside of the pulleys and then snapping when the slack is taken out at the bottom of the rotation causing it to snap. Sounds good but...
I was running a K060400 which is 40 3/4, on my MMS/3.4 set up. This belt still has plenty of room to tighten down on the tensioner.
I am thinking of going to a K060380 which is 38 3/4. It might be a little tight going on but I won't have much slack to take out with the tensioner.
Thoughts/comments on the above theory?
J

 

I would give a shot in mis-aligning the s/c in the opposite way it 'could' flex the brackets under load. Not alot, but 1/16" or maybe 1/8" overall from one pulley to another (measured with straightedge). You could do this by just installing small shims on one side of the mounts. Or, maybe is it easy for you to get to a dyno ? You could video/watch (with saftey glasses ) the s/c while it is on the dyno under load.... Idea being that if there is visable flex there, you may have found your problem.

I am sure that keying the crank like you say you are, and figuring out how to get the pulley to have very little runout would not hurt.....

Shooting out ideas,
'J
98 T/A
369ci Iron Block
8.5:1
FI plans, but what ?

 

Well I had to go with a K060400 (40 3/4)
The parts stores around here didn't have the k060380 in stock so I bought a 390k6 which was 39 5/8 long and the above mentioned 400 belt. The 39 inch belt was way too small. I tried to get it on but no dice. So on went the 40 incher again. Hopefully it will live. So if you have a MMS/3.4 pulley combo the 40 3/4 looks to be your best bet.
Time to hit the sack,
J

 

Chris our dyno guy won't go for that. Safety glasses won't help much if the crank comes out to play
Yeah these brackets flex way too much and that's with arm strength. I can't imagine what engine torque is doing to the damn things. They really need to be braced somehow. I will get a good look at the set up when the engine is out of the car when we swap motors. Then I can have something made up to help with the flex.
Thanks for the ideas tho,
J