Problems with crank pulley bolts snapping?

[eunos1800]

Hi Guys,

I've had my BRP hotside fitted for just under 1 year now, about 3 months ago i bought a Auto-tensioner kit and fitted it.

Yesterday the crank pulley complete with the AC, Power steering, Alternator pulley came off the car while driving.

http://i32.photobucket.com/albums/d43/cbr6fs/SmallIMG_3441.jpg

All 4 bolts were sheared and all 4 were sheared at around the same length, and fairly deep, so i am sure they hadn't worked loose but had actually snapped.

http://i32.photobucket.com/albums/d43/cbr6fs/SmallIMG_3444.jpg

As the newest part of the SC kit is the Auto-Tensioner I'm wondering if this could have caused the bolts to snap.


Anyone else experience anything like this?



Cheers
Mark

[Banshee]

Ouch...There was a discussion about this a few months ago. Consensus was that the bolts were too long, and bottoming out before they were fully tighten.

[eunos1800]

Yea Unfortunately i wasn't able to turn the engine off quick enough so the radiator also blew, (high pressure caps and plastic radiator, not a good combination).

http://i32.photobucket.com/albums/d43/cbr6fs/SmallIMG_3436.jpg



Did a cam belt change while everything was out, so not a total loss.

http://i32.photobucket.com/albums/d43/cbr6fs/SmallIMG_3447.jpg



Cheers
Mark

[J_Man]

I was thinking about starting a thread about this on Miataforum, but I've been busy lately (and a bit lazy too) ...

Recently I was playing with the crank pulley parts of my '94 (adding a trigger wheel) and I noticed that the key pin on the pulley boss was bent a little bit. Which means over these years of performance driving, the supercharger was putting more load on the crank pulley than the stock 4 tiny 6mm bolts could handle. Yup, my bolts were torqued to spec and loctited. The next thing to go were the bolts

My solution -> a couple of months ago I re-taped the pulley boss bolt holes to 8mm and used 12.9 mm bolts. Now the crank pulley is attached so much better to the pulley boss

This is a must do mod for anyone with a supercharger who is planning to stay in boost a lot

[Banshee]

So how are you able to get a drill into that tiny space to tap the new hole?

[Bill @ Fast Forward]

Take the main crank bolt out and remove the crank pulley boss to properly drill and tap it?

[J_Man]

So how are you able to get a drill into that tiny space to tap the new hole?

You don't have to drill while the stuff is on the car.
The pulley boss is removable (and is held in place by the big crank bolt). It takes 15 minutes to take it all out (pulley boss, pulley, trigger wheel and spacer).
You don't have to remove the timing belt when doing this.

I used a new pulley boss - because I needed the thinner Mazda one, since I was adding a '99+ trigger wheel which my '94 didn't have stock - this project of mine was the reason I took it all apart and led me to finding the bent key pin.

But if your key pin is bent, you don't have to replace the entire boss - Mazda sells just the key pin (this is different than the woodruff key) as a separate part too - just look in the part diagrams on the page with the pulley and pulley boss.

At home I also have a bunch of pictures comparing the stock vs the 8mm bolts setup, I just haven't put them online yet ...

[J_Man]

Take the main crank bolt out and remove the crank pulley boss to properly drill and tap it?

Yes, that's what I did. I ordered online a good tap, the corresponding drill bit and the 12.9 grade allen head bolts (you can't use hex head because the heads won't fit) from McMaster.

For my particular setup - the thinner pulley boss ('96+'05), the '99+ trigger wheel, and the OEM pulley which uses a separate spacer (not the stamped OEM pulley) and I don't have a separate supercharger belt pulley - the max length bolts I could use (to utilize as much thread of the pulley boss holes as possible) were 8x18mm. The proper length bolts for your setup might vary - you have to measure.

And different length bolts are needed for the Miatas which use the stamped crank pulley. Mazda has mixed these pulleys over the years since mid nineties so it can't be guessed in advance which pulley do you have stock. You just have to look at it. And Mazda sells different OEM bolts for the two type of pulles.

I torqued the new 8mm bolts to 30 lbs/ft (12.9 grade !!! :))

[J_Man]

Also, to fix these bolts even if you have a failure, you don't have to take out valve cover, timing belt covers, etc. - what the guy above did.

It is much easier to fix than what is shown. All you have to do is remove the big bolt (and the 4 tiny bolts if they are not already broke), then take pulleys/boss out. Fix it and bolt it back in.

[Banshee]

Thanks, I was told never to touch that big bolt. Bad things can happen.

[eunos1800]

Also, to fix these bolts even if you have a failure, you don't have to take out valve cover, timing belt covers, etc. - what the guy above did.

True,
I had been waiting to do the cam belt service, so while the radiator and everything was out i decided that it would be a good opportunity :)

Actually removing the sheared bolts is pretty simple, even easier if you have the stock ARB's.
I had to drop my FM ARB to get at the pulley bolts, which of course means dropping the undertray.
This actually takes longer to do than to remove the sheared bolts :(

The bolts were sitting flush and were loctited in place.

As i said in my earlier post, its strange that with the stock tensioner the crank pulley and bolts where fine for 9 months or so, but after only a couple of months of the Auto-Tensioner they shear.

I know for a fact that the Auto-Tensioner puts a hell of a lot more Tension on the SC belt than you can do with the stock Tensioner setup.
Maybe this extra tension coupled with the extra leverage that is experienced from the SC crank pullet sticking out further caused the failure.

I guess the only way to see its to sit and wait for other crank bolts to fail :(


As a solution for me personally, i will monitor the bolts and just step up a size at the slightest sign of trouble.


Cheers
Mark

[Banshee]

Tom,

What grade bolts are supplied with your pulley?

[eunos1800]

Tom,

What grade bolts are supplied with your pulley?

No idea about anyone else, but no bolts were supplied with my pulley.


Cheers
Mark

[Tom @ Fast Forward]

My crank bolts are the highest grade available:


Head Style Standard Hex
Material TypeSteelGrade/Class Class 10.9
System of Measurement Metric
Thread Size M6
Metric Thread Pitch 1 mm
Length 35 mm
Head Width 10 mm
Head Height 4 mm
Thread Style Right Handed
Thread Length Fully Threaded
Thread Fit Class 6g
Rockwell Hardness C32-C39
Minimum Tensile Strength 145,000 psi
Specifications Met Deutsche Industrie Normen (DIN)
DIN Specification DIN 933

[Tom @ Fast Forward]

No idea about anyone else, but no bolts were supplied with my pulley.


Cheers
Mark

When I just sell the pulley, I don't include the bolts and spacer. I 'assume' (perhaps a bad idea) that I am simply replacing the pulley. With my kits, I include the spacer and bolts.

[eunos1800]

Hi Tom,

A happy new year to you.

Have you experienced or come across this problem before?

[Tom @ Fast Forward]

Hi Mark,

No. I have not seen that problem before. I would think that, as long as the pulley is seated properly and the bolts are long enough, there should be no problem. If the bolts are too long and bottom before thet pull the pulley up tight, I could see it happen. The bolts should be 35mm and 10.9 series. The pulley has to be flat and pull up tight.

The stamped main pulleys require the addition of a 1/4" spacer. The cast main pulleys don't use the spacer. If your main pulley came with a thin spacer, it must also be still used. The SC pulley, if properly installed, should have about 1/16" space from the main crank pulley. If the rib face pulls up tight to the main pulley, the spacer is missing and the bolts could shear. If it sticks out ~1/4" away from the main pulley, the spacer is not required, the bolts will be too short and they may shear as they are sufficiently threaded into the holes.

[eunos1800]

Thanks for the response Tom.

If you look at the pics of the crank pulley boss you can see that most bolts have sheared inside the holes, more than one taking a chunk of the surrounding metal with it.

http://i32.photobucket.com/albums/d43/cbr6fs/SmallIMG_3444-1.jpg

I was in 2 minds on drilling the holes out to a size up and retapping as a 8mm thread, but i was then worried i would weaken the pulley.

Do you have plenty of the mounting bolts you use in stock?
If i send you an email with my address do you think you could send me a packet?
Obviously i will reimburse you with the cost and P&P.


Cheers
Mark

[Griff]

I had this happen when I fitted a BBK with my JRSC and the bolts were too long.

I think if you have any doubts I'd just got to a larger size... I can't see it weakening the pulley by any significant amount.

[Tom @ Fast Forward]

This is a correct install with the spacer. Crank pelley, spacer and SC pulley are all in tight, flat contact.

http://www.fastforwardsuperchargers.com/crank-pulley-alignment%201.jpg

This is incorrect as the Crank pulley and SC pulley contact at the ribs (no gap) and the screws can snap/shear.

http://www.fastforwardsuperchargers.com/crank-pulley-alignment%202.jpg

The crank pulley is drawn for looks and may not be accurate in size. If it were a cast pulley, the inside would be thicker and fill the gap, not requiring a spacer. The cast pulley is basically 1/4" thicker in that area.

[oe_tuner]

My crank bolts are the highest grade available:


Head Style Standard Hex
Material TypeSteelGrade/Class Class 10.9
System of Measurement Metric
Thread Size M6
Metric Thread Pitch 1 mm
Length 35 mm
Head Width 10 mm
Head Height 4 mm
Thread Style Right Handed
Thread Length Fully Threaded
Thread Fit Class 6g
Rockwell Hardness C32-C39
Minimum Tensile Strength 145,000 psi
Specifications Met Deutsche Industrie Normen (DIN)
DIN Specification DIN 933

Tom,

The bolts in my kit seem to fit fine, but I noticed the heads had 8.8 stamped on them and not 10.9 (which I thought was the grade marking).
Did I get the right grade bolts in my kit?

Thanks!

[Tom @ Fast Forward]

I use those interchangeably with the black 10.9 version. The stock Miata bolts are also 8.8, I believe. There are a lot of the 8.8s out there. The problem is not the strength of the bolt as much as the proper install as shown in the pictures. Be careful when you torque them down. Mazda calls for them to be 8-13 ft-lbs. I prefer around 10 ft-lbs. If you torque them to 30 ft-lbs, as has been suggested and they snap, call J-Man.

[dazooom]

As usual.....GREAT customer support from Tom. Doesn't even matter if it's Sunday evening, with exciting football playoff games or not, he's there tending to business! Not only explaining how the pulleys/spacers should bolt together, but pictures, too! And communicating with me on how to ship an important parts package out to me, tomorrow....:biggrin:

[J_Man]

If you torque them to 30 ft-lbs, as has been suggested and they snap, call J-Man.

If you reread my post 30 lbs/ft only about the bigger 8mm, 12.9 grade replacements I did. Try snapping them with 30 lbs/ft :) you won't, you'll have to try quite higher thanthat. Of course if one tries to do that with the 10.9 grade 6 mm bolts these will snap long before nearing that number

[J_Man]

The stock Miata bolts are also 8.8, I believe.

The stock 6mm ones for the crank pulley from Mazda are 10.9 grade. At least the ones I got from Mazda few months ago for some research had 10.9 marking on the cap

[Tom @ Fast Forward]

Mazda recommends 12-14 Ft-lbs for 8mm bolts.

[J_Man]

The stock 6mm ones for the crank pulley from Mazda are 10.9 grade. At least the ones I got from Mazda few months ago for some research had 10.9 marking on the cap

I just checked the bag with the original bolts which came on the Miata in '94 - these are 10.9 grade too. So, both original and current gen crank pulley bolts from Mazda that I have are 10.9 grade

[J_Man]

Mazda recommends 12-14 Ft-lbs for 8mm bolts.

This is a correct value for 8.8 grade 8mm bolts

I'll try to find and post a table with torque numbers about different bolt sizes and grades

[J_Man]

Here, a table with standard torque values for different size and grade SAE and metric bolts:

http://www.dansmc.com/torque_chart.htm

10 lbs/ft is spot on for the stock 6mm 10.9 grade bolts

[Tom @ Fast Forward]

Great job. Great numbers.

Just remember folks, if you use those numbers and they snap, call him.

[J_Man]

Great job. Great numbers.

Just remember folks, if you use those numbers and they snap, call him.

All your calls are welcome :euro:

[oe_tuner]

I use those interchangeably with the black 10.9 version. The stock Miata bolts are also 8.8, I believe. There are a lot of the 8.8s out there. The problem is not the strength of the bolt as much as the proper install as shown in the pictures. Be careful when you torque them down. Mazda calls for them to be 8-13 ft-lbs. I prefer around 10 ft-lbs. If you torque them to 30 ft-lbs, as has been suggested and they snap, call J-Man.

So Tom,

Based on the chat below the post, and from what I found out about bolt grades, clearly they are not interchangable. :excl: Will you be sending me the correct spec bolts for my kit?
Based on the failures described here and the fact that Mazda uses 10.9 on a pulley with less load, I do not feel comfortable using the 8.8 bolts you sent me.

[Tom @ Fast Forward]

No problem. I'll send some out.

[Bill @ Fast Forward]

Would it be beneficial for those of us using 6mm bolts to step up to 12.9 grade? Or are there other properties of the higher grade that could be bad?

I have had the bolts on and off enough times now that I think I am going to replace them with new ones. I am a sort of pulley addict :).

Bill

[J_Man]

If you want 12.9 grade bolts, open
www.mcmaster.com

and type part number 91290A334

There you can also see a technical drawing, a 3d model, etc.

You will need 5mm hex socket for allen head bolts to torque these

The price is $10 for a box of 100 bolts

These are 35 mm long, M6, pitch 1.0 - so they match ONLY the size Tom posted above.

Everyone else using BRP crank pulleys or homemade kits or something else - your bolt leghts might vary because of the different setups, different pulley thickness from different manifacturers, etc. - DON'T blindly jump on the bolt length - talk to your kit supplier first and if you can't find the proper bolt length (so you utilise the full boss thread available and yet not bottom out) you need, or disassemble the parts, measure and calculate!

[J_Man]

Would it be beneficial for those of us using 6mm bolts to step up to 12.9 grade? Or are there other properties of the higher grade that could be bad?

I have had the bolts on and off enough times now that I think I am going to replace them with new ones. I am a sort of pulley addict :).

Bill

Since you like to play with hardware, do what I did. Drill and tap for 8 mm / 1.25 mm pitch and put in 12.9 grade bolts. Then if you some day go with 150mm or bigger crank pulley and stay for a month in boost at the race track you will be sure the crank pulley will be the last thing to give away ... :biggrin:

Look at these pics. One shows what 4 years of racing at least once every month with my Coldside M45 did to the pulley boss. They key pin got so bent, showing that the stock 10.9 grade 6mm bolts torqued to the number Mazda shows in the workshop manual couldn't clamp the pulley to the boss well enough to handle the power the supercharger was using - and I am using a M45, nowhere close to high power R4 setups.

The second picture is a comparison between the OEM 6mm bolts and the 8mm 12.9 ones from McMaster I replaced them with. The replacement ones are much beefier and the much higher torque they can take = pulley clamped much stronger to the pulley boss

[Bill @ Fast Forward]

Actually the most pulley I am going to run is a 130 and probably will just stick with the 120. But putting in larger 8mm bolts for engine #2 before it goes in looks like a good idea. Especially since I will be doing a timing belt change anyway. I notice in the picture of the comparison of the two bolt sizes that the pulley boss you used for the 8mm looks different?

Bill

[Tom @ Fast Forward]

I'm sure J_Man will tell you all why I am wrong. He does a great job of that on a regular basis. It appears he has finally picked a subject that has put fear of catastrophic failure in your minds. However........

Would the 8mm be better than the 6mm bolts? Perhaps. Why not go to 10mm bolts then? Would they be better than the 8mm bolts? Probably. Does that make the 8mm bolts bad? Not at all. Does the fact that the 8mm bolts are better than the 6mm bolts supplied make the 6mm bolts bad. Absolutely not, for exactly the same reason. Are 12.9 grade bolts better than 10.9? In some applications. Are 10.9 grade bolts better than 8.8? In some applications where clamping force is the critical requirement. Does that make 8.8 bad for this application? Absolutely not.

Panic is easy to create when ones shows the effect of an accident but not the cause. The bolts in the pulley disaster shown could have been 12.9 grade and still have occured. The problem is not the size or grade of the bolts used but the application and/or the mis-application of the bolt. The application here is not really one of tension or compression but shear. These bolts are under stress of shear. I'll bet that one of two mis-applications caused that accident to occur. First, there was an air gap (missing spacer?) in the chain of devices that were being bolted together; or second, the bolts were over torqued.

We must keep in mind that the reason for the torque on the bolts is BASICALLY to keep them from un-screwing and coming loose; and secondly, to keep the pulley tight enough as to not be able to impact shear the bolts. The more torque you apply to the bolts, the more tension load you set on them and the more likely they are to snap under load. Even if I were to use 8mm bolts, I would still torque in the 8 to 13 ft-lbs as that is sfficient to keep the pulleys tight and not pre-load (stretch) the bolts. Just because they are good for 29 ft-lbs does not mean that it is prudent to do that. If it were one bolt or nut and it was on center with the axis of rotation, I would get as big as I could fit and torque it as tight as I could.

I would venture that, in this application, grade 8 4mm bolts properly fitted and torqued would last the life of the car. With that said, if you change from the bolts supplied or torque them to higher values than called out in the manual, you are on your own. It is not the size of the bolt or the grade but the proper application that matters.

It appears that, for the moment, the world is still safe from coming to an end. ;)

[Bill @ Fast Forward]

It appears that, for the moment, the world is still safe from coming to an end. ;)

Whew! Had me worried for a minute there!!

[J_Man]

Well, I was using the stock bolts because I thought these were ok. I never sheared them, but with with all that time of engine going between boost and decellerating the pulley moved and bent the pin. My OEM bolts were torqued properly to Mazda workshop manual specs with a good calibrated torque wrench and loctited so they don't move. The day I noticed the slip they were still torqued at what Mazda says. And I am not even using an extra pulley - just the OEM Mazda one.

I am just sharing my experience and my solution. 10mm you say? I'll keep an eye on the pulley this racing season and the following ones and if the current clamp force is not enough and still lets the pulley slip, I will upgrade. I doubt I will need to go up to 10mm though - others experienced folks at Miataforum already had similar experience with 6mm bolts and racing, upgraded to 8mm and never had problems since. I doubt my case will different.

I am not saying everyone should rush and change their bolts to 8mm ones. Some people go in boost once in a decade, they don't race their cars often (if ever at all) and most likely the stock size bolts will have life longer than their own.

I'm sure J_Man will tell you all why I am wrong. He does a great job of that on a regular basis. It appears he has finally picked a subject that has put fear of catastrophic failure in your minds. However........

Would the 8mm be better than the 6mm bolts? Perhaps. Why not go to 10mm bolts then? Would they be better than the 8mm bolts? Probably. Does that make the 8mm bolts bad? Not at all. Does the fact that the 8mm bolts are better than the 6mm bolts supplied make the 6mm bolts bad. Absolutely not, for exactly the same reason. Are 12.9 grade bolts better than 10.9? In some applications. Are 10.9 grade bolts better than 8.8? In some applications where clamping force is the critical requirement. Does that make 8.8 bad for this application? Absolutely not.

Panic is easy to create when ones shows the effect of an accident but not the cause. The bolts in the pulley disaster shown could have been 12.9 grade and still have occured. The problem is not the size or grade of the bolts used but the application and/or the mis-application of the bolt. The application here is not really one of tension or compression but shear. These bolts are under stress of shear. I'll bet that one of two mis-applications caused that accident to occur. First, there was an air gap (missing spacer?) in the chain of devices that were being bolted together; or second, the bolts were over torqued.

We must keep in mind that the reason for the torque on the bolts is BASICALLY to keep them from un-screwing and coming loose; and secondly, to keep the pulley tight enough as to not be able to impact shear the bolts. The more torque you apply to the bolts, the more tension load you set on them and the more likely they are to snap under load. Even if I were to use 8mm bolts, I would still torque in the 8 to 13 ft-lbs as that is sfficient to keep the pulleys tight and not pre-load (stretch) the bolts. Just because they are good for 29 ft-lbs does not mean that it is prudent to do that. If it were one bolt or nut and it was on center with the axis of rotation, I would get as big as I could fit and torque it as tight as I could.

I would venture that, in this application, grade 8 4mm bolts properly fitted and torqued would last the life of the car. With that said, if you change from the bolts supplied or torque them to higher values than called out in the manual, you are on your own. It is not the size of the bolt or the grade but the proper application that matters.

It appears that, for the moment, the world is still safe from coming to an end. ;)

[J_Man]

It appears that, for the moment, the world is still safe from coming to an end. ;)

For now ;) Until the North Koreans or the Iranian start throwing nukes ... :online2long: :rofl: Can our Eaton blowers stand a nuclear blast?

[eunos1800]

The bolts that were fitted were 8.8's.

These were the bolts that BRP (or what ever its called this week) sent out with the complete kit.

So if any of you guys purchased a BRP kit i would check your bolt ratings.

http://i32.photobucket.com/albums/d43/cbr6fs/SmlPicture005.jpg

http://i32.photobucket.com/albums/d43/cbr6fs/SmlPicture016.jpg

http://i32.photobucket.com/albums/d43/cbr6fs/SmlPicture017.jpg



Cheers
Mark

[Tom @ Fast Forward]

Mark,

Was the pulley properly seated? Did you use the thin factory sapcer if it had one? Is you main pulley the stamped or cast pulley? Did you have the 1/16 to 1/8 space as shown in my pictures or were the two pulleys touching as shown in the second picture? What did you torque them to? What WHP are you making?

I ask because I have the 8.8 bolts in my 99 with 210WHP (well, someplace between 210 and 216 depending. I said 216 one day and someone corrected me, as usual. :)) and they have been there a long time (30K mikles?).

[J_Man]

... and someone corrected me, as usual. :))

:rofl: too funny. I almost spilled my drink over the keyboard. Off to get some popcorn

[Tom @ Fast Forward]

Mark,

One more question. I see it looks like you used split ring lock washers under the head of the bolt. Were they long enough to compensate for the difference? Could you measure from the bottom of the head to the end of one of the snapped bolts? Whether it is my kit or BRP's kit, the size is 35mm long. Do you know how much of the tip was left in the tapped plate?

[eunos1800]

Was the pulley properly seated?.

Yep, 100% sure as i had problems with a wobbly pulley when i first fitted the 105mm

Did you use the thin factory sapcer if it had one?

No factory spacer on mine

Is you main pulley the stamped or cast pulley?

Can't say as i noticed, I'll take a gander tomorrow.


Did you have the 1/16 to 1/8 space as shown in my pictures or were the two pulleys touching as shown in the second picture?

Don't know the size of the spacer but there was/is one fitted and the SC and crank pulleys were not touching.

What did you torque them to?

13 Nm

What WHP are you making?

No idea, 65/105 (9psi) Hotside, so I'm guessing around the 200bhp mark.

Had the SC fitted for near on 1 year and about 35000 miles.


Cheers
Mark

[Tom @ Fast Forward]

If you used the pulley spacer, it must be stamped. The cast pulley is thicker and doesn't use the spacer.

[Tom @ Fast Forward]

They went out UPS today.

So Tom,

Based on the chat below the post, and from what I found out about bolt grades, clearly they are not interchangable. :excl: Will you be sending me the correct spec bolts for my kit?
Based on the failures described here and the fact that Mazda uses 10.9 on a pulley with less load, I do not feel comfortable using the 8.8 bolts you sent me.

[oe_tuner]

Thanks Tom!

I did some research on bolt grades, clamp loads, torque specs and such.

Based on what I have read, an 8.8 M6 bolt should not even be torqued to 10lb-ft. This can put the bolt into an over stretched condition and could cause the bolt to fail if not immediately, then eventually.

These sites have some useful information about metric bolt specs.
http://www.imperialinc.com/pdf/A_FastenerTorqueCharts.pdf
http://euler9.tripod.com/bolt-database/22.html

The M8 bolt idea seems like a good idea, but a lot of work. It looks like the parts have enough meat on them to take the additional hole size. Your clamp load is limited by the torque you can apply to the fasteners, so if people are having problems with the pulleys (assuming they are clean and assembled correctly) slipping then changing to M8 would help. Considering the pile of parts stacked under the pulley (if you have the stamped one), the additional cantilever of the new pulley position, the belt and tensioner load and the increased torque input from the SC being driven, it is not suprising that the little bolts may not be up to the job.

Anyway, thanks again for sending the correct bolts out today. I appreciate your all quick responses.

[jwalton]

Thanks Tom!

I did some research on bolt grades, clamp loads, torque specs and such.

Based on what I have read, an 8.8 M6 bolt should not even be torqued to 10lb-ft. This can put the bolt into an over stretched condition and could cause the bolt to fail if not immediately, then eventually.

These sites have some useful information about metric bolt specs.
http://www.imperialinc.com/pdf/A_FastenerTorqueCharts.pdf
http://euler9.tripod.com/bolt-database/22.html

The M8 bolt idea seems like a good idea, but a lot of work. It looks like the parts have enough meat on them to take the additional hole size. Your clamp load is limited by the torque you can apply to the fasteners, so if people are having problems with the pulleys (assuming they are clean and assembled correctly) slipping then changing to M8 would help. Considering the pile of parts stacked under the pulley (if you have the stamped one), the additional cantilever of the new pulley position, the belt and tensioner load and the increased torque input from the SC being driven, it is not suprising that the little bolts may not be up to the job.

Anyway, thanks again for sending the correct bolts out today. I appreciate your all quick responses.

Oh crap... Hey Tom, if you happen to be running by Mike's Place in the next week or so, could you bring some of the better bolts to him along with your BTB kit (might as well, besides you can see if I got one of those awesome BRP "enhanced" superchargers)? Obviously, just add it to my motor rebuilding tab <sigh>.

[Tom @ Fast Forward]

Jim,

Will do. It won't be until Thursday/Friday.

[eunos1800]

Mark,

One more question. I see it looks like you used split ring lock washers under the head of the bolt. Were they long enough to compensate for the difference? Could you measure from the bottom of the head to the end of one of the snapped bolts? Whether it is my kit or BRP's kit, the size is 35mm long. Do you know how much of the tip was left in the tapped plate?

Everything looked fine.

When i drilled out the sheared section there was a gap between the end of all the screws and the end of the threaded hole.

I've no idea which crank pulley i have, how do i spot the difference between the 2?

The was definitely no factory spacer on my car.


As for the SC pulley and crank pulley touching as shown, i don't see anyway they can touch, the 105mm SC pulley I'm currently using is smaller than the internal dimensions of the crank pulley.

Saying that though the SC pulley is sitting inside the crank pulley.

http://i32.photobucket.com/albums/d43/cbr6fs/Picture551.jpg

http://i32.photobucket.com/albums/d43/cbr6fs/Picture548.jpg

http://i32.photobucket.com/albums/d43/cbr6fs/Picture547.jpg


Cheers
Mark

[Tom @ Fast Forward]

Thanks Mark. When mounted, it should look like one of the two pictures. If they touch like the second picture, you will probably havee problems.

For those of you in the USA, I stopped at our local ACE Hardware and they have the Allen head SHCS 6x1.0x35mm in 12.9 hardness for $0.30 each. $1.20 total.

[Bill @ Fast Forward]

Good info Tom! I will be stopping by ACE!