blu00rdstr

I removed the tensioner from the MMS bracket and now have 85% wrap on the blower pulley. The belt used to depart the blower pulley early and route around an idler pulley to get to the tensioner. The belt is now 9" shorter and much tighter. The tensioner was then used to tension the alternator, it is reversed and sits in front of the alternator.

I used two long bolts to place the tensioner between the alternator and the top mounting hole. I can't believe how easy it was. Only mod was to notch the tensioner, and cut 3/8" pipe for spacers.

I unbolted the ribbed pulley from the tensioner, then ran a 10-1.50x100mm bolt through the alternator into that same pulley hole with a 1" spacer between the tensioner and alternator.

I ran a bolt through the nearest tensioner mounting hole into the alternator mounting bracket with a 2" spacer. (needs a 10-1.50x150mm bolt)

I replaced the Drive Rite 960K6 (96" 6rib) belt with a Drive Rite 870K6 (87" 6rib).

Front view of tensioner on alternator:


Side view of tensioner on alternator (no flames, couldn't find 6" metric bolt):


Major pulley wrap :





[Modified by blu00rdstr, 3:02 PM 3/25/2004]

boblackhardtop

got the idea but picts worth a thousand words

corvettebob1

Great idea, will it work with a stock ATI bracket?
What's the difference between a MMS bracket and the ATI?
Has anyone used 2 large idler pulleys on the stock bracket?
Last year ATI sent me a new set of pulleys and the lower pulley is larger then the outboard one, can I use a second larger pulley to get more wrap?

blu00rdstr

I don't see why this wouldn't work with the stock ATI bracket. If I recall correctly, on the ATI bracket, the belt also departs the blower pulley early to go to the tensioner.

I updated my original post to include pictures.

NOTES:

1) I need to replace the mounting bracket bolt with a full length bolt, I'm using a connecting nut between two bolts right now.

2) I also need a spacer inside the bracket, I noticed that over-tightening the bolt squeezes the bracket arms together.

3) I also could've trimmed the tensioner better, I thought it would be tighter. A straight flat cut would work, or I could just trim off all the flange for asthetics.

4) The tensioner is almost overly effective when applied this way. The belt really twangs when plucked. No breakage yet. Note that the alternator does not pivot away from the belt, it pivots in a way that any force applied by the tensioner is leveraged and multiplied.

HIGHRPM

Hi Bill, Good idea..... If you need any help with spacers and custom parts give me a call... I have a machine shop and I'll help you fab up what ever you need.


[Modified by HIGHRPM, 2:30 PM 3/25/2004]

boblackhardtop

American ingenuity

blu00rdstr

Thanks! I have other ideas to share with you later.

cnationshb

pretty clever

QuickSilver2002

Great Idea!!!!!!

I bet it makes changing the belt really easy.

denscor

great idea you will have to show us how you did

blu00rdstr

Thanks guys.

The reason I did this was to get rid of the thick layer of belt debris on the MMS bracket (as Highrpm saw). This seems to have solved the belt debris issue. Also to increase boost at higher rpm, which I thought I was losing due to belt slippage. I didn't see a large increase in higher rpm boost, but I've gained lots of torque in part-throttle and the low to mid range.

Driving a FI car without belt slippage is...different. It does things now it didn't do before. I wanted to watch the boost gauge, so in second gear at 40mph I squeezed both the gas and brake, and it started doing a burnout. From a roll in second I can roll onto the gas gently (from part to full throttle in 1-2-3 seconds) and it starts breaking loose before WOT. Before I could start holding full throttle halfway through second since I could feel it breaking loose but kept straight. Now it spins harder and wants to start going sideways if the road is crowned a bit.

Something I hoped would happen but didn't, was to increase boost numbers at higher rpm WOT. I think I maxed out the P-1SC.

corvettebob1

blu00rdstr,
Did your mod today but I see some real problems with it right up front.
First to make the tensioner work you have to leave the bolt loose that the alt pivots on and the the 2 bolts going to the tensioner.
I know they can be loctited so they dont back out but I see a problem down the road with a broken alt. bracket and or alt housing.
Because of the spacers required to move the tensioner away from the alt the bolts are long and deflect now not being able to tighten them down will cause them to flex and eventually break the alt/pwr steering bracket and possebly the alt housing itself.
Another issue is the alt housing is almost touching the left shock tower strut on the frame.
This may be cured by a shorter belt, maybe a better idea would be to just build a manual tensioner like we used to have on cars, you know just a arm with a slot for adjustment.
Great thought though, keep the ideas coming.
Gotta love that belt wrap and getting rid of 2 idler pulleys.

blu00rdstr

Yeah, but does it make more power now?

I think if the bolts are just a bit overlength, they'll tighten down and still allow it to move freely. But it definitely should have a spacer inside the bracket.

I think if the bolts are hardened they won't flex.

The alternator shouldn't come too near the shock tower, I have a 3.5" pulley and used a 870K6 belt. On my install the tensioner is at the last ridge. I tried a 1/2 shorter belt (865K6) but it was too short, and would be too tight.

As far as a manual adjuster, Andy of A&Acorvette has a manual adjuster for the alternator. Be careful of getting rid of a tensioner, I've heard that belts may snap if only a solid tensioner is used.

How does it working for you? So far the only problem I've had was a pulley bearing seize up.

corvettebob1

When I tighten the bolts down the tensioner is locked in place, which is what I would expect since it has to pivot through the spring.
I do have the spacer between the ears of the bracket so there is no problem with crushuing the alt. bkt.
However the use of hardened bolts will not resolve the deflection problem, in fact the bolts I used were hardened. (the only ones I could find in that size)
If we welded an ear on the alt bkt for the bottom bolt of the tensioner it would work properly because the whole tensioner would not need to rotate.
You cannot get enough clamp load on the single bolt to hold it in place for long.
As for the belt, mine is a .6 longer then yours because I have the larger idler pulley from ATI in the lower position on the blower.
I don't think I can get the 87" belt on but I did find an 87.2 belt last night.
I will try a shorter belt today but I am going to a solid tensioner just for piece of mind there should no problems with it if you don't over tighten the belt.
My real concern is the long bolts cantilevered out with no support over the belt, I just have horror thoughts if 1 breaks or lets loose at WOT or even at idle.

blu00rdstr

I wish it could be done without spacers, but the belt is in the way. Maybe someone more creative than I could make a bracket to position it flush and add some bushings to allow it to pivot. It's basically a no-cost mod now.

blu00rdstr

Update after two weeks of daily driving:

1) I expected some problems with bolts coming loose or bending, that hasn't happened.

2) The top of the tensioner flange hits the hood and cut through the insulation. This would need to be trimmed.

3) There's a reinforcing bracket on the fender well right next to the alternator. As the belt stretches, the alternator body gets closer to the bracket. The alternator makes contact with this on right turns, creating a right turn vibration. A belt only 1/2" shorter is too short to be installed, a belt 1/2" longer is too long to tension. Due to the direction the alternator pivots in, applying the tensioner this way does not provide enough adjustment travel.

Summary: This was an interesting experiment, a big advantage was a major improvement on the blower pulley wrap and traction. However given the drawbacks, the right way to go in the long term seems to be the A&A pulley setup with the tensioner between the blower and crankshaft, which also delivers the same pulley wrap and 10" shorter belt.

blu00rdstr

One more update for the records...

Two changes made:

1) Ground the remaining flange off the tensioner, this gives the hood clearance.

2) Clearanced the alternator, it taps the brace on the frame which is for the shock mount. Removed alternator, placed the side of a large deep socket against the brace, and whacked it with a hammer until I had a nice concave socket impression. Note: Causes ears to ring for a good half hour.

Zero belt debris on blower pulley to date.

However, now I'm beginning to get some belt squeal from the crank pulley, and boost has again dropped to 6psi. Amazing what I'll do to avoid the $1,000 or so for the 8-rib upgrade.

Terry Burger

A&A has a pretty good deal on their 6-rib bracket, you might want to try that out.

SideStep

Does Andy's latest 6-rib bracket limit the belt slip significantly when compared to the stock ATI setup???

Terry Burger

I think it's a big improvement over the stock ATI bracket. I particularly like that its rather simple and that you wind up with a much shorter belt.