These belts did a strange thing

[green69rt]

I was installing a dual belt on my car.  It runs from crank to AC compressor to Alternator.   So two belts the same stock number.  I wasn't paying much attention and installed them with the lettering on the belts in different orientation, one read normal and the other read upside down. I could tighten one belt but the other had so much slack that I could almost remove it.   I though I had a bad belt.  Took them off and noticed the lettering so decided to try both with the lettering readable.  Problem gone!!  

Is this some secret that you professional mechanics know?  I don't ever remember reading anything about this.

Picture shows the good installation.

[XH29N0G]

Doesn't it bother you that the lower one needs to be slipped a little more over to the right?




That looks very good.  I know nothing about the orientation and fit.  I had thought they were symmetrical in profile, so it wouldn't matter.

[Nacho-RT74]

its simply than the aligment on our engines is not a NASA science or CNC build LOL... so there is way much tolerance on the pivot and adjusting bolts along with brackets. So one of them can be allways get more tight than the other.... or not.

[John_Kunkel]

I can't explain why turning the belt around made it fit better, makes no sense, but check it again after it runs a while.

It's well known that V-belts with the same part number will vary in length, that's why belts are often sold in "matched pairs". Matching belts involves finding the mold number on the belt and matching it to another belt with the same mold number.

[green69rt]

If I get real ambitious, I might take them apart and show the difference (Probably won't happen.)  My two belts didn't set down in the grove the same amount.  And the difference was not small, lots of slack in one. I could pull the loose belt out by 1-2 inches between any two pulleys.  I took the belts off after seeing the problem because I wanted to measure them.  I couldn't find any difference in the measurement and that is when I decided to mount them with the lettering on both belts up.  It's a mystery.   

[green69rt]

Turns out I have a picture of the belts installed wrong.  You can see how much difference there is in the slack.

[Just 6T9 CHGR]

I can tell you that after a few "spirited" high RPM blasts, the belts will not be in alignment anymore 

[Nacho-RT74]

I'm not an expert on belt setups for pre 71 but if pre 71 cars are like  71, the belt setup is wrong based on the stock setup

Alt upper bracket is diff on AC cars, but that's mainly just because the stock RV2 compressor uses some of the non AC alt bracket location bolts.

Bottom ALT bracket is diff to with a provision running to one of the engine mount bolts

On AC cars, water pump runs on its own belt with an iddler. Steering pump too, but without iddler

But also does look the compressor is aftermarket?

[green69rt]

I'm not an expert on belt setups for pre 71 but if pre 71 cars are like  71, the belt setup is wrong based on the stock setup

Alt upper bracket is diff on AC cars, but that's mainly just because the stock RV2 compressor uses some of the non AC alt bracket location bolts.

Bottom ALT bracket is diff to with a provision running to one of the engine mount bolts

On AC cars, water pump runs on its own belt with an iddler. Steering pump too, but without iddler

But also does look the compressor is aftermarket?

Yes, you got some of it right and I did also.  I ended up piecing together all the brackets until I could get everything to line up.  Not easy, but it's OK now.  Ended up not needing the alt bracket from an AC setup.  It would be interesting to see what other use.

[Nacho-RT74]

Use the correct bottom alt bracket is better. Will give you a stronger alt fitment which is important when you turn on the AC with the compressor drag added to save from heavy vibrations.



sure this is a NEED with the RV2 compressor, but with the long distance between alt and compressor belts slaps A LOT, and vibration is increased.

For whatever reason when I got my car ( 400 with air ) it had the regular bottom bracket, and on a long trip the vibration made to break the top bolt at the rear provision!!!

this was acually not related to the belt deal you have, but about that... mmmm I'm thinking on alt or compresor being not completelly parallel with crank but going inwards on front. couple of milimeters makes a huge difference

[green69rt]

Use the correct bottom alt bracket is better. Will give you a stronger alt fitment which is important when you turn on the AC with the compressor drag added to save from heavy vibrations.



sure this is a NEED with the RV2 compressor, but with the long distance between alt and compressor belts slaps A LOT, and vibration is increased.

For whatever reason when I got my car ( 400 with air ) it had the regular bottom bracket, and on a long trip the vibration made to break the top bolt at the rear provision!!!

this was acually not related to the belt deal you have, but about that... mmmm I'm thinking on alt or compresor being not completelly parallel with crank but going inwards on front. couple of milimeters makes a huge difference

I spent a lot of time on my setup to make sure all the pulleys lined up.  None are out of parallel by more than two MM.  Some seem dead on.  I will check the belts when I run the engine.   

[john108]

Mitch

I Hope this picture will help a little.
John

[Nacho-RT74]

That's 68... since 69 alternator setup changed

[green69rt]

Still, interesting to see.

[green69rt]

Took a picture of them correctly installed.  Belts are dead even.

[Nacho-RT74]

what it was wrong ? I can't see difference on the setup againts the other one 

[green69rt]

what it was wrong ? I can't see difference on the setup againts the other one  

Look closely at reply #5, you can see that the two alt belts have different amounts of slack.

The setup is the same from reply #5 to reply #14, the difference was that the lettering on the belts.  If the lettering on one belt is upside down of the other then you can't tighten them equally.   If you can read the lettering on both belts normal then they work fine.     Look at post one,  this is the correct arrangement for the letting.

[Nacho-RT74]

Yes I know about the diff slack on #5 what I didn't know is JUST reversing the belt made the difference ? WOW!!!! that´s new to me. I have allways installed both matched but just for the look, not really for some other reason!

[jlatessa]

I agree, there was something else going on the first time???

Joe

[green69rt]

I agree, there was something else going on the first time???

Joe

I don't know what it could be.  I just took the belts off and reversed one and put them back on.  No other work was done.  I guess I could do another test and reverse one belt and see if the problem comes back but probably won't do that.

[jlatessa]

That would be a good test and really end the speculations...LOL

Joe

[Paul G]

Belts will stretch. Need to be checked/readjusted after some miles of use. In #5 were all the bolts tightened down? Things can be a little off angle until all the bolts are tight.

[john108]

I may be wrong but I think the belts are made on precision equipment.
Our 3 and 4 belt 50+ year old pulley wheels are very non-precision. The side angles vary enough letting the belts fit higher or lower at each belt.
Not much, but enough to notice.  When tightened and run, one may stretch more than the other or fit tighter in its channel.