Gilmer Drive Belt - Tension?

[V-MAN]

I posted this on Backdraft website but no response as yet:

Can you tell me what the recomended belt tension should be on the 2" Gilmer Dive Belt. Mine has never been real tight but has always provided charging via alternator. I've been reading around the net and I get a huge range from "very tight to keep it loose" but nothing specific ...

If you could give me a recomended tension (I have a belt tension gauge) or deflection measurement from alternater to waterpump on the belt I would appreciate it greatly. The alternator is still charging but belt is pretty loose and I'm concerned about jumping a tooth or worse coming off the pully. I'm sure it's too loose because I can move the belt a good 1/2" sideways (across WP pully) and the teeth on pullies are getting "shiney" from belt moving.

Thanks

[Jerry Clayton]

you are using a 2" gilmer belt for alternator and water pump???? or is that a mis print and you meant 1/2"???

Anyway, tho, for narrow gilmers I use a method that has been successful/reliable for 50 years--take the mid part of the belt span(distance between pulleies) and twist it---you need to be able to twist it 90*, no more, no less--------with just your fingers, not a cresent wrench!!!!!!!!

[V-MAN]

Originally Posted by Jerry Clayton

you are using a 2" gilmer belt for alternator and water pump???? or is that a mis print and you meant 1/2"???

Anyway, tho, for narrow gilmers I use a method that has been successful/reliable for 50 years--take the mid part of the belt span(distance between pulleies) and twist it---you need to be able to twist it 90*, no more, no less--------with just your fingers, not a cresent wrench!!!!!!!!

Thanks Jerry, yep it is 2" belt. My concern is I can easily slide the belt on the pully (easier then before). The 2" Gilmer drives the alt and wp from the crank. I have a reg v belt that drives the ps. I know there have been many issues with too tight and destroying bearings in alt and wp using the large gilmer drive.

[vector1]

probably what jerry said but a drive belt on a harley one guy recommended 45-90 degrees twist. if you skip a tooth you will hear it, even over the noise of the exhaust, sounds like a tappet gone flat.

[V-MAN]

Originally Posted by vector1

probably what jerry said but a drive belt on a harley one guy recommended 45-90 degrees twist. if you skip a tooth you will hear it, even over the noise of the exhaust, sounds like a tappet gone flat.

Thanks vector1 - I think I will tighten the belt a bit but leave loose enough not to cause any bearing faiulure (hopefully) ... maybe 3/8 deflection?

[D-CEL]

Here is my experience. My dad ran one of those rigs on a BBC for several years. It was a pain in the arse! When you got it tight enough to not fly off, it would destroy the alternator in less than 500 miles. So much was the problem that he would carry one spare in the trunk, one in the garage and one being rebuilt. You read that right 4 alternators! Admittedly, his belt was longer, but it was a nightmare. I convinced him to swap it for a vintage air serpentine system and it’s been trouble free ever since.

Jason

[Jerry Clayton]

that is definitely the wrong choice of components--they used 2 inch belts to drive 6:71 superchargers--
there are many quality belt drive suppliers around, from the street rod to Nascar guys--
try looking at Jones or CV Products(big Nascar supplier in NC) or maybe even Street and Performance--- no need to do the $2500 setups

[D-CEL]

I like a hard anodized, NASCAR type pulleys myself, but it seems that most guys want to have the shiny parts. And if you run lots of accessories (a/c, ps, alt and wp) the Vintage Air system is a very nicely designed, complete, albeit expensive package.

JASON

[V-MAN]

Originally Posted by D-CEL

Here is my experience. My dad ran one of those rigs on a BBC for several years. It was a pain in the arse! When you got it tight enough to not fly off, it would destroy the alternator in less than 500 miles. So much was the problem that he would carry one spare in the trunk, one in the garage and one being rebuilt. You read that right 4 alternators! Admittedly, his belt was longer, but it was a nightmare. I convinced him to swap it for a vintage air serpentine system and it’s been trouble free ever since.

Jason

Jason

WOW, sounds like PITA for your dad. I haven't had any issues [fingers crossed now] and this Gilmer system has been on car since new. I was just doing yearly maint and found the belt was looser then before and wanted to adjust it. If I was having issues like your father I would swap it out also! I adjusted the belt with 3/8 deflection (engine hot). It is tiighter then it was but hopefully loose enough not to cause me a problem ... thanks again.

Originally Posted by Jerry Clayton

that is definitely the wrong choice of components--they used 2 inch belts to drive 6:71 superchargers--
there are many quality belt drive suppliers around, from the street rod to Nascar guys--
try looking at Jones or CV Products(big Nascar supplier in NC) or maybe even Street and Performance--- no need to do the $2500 setups

Hey Jerry - When I bought the car I was surprised to see belt system myself. Everything has always worked fine and I do like the way it looks under the hood. Backdraft did the engine install themselves and they still sell this same kit for their cars so it does work and has always been trouble free for me. I am just getting some maint done and car ready for the year when I noticed belt was looser then it was. I adjusted the belt with 3/8 deflection with engine hot.

My problem is I am an A&P Mechanic so in my world EVERYTHING has TQ value, and specs ... I am probably more anal then most owners/mech because of my background. My friends always busting on me for being "too precise" (their words) when working on bikes and cars ... their always telling me "it's not a *#%@^ airplane Don". I TQ every nut, bolt and screw on any ride I work on ...

[Jerry Clayton]

V-man

I know where your coming from --I went to work for Capital airlines in 1961, merger with United ----worked on the ramp after the merger until they let me transfer to maintenance in early 62-- eventually retired as a B777 captain--
along the way, I have been involved with top fuel, funny cars, (Keeling&Clayton California Charger) Pro Stock (one of the first cars to run 7 sec and over 170) dirt late model stock cars, stock block Indy cars, GoKarts, etc, etc--

Sometimes the problem with over engineering is that out on the road, you can't get a $100 part but can get a $100 tow----

You have a system that you could winch the car with ---a simple CV Products or serpintine 6or 7 rib belt will do far more than what you need and you can find belts at any auto parts store--

But it is cool looking---hook it up to a 6:71 blower---

[Trueoo7]

3/8 deflection is what I've alway seen, be it a lawn mower to cars. I've seen bad things happen when it was tighter but 3/8 should be good. Does yours have the whine like it is hooked up to a supercharger like Miller Speed pulleys?

[henrik]

Loose!!!

I too have the 2 inch Gilmer Belt Drive, and when installed it was too tight = the aluminium wheel expanded and the Belt broke :-(

Best way to test it... make is loose enough that you can moove it (at least) 1 inch upwards - take the car for a drive and then feel how much you can move the Belt.

Remember the belt works with teeth - not friction :-)

[GBowman]

1"??? WOW that seems really loose-I have the same set up on my BDR-I've only got 1100 miles on it but I adjusted to about 3/8" total movement hot. 1" seems like it would possibly allow the belt to jump the bevel on the crank pulley???

[V-MAN]

Originally Posted by GBowman

1"??? WOW that seems really loose-I have the same set up on my BDR-I've only got 1100 miles on it but I adjusted to about 3/8" total movement hot. 1" seems like it would possibly allow the belt to jump the bevel on the crank pulley???

Gary

I set mine to 3/8 deflection, that's a general "rule of thumb" for belt tension. I asked the question originaly to see if there was a 100% answer measured by deflection or pressure (thinking maybe gilmer had specs). I believe that 1" slack the belt would probably be thrown off the pullies ... I don't think there would be anyway for it not to be. The idea is to have it tight enough to charge the battery and stay on pully system. Too tight risk destroying the bearings in alt, water pump etc and too loose then be flung off, slipping and damaging the belt not charging.

[GBowman]

I am sticking with the 3/8...saw a thread on another site where they were going with 15mm which was working well. We will see...I do think the pulleys are expanding once hot which makes the belt tighter (which goes against conventional wisdom). I think folks with this set up are used to the cold belt being the tightest and are adjusting for a hot belt and not allowing for pulley expansion.

[RICK LAKE]

V-man Like Jerry been around racing a long time. If the motor is hot we ran between 1/4" and 1/2" of deflection. The problem is wear and tear on the bearings of the water pump and Alt. As long as the belt is not jumping teeth when hot I would leave it alone. Everything tightens when the pulleys, belt, and motor bay cools off. The belt is going to walk unless you have the pulleys all trued and at the same depth on the motor. We used to drill holes in the pulleys to help remove the air trapped with the motor running. This made the motor quieter and I think helped get a better deflection of the belt running. Rick L.