L Series Gilmer Belt Drive

What is a Gilmer belt?
Very simply Gilmer belts have ribs that run the width of the belt instead of the length of the belt just like a timing belt on a modern engine.

Gilmer belts are heavily used in performance applications as they eliminate belt slipage. Applications generally include driving superchargers using 1.5" to 2" and in extreme cases 3" wide belts, they are also used for driving external oil pumps in dry sump systems and mechanical fuel pumps in high power applications using smaller 1" belts.

Why do I need a Gilmer belt drive?
You probably don't... but if you dig the whining sound they make and like how they look, then why the hell not?

What are the advantages?

• Zero belt slipage
• Stronger belts
• They sound great, they have an unmistakable whine.
• They also look great, large belts, large shiny pulleys, what's not to like?

What are the disadvantages?

Because the belt is so wide and the way the teeth are designed there is a fair amount of resistance, you'll loose a bit of power to turn a Gilmer belt.

If you run the belt too tight you'll also risk wearing out the bearings in your water pump and alternator faster.

But who cares right? they look great and sound even better, they are a great finishing touch to almost any engine bay and can be done on a Datsun L series motor pretty cheaply and easily.

This is a Gilmer drive kit for a Small Block Chevy V8 with a short water pump, this kit requires minimal work to fit to a Datsun L series engine with only light machining work.

What you need:

• Small Block Chevy Gilmer kit for short water pump
• 345L belt, most SBC kits are supplied with a a 390L belt, this is too long for an L series engine, ask the supplier to swap the belt for a 345L.
• A spare (or your current) main pulley to have machined down to bolt the main pulley to.
• Stepped drill bit to bore the water pump pulley hole to 22mm.

How much does it cost?

This will vary, I purchased my kit on eBay and chose the seller based on if they could swap the belt for a 345L. I found a seller who would do that and purchased the kit, only to have it arrive with a 390L belt and the seller refused to cover return postage cost... go figure?

Gilmer kit ~$160

Machine shop to modify main pulley $80

Custom tensioner $40

Misc Stainless Allen Head bolts $15

Alloy Alternator fan $35 (not required but I wanted a better looking fan)

How do I fit the kit?
It's not quite a bolt on job but it's not very difficult either.

The alternator pulley will bolt straight on in place of you're current pulley if you have a Datsun/Nissan alternator with no mods.

You may want to try different configurations of the spacers and washers to get the belt alignment you're after, as can be seen in the photo to the right the alternator pulley has guides to prevent the belt coming off and is what dictates where the belt will sit on the other pulleys.

The water pump pulley almost bolts on, the centre spiggot hole on a small block Chev water pump is much smaller than on an L series engine and needs to be bored out to approx 22mm. I decided to use all new stainless Allen head bolts as they look neat and are cheap enough.

Also worth noting is that the bolt holes don't quite line up, however you can get them in without having to ream or slot the holes.

The hardest part is the main pulley, you will need to machine off the belt V from a stock pulley to leave a flat surface to bolt the new main pulley to, I had a local fabrication/engineering shop handle this as I don't have access to a lathe.

Don't forget to replicate your timing marks!

Stock unmodified pulley.

Belt V machined off in a lathe, a small lip left to recess the pulley slightly and a step was left in the face to help centre the new pulley.

It sits in there just right.

Holes drilled and tapped to bolt the main pulley down, it would be wise to thread lock the bolts and use spring washers before final installation as you'd hate to loose the pulley while driving, not only would it damage the pulley it would be a pain to repair on the side of the road.

The end result looks something like this, this was just a trial fit shortly after receiving the kit, it doesn't look nearly this ugly I swear!

Lastly, something to consider is your belt tensioner, I quickly found that getting enough tension on the belt with the stock 610 tensioner was almost impossible, so after poking around a couple of hardware shops I settled on the below setup.

It's a Turn Buckle or Bottle Screw which ever you'd like to call it intended for tensioning chains and stainless cables on shade sail installations, with the standard ends swapped for M8 Rose Joints, note that as it is a turn buckle that one end has left hand thread and the other end is right hand thread, you'll need to buy a LH and RH rose joint.

And a quick video of how it sounds.

References and credits:
I didn't come up with the belt length, burubado over on OzDat worked that out, all credit goes to him:
http://ozdat.com/forum/viewtopic.php?f=28&t=24510