Tensioning the Engine Drive Belt

Correct Tension Reduces Wear

This pic shows the Engine Drive Belt which gave us a problem over the New Years Eve Cruise. The problem is that it's nearly impossible to tension the belt correctly simply because of the lack of leverage against the Alternator Body.

So I plan on making a Tensioner using a piece of Threaded Rod, inside a piece of Square Aluminium tubing and a long hex nut.

The idea is to apply pressure between the Alternator Pulley and the Engine Crankshaft Pulley using the tensioner and then, when tension is correct, tighten the Alternator securing bolts at which time the Tensioner can be removed.

Here's my 1st model. 

One end has a cross bar that is bolted into a slot in the end of the Square tubing.

The other end has the long nut with about a 1/2" of the threaded rod exposed.

The end of the threaded rod has been ground to a shape that approximates the pulley grove.

In this pic, the tensioner is adjusted to it's minimum length. I won't know if that is too long until I get to the boat and try it. If it is too long, I'll simply cut the length of the square tubing.

I used a 4 1/2" Metal cutting wheel in my grinder to shape the end of the threaded rod.

Original plan was to cut a slot into the end of the rod and make a 2nd bar, similar to the other end and mount that in the rod, but I thought I'll keep it simple.

The black marks are simply what I used as a guide when cutting the angle on the end of the rod.

The Flat bar is about 2" long and inserted into a slot cut into two sides of the Aluminum Square tubing. Then drilled and thru bolted with a nyloc nut to secure the bar to the tubing.

This shows how the threaded rod is simply inserted into the square tubing. 

The threaded rod is 6" long 

The Long nut is 2" long

The Square tubing is 8" long

So this allows the tensioner to expand from a minimum of about 10 1/2" up to about 14", I may have to cut the square tubing down if the distance from the inner surfaces of the pullies is less than 10 1/2" - I'll take my cut off grinder with me.

Here's the tensioner extended simply by turning the Long Nut.

Another job for tomorrow - check to see if it works.

Well that was a surprise, it did need to be shortened.  I used the tape to mark the correct length.

After a couple of minutes with the cut off wheel, it's now just under 7" long fully retracted.

The angle of the parts that meet with the pulleys need to be increased (they are too fat and I'm concerned that they may bend the pulley belt faces.)

The threaded rod was also shortened.

This pic shows the new max length of approximately 8.75"

Engine Drive Belt Tensioner

Success! It works like a charm!

I was able to ease off the Alternator Support Arm bolt (1/2" Wrench) and the Alternator Support Bolt (11/16") and the Alternator Arm attachment bolt (1/2") .

Then insert the Tensioner, tighten up on the Hex Bolt to apply tension fo the drive belt. Once at the desired tension, tighten up the 3 bolts and remove the tensioner.

No Sweat, No damage, no busted knuckles. 

Sweet!

See you on the water.