1968-74 427/454 with C-60 Idler Pulley

[Joe L.]

I'm curious about something having had no personal experience with it.

As many know, 1968-74 big blocks with C-60 used an idler pulley in the engine pulley system. Without C-60 these applications used a captive belt between the balancer and water pump pulleys. With C-60, a longer belt was used with an added idler pulley assembly.

There were two different designs used over the period, though. For 1968 only, the idler pulley assembly included a standard grooved pulley. The belt ran through the grooved pulley and OUTWARD tension was adjusted at the idler pulley bracket.

For 1969-74, things changed. The idler pulley bracket changed to a different configuration and, more significantly, the pulley changed. The pulley now included no groove. In addition, the belt routing changed. Instead of the "V" section of the belt riding in the pulley, the rear of the belt rode on the pulley, with the pulley exerting INWARD pressure on the belt. The inward pressure was adjusted at the idler pulley bracket. However, the width of the pulley and the width of the rear of the belt were about the same so there was little tolerance for any lateral displacement of the belt and no mechanism for insuring the lateral placement of the belt.

The 69-74 configuration seems very "unstable" to me. I've wondered for years why the change was made from the 1968 configuration to the 1969-74 configuration. I'm sure there was a good reason for it but I've never figured it out.

My question is this: for those that have lived with the 69-74 configuration for awhile, have they ever experienced a circumstance in which the belt became displaced from the pulley?

[Mike M.]

Re: 1968-74 427/454 with C-60 Idler Pulley

in 1983, I bought a 74 454 c-60 from a good friend, who was the original owner. it had 19990 miles on it when I got it. it was a 4 speed, 370 rear. and my friend ran the piss out of it for the 19k miles, as he was a proponent of miller lite, bud lite, and any other lite he could come up with. it spite of 6500RPM runs, the belt never left home. it still had its original belt when I sold the car to my son in law 3 years ago, who also favors the elixir of hops. however, he has been vary gentle on the old 74 since he's had it.it still retains its original belt. mike

[Joe L.]

Re: 1968-74 427/454 with C-60 Idler Pulley

in 1983, I bought a 74 454 c-60 from a good friend, who was the original owner. it had 19990 miles on it when I got it. it was a 4 speed, 370 rear. and my friend ran the piss out of it for the 19k miles, as he was a proponent of miller lite, bud lite, and any other lite he could come up with. it spite of 6500RPM runs, the belt never left home. it still had its original belt when I sold the car to my son in law 3 years ago, who also favors the elixir of hops. however, he has been vary gentle on the old 74 since he's had it.it still retains its original belt. mike

Mike------


Thanks.

[Keith K.]

Re: 1968-74 427/454 with C-60 Idler Pulley

The short answer to your question is no. I have owned my '74 LS4 C60 car since 1975. The '74 LS4 also has an A.I.R. pump, so with AC and power steering there are four belts on this engine. The belt from c/shaft to water pump is very tight and very difficult to install even with the idler removed. I changed them when the car was about 20 years old and then again a year or so ago. Hopefully I'll never have to do it again.

[Dick W.]

Re: 1968-74 427/454 with C-60 Idler Pulley

in 1983, I bought a 74 454 c-60 from a good friend, who was the original owner. it had 19990 miles on it when I got it. it was a 4 speed, 370 rear. and my friend ran the piss out of it for the 19k miles, as he was a proponent of miller lite, bud lite, and any other lite he could come up with. it spite of 6500RPM runs, the belt never left home. it still had its original belt when I sold the car to my son in law 3 years ago, who also favors the elixir of hops. however, he has been vary gentle on the old 74 since he's had it.it still retains its original belt. mike

What? No Beast?

[Joe L.]

Re: 1968-74 427/454 with C-60 Idler Pulley

The short answer to your question is no. I have owned my '74 LS4 C60 car since 1975. The '74 LS4 also has an A.I.R. pump, so with AC and power steering there are four belts on this engine. The belt from c/shaft to water pump is very tight and very difficult to install even with the idler removed. I changed them when the car was about 20 years old and then again a year or so ago. Hopefully I'll never have to do it again.

Keith------


Very interesting. This might mean that the 1968 set-up is better from an ease-of-installation perspective.

[Mark E.]

Re: 1968-74 427/454 with C-60 Idler Pulley

Pulleys with a convex surface and flat belts are very stable and self-centering. It's a design used in industrial applications.

Maybe Chevy used it on the big-block because it's a more compact configuration. The front of this engine is crowded.

[Joe L.]

Re: 1968-74 427/454 with C-60 Idler Pulley

All------


Well, I did a little more digging into this and I learned something I was not previously aware of. For the 1969-74 period, big block installations without C-60 and with C-60 both used the same 31-7/8" length, captive belt. For the with C-60 applications, the idler was added to increase tension on the belt by exerting inward pressure on the belt. So, for example, by adding the idler to a non C-60 application one would not do away with the captive belt and gain an easier to install water pump belt.

The 1968 configuration would probably allow that, though. For 1968, the without C-60 big block applications used a 31-7/8" captive belt. However, with C-60 used a 33-1/2" belt in conjunction with an idler. Presumably, this means the belt was not captive, could be more easily installed, and adjusted at the idler bracket.

[Keith K.]

Re: 1968-74 427/454 with C-60 Idler Pulley

All------


Well, I did a little more digging into this and I learned something I was not previously aware of. For the 1969-74 period, big block installations without C-60 and with C-60 both used the same 31-7/8" length, captive belt. For the with C-60 applications, the idler was added to increase tension on the belt by exerting inward pressure on the belt. So, for example, by adding the idler to a non C-60 application one would not do away with the captive belt and gain an easier to install water pump belt.

The 1968 configuration would probably allow that, though. For 1968, the without C-60 big block applications used a 31-7/8" captive belt. However, with C-60 used a 33-1/2" belt in conjunction with an idler. Presumably, this means the belt was not captive, could be more easily installed, and adjusted at the idler bracket.

Very interesting - I can confirm the 31-7/8" belt which was a chore. So if '68 used a longer belt, was the idler larger diameter?

I also found that I have a '73 AIM - it shows the 454 with C60 to have the same belt as the '74 for the water pump with idler - however, in '73 the 454 with C60 & N40 PS only used 3 belts where the '74 uses 4 belts. The '73 454 has one long belt from c-shaft to water pump to generator to power steering pump. The '74 belt goes from c-shaft to water pump to power steering pump, then an additional belt from power steering pump to generator which looks like a better design.

[Joe L.]

Re: 1968-74 427/454 with C-60 Idler Pulley

Very interesting - I can confirm the 31-7/8" belt which was a chore. So if '68 used a longer belt, was the idler larger diameter?

I also found that I have a '73 AIM - it shows the 454 with C60 to have the same belt as the '74 for the water pump with idler - however, in '73 the 454 with C60 & N40 PS only used 3 belts where the '74 uses 4 belts. The '73 454 has one long belt from c-shaft to water pump to generator to power steering pump. The '74 belt goes from c-shaft to water pump to power steering pump, then an additional belt from power steering pump to generator which looks like a better design.

Keith------


The 1968 idler configuration was completely different. The pulley was a v-groove and the belt rode in the groove. The idler pulley exerted OUTWARD pressure on the belt. The 1969-74 configuration the pulley was grooveless and the pulley exerted INWARD force against the rear surface of the belt.