The Stovebolt Site Forums The Parking Lot Tons 'o Fun 3800-PTO

I am new to posting on this forum and I think its a great site.My question is can the pto stay in gear while driving the truck at normal speed.I have a sanden AC compressor that I'd like to connect to it.I can get the RPMs I need with a 7"pulley and use a switch on the clutch pedal to drop the electric clutch when shifting.I have used this truck for 35 years and started a frame up last year . rebuilt the org. 235. It only has a single 3/8 ft.pulley and I'd liked to keep the engine clean. Any info about the PTO or the concept would be great

Hy tonyt, while you could run your compressor off of the trans. p.t.o., I would get a two belt balancer and run it that way. I have seen the balancer available at the balancer rebuilders sites, have a look in the Tech Tips section or do a search for harmonic balancers, hope that helps.

The PTO is only designed to operate at a little more than an idle.
Running it full speed is not a good idea.

Look into a double pulley balancer.

Grigg

PTO's all run at a given percentage of engine RPM and some are quite low, i.e, 32% for example. Assuming your transmission is an SM420 or original 4 speed a typical single gear PTO runs at approx. 65% and they don't like more than about 1000-1200 RPM so your engine speed could not exceed about 2000. That isn't enough to drive the truck and go anywhere. Many of the old single gears had bushings in lieu of bearings. Hard telling what you have however. Also it must be engine rotation to operate your AC compressor.

So the advice you have already gotten is correct.

Thanks for the advice. I am having a hard time finding a double pulley that does not hit the back of the fan,but I will keep looking.Any info on that would be great.

With a water pump relocation plate and a 216 water pump on a late 235 you should not have any fan and pulley clearance issues.
The upgrade will help you keep cool better too.

Some searching in the engine and drivelines section will show you all you need to know about the adapter plate.

Have you said what model truck this is, and what year model engine?

Grigg

Thanks, I'll search the relocation plate. The truck is a 1954 3800 chevy with the org. 235 motor.Do you think I'll have a problem with the extra torque on the pulley/crank connection since the pulley is not bolted to the crank.

A 1954 235 motor does not need a relocation plate. How much space do you have between the front of your harmonic balancer and the fan?

The press fit should be sufficient to transmit the torque.

Grigg

Driven air-conditioning compressors for years with the harmonic balancer on a 235 chevrolet. They used to use an add on pulley that bolted to the front of the balancer. Bolted into the two bolt holes used to pull the balancer with!
Just an old coots two cents worth..............

The bolt on front pulley sounds like the way to go .Any one know where I could find one? I whould have to move the fan ahead about 3/8" ,I can shim that ,the pump shaft is 1/2+ long.