Technical V-belt / Pulley Engagement enough??

I was just ***embling the pulleys & alternator and thought maybe the engagement of the belt in the water pump pulley doesn't look adequate. The crank & water pump pullies are both 7.100" diameter and the alternator pullie is 3". Engagement appears to be just about 40° of the pulley. Just wondering what y'all think of this, or am I over doing it again?? Appreciate your opinions.

 

Do you intend to drive a radiator fan from that water pump pulley?

 

I’d roll that alternator outward some.
And if it squeaks, consider switching pulleys to doubles.
I did and it seems to work well.

 

Doesn't look adequate to me.

Looks like lower is multiple belt, if so I'd run a double water pump pulley and just run one of the belts between those two pulleys then you could leave the alternator and it's pulley and belt alone.

Down side to doing this is you have to remove the water pump pulley to change the belt.

Had several buddies run them that way back in the day with sbc's running high rpm street racing..

...

 

Yep, needs more wrap on that water pump, especially if a fan gets involves. Lots of ways to skin that cat, just need to pick one that works.

 

^^^^^^^This^^^^^^^
Is there a reason it is mounted so high, seems a bit "in your face"!

 

I had a similar "problem" on my Model A build. There wasn't a lot of belt wrap around the water pump pulley. I fretted over it for a while, but there isn't much room to change things on a nailhead. You either hang the alternator way out off one head or you make a bracket to tuck it in. I've had the car on the road for 3 years now and no problem with heating. However, I am running an electric fan.

This is the best picture I have that demonstrates the amount of belt wrap. It looks similar to what you have.

 

I ran a few '50 Olds with '53 4bbl intakes that ended up with that amount of belt contact. No problems.

 

Rule of thumb, if you put a wrench or socket on Alt bolt & turn C-Ws & crank turns , the belts has enough tension and contact
Engine shown is close to 600 of torque
Single belt

 

On my 250, my crank pulley would squeal, so I added a belt from water pump to crank. It somewhat stretched over and fit in the grooves, hopefully not so tight it wears out the water pump. So far its working good, it took a couple of sizes and different brands to find one " just right ". The store brands and name brands are not the same sizes.

 

GM didn’t build Chevrolets that way for a reason but with a low amperage load it may work fine. A loaded up AC unit at night with giant stereo blasting may not be so good.

 

I ran something very similar on a SBC several years ago. There just isn't enough wrap on the water pump pulley. My car would throw the belt. I ended up buying double-row pulleys and added a second belt from the crank directly to the water pump (no adjustment to the belt obv, just loosen the water pump pulley and "skootch" it on). That stopped the original belt from being thrown and kept the water pump rotating. Because there is so much wrap from the short belt, it doesn't need to be overly tight in order for it to function well.

Although the short belt did solve my problems, in the end I tossed the short pump and went with a long pump and factory alt mount so I could more easily add power steering. I haven't touched a short pump since.

 

The only time I have seen thrown belts
On single V was wrong belts for pulley
Just because it fits does not mean correct belt for the V / taper for that pulley or the other one's ...
& most time trowing belt there also flex in Mounts or bearing's , pulleys are Not in Line , a Long belt more unstable
So lineament more critical.
& belts are Not same from Brand to Band ,,

Look up V belts & you will see theres
@ least 5 different 3/8's V belts.

 

I had the same problem with that setup. It would squeal every time I started it. It cooled just fine, but that squeal was embarr***ing. I run a PS unit also. The PS belt ran from crank directly to PS pump. I changed the fan pulley from a single to a double and ran the PS belt up over the 2nd fan pulley then to the PS pump. Problem solved.

 

Yes, I'll be using an original '36 radiator......I hope!

 

I agree & thanks for your input.

 

I'll give it a look - thank you!

 

It's the set-up that was on the car when I bought it. Don't care for it all that much, just trying to use what I have.

 

Thanks for the response & the photo, I appreciate it

 

Excellent info, thank you!

 

Wow! Even after all these years on HAMB, I'm blown away with the ***istance offered! I shouldn't be overwhelmed, because I've seen it in the thousands of posts I've read, but when you receive it yourself, it's still surprising.

Can't thank you all enough for your help, but I'll try to p*** it on!

 

I was a little concerned about the wrap on the water pump pulley; not a good picture; but you can judge by the location of the alternator. Has worked OK with no problem for a few years.

 

Mine is somewhat similar and I had the same concern. 50amp alt, electric fan, no power hungry accessories besides the fan. Thankfully runs fine! I'm planning on fitting an idler though, if I can get around to it! I have a long list of things to do elsewhere so I might never get around to it!

Chris

 

As a mech Eng, I always wonder about these types of questions. I recall using a Gates power transmission calculator back in the day, but can’t seem to find it on the interweebs. Common “practice” seems to say to have at least 120 degrees on wrap, which kinda makes sense, and then I look at the wrap on the water pump pulleys on my Ford flathead V8 which isn’t much, maybe 90 degrees. If it was just the water pump, I would guess it should be good enough, but adding a fan maybe not. A fan can draw upwards of 30 hp or more at high revs. If others are saying they have no issues with similar setups, I guess I would try as is.

 

Always wanted to be a mechanical engineer. Then they saw my welding and what I can do with a set of channel locks, and they posted my photo at the college entry doors with a big red cross through it

The amount of degrees that a belt wraps around a pulley is the "arc of contact". A lot of references recommend 120 degrees as the minimum arc of contact, but many, many engines have less than that. The amount of grunt that can be transferred through a belt is proportional to the arc of contact. The table below gives the correction factors:


So if you can get 10HP through a belt with 180 degrees of arc, then reducing it down to 91 degrees means you could still transfer 7HP.

Reference for this table is here:
BANDOCAT.QXD

Cheers,
Harv

 

Yep. Interesting. Was thinking about this after I posted, and of course arc of contact is dependent on pulley dia. As you can see in the OP pic, alt pulley is significantly smaller in dia than the water pump pulley dia. So, for fun, and comparisons of “arc of contact” between the alt and water pump pulleys, ***ume alt pulley is 3” dia and has 160 degrees of contact. Arc length is then 4.19”. ***ume pump pulley is 7” dia, and has a 40 degree angle of contact, then arc length is 2.44”. Quite a big difference, and ***uming alt power requirement is significantly less than that of the water pump/fan power requirement, one would speculate then that the arc of contact is insufficient for the pump/fan pulley, but of course this is all speculation. lol!

 

When talking about Alternators , there is a big swing in how Much Amps
They put out @ engine Rpm's Vs
Alternator pulley Rpm's , A hand held Photo Tac / Rpm's or hand held Rpm Tach,
Most Engine Rpm's Ones want the Engine to Idle Below 850 , typical
Gm Alt that puts out 60 ish amps ,
@ idle 850 rpm's 15-20 amps , then @
1,500 rpm's the out put amps will be
60 ish amps ,
Clamp around Amp meter needed.
Typical volt meter only good for 10 Amps .

Charge wire Makes big diffrents /required.
60 amp Alternator needs 10 awg charge wire , A typical 100 amp Alternator needs a # 4 awg charger wire ,
150 amp Alt # OO then even bigger
#O 1 more bigger amp Alternator puts out.
One Company website to go to is
Power Master or other Name band for
Tech & all the different Alt ,
Then Battery size Not CCA but Battery reserve size Mints Vs amp draw in system to see if Alt can keep up with .
Think of your battery as a gas tank
& alternator is the gas pump filling the gas tank..

 

Judging from the picture, I believe if the alt was dropped straight down a couple inches the amount of the belt contact with the water pump would improve. That alt is sitting up pretty high, that could provide a lot of unnecessary belt deflection between the water pump pulley and the alt as well, which won't help with the minimum belt water pump contact.