alternator pulley with fan mount

35 rancho

35 rancho

Member
Got my 35 pickup discharging my battery at idle. It's a 12 volt with alternator. the stock 40 block in the 35 needs the fan mounted on the gen/ alt area. Or go with a plastic fan on the radiator. (which I did not want to do) The alt. pulley is to large and the ratio is not correct. I've been eye balling the pulley in the speedway cat. made by offenhauser.:confused: Anyone with similar problem??
 
Get the pulley to small and it don't have much surface for the belt to grab then you tighten it to much and have problems with the water pumps. You need the stock pulley with the drilled and tapped holes for the fan right near the edge of the outer diameter of the pulley. Use that and take whatever charge you get. There was one of the pulley's pictured on here a week ago. G.M.
 
Are you using a one-wire alternator? If so, the alternator may not have sufficient residual magnetism to fire off at low speeds. A two-wire setup might help.

What pulley are you using now? I assume a stock Ford unit. There are some choice of diameters, but all are constrained by the fan-mount bolt circle.

The Offy pulley in the Speedway catalog appears to be almost as small as possible given the need to mount a stock Ford fan. Call Speedway and ask for technical assistance - they can give you the dimensions. It may not be much smaller than the one your are currently running. One possibility would be to machine the Offy pulley to mount the belt deeper in the groove. The Ford pulleys are too thin for this. For reference, stock GM pulleys are pretty small (3.0" or even smaller diameter), so there's no problem in using a pulley much smaller than the stock Ford ones with reasonable belt tension. John R.
 
John R>>>all are constrained by the fan-mount bolt circle.>>>

A 3" X 3" square 1/8" thick steel plate mounted between the rotor nut and pulley can bypass this constraint. The 1/4"x20tpi fan-mount holes can be drilled and tapped at the corners of the plate.

Jack E/NJ
 
Yes, if using something other than an OEM Ford fan-mount pulley, a plate to mount the fan would work, assuming it was properly mounted to the pulley or armature shaft. However, said plate should be 1/2" thick. The Ford bolts are 1/4 x 28, 1/2" long. Also, the threads in OEM fan-mount pulleys are 0.4" deep, making it obvious to the budding mechanic that a lock washer is required. John R.
 
Hey guy's thanks for the info. I'll get a hold of a tec at speedway Monday. My crankshaft pulley is 5" and the alt has a 4.25" pulley. A stock gen pulley is about 4.25. All my model A's alt's have a 2" pulley. Go figure?? I'm going to let Jeff at Certified auto electric resolve this problem. mean time I'll search for a 10" crankshaft pulley on ebay.
 
You should have minimal problems using the aftermarket pulley that has the fan mount provisions, a GM one wire alternator and a stock lower pulley is just fine. The main issue is the choice of fan units. There are a number of original fans from different years and the radiator to fan spacing is the most important choice. Before choosing a fan you must know the distance spacing from the edge of the radiator hose to the center line of the alternator pulley as well as the top tank of the radiator to insure that you choose a fan that will not be too large. Because you can adjust the belt length tension upward slightly this measurement should be taken with the alternator bracket at the lowest position. To be safe you should have about 1" of clearance between the tip of fan blade and any hoses or tank.
 
John R>>>Yes, if using something other than an OEM Ford fan-mount pulley, a plate to mount the fan would work, assuming it was properly mounted to the pulley or armature shaft. However, said plate should be 1/2" thick.>>>

Sorry I forgot to mention the bolt heads would face the fan belt or studs brazed into the 1/8" plate if more belt clearance is needed. The fan would then mount on the studs with nuts and lock washers. As John R suggests, a 1/2" plate would probably be better for bolts heads facing the radiator but would require a counter sunk center hole to accomodate the nut on the rotor shaft. As Dick S mentioned, radiator and hose clearance might be an issue.

Jack E/NJ
 
up date! Speedway could not get the exact measurement aprox 3, 3.25" ?? on the pulley. But I did get a schooling on low and high speed cut in. Jeff at certified is working on a smaller pulley. If I can get the alt at 1000 rpms when I'm at idle every thing should work fine. I guess the latter flatheads have a 6" crank pulley. Thank You everyone for the feed back. Ford Barn has been very helpful.
 
EJ Whitney Co in Fullerton,CA converts the orig gen to an alt and it all looks stock ,also uses the orig pulley so your fan will work.I have had 2 (35 & 36)done by him and very pleased.
 
The stock ford generator pully for a threaded generator armature will mount on a GM alternator,been running one for 15 years
 
I've had great results using a '37 3 brush pulley that I bored and threaded to fit
the GM one wire alternator. The thread is an odd ball 20 pitch that I machined
when I could not find a tap. I have a few in my stash if you are interested. E mail
me off site if you wish.
Charlie ny
cas5845@yahoo.com
 
I went the alternator route at one time but I eventually abandoned the idea and went with a 30 amp Ford two-brush on my '35. I had two concerns. The first was the extra weight of the fan on the front bearing of the alternator. I had visions of early bearing failure as a result of the fan weight. The second concern was the speed of the fan. To get the alternator to charge at low speeds I used a modified '39 generator end plate fitted to a GM alternator. However, the original Ford pulley needed to be smaller so I used a smaller diameter pulley to up the alternator speed. Everything worked as planned but then things became scary. The fan was really flying around at idle. It didn't take much imagination to picture what that fan would be turning at 50 mph. Couple that with the fact that the fan is only held to the Ford pulley with four 1/4" bolts 1/2" in length and I decided that the risk of turning my radiator and/or hood into a piece of modern art was not worth the extra output that an alternator would provide. As a result, I went with the later (slower speed) model generator. Evidently, others have complete confidence (and experience) in what they are doing and maybe my fears are overblown but I feel somewhat more comfortable with my generator which serves me well. MHO

Tom
 
If you can find a v8 60 generator pulley it will be a little smaller dia. than the 85. You can tell the difference because the bosses for the fan are very close to the od of the pully. It will increase the rpm of the alt. some.
Regards, Don
 
I have the same concern that Flatheadfan mentioned. The front bearing used in an alternator may not take the additional load caused by adding the rotating mass of the fan.
 
On my 39P/U I'm going with the 1 wire Ford alt/bracket from certified. Ordering a reman. radiator from brassWorks in a few weeks with built in shroud and a 12v fan.

I looked @ getting the pulley with the adapter for my original gen. fan but that little 4 blader on an alt seemed a poor design. I'm converting to 12V any way so a 12V elec. fan was my choice. Will let you know how I make out. Ford alt. on a flathead, now your talkin:D
 
When I got my alt from Mr Becker in Ohio it was mounted on an original ford gen bracket. The first thing I did was to mount it on an old manifold and check the mounting bosses on the pulley. They were all over the place which made the fan run out. I massaged them so all were within a few thousandths and the fan runs very true now. I was told by many people that the bearings in the 1 wire GM alts. are more than enough to handle the fan. I have almost 20000 on mine with no issues, maybe just lucky.
Don
 
I have one of Becker's alternators on my 35 PU. I sent him the front end of a stock Ford generator, with holes, not slots, and he mounted the G M one wire alternator on it. Works like a charm. I need to get another for a spare.
 
Becker's alternator design uses the front housing/intake mount from a three brush generator that normally has a fan mounted to pulley. The bearing in that front generator housing is designed to withstand the load of a four/six blade fan. Becker's alternator shaft rides in that heavy duty front generator bearing and therefore his design works well with a pulley mounted fan. Now if you mount a pulley and fan directly to an alternator those front bearings may not withstand the additional loading.
 
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