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Belt issues
Posted by: CREATIONBLUE ()
Date: May 02, 2022 11:57AM

Last week I shredded a fan belt on the way home from a road trip. It wasn’t that old but ok it happens. Fitted a new one on the side of the road and drove the mile or so home and checked it. It looked pretty worn already with lots of rubber in the engine bay. This week I adjusted it when the engine was cold and then ran the motor and it was making a strange noise around the alternator area. Anyway, today I went for a drive, a mile down the road the generator lamp came on and sure enough the belt flipped! Never ever had this before! During the week I ordered A Gates 3V560 which had good reviews on this very forum, it arrived yesterday and I had it with me so again by the side of the road I fitted it.

Now I’ve noticed when my belt isn’t quite running right the alternator doesn’t give out a voltage and the gauge shows only 12volts and this is an indication to me somethings not right. So when i pulled away with the new belt on I wasn’t getting 14v so ran a couple of miles and retightened it. All was well for a few miles when the voltage dropped. Out I get, and the belt was running but had turned in the groove!? So slackened things off and straightened it and off I went. 14volts indicated happy days! Unfortunately this scenario happened a further 3 times. The pattern was that I’d get up to cruising speed around 40-50 mph then slow down to a junction, this would cause the belt to flip but stay on!

Experience tells me that let things cool down and it’ll be ok after that. Stopped for lunch and then carried on home, that journey was around 20 miles, both fast and slow roads with lots of braking and the belt behaved and not once caused me a problem!

I’ve read a lot about belt’s recently, I’ve never had a problem before, nothings changed in the alignment of the pulley’s etc yet I’m having this issue now with the 3rd belt in a week.

Any thoughts appreciated. Remember I’m running a ‘65 110 reversed rotation motor in the back of my ‘70 vw bus with a 4sp manual.

Re: Belt issues
Posted by: American Mel ()
Date: May 02, 2022 12:48PM

How tight are you running it?
While it seems contrary to logic, running a belt too tight will cause it to flip, throw, and even break.
The general rule of thumb is to leave it just barely loose enough to rotate the Alternator fan with two fingers when the engine is cold.
Reverse Rotation does change things a bit, but I would think the loose rule still applies.
I am sure others will chime in.

WA. state, 1 mile south of the Canadian border, I am not at the end of the world, but you can see it from here.

Re: Belt issues
Posted by: CREATIONBLUE ()
Date: May 02, 2022 01:16PM

Yes I’ve adjusted it so that i can turn the alt as described when cold. When the Alt stops making volts it’s gets hot and the belt also gets hot. All very strange as the Alt is turning all the time but will only make volts when the belt tension is at the sweet spot. At least it’s an indication when something is wrong with the belt or I’d have trashed two today otherwise.

Re: Belt issues
Posted by: aircooledairhead ()
Date: May 02, 2022 02:47PM

I’m pretty sure there are bearings on the alternator shaft. If these bearings are worn they may be resulting in variations in belt tension. Can you borrow a known good alternator and see if the issue goes away?
You could also check the idler pulley bearing. I had one seize and the belt yanked and the cast bracket cracked between the bolt holes. If that bearing is failing it could also cause belt issues ( as can the blower fan bearing).
The issue with the alternator voltage points me to testing those bearings first.
Good luck.

Re: Belt issues
Posted by: CREATIONBLUE ()
Date: May 03, 2022 12:16AM

The alternator is fairly new, changed when I rebuilt the motor and hasn’t done that many miles. Think I’ll check the idle pulley bearing again tho as I’ve never had that apart. Anyone know what the replacement bearing is for this or even if it’s serviceable?

Re: Belt issues
Posted by: RobertC ()
Date: May 03, 2022 12:54AM

> When the Alt stops making volts it’s gets hot and the belt also gets hot.

Do not understand alternator getting hot. Belt would get hot if it is slipping - which means there is "drag": Alternator load or pulley not rotating correctly.

Need to use a stethoscope to listen to all bearings. You could also use a long screwdriver, but you need to keep hair / fingers out of pulley / belt.

On a reverse rotation engine, I do not know if belt guides are used.

Idler Pulley Bearing: Was a special bearing. Now believe (memory?) that a modified water pump bearing is used. Corvair vendors supply bearings - and rebuilt idler pulleys - need heat to replace bearing in bracket.

Do you have the correct fan on the alternator for a reverse rotation engine? I know nothing about reverse rotation engines.

Personal affliction: Consider any belt that has flipped in the pulleys to be compromised (stretched?); belt needs to be replaced. Once it flips; it easily flips again.

Re: Belt issues
Posted by: vairmech ()
Date: May 03, 2022 04:40AM

> The alternator is fairly new, changed when I rebuilt the motor and hasn’t done that many miles. Think I’ll check the idle pulley bearing again tho as I’ve never had that apart. Anyone know what the replacement bearing is for this or even if it’s serviceable?

Do you have the correct fan on the alternator? Did it come from a Corvair vendor or the auto parts store? If the store then there is a 90% chance it has the wrong fan/pulley on it.

There is also another possibility that I found on the race car. When I couldn't keep a belt on for more than 3 laps after changing everything, I looked at the last thing to think of and that was the top fan bearing. The bearing shaft has slipped down into the cover by 1/8"! That was enough to upset the belt geometry so the belt would not stay on at higher RPM. I didn't post anything here about it cause no one here really cares about racing.

Ken Hand
Handy Car Care
248 613 8586


Re: Belt issues
Posted by: JimBrandberg ()
Date: May 03, 2022 05:37AM

I'm wondering about the alternator. I've often found that the belt can be very loose but the alternator is still charging, at least the light isn't coming on. Getting hot doesn't sound like a good sign.
Often an alternator you buy from mainstream sources will have the wrong direction fan. This is supposed to inhibit cooling but I've seen plenty that seem to be fine. I've also seen pictures here where they were clearly not fine. Correct fans are getting scarce so I'm sometimes reluctant to put one on when someone else did it. It's like Elaine Benes deeming someone sponge worthy.

Jim Brandberg
Isanti, MN

Re: Belt issues
Posted by: American Mel ()
Date: May 03, 2022 07:30AM

Just a reminder, Rev-Rot is NOT going to use the stock Alt. fan.

WA. state, 1 mile south of the Canadian border, I am not at the end of the world, but you can see it from here.

Re: Belt issues
Posted by: Saxon ()
Date: May 03, 2022 07:47AM

When howling with noise, I replaced my alternator bearings front and back with the following parts from O'Reilly. Back in summer of 2019.

With a lot of knowledgeable advice from Seth, it was an easier assembly job. It was the first time I had used an air gun and compressor.

BCA MNJ471s - $7.99

BCA203F -$13.99

Northern CA
66 Monza Coupe 4-spd 140

Re: Belt issues
Posted by: corventure Dave ()
Date: May 03, 2022 09:44AM

Standard trans or automatic? Early steel fan or 64+ Mag fan?
If std trans, how aggressive are you between gears?
Do you have the belt retainer on the idler pulley and if 64+
the fan shroud? And how close are they adjusted to the pulley's?

From there I agree with above. Bearings and alignment are a place to then check.

Corventure Dave

Re: Belt issues
Posted by: CREATIONBLUE ()
Date: May 03, 2022 02:35PM

Thanks for all the replies

The alt has the correct fan for a reverse rota engine and a disk that helps to keep the belt on the alt (a prob on a reverse motor without it) all bought from Clarks.

I know the way the alternator responds to being turned and not making Volts as I had it burn out the rectifier a couple of years ago and the thing got real hot. I constantly check it every time I stop, if it’s cool to touch all is good. Hot and it’s not making volts.

I should and would swap it for a new one but they are not available here in the uk and shipping and duty makes it real expensive. I may have to buy one tho if this continues.

The fan is the later one that works both ways. All seem to spin without resistance or noise.

I’ll keep you all posted if I get to the bottom of the problem

Re: Belt issues
Posted by: MattNall ()
Date: May 03, 2022 04:01PM

Voltage regulator issue? Make sure you are not seeing over 15 volts!

Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!

Re: Belt issues
Posted by: CREATIONBLUE ()
Date: May 05, 2022 12:46AM

Well funny you should say that! I’m getting 15volt! When I had the alt repaired, I keep getting high voltage. Took it back to the show like 3 times but it shows fine on their equipment but back on the engine shows high… Is this why the belt is playing up? Although the alt has been like this for the last 2 years and the belt only just started to twist.

Re: Belt issues
Posted by: DaveO90s4 ()
Date: May 05, 2022 01:04AM

Please confirm that your engine is teverse rotation. If so, i know exactly what is causing your problem and I have engineered a solution to it.



Re: Belt issues
Posted by: CREATIONBLUE ()
Date: May 05, 2022 01:16AM

Yes Dave it’s a reverse rotation engine coupled to a vw manual 4speed

Re: Belt issues
Posted by: DaveO90s4 ()
Date: May 05, 2022 01:35AM

Ok. I will reply oriperly within the next two hrs (dinner time here in Australia)

Re: Belt issues
Posted by: DaveO90s4 ()
Date: May 05, 2022 02:38AM

Ok Creationblue, dinner over, time to post.

I am running a reverse rotation corvair engine in my Porsche 914. I was initially having issues very similar / almost identical to yours. Those problems have now all been overcome and I have no discernible belt wear and certainly no belt flipping or tossing since implementing the 'fixes' I am about to describe below, in the order that I tackled them (easiest and cheapest first etc).

1. Make sure that the alternator and the fan and the idler pulley all rotate smoothly and easily without a belt.
2. Make sure that all pulley grooves are clean and shiny (no rust etc).
3. Make sure that your alternator pulley is of the correct dimension (e.g.diameter / circumference) and groove width. The pulley on mine was not the correct size and I replaced it with a pulley from a '64 Corvair. For reasons I now forget the '64 pulley is a one year only pulley and for some (forgotten) reason is particularly suitable for our reverse rotation applications.
4. Don't bother with any belt guides in the OEM locations - our belts run in the opposite direction so the OEM belt guide is on the wrong side to do any good (I still have my belt guide in place and adjusted to spec. but I have no doubt it is doing nothing).
5. As already said, make sure you really really really do have the correct belt. The belt is meant to run on the internal angled part of the groove, not at the bottom of the groove. This is important / critical.

So those are the easy simple things to do, and are in my view essential pre-requisites for success. But all of those did not fix my belt flipping problem. The next bit fixed the problem for good. A bit of introduction discussion first.

With V belts (as in our engines) it is absolutely critical that the belt ARRIVES (in the direction of belt travel) at the next subsequent pulley in direct straight alignment - or as near thereto as possible. The GM engineers achieved this by location of the three fixed pulleys (location, alignment, size) and also the belt tension pulley mechanism. So on a normal rotation engine with a normal belt tension system, the belt tension adjustment essentially moves the tensioning pulley on a horizontal plane fore and aft (through an imperceptible arc). That means that the belt may DEPART the crank pulley at an angle - depending on where the belt tension pulley is adjusted to - but will always arrive at the belt tension pulley straight on (having allowed for the belt 'twist' between those two pulleys). Fantastic. Great engineering I reckon. It all works great when set up properly.

BUT but but now consider this exact same OEM arrangement with the belt turning in the opposite direction. The belt leaves the fan pulley and arrives at the idler tension pulley. OK. Now imagine the idler pulley is towards the outer limits of its adjustment fore or aft adjustment in order to achieve acceptable belt tension (for whatever reason, wrong alternator pulley, wrong belt, whatever). So now the belt leaves the idler pulley, heads down to the crank pulley and ARRIVES at the crank pulley very far from straight on to the crank pulley receiving groove. The belt may tolerate this for a while, but then it will begin to complain about not entering the crank pulley straight on, will flutter and flutter and eventually twist - and twist and twist.

To overcome this I designed and had made a very different belt tensioning pulley bracket to mount in the OEM location (no change to engine case etc). This bracket allows the user to adjust belt tension by winding adjustment screws that RAISE or LOWER the belt tensioning pulley. This is designed and constructed to always have the belt arriving straight on the the crank pulley groove, irrespective of pulley adjustment height (the higher the adjustment, the tighter the belt, of course). So now imagine that the adjustment is wound fully up (or down). The reverse rotation belt will DEPART the fan pulley at a slight angle (angled DEPARTURE not being critical, and anyway this is the single longest straight belt run on a corvair engine, so belt angle effect is minimised), ARRIVES at the belt tensioning pulley square on (allowing for the belt twist in this section), and both DEPARTS the belt tension pulley straight and ARRIVES at the crank pulley nicely aligned to be received into the crank pulley V.

In other words, this system simply applies GM engineer Corvair belt arrival logic to a reverse rotation engine.

Ever since doing this I have had absolutely no belt issues whatsoever.

I had two such devices made, one of course is on my car and the other is with a CCF member in the US. That one in the US might serve as a template to have another made at a 1/2 decent engineering shop?

I will see if I can find any photos of what I describe above.

Hope this is of help

PS - about the alternator fan blade direction. Some say this is critical, others say you can get by with the normal (ie 'wrong' for our reverse rotation engines) blades. I am using 'normal' blades, the pulley that was compatible with my reverse alternator blades was the wrong pulley and was part of my belt problem.

Hope this helps.


Re: Belt issues
Posted by: DaveO90s4 ()
Date: May 05, 2022 02:54AM

I can't seem to find photos specifically for my revised belt tension bracket, but here is a photo of the engine with that bracket in place, and i think that will give you the some idea of what it looks like and how the adjustments works. Pls ignore the belt tension or lack thereof - I was busy playing with throttle bodies when i took this photo.

Once again, hope this helps.

Any questions just ask.


Re: Belt issues
Posted by: DaveO90s4 ()
Date: May 05, 2022 03:07AM

Found some photos - trying to resize 'em

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