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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 05:37PM

Rat643, are your comments based on a reverse rotation engine too?

This is all good stuff and is starting to make sense now. As purchased, the engine had a 57” belt and a too small alternator pulley. That combination meant I had to have the idler pulley far away from the engine to get correct belt tension. And as a result lousy idler to crank belt alignment. Now I have corrected both: I have the correct larger diameter alternator pulley and the correct (shorter) 56” belt. Now my idler pulley has to be set too close to the engine for correct idler to crank alignment when the belt is at correct tension. My measurements on my car suggest the pulley should ideally be adjusted outwards by 15mm (2/3rds of an inch). I believe I can buy locally a belt of the correct profile that is 15mm longer than the 56” belt (1437 mm v 1422 mm).

I will give that a go before thinking about more esoteric fixes.

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Re: Fan belt ‘cracks’
Posted by: Frank DuVal ()
Date: March 01, 2019 05:39PM

Hmm, 56" worked for GM on 1.8 million vehicles....winking smiley

Never had an issue with 56" belts myself. After the initial stretch they are close to vertical running, slightly towards the front of the car. I did have to put on a 56" low quality belt (Road King?) on a club member's car once at a Christmas parade. That belt had been sitting in a car for years. I had to really pry it onto the pulleys, and yes, the idler was up against the stops! I told him to go buy a new belt soon.

Now, if the crank pulley to idler runs straighter (more 90 degrees), maybe Dave should try one. 1448 mm.

Dave, can you stick a slim straight edge against the harmonic balancer to see where vertical is, even though you cannot see straight in the area? Between the balancer and the rear housing area, using a mirror on a stick.

Frank DuVal

Fredericksburg, VA

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 06:04PM

Hi Frank. Yes I have just completed this task. I will crest a diagram of my measurements and will post those soon. I agree with you entirely about the 56” belt working fine for these engines for many years. GM engineers got it right. But as built it doesn’t mater too much about idler : crank pulley alignment, since the belt can depart the crank at an angle and still arrive at the idler correctly aligned. Whereas on my reverse rotation engine this has the belt arriving at the crank at that angle. And therin I think is my problem. I don’t understand why I am having this problem when other reverse rotation owners do not experience it. But I do think I now understand my particular problem and I think I have identified a solution to that in my particular case - a slightly longer belt.

I appreciate all the input.

Schematic diagrams to come soon-ush (have been ordered by my darling wife to now stop for lunch).

Cheers

Dave

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 07:04PM

Here's my diagram.

My process was:-

1. Establish centre line of crank pulley 'V' in relation to outer edge of harmonic balancer. 15 mm (see item F on diagram)

2. Measure how far outer face of belt sits within the idler pulley. 5 mm (see item C on diagram).

3. Allow for 1/2 the width of the 10 mm belt itself to derive centre line of belt. 5mm

4. Establish position of outer edge of idler pulley in relation to outer face of harmonic balancer (15mm less 5mm less 5mm = 5mm) (see item B on diagram).

So if the closest point of the outer edge of the idler pulley is 5 mm closer to the engine than the outer face of the harmonic balancer, the belt will arrive at the crank pulley 'straight on'.

If 5mm is the ideal, then my 20 mm is about 15 mm out - and would be cured by a belt that is 15mm longer.

(As I say, I don't know why I am having this problem and I have moved on away from figuring out the 'why' - having satisfied myself that all bearings are running true, no rust in pulleys, etc, I'm now focusing on the solution irrespective of the cause of the problem).

Hope the diagram is legible

Cheers,

Dave

Dave O

1975 Porsche 914 with 140 HP Corvair reverse rotation engine, zenith 40 TINS, Otto 20 (or 30?) cam, etc, Australia

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Re: Fan belt ‘cracks’
Posted by: MattNall ()
Date: March 01, 2019 07:15PM

Makes sense!! Do it!





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Re: Fan belt ‘cracks’
Posted by: Frank DuVal ()
Date: March 01, 2019 07:19PM

Actually a good diagram of what is happening.

Hey, someone turned your diagram!grinning smiley

Find the belt and try it.

Frank DuVal

Fredericksburg, VA

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 07:27PM

Thank you both for your prompt and supportive responses. Yip, I'm just gonna do it and gonna get me a 1437mm (56 1/2") belt.

And to the clever person who rotated my diagram, thank you very much.

Best regards to all,

DaveO

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 09:12PM

Made a high tech tool for assessing alignment of idler with respect to crank pulley - patent pending ha ha. Measures centre of idler bearing shaft to firewall (in Porsche 914, remember!)

V = belt arrives vertical at crank and is the ideal, subject to belt tension of course.
V-15 and V+15 are 15mm either side of ideal. (I'm currently a V-15 albeit with correct belt tension)

Now in my in-car fan belt replacement tool kit for use sometime down the road (pun intended).

Cheers to all

DaveO



Edited 1 time(s). Last edit at 03/01/2019 09:15PM by DaveO90s4.

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 01, 2019 09:13PM

Now attached.

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Re: Fan belt ‘cracks’
Posted by: MattNall ()
Date: March 01, 2019 09:15PM

Well worth the effort!





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Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 07, 2019 10:52PM

Hello all. Update. I am new very confident that I have found the cause of my fan belt problems and am also pretty (very?) confident that I have identified the solution. It will require a bit of time to confirm since I am going away for three months in two weeks time. If I get it done to a reportable stage I will post progress in a new ‘reverse rotation idler pulley’ thread.

Once again thanks to all who have provided me with input and comments.

Best regards

DaveO

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Re: Fan belt ‘cracks’
Posted by: MattNall ()
Date: March 07, 2019 11:02PM

Have a safe and hopefully fun trip!





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Sea Mountain, between Charleston Harbor and Coos Bay! SW Oregon Coast
Click HERE for My Website...Click HERE for My TechPages!
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Re: Fan belt ‘cracks’
Posted by: JimBrandberg ()
Date: March 08, 2019 05:43AM

I tried several different belts on my racecar.
57" sounds long but I can't argue with someone's results.
I went to fan belt supply websites and bought different lengths. 55 5/8, 56 1/2... I don't remember the specifics but come across them on my hook full of misc. belts.
10mm is close to 3/8 and opens up more possibilities.
7/16 is only good for a fan belt toss in my opinion.

7000 RPM racecar is sort of a different thing. Downshifts would cause trouble. I had a silicone spray ritual before every session.
Ultimately I went to a vertical fan.

I like the regular Clarks belt but the Otto seems too stiff to me. Others might like it that way.

Just to throw something out there, could you fabricate belt guards in alternate locations for your reverse turning situation? Maybe it's already been discussed and I missed it.

Some of my experimentation was due to different pulleys to slow the fan speed which doesn't really enter into the discussion here.

Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Fan belt ‘cracks’
Posted by: DaveO90s4 ()
Date: March 11, 2019 03:13PM

Hi Jim and all. Thanks for your input Jim. I have found that a “SPZ1437” belt is within a couple of mm of the ideal length for my application. This provides for almost perfect belt alignment arrival at crank when the tensioner is set to give correct belt tension. From my reading the SPZ is the metric equivalent of the 3v, same v angle, same depth and within 0.2mm of the 3v top width. I think in imperial terms an SPZ1437 would be called a 56 1/2” belt. The SPZ1437 is on the car and is tracking very nicely.

I have decided not to fabricate modified belt guards - it always tracks nicely around the alternator, fan and idler pulleys. And nicely around the crank pulley too - provides it enters the crank pulley nicely. 56” belt won’t, 1437 belt does.

I will still proceed with my idea for a modified idler pulley arm so that I can retain my nice ‘idler to crank’ vertical alignment as and when I tighten the SPZ1437 belt.

Cheers all

DaveO

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