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I truly hate seeing belt flop on these engines. Before we get into operator "error", I have a German made pulley on my engine, high-quality crank pulley, Continental belt, and everything is adjusted correctly. So, no. That's not the issue.

With the choice of forking out $250 for a ribbed belt/tensioner system, then having to redrill the crank pulley for the magnets my crank sensor needs, also having to modify my crank sensor bracket, changing out the studs on the alternator stand because the ribbed belt system would need longer studs, etc--I opted to buy a compact tensioner and fab. up my own for less than $50.

Got a tensioner designed for motorcycle chain tension from Amazon on the interwebs along with a pack of v-groove 3/8" wide PGN industrial bearings. Amazon only sells these bearings in an 8-pack but I found out later you can buy them direct from PGN directly in whatever quantity you want.

Anyhoo, make a short story long, I had to figure out where to mount the tensioner and what to mount it to. No surprise there's not a lot of space. Wasn't going to fit on the inner area of the belt pushing it out, so it was going have to ride on the backside of the belt for tension. The bearings have a v-groove in them which is fine for what I needed because I simply take two of them and stack them side by side, however on of each of the grooves needs to be machined flat. It took about 1/2 hour on the lathe to machine each bearing.

The shaft that the bearings ride on and sits in the tensioner also needed to be machined down which took another 45 minutes. Also had to cut, machine and weld a little collar clamp to hold the bearings on the shaft, drill the shaft for a cotter pin as extra failsafe, then turn my attention to fabbing up the mounting bracket.

The tensioner fits nicely riding against the alternator using two of the alternator housing screws for securing and the rear bolt on the throttle body as a third mounting point. Drilled some flat bar for speedholes and bent it on my tubing bender. Did a test fit and test run then pulled everything off and powder coated it silver.

The whole thing works great, couldn't be happier with it.

No, that's not Megasquirt BTW.

https://youtu.be/zHHZ0HiHM2U

That's slick. And ingenious.

Thanks

Jadewombat wrote: ↑Sun May 17, 2020 7:51 am I truly hate seeing belt flop on these engines.

So tighten the belt.

Jadewombat wrote: ↑Sun May 17, 2020 7:51 am Continental belt,

This is part of your problem. Conti belts are junk. Get a Gates.

Very nice. How many rpm's are you turning that you needed this to keep the belt in place?

Bruce2 wrote: ↑Tue Jun 16, 2020 12:18 am
I truly hate seeing belt flop on these engines.

So tighten the belt.

[/quote]

What, like I didn't think of that??? It IS tight to factory specs. genius, watch the video again.

CB would have never sold a single tensioner/ribbed belt system if there wasn't a need for it.

Tom in PA wrote: ↑Tue Jun 16, 2020 6:08 pm Very nice. How many rpm's are you turning that you needed this to keep the belt in place?

I have my rev. limiter set to 5500, although it flops at lower speeds also.

Jadewombat wrote:

Bruce2 wrote: ↑Tue Jun 16, 2020 12:18 am
I truly hate seeing belt flop on these engines.

So tighten the belt.

What, like I didn't think of that??? It IS tight to factory specs. genius, watch the video again.

CB would have never sold a single tensioner/ribbed belt system if there wasn't a need for it.[/quote]
It’s a nicely done mod and makes for easier maintenance which is exactly why it’s standard on every modern car.

However, I do suspect your belt tension was too loose. Bugs drove around for a few decades before someone did that mod and belts managed just fine most of the time.

The correct tension is quite tight. The 1/4 turn is an easy test but the correct spec is 10mm deflection when you push the belt half way between the two pulleys. You should also be able to turn the engine with the alternator pulley nut (stock compression), without the belt just slipping.

Now you have a low maintenance solution that works and that’s cool too.

The tension on the belt is very tight. I can barely get half a twist at the midpoint and it's 1/2" side to side when you push on it. I can rotate the engine by turning the alternator nut. If I take even one single shim out to tension it up more it is very difficult to turn the engine--which would mean putting a lot of load on the case and the alternator bearings.

We're dealing with a vibration that needs to be dampened. Again, from the other thread even Porsche put tensioners on their cars in the later air-cooled years and there's a whole slew of things VW could have improved upon with the cars, but there wasn't much need to after ~1975 when they already had water-cooled cars selling.

One of the things not talked about is how the belt reacts when going around the pullies. To be simple about it the belt. because of it's mass, wants to straighten out (not sure what the real word would be but the belt gets a bulge in it as it leaves the pully hence the contact area of the belt on the pully is reduced. Using the tensioner helps keep (reduce the bulge) the belt in contact with the wheel longer hence the helps reduce the changes of belt slippage.

Lee

Nice work, and Gates belts do seem to work better, even the ones made in Mexico.

Corvairs had much longer belts and from all accounts far worse issues chucking them, particularly as they bent it 90 degrees, fan was flat on top of the engine...(some of this was stretch, this was in BK time==before kevlar)
The racer proven fix: a guide pulley or even just a rub block as a tensioner on the side that gets loose under load to keepitfromflapping.
Of course the racers cut their magnesium fans down to 7"-9" ish as well... std was around 11" iirc.

Yes, I've thought about that, too Lee. Although the belt has some give to it to conform to those surfaces, The efficiency in energy transferred from the crank pulley to the alt/gen pulley is never quite ideal. Since the contact is on the belt walls against either pulley, if the tension is too tight the inner part of the belt would be making most of the solid contact (and doing the work), too loose and the outer portion of the belt doing most of the work.

It's easy to see why the manufacturers went to ribbed flat belt.

Thanks Guys, I'll try a Gates next time.