Throwing my belt at 7050rpms. Why?

[VW_Jimbo]

Hey all! I have been having a blast in the Bug, now that the tranny holds itself together! Thanks Scott at MCM! Super fun to drive! However,.......

My engine keeps throwing the generator belt, if the RPMs get above 7000. Why? What am I not seeing or accounting for?

Back story, as most have seen my threads. I spent a few extra bucks for nicer stuff (twice), then getting it all dynamically balanced (twice), so that I could spin it up 8500. My calculated redline, based off of some material facts and off of some feed back from a few friends that have built engines that spun that fast. I did everything I was supposed to do, but every time the engine hits 7050, the belt get shredded and flies off. Check out the pictures. Not a horrible issue to have, except for the two times the engine has gotten past this magical number, 7050. Then the charging light goes on and I turn the key off! Coasting to the closest parking spot.


Let me know what you all think and any options that are out there. Thanks!

Since I did not have a spare on the second time it happened, I had to turn the belt inside out and run it the two miles back to the house. It worked!

I am guessing that spot that is missing is the one down on the crank, but really have no way to prove it. Why would a belt disintegrate like this? The tension is spot on. Never experienced anything like it before!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[rodeking]

Belt not designed to take the forces made by those rpms? Smaller crank pulley to slow down belt speed?

Or maybe tension the belt even tighter so it doesn't stretch as much at the high rpms. That puts more load on the gen bearings though.

[Xevin]

Maybe go beltless and ad this to your pulley

https://www.oreillyauto.com/flux-capacitor
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Keep on Busin'

[oprn]

"7050 rpm" is the key to the problem. Nothing on that engine was designed by VW to take that kind of speed.

I have a similar problem with the implement tires I have on the front of my sand rail. They shake so bad at 70 mph that the front end disappears in a blur and I can see day light under the front wheels. These things happen when we do stupid things to parts that are not designed for what we are subjecting them to!

[ALB]

I once had the same problem (at about the same rpm)- if you really want the thing to spin that fast on a regular basis you need a power pulley.
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On a lifelong mission to prove (much to my wife's dismay) that Immaturity is Forever!!

[vwracerdave]

Simply put you have reached the limit of the fan. The fan can not push any more air above that speed and turns into a brake. The crankshaft continues to go faster but the fan can not. I have experienced the same issues on the drag strip. With a stock sized pulley I can not turn above 6800 RPM as I have always thrown the belt. I turn 7200 RPM with a power size pulley and no problems throwing the belt. Your only solution is not rev that fast with the stock size pulley.

DO NOT UNDER ANY CIRCUMSTANCES INSTALL A SERPINTINE BELT SYSTEM. It will not fix the problem, it will only make it worse.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[FreeBug]

Hi, please gdt that fuel filter out of the engine compartment, close to the spark machine, without clamps, ESPECIALLY as you're throwing belts around.

Happened to me once, full size pulley at around 7000-7500 rpm, and it blew the "1300" emblem off the lid. That's enough momentum to pull off a fuel hose. Best place for a filter is just under the tank. Check, you might already have an old one there, too.

Maybe try running a thinner belt, sits down further in the groove, and maybe try running the belt a bit slacker, letting it slip more. Just ideas.

[VW_Jimbo]

[VW_Jimbo]

[mcmscott]

[DeathBySnuSnu]

You are hitting the max hp you can transfer by a single belt. Fan would keep on going IF you could get the hp to it. BUT putting a serp belt or a configuration of belt that can move the hp.....the fan will explode. Hence the welded fans.....
I do not know how many rpm or for how long a stock or welded fan will take.
It is slipping and overheating the belt. Then the belt comes apart.

http://www.offroadvw.net/tech/wes/fan.html
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[FreeBug]

[Vanillagurilla]

[modok]

What kind of belt is that?
Try a gates or dayco raw edge belt,and set it up snug....not too tight.
Nothing wrong with the stock pulleys, but to run over 6500 rpm often it would be smart to run a smaller cooling fan OR a power pulley, so the belt does not overheat so bad. Think about it, on ANY car, the alternator isn't rated to go over 10K rpm, but do the math and at redline it would......so it must be the belt slips.

[ralf]

[Cusser]

[oprn]

[HotStreetVw]

What are the specs on the engine? CCs, heads, carbs?
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4inBhore
50 Split - 2724cc NA. Haltech injected
62 Notchback - 2542cc Turbo WIP

[Zundfolge1432]

[jpaull]

Jim, Is this your engine with the Engle 110 cam?