[Jack Peters]

John Langer in Dragzine Newsletter.
Here is the link. Did not read in depth but good pics and article. Hope it works. If not someone put the correct one.
Congratulations....
http://www.dragzine.com/news/john-la...anmca-atlanta/

[jm455ho]

Nice write up

[Elarson]

Cool, thanks.

Eric

[Stan Weiss]

John,
Great write-up.

Do not know if it just the angle or the picture but that intake valve relief in the piston looks huge.

Again maybe it is just the picture but it looks like only the intake lifter bores are bushed.

Stan

[Half-Inch Stud]

What made the timing belt jump? A 20 year old BOP belt? Drive gear worn to nubs?

[PAUL K]

Originally Posted by Half-Inch Stud

What made the timing belt jump? A 20 year old BOP belt? Drive gear worn to nubs?

Good read, thanks for the link.

[Jack Gifford]

I would also like to learn more about the belt-slip deal.

[John Langer]

Originally Posted by Stan Weiss

John,
Great write-up.

Do not know if it just the angle or the picture but that intake valve relief in the piston looks huge.

Again maybe it is just the picture but it looks like only the intake lifter bores are bushed.

Stan

Both are bushed. They might not both be in the stock location

[John Langer]

Originally Posted by Half-Inch Stud

What made the timing belt jump? A 20 year old BOP belt? Drive gear worn to nubs?

Change the belt every year...

[Half-Inch Stud]

Not busting on you, just crappy text. Was a good read and indicated a jumped cam timing, so that begs the reader to want to know how or what dynamic was able to get the timing to jump.

From the school of "they all fail the same way" so root-cause is very interesting.

[455firebird1969]

Good ink, congrats, you've earned it. Lean is Mean.

[v869tr6]

Cool to see the write up on John's car. Thanks for posting the link.

[JSPONT]

Any Pontiac getting ink is great! Congrats
My friend who runs low 7's and changes his belt every season, had one do the same thing, but a little worse. Junked the block/pistons and heads! Scary how a $40.00 dollar item can screw up $30000.00 engine

[Half-Inch Stud]

Originally Posted by JSPONT

Any Pontiac getting ink is great! Congrats
My friend who runs low 7's and changes his belt every season, had one do the same thing, but a little worse. Junked the block/pistons and heads! Scary how a $40.00 dollar item can screw up $30000.00 engine

So, let's get to the root-cause, because it is not a random mishap. HIS

If i had to guess at a the failue mechanism: the engine presents too much instantaneout torque at some operating point along with the cam train providing too much torque load, and the belt stretches enough to allow the cogged belt teeth to deflect and "hop the gear. i"m eager to guess the hop occurs at the crank gear.

Gates has 2 types of belts: Power Grip & Poly chain. These belts also differ in tooth cut, and my read on that is that BOP picked the better type. I studied the Gates belt load curves for this "Timing belt" size class and the Gates load tables say " you are on your own above 5000 rpm." I mean Gates provides no belt assurance above 5000 rpm, but professionals sure use these belts > 5000 in their designs.

We had a 60 hp UAV rotary engine that picked the other Gates belt type and that underdrive eventually worked reliably, but had a thick rim flywheel and rubber-dampened " love-joy" coupling add-on to attain reliability. Otherwise it would break the underdrive to the propeller from the instantaneous engine shaft torque (10x the average shaft TQ), so the flywheel dampened the source while the "love-joy #6?" dampened the propeller connection.

I remember the GT2 being appropriate for "timing chain" use , but the use of a bacside idler to take out slack was bad. An inside toothed idler may have been reasonable to set tension.

[Stan Weiss]

Originally Posted by Half-Inch Stud

So, let's get to the root-cause, because it is not a random mishap. HIS

If i had to guess at a the failue mechanism: the engine presents too much instantaneout torque at some operating point along with the cam train providing too much torque load, and the belt stretches enough to allow the cogged belt teeth to deflect and "hop the gear. i"m eager to guess the hop occurs at the crank gear.

Gates has 2 types of belts: Power Grip & Poly chain. These belts also differ in tooth cut, and my read on that is that BOP picked the better type. I studied the Gates belt load curves for this "Timing belt" size class and the Gates load tables say " you are on your own above 5000 rpm." I mean Gates provides no belt assurance above 5000 rpm, but professionals sure use these belts > 5000 in their designs.

We had a 60 hp UAV rotary engine that picked the other Gates belt type and that underdrive eventually worked reliably, but had a thick rim flywheel and rubber-dampened " love-joy" coupling add-on to attain reliability. Otherwise it would break the underdrive to the propeller from the instantaneous engine shaft torque (10x the average shaft TQ), so the flywheel dampened the source while the "love-joy #6?" dampened the propeller connection.

I remember the GT2 being appropriate for "timing chain" use , but the use of a bacside idler to take out slack was bad. An inside toothed idler may have been reasonable to set tension.

Hey Mark,
Serious question. Having a brain freeze here. If my crankshaft is turning 10,000 RPM and my camshaft is turning 5000 RPM what is my belt speed?

PS - The more I think about this. The more I believe that one would also need to know the belt length and the diameter of both pulleys. As the belt speed would be slower the longer the belt was. Just to clarify that would be slower belt speed in RPM not velocity.

Stan

[BruceWilkie]

Distance in a given time interval is how belt speed is expressed.
Drive pulley circumference determines distance belt moves.

You usually use same time interval as drive pulley. IE distance per minute if rpm is used, but it can be seconds hrs days etc . As well distance can be expressed in any distance expression. Inches per second and feet per minute are commonly used when referencing belt speeds.

Btw belts typically leave at the entrance of a DRIVEN pulley because the drive pulley is pulling belt which tensions it.

[Half-Inch Stud]

Originally Posted by Stan Weiss

Hey Mark,
Serious question. Having a brain freeze here. If my crankshaft is turning 10,000 RPM and my camshaft is turning 5000 RPM what is my belt speed?

PS - The more I think about this. The more I believe that one would also need to know the belt length and the diameter of both pulleys. As the belt speed would be slower the longer the belt was. Just to clarify that would be slower belt speed in RPM not velocity.

Stan

Yea, i don't recall exactly but the Gates load tables have belt speed contours and hp contours for gear ratios. then there is the pesky "keep-out zone" contour representing the hp limit and 5000 rpm constraint. So the load tables shows some graphic relation to gear speed and belt speed (6500fpm)

Bang the cam gear diameter againts 6500 fpm to see if that is over 5000 rpm.
Take the crank gear (1/2 cam gear dia) and 10,000 rpm to see if that goes above 6500 fpm.

Gates Poly Chain Design Manual;
https://www.ahrinternational.com/PDF...anual17595.pdf

Gates Powergrip GT2 Manual (Design?);
http://docs-europe.electrocomponents...6b8002d3b7.pdf

[Stan Weiss]

Bruce / Mark,
Thank you.

Stan

[Half-Inch Stud]

Originally Posted by BruceWilkie

........Btw belts typically leave at the entrance of a DRIVEN pulley because the drive pulley is pulling belt which tensions it.

Agreed for Vee & Serpentine.

The cogged "gilmore" belts, particularly the GT2 may differ;a single tooth is forced out of the gear pocket from excess load, causing the total free belt length to stretch. When LAST tooth on the DRIVE belt wants to pop-up it encourages all the few remaining belt teeth to ride up in unison (all while under extreme load from instantaneous TQ).

Anyway, is what i suspect. Take a look at the tooth profile. Great for a chain, not great for a rubber-band, and not great for a "glass belt with out-of-spec play/slope

Makes me stubbornly clear on the failure happening on ACCELERATION, not de-celleration.

@Stan, the geeks gotta help the ECM...stay out of the ditch.

[LiL Jack]

Congrats John, I hope u get the fuel issue squared away before the next race.

Shank that PR next time u see him.