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· L&M Engines
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Discussion Starter · #1 ·
We have seen many timing component failures, particularly the GT500, this year due to rev limiters.

The dynamics involved when an ignition rev limiter engages is beyond the scope of this post.
I was always a pessimist of rev limiters since the 60’s when they appeared, but at that time we didn’t have 6 feet of chain with its low natural frequency and its own dynamics occurring naturally being influenced by the out of phase dynamics caused by the rev limiter, so it was not a big problem at that time.

I attached pictures of a fresh built 03 Cobra engine that had a battle with a rev limit situation and lost.

Michael
 

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· 4.6 ways to waste money
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Ouch.

Good to see you posting Michael. I hope you continue to do so, sharing some of your knowledge of the modular platform.
 

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+1 on the postings. Jon always has good things to say about Michael. ; )

That's a LOT of damaged valves and possibly guides, uggh.... I've been there, but it wasn't the result of a rev limiter. It was a sheared cam bolt that took my driver's side bank out.

How do the cam journals and towers look? I've seen several times where the cam seizes in the tower, stops turning, and gears and chains break.
 

· Yes...it can be done
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Wow. That's incredible. Those gears are very very hard. After a day of grinding on primaries, seeing the key sheared off and a secondary cracked into three pieces is a stunner. First guess is a snapped secondary chain.
 

· L&M Engines
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Discussion Starter · #5 ·
+1 on the postings. Jon always has good things to say about Michael. ; )

That's a LOT of damaged valves and possibly guides, uggh.... I've been there, but it wasn't the result of a rev limiter. It was a sheared cam bolt that took my driver's side bank out.

How do the cam journals and towers look? I've seen several times where the cam seizes in the tower, stops turning, and gears and chains break.
Lube was good, no cam bore damage.
Seizure is lack of oil or debris.

Jon told me about you wrestling with a 4V on the kitchen floor. We had private snickers over your FOD encounter.
We've all had similar circumstances in life and laugh after the pain goes away.
 

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I just broke a secondary chain back in September, havent gotten around to messing with it. The chain did break, gears are fine, cam bolts intake, keyways fine etc. I did get around to putting a socket on the intake gear and it seems as if the cam is welded to the head.

This is kinda ironic you mention rev limiter, cause I tapped mine at the track on a test hit on a 1-2 shift. I took the car back to the pits and then went up to race and it broke rolling out of the burnout box. Im hoping it was debris or something and I didnt lose the motor/whole head. Might be time for some GT CAMS.
 

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Is this really a case of the rev limiter causing cam sprockets to fail, or is this just a defective part? With about 20,000 03/04 Cobras on the road, I'd think we'd have seen this dozens of times over by now if simply hitting the rev limiter is the culprit.
 

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Interesting post.

Any idea how high the rev limter was set?

Were these stock or aftermarket cams?
 

· L&M Engines
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Discussion Starter · #10 ·
Is this really a case of the rev limiter causing cam sprockets to fail, or is this just a defective part? With about 20,000 03/04 Cobras on the road, I'd think we'd have seen this dozens of times over by now if simply hitting the rev limiter is the culprit.
Good question.

We have seen 5 or 6 GT500 fail this year directly attributed to rev-limiters.
Looking at my history, I see, 3 Cobra rev-limit failures in 3 years.
The blessing of the 03 Cobra and others is, it uses a 10 mm pitch chain drive whereas, the GT500 uses an 8 mm chain system. By the way, the Ford GT uses a 10 mm silent link setup, same as the Cobra.

The major reason the GT500 fails is the fact that it uses an 8 mm pitch the OD of the lower sprocket requires it to be smaller and that makes the cross-section to be thin at the key slot. With a 10 mm pitch the cross-section for the proper tooth count is much thicker.

My responsibility to a customer is to determine if it is part failure or operational causes that cause a failure and this ensures we don't build in a failure down the road.
All of the failed engines that come in our door must have the failure cause and effect determined so we don't tread on the same ground.
 

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Glad to hear the 03's have the more robust parts. It's odd that Ford would use a weaker setup in the GT500 than the GT. Was it just for cost savings? Some type of space limitation?
 

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So the valve covers clear the frame rails installing the engine at the factory.
Compromise a critical engine component design for packaging?! :censored:
 

· L&M Engines
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Discussion Starter · #16 ·
How some great info.

How long was the car on the rev limiter? How fresh was the motor?
We delivered a short block 4/13/11, maybe the customer installed it June-July.

Age has nothing to do with it.
We have seen this occur on day one or 1000 days.

Tommy P. with the GT500 that did 8.60 et had a couple of days to do it.
 

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We delivered a short block 4/13/11, maybe the customer installed it June-July.

Age has nothing to do with it.
We have seen this occur on day one or 1000 days.

Tommy P. with the GT500 that did 8.60 et had a couple of days to do it.
And he also ended up putting all GT engine dress on the front if I'm not mistaken. If I were assembling a Shelby motor, that would be the first thing I changed.

Good stuff.
 

· L&M Engines
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Discussion Starter · #19 ·
And he also ended up putting all GT engine dress on the front if I'm not mistaken. If I were assembling a Shelby motor, that would be the first thing I changed.

Good stuff.
Tommy put the 10 mm stuff on and the front dress, although it's not required, raised the engine into the compartment and halfway up (the only time you can do this) put the valve covers (very expensive and required) on.
 
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