Throttle shaft broke
08-23-2010, 10:14 PM
#1
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Throttle shaft broke
My throttle shaft broke this weekend. Had towed around 3 hours to run a great event with the Renegade Miata club at Devens airfield in Mass. First run in second session, right when I was getting into the groove of the massive grip from the Hoosiers, ******* THROTTLE SHAFT BROKE! Apparently, it is common, there is a thread on m.net. Sucks. It broke at the pax side screw holding on the butterfly. Then the throttle bell crank fell out of the throttle body.
We rigged something to get it on the trailer to pull back home.
Sucks, I was just starting to go fast...
We rigged something to get it on the trailer to pull back home.
Sucks, I was just starting to go fast...
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08-23-2010, 10:59 PM
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+1
Hard to believe, still. I'm reading on it: http://forum.miata.net/vb/showthread.php?t=302371
I was buzzing the **** out of the car Saturday, that is surely the reason. I didn't really expect mechanical troubles out of 1.6 n/a power, but so be it. I hope there might be a fix for it.
Hard to believe, still. I'm reading on it: http://forum.miata.net/vb/showthread.php?t=302371
I was buzzing the **** out of the car Saturday, that is surely the reason. I didn't really expect mechanical troubles out of 1.6 n/a power, but so be it. I hope there might be a fix for it.
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08-23-2010, 11:50 PM
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PAX is professional autocross index. It'd be better to call it RTP, which is 'racer's theoretical performance.' It's a way to index differently classified cars with a multiplier to equalize times. Some clubs use it to make a "Pro" class, some base season points on it. It is a reasonable way to figure your times versus others in your club to see where you stand in the rankings.
I have to check the throttle opening amounts to see if it was caused by the linkage trying to move the throttle crank beyond WOT. This would put stress on the shaft. If not, it's harmonics or something. I'm thinking maybe the brazed screws and butterfly would be good insurance.
I really was laying against the limiter for extended periods of time. It was just that type of course, and I'm on 13" wheels, so I'm gearing limited on longer courses.
I have to check the throttle opening amounts to see if it was caused by the linkage trying to move the throttle crank beyond WOT. This would put stress on the shaft. If not, it's harmonics or something. I'm thinking maybe the brazed screws and butterfly would be good insurance.
I really was laying against the limiter for extended periods of time. It was just that type of course, and I'm on 13" wheels, so I'm gearing limited on longer courses.
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08-24-2010, 02:47 AM
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As violently as my whole car vibrates when I'm near redline, I wouldn't be surprised if a BP could break a throttle shaft from any application. I can't think of any other car I've driven that shakes so damn bad at high rpm.
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08-24-2010, 04:04 AM
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Breaking news, BPs have harmonic issues. Throttle plate stop won't do anything. Rev it past 7k normally and it's just a maintenance item. I think Emilio has broken like 3 or 4 of them.
I read a post from somewhere about an EP builder who was spinning them to ~9200rpm. He said that they were breaking some crazy ****, like oil pan bolts and intake manifold studs. I broke a few IM studs on my old '99 motor.
I wonder if the B18 shaft is any better.
I read a post from somewhere about an EP builder who was spinning them to ~9200rpm. He said that they were breaking some crazy ****, like oil pan bolts and intake manifold studs. I broke a few IM studs on my old '99 motor.
I wonder if the B18 shaft is any better.
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08-24-2010, 08:52 AM
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lol at the pax part of the discussion. I forgot I originally typed that.
Apparently guys have broken them even with the IM bracing in place. Mine is not present, so that's my data point.
Given what Sav wrote, the harmonics probably don't get any better at higher RPMs. I was sustaining ~7200 rpm when the problem happened, and I was hoping that a new 8k limit might bypass the problem. Probably not...
Apparently guys have broken them even with the IM bracing in place. Mine is not present, so that's my data point.
Given what Sav wrote, the harmonics probably don't get any better at higher RPMs. I was sustaining ~7200 rpm when the problem happened, and I was hoping that a new 8k limit might bypass the problem. Probably not...
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08-24-2010, 09:23 AM
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Four years now of spinning my own engine to 7800rpm and it is still there, intact. It's my daily driver and I do make it feel uncomfortable any chance I get (pretty much most of the time).
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08-24-2010, 01:23 PM
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Breaking news, BPs have harmonic issues. Throttle plate stop won't do anything. Rev it past 7k normally and it's just a maintenance item. I think Emilio has broken like 3 or 4 of them.
I read a post from somewhere about an EP builder who was spinning them to ~9200rpm. He said that they were breaking some crazy ****, like oil pan bolts and intake manifold studs. I broke a few IM studs on my old '99 motor.
I wonder if the B18 shaft is any better.
I read a post from somewhere about an EP builder who was spinning them to ~9200rpm. He said that they were breaking some crazy ****, like oil pan bolts and intake manifold studs. I broke a few IM studs on my old '99 motor.
I wonder if the B18 shaft is any better.
Bob
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08-28-2010, 10:39 AM
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Jesse Prather Motorsports has a solution: an "alternate material" shaft with no screw holes and the butterfly is epoxied in place. His replacement shafts for 1.6 throttle bodies have the correct spline for upgrading to a 1.8 TPS. He charges $400 plus a core throttle body. You can contact Jesse at jprather34@***.net and though this is not shown yet on his new site, the URL is: http://jesseprathermotorsports.com
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