Throttle shaft broke - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


Engine Performance This section is for discussion on all engine building related questions.
Sponsored by:
Sponsored by:

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 08-23-2010, 11:14 PM   #1
Elite Member
Thread Starter
iTrader: (8)
 
Join Date: Jun 2009
Location: Albany, NY
Posts: 1,523
Total Cats: 4
Default 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...
webby459 is offline   Reply With Quote
Old 08-23-2010, 11:26 PM   #2
Elite Member
iTrader: (2)
 
fooger03's Avatar
 
Join Date: Jan 2009
Location: Columbus, OH
Posts: 4,133
Total Cats: 188
Default

at least there weren't any stray pieces that made their way from the breakage to you cylinders...
fooger03 is offline   Reply With Quote
Old 08-23-2010, 11:59 PM   #3
Elite Member
Thread Starter
iTrader: (8)
 
Join Date: Jun 2009
Location: Albany, NY
Posts: 1,523
Total Cats: 4
Default

+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.
webby459 is offline   Reply With Quote
Old 08-24-2010, 12:32 AM   #4
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

what does "pax" stand for?

I've heard you can adjust the stop to prevent this from happening. Hopefully its true.
hustler is offline   Reply With Quote
Old 08-24-2010, 12:50 AM   #5
Elite Member
Thread Starter
iTrader: (8)
 
Join Date: Jun 2009
Location: Albany, NY
Posts: 1,523
Total Cats: 4
Default

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.
webby459 is offline   Reply With Quote
Old 08-24-2010, 01:37 AM   #6
Elite Member
iTrader: (24)
 
Join Date: Jul 2007
Location: Cypress, TX
Posts: 3,778
Total Cats: 35
Default

Pax also stands for "Passenger"...
Bryce is offline   Reply With Quote
Old 08-24-2010, 03:30 AM   #7
Junior Member
iTrader: (2)
 
rbluemx6's Avatar
 
Join Date: Apr 2009
Location: San Antonio, TX
Posts: 179
Total Cats: 0
Default

Years ago when I was driving my brother's turbo BP mx3, the throttle shaft broke on me while I was boosting in third gear. It was a FORD 70mm throttle body. Nothing is safe from it happening.
rbluemx6 is offline   Reply With Quote
Old 08-24-2010, 03:47 AM   #8
Elite Member
iTrader: (4)
 
MartinezA92's Avatar
 
Join Date: Aug 2009
Location: Mountain View, CA
Posts: 1,702
Total Cats: 28
Default

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.
MartinezA92 is offline   Reply With Quote
Old 08-24-2010, 05:04 AM   #9
Supporting Vendor
iTrader: (31)
 
Savington's Avatar
 
Join Date: Nov 2006
Location: Sunnyvale, CA
Posts: 14,367
Total Cats: 1,331
Default

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.
Savington is offline   Reply With Quote
Old 08-24-2010, 05:06 AM   #10
Elite Member
iTrader: (24)
 
Join Date: Jul 2007
Location: Cypress, TX
Posts: 3,778
Total Cats: 35
Default

Sounds like a good candidate for balance shafts.
Bryce is offline   Reply With Quote
Old 08-24-2010, 08:30 AM   #11
Junior Member
iTrader: (4)
 
Join Date: May 2009
Location: Novi, MI
Posts: 308
Total Cats: 1
Default

Guess that explains the IM brace that everybody always takes off. We may need it after all. haha.
Larimer is offline   Reply With Quote
Old 08-24-2010, 09:01 AM   #12
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

dog **** > Miata motor
hustler is offline   Reply With Quote
Old 08-24-2010, 09:30 AM   #13
Boost Czar
iTrader: (61)
 
Braineack's Avatar
 
Join Date: May 2005
Location: Chantilly, VA
Posts: 72,892
Total Cats: 1,792
Default

Quote:
Originally Posted by Bryce View Post
Pax also stands for "Passenger"...

and pixel stands for picture element.
Braineack is offline   Reply With Quote
Old 08-24-2010, 09:52 AM   #14
Elite Member
Thread Starter
iTrader: (8)
 
Join Date: Jun 2009
Location: Albany, NY
Posts: 1,523
Total Cats: 4
Default

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...
webby459 is offline   Reply With Quote
Old 08-24-2010, 10:05 AM   #15
Tour de Franzia
iTrader: (6)
 
hustler's Avatar
 
Join Date: Jun 2006
Location: Republic of Dallas
Posts: 29,114
Total Cats: 351
Default

This is why I roll "low and slow", which is the same way I BBQ human.
hustler is offline   Reply With Quote
Old 08-24-2010, 10:23 AM   #16
Supporting Vendor
iTrader: (10)
 
Reverant's Avatar
 
Join Date: Jun 2006
Location: Athens, Greece
Posts: 5,441
Total Cats: 198
Default

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).
Reverant is offline   Reply With Quote
Old 08-24-2010, 02:23 PM   #17
Elite Member
 
Join Date: Jul 2005
Location: Anacortes, WA
Posts: 2,479
Total Cats: 116
Default

Quote:
Originally Posted by Savington View Post
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.
One guy here in a 1.6l DP miata regularly sees 9000rpm he has had the oil pressure sensor brake off twice.

Bob
bbundy is offline   Reply With Quote
Old 08-24-2010, 02:33 PM   #18
Elite Member
iTrader: (4)
 
MartinezA92's Avatar
 
Join Date: Aug 2009
Location: Mountain View, CA
Posts: 1,702
Total Cats: 28
Default

Quote:
Originally Posted by Bryce View Post
Sounds like a good candidate for balance shafts.
Petition for one of the smarter people on the forum to fab a balance shaft kit for our engines.
MartinezA92 is offline   Reply With Quote
Old 08-28-2010, 11:39 AM   #19
Supporting Vendor
 
MiataRoadster's Avatar
 
Join Date: Dec 2006
Location: SoCal
Posts: 271
Total Cats: 4
Default

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 [email protected]***.net and though this is not shown yet on his new site, the URL is: http://jesseprathermotorsports.com



MiataRoadster is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Garrett Turbo, 1.8 Oil Pan, & Misc. Stuff nbdooey Miata parts for sale/trade 9 08-30-2017 10:50 PM
OTS Bilstein to motorsports ASN conversion stoves Suspension, Brakes, Drivetrain 5 04-21-2016 04:00 PM
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
Time to start learning and play with tuning The Gleas MEGAsquirt 3 10-01-2015 10:30 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 05:14 AM.