21 replies to this topic

[Joe (dad) Jordan]

Hey all,  It has been disgussed in great detail about throttle body shafts breaking on Miata's.

 

Here is a lengthy discussion on the subject.  http://forum.miata.n...ad.php?t=302371

 

I also put together a video of the last 2 we have broken in 2 different cars for you to view here.

 

http://youtu.be/xicZNrHn7Gw

 

Many believe it is vibration at high speed,  with some help from Lewis at Rush Motorsports he believes it is the throttle idle stop gets out of adjustment due to wear  and the shaft over rotates when you come off the throttle at high rpm's.  In looking at the video I think Lewis may be on to something.  So all you 1.6's out there check the gap on the idle stop screw and make sure their is none.  Every spare that I have checked their is a gap......so start adjusting,

 

If anyone has any more experience with this I am all ears

 

Thanks

[Bruce Wilson]

Had one break in our enduro car at about 9am when we were leading the 25 hour by 8 or 9 laps (and never one since!)

 

1) Make sure you regularly check and adjust to be sure you're at full throttle with your heavy footed driver PLANTED and STOMPING on the pedal.  If the TB is stressing in the slightest way, you're going to lose it eventually.  It's really not that hard to get it just right and recheck twice a year

 

2) Not sure if comp motor mounts help with this -- I suppose it could.  But I've never had it happen in my personal car, which has them. Plus I adjust every time I the motor is put back in.

 

3) You may want to weld a sold piece of steel below the pedal to eliminate the flex in the floor if Joey's a real stomper.

[Joe (dad) Jordan]

Thanks Bruce.

 

We check #1 regularly we are paranoid so check it every race!

 

We will try the comp motor mounts thanks....  I don't think he's a stomper but I will rig a go pro to be sure!

[Marc Cefalo]

Joe we lost numerous tb shafts in one of our f prod car years ago. the other for three years never had a problem. The one w problems had a 7 pound flywheel, aluminum motor mounts and a different crank pulley. The other car was my fathers which was basically a 1.6 spec miata with cams.

After speaking with numerous engine builders we attributed the breaking of the shafts due to harmonics in the motor. Maybe it wasn't balanced correctly but the solid mounts, different harmonic balancer and light flywheel didnt help the situation.

It was soo bad that we would qualify the car with a screen behind the tb to catch debris if the shaft broke, pull the screen for the race adjust hope it wouldn't break.

Pm me if you want to discuss the problem further, sorry you guys are having issues with them.

[SaulSpeedwell]

Combination of what others said.  When you floor the gas you better hear and feel a hard "tap tap tap" down at your foot, and still have a slight bit of slop before hitting the full throttle stop at the throttle body itself.  Otherwise, you are stressing the throttle shaft every time you floor it.  MANY 1.6s I have sat in and drove have this problem! 

 

Even on a car that is "correct", this gets screwed up during engine changes because of slop in where the cable bracket attaches to the intake manifold.  It also gets screwed up when people "bend" the throttle pedal to improve the pedal position.

 

I sort of buy Lewis's idle stop argument, but there is a dashpot that "catches" the throttle lever on its way back to idle and helps it close slowly?

[Michael Colangelo]

Is this a 1.6-only problem or does it also happen on 1.8 (NA and NB) cars, too?

[Joe (dad) Jordan]

Is this a 1.6-only problem or does it also happen on 1.8 (NA and NB) cars, too?

 Hey Michael pretty sure it happens in most, more frequent in high horsepower cars like production and STL, but since my 1.6 is older than my driver 1991 for the car and 1994 for the driver it is showing it's ugly head.

 

Also the fact that our Spec Miata 1.6 we have makes so much horsepower they must check the cams  should also be considered.

[Bruce Wilson]

Look for that slop Mr. Speedwell mentions.  The goal is to get WOT and that is achievable without stressing the part that breaks.  Also when our tb broke in the 25, I could see that it had been half broken (visible rust) long before the race.  They usually break at the point where there's a hole drilled in the shaft, so visual inspection or maybe magnaflux may be in order for future TB candidates.

[SaulSpeedwell]

Look for that slop Mr. Speedwell mentions.  The goal is to get WOT and that is achievable without stressing the part that breaks.  Also when our tb broke in the 25, I could see that it had been half broken (visible rust) long before the race.  They usually break at the point where there's a hole drilled in the shaft, so visual inspection or maybe magnaflux may be in order for future TB candidates.

 

Yes! ... your throttle shaft may have been compromised by the previous owner, previous adjustment, previous engine change.  Another clue is if you have to use all the available adjustment to get your idle in spec, you are MORE likely have a twisted (i.e. "pre-fatigued") throttle shaft (but of course, you might have wonky timing, AFM, or vacuum leaks too).

 

Just make sure the pedal bottoms AT THE FIRE WALL, and the throttle plate still has an eyelash of travel left to go .... and then you have done the best you can.

 

It is possible on all cars, but it seems more common on the 1.6 - I'm not sure why. 

[KyleLoustaunau]

+1

http://postimg.org/image/c7aoq55ex/

[Bruce Wilson]

Ouch!

[Joe (dad) Jordan]

+1

http://postimg.org/image/c7aoq55ex/

Wow Kyle did that happen at Sears Point today?

[Ron Alan]

The crazy thing is that screw got sucked in and around and spit out and the motor still ran....down on power a little

[KyleLoustaunau]

Nah it happened last year

[Brandon]

 

[Bench Racer]

Joe-dad, I could run through the many broke shafts on the F production car and Spec Miata cars, except Ron would question the the crap out of any thing that isan't said by Mike, Dave , Jim or a couple others. Take all the things into account that Saul stated, then take into account the reasoning why the production car classes don't run a flex plat flywheel and they all run a good damper, along with they all keep the aluminum support arm for the intake in place, they all keep the formed steel bracket from the throttly body the the intake in place, many isolate the throttle body from the intake with a thick rubber gasket (this can also be improved) and then look at the extended weight on the throttle body shaft. When one installs a $700.00 throttle body shaft/butterfly that has an EDM'ed slot with epoxyed butterfly to shaft (no screws) they still break but less frequently. The production cars rev to only approx 8,200 rpm with intent because when the reve with the required stock rods beyon the rods fail.

Outside of the info Saul provided the main root cause of broken throttle body shafts are the engine harmonics.

 

If you want solid info from outside the box, call Jesse at Jesse Prather MotorSports the builder of many fine production cars, Spec Miata cars and a few ITA cars. Tell Jesse, Dewhurst sent you.

[Joe (dad) Jordan]

Joe-dad, I could run through the many broke shafts on the F production car and Spec Miata cars, except Ron would question the the crap out of any thing that isan't said by Mike, Dave , Jim or a couple others. Take all the things into account that Saul stated, then take into account the reasoning why the production car classes don't run a flex plat flywheel and they all run a good damper, along with they all keep the aluminum support arm for the intake in place, they all keep the formed steel bracket from the throttly body the the intake in place, many isolate the throttle body from the intake with a thick rubber gasket (this can also be improved) and then look at the extended weight on the throttle body shaft. When one installs a $700.00 throttle body shaft/butterfly that has an EDM'ed slot with epoxyed butterfly to shaft (no screws) they still break but less frequently. The production cars rev to only approx 8,200 rpm with intent because when the reve with the required stock rods beyon the rods fail.

Outside of the info Saul provided the main root cause of broken throttle body shafts are the engine harmonics.

 

If you want solid info from outside the box, call Jesse at Jesse Prather MotorSports the builder of many fine production cars, Spec Miata cars and a few ITA cars. Tell Jesse, Dewhurst sent you.

Thanks Bench  I have talked to Jessie.  He will be getting a throttle body from me soon for the STL car, but the spec miata I guess I will just have to risk it....Scary as it is to worry about hurting a motor because of this.

[Ron Alan]

Geez Dave...others is a big group you think?? For the record, I don't think anyone who is on here regularly thinks you are a poser
I remember playing a harmonics in 3rd grade

[Ken SM94]

Hello, my name is Ken and I'm a stomper.....

 

The problem is that the bottom of the pedal hits the floor before the top does.  Sitting in the pits it will seem just fine, but out on the track in the heat of the battle you put pressure on the top part of the pedal, where there is a gap to the firewall, and it will flex.  Any flex beyond the point where the bottom of the pedal hits the floor and you're putting a lot of pressure on the throttle body.

 

I have a "dead pedal" plate welded under the throttle pedal to act as a stop.  It's installed at the same angle as the pedal so you can stop all you want with no extra pressure on the cable.

 

I seriously doubt these failures have anything to do with vibration or motor mounts.

 

Ron, don't question me on this.  :^)

[Joe (dad) Jordan]

Hello, my name is Ken and I'm a stomper.....

 

The problem is that the bottom of the pedal hits the floor before the top does.  Sitting in the pits it will seem just fine, but out on the track in the heat of the battle you put pressure on the top part of the pedal, where there is a gap to the firewall, and it will flex.  Any flex beyond the point where the bottom of the pedal hits the floor and you're putting a lot of pressure on the throttle body.

 

I have a "dead pedal" plate welded under the throttle pedal to act as a stop.  It's installed at the same angle as the pedal so you can stop all you want with no extra pressure on the cable.

 

I seriously doubt these failures have anything to do with vibration or motor mounts.

 

Ron, don't question me on this.  :^)

Thanks Stomper!  I will look at this and see what I can do!  I think I know exactly what your saying and I will make sure it doesn't happen...  Appreciate it.