Harley Davidson V-Rod Forum banner

broken throttle shaft

9K views 44 replies 20 participants last post by  TEAZZR 
#1 ·
I had a failure on the front cyl throttle shaft yesterday.now i thought this problem was limited to the 58mm bore shafts but no.mine are still the standard 53mm bores but running stage two cams with powerline exh.firstly, i had a cracked head then this and am wondering weather these cams are worth the unreliability i am experiencing with this motor. i have over 50000km on these cams and 70000+ on the motor,not nearly enough to call it wear and tear.Are others out there having failures also with the standard shafts/ 53mm bores?
 
#3 ·
Pecee, I have the same set up as you on my 08 Dx. However, I only have 30K miles on mine, and so far, have no problem with heads and/or throttle shafts. Also, I do ride my bike hard. The low mileage is do to splitting riding duties with a 93 Softail and a 91 FXR that eventually I sold to my buddy. A while back, I asked this same question to Scott (Ohio Vrod) and was told that no problem with the stock Tbodies. So far, that seems to be the case to my knowledge. Still, I check mine from time to time. I know this doesn't help much, wish I could give you more. Good luck, Bro.
 
#4 ·
Broken throttle shafts are caused by excessive vibrations/wear .. The buterflies were probably fluttering. With the miles on your bike & running the stage II cams I think it is just that. Service the upper end and replace the broken TB. ( I wouldn't fix it unless you rebuild the whole thing. )
 
#5 ·
I think that a long duration of stage II cams could have something to do with the saft failures. A low rpm compression pressure back flow (reversion) can cause some extra load and vibration for the safts.
 
#7 ·
Scott (OhioVRod) has also come up with a design to upgrade the shafts to thicker shafts to reduce/eliminate breakage. They tend to break at the screw, then drop the screw into the motor (NICE!).

Rick
 
#9 ·
Sorry, did I a technical or commercial mistake?
No meaning to scare anyone.
 
#11 ·
ok, I'm not a native english, sometimes do not catch the message.:hmm:
 
#15 ·
I think Scott Tig's the screw to the shaft. Welding the butterfly to the shaft, would make this pretty much impossible to disassemble in the future.

Though I do like his idea of larger diameter shafts - which he pretty much does as part of his 58mm upgrade to stock TB's (which he can also upgrade on one's already done, and Destroyer TB's).

There is some reversion (if you want to call it that) from the higher lift/faster ramp/overlap of these cams - as evidenced by the seeming inability of (supposed) autotuners to cope with the intake charge "bleeding through" during overlap and causing the WideBands to freak out and lean the mix. Also the observation of how much noisier these cams are. There probably is more vibration and potential "puffing" against the back of the butterflies (at least more than with stock), putting extra stress on the shafts, causing premature breakage.


Rick
 
#14 ·
Yes ,you guys are all right as to the cause im sure.I have taken the old t/body to a master machinist and discussed the issue.He is of the belief that a full shaft slotted for the butterfly will be better than the original half shaft .he is going to make new shafts in that config for me.he wasnt too keen on using tool steel tho because he felt it wouldnt stand the vibrations and probably crack too.welding was not an option.he will screw and loctite the butterflys in.no peening.
 
#17 ·
Wouldn't necessarily say "recommended now".

There have been many instances of these shafts breaking at the screw - and not just with SEII cams. My old airhead mechanics have a shelf of broken airhead TB's with the same symptom - shaft broken at screw.

So I'd say it's more of a "design deficiency" than anything else. The 58mm TB, with even more surface area, on the same diameter shaft is probably more likely to break than the OEM sized bores due to additional loading.

I was considering sending my stock TB to Scott to get bored out to 58, and get the fat shafts installed, then swapping out my Destroyer one and getting that upgraded also.

Would I "recommend it" per se'? I dunno - to me, on a modified motor, it would probably be cheap insurance - if you were planning on doing a TB upgrade ANYWAY.

OTOH - do I lay awake at night, staring at the ceiling fan - because I haven't done this to mine yet?

Nah...

Rick
 
#18 ·
I'm running 58mm TBs and I've had both shafts broken, with the rear shaft broken twice and the front once (None of these were Scott's tool steel shafts, which he came out with after I broke the first one). I would never argue with Ken on any of this stuff, but at least two of my breaks did not occur at low RPM, they occurred when I hit the limiter. That could still be a reversion issue I guess, since the spark was cut off and the front cyl turned into nothing but a fuel/air pump?? At any rate it isn't nice when it happens.

Also, Scott is not exactly TIG welding the screws, he told me he's just hitting them with a TIG welder with no electrode in it to fuse the screw to the shaft with heat.
 
#20 ·
We make all our 58mm Throttle Body w/ half shafts or what we call them in the shop TB check pieces. To make one solid shaft with a slot in the middle would cost a lot of money to produce our new units once bolted and tig welded seem to be the trick. We only use the tig torch and we hit the pedal for a second just enough to melt a thread or two back into the throttle shaft.
 
#24 ·
I will post pics of the new full t/b shafts once i get them back.I will have to wait due to work load but im sure it will be the fix.Im not saying Scotts are not the way to go but its easier to get a local boffin to make them for me,because New Zealand is a long way from there.
 
#35 ·
Shit!
Have You ever touched to the screw?
 
#45 ·
As freudie1 stated: the broken shaft replacement is not fun @ all. Mine took a crap a couple of years ago. I did alot of final adjustments to my machined shafts when I installed them to make sure there was no binding on the bores when closing . I even went through heat treating mine to increase the strength & hardness of the damb things. Only time will tell if they last.
 

Attachments

Top