splcrazy

what size bolt are you guys using to do the pinion bolt mod , and how are you doing it , do you drill a hole straight though the pinion and through the bell aswell then re tap , im guessing a m5 bolt is the max that will work best . can you put a long bolt through the pinion into the bell and put a nut on the end of the bolt where its in the clutch bell?

Foxy

I hear people were drilling the pinion and clutch bell to M5 and then tapping. I don't see the benefit of drilling straight through and nutting the screw, as it would reduce the amount of thread being gripped, but I suppose it's another option.

da mad maori

it makes it easier to remove when and if it brakes again... it'll just fall out rather than haven to drill it out of the bell

im gunna have to drill mine out..... i tryed screwing a longer m4 bolt into the bell, put spur on then nut it.....
but its still stretching.....

its annoing to say the least

Cheers
Ryan

Foxy

Yeh, I see what you mean, but I don't think I'd do it. Due to the fact that the possibility exists when drilling that far through, to go very slightly off centre, or create a fractionally bigger hole than the screw, I would be worried about balance issues. A tiny issue of balance becomes huge at 16k rpm and could cause a significant vibration destroying bearings and plastic spurs. Maybe I'm overstating it, what do you think about that?

da mad maori

because the hole is so close to the centre, drilling slighty off wont create too much vibration... no more then a bit of gunk on a stock cy flywheel
although thats no reason to plouge a hand drill in at any angle lol
you would have the bell and pinion "still in" the clutch carrier to keep them alined then using a drill press to drill straight down.

but im baffled what is causing this??? ild like to figure that one out..


maybe the engine "on some" is ever so slighty missalined causing the pinion and spur to be "kinked" in the mesh

i noticed my bolts (3 so far) were stretching ALOT before braking

mmmmmm please discuss so we can come up with a mod to fix this as only some are doin it


Ryan

Foxy

I believe its a simple side effect of torque. the thread direction of the clutch bell bolt is such that rotation of the engine tightens the bolt. The very torquey engines tighten it more and more, and eventually it snaps. That's what I believe anyway.

I understand that a regular M5 bolt (drilled through or tapped) is a working solution, I have seen it posted in the other place.

TurtleRacing

The M5 has been working, I have had quite a few people send me their pinion gear to drill out for them. Everyone is happy with the M5 so far. Also, the screw does NOT locate the gear, at all. The pinion locates in the bearing, it shares the outer bearing with the bell, if you drilled that far off center, you wouldn't be able to screw the pinion and bell together.

I believe there will be another option soon though.

Argess

My 2 cents worth:

I suspect the gear can wobble under load....back and forth along the keyway, as the inner face of the pinion doesn't touch the top face of the CB. Looks like it might be because of normal play in the two bearings and flexing of the bearing housing.

So, there will be rotational positions of the pinion where there may be some shear exerted on the bolt. And, if there is some side-loading on the screw, and if this changes twice per revolution, fatigue can be expected due to the alternating loading of the pinion in single shear.

So I conclude that it is fatigue causing the failure. This seems to be supported as the screw usually breaks flush with the CB (along the parting line between the pinion and CB). Happened to me twice. First time was the factory installed screw. After I re-did it with loc-tite and made sure it was tight, it was fine for a long, long time. In fact, it was fine until I had it out to change something or other and forgot to loc-tite it in. The screw loosened and broke quite quickly that time. My fault.

So far, when I just loc-tite the 4mm one in place and make sure it is good and tight, it seems to last. If I ever have more trouble, then I'll switch to a 5mm bolt.

By the way, I can't see the pinion expanding enough from heat to stretch the bolt to failure. Don't forget, the bolt elongates as well when it gets hot, plus the plastic carrier would totally deform if the heat got that high.

I don't think Loc-washers really don't do much. By the time a bolt is loose enough that the lock-washer can help, it's also loose enough to fatigue as the pinion to CB joint wobbles, and some fatigue must occur. A flat washer should be fine in this application.....and loc-tite......and a firmly tightened screw......and maybe one that is 5mm ......

TurtleRacing

If the top of your keyway is touching your gear, there is either something wrong with the gear or bell. If it's one of my bells, lmk, I will fix it. But my bells are designed so the face of the pinion mates with the face of the gear. There is no way that they should mate on the face of the key. With the proper mating, the pinion will not move in the bearing.

splcrazy

Instead of having a keyway . Machine a hex on the bell and one for the pinion so its a secure fit then we can put even larger bolts

Argess

When I cahnge to 5mm, I am going to see if I can find a M5 bolt with a long shank (part with no threads). Then I'll drill straight through and use a lock-nut.

This does two things:

1/ The shank part of the bolt is in the area of fatigue, and is much stronger than the threaded part, and:

2/ If it does break, no unthreading to do.....two parts just fall out.

ps: no need to go metric....could use an 8-32 allen head for example...or maybe a
10-32.....will have to measure to find out......

splcrazy

Its a good idea . But maybe good luck finding a m5 long bolt with a shank. What metal bolt is best to use ? A steel high tensile or 316 stainless steel

jasrx

how long duz the bolt have to be?

splcrazy

i dunno i like the idea of drilling straight through so if the bolt snaps you got two parts that fall free, but then that can cause even more damage if the nut part in the clutch bell area falls off into the rotating clutch shoes just imagine what will happen if that occurs lol CRUNCH , i have 50mm long regular steel m5 bolts to do this dont know yet if thats long or short enough ill see when i pull it apart on the weekend, but i dont have the nuts i need to buy them . I think it would be alot safer to drill the pinion and bell and tap the m5 thread in the pinion & bell too and still use a nut on the other end so to give it strength and so it doesnt come loose

and maybe reverse tap from behind the bell and pinion and screw the bolt in the other direction so when the pinion and spur is rotating its less stress on the bolts what do you guys think about maybe this method ?

da mad maori

tapping a hole in both pinion and bell wouldnt really offer any advantage over tapping just one. (tapping bell only or pinion)
it might even cause a slight gap in between them... ild just tap one of them.....

Ryan
PS dont drill a 5mm hole and then reach for your taps lol... the hole needs to be around 4.5mm maybe alittle less
its amazing how many people fall victim to that

jasrx

u will need a 4.2mm drill bit for a 5mm tapp

splcrazy

i did the bolt mod and it works pretty good so far , i tapped a m5 hole in both pinion and bell and put a nut on the other end , the bolt i used was m5 regular steel , i will see how that goes , if it snaps again i will use steel high tensile . the length of bolt you need to do this with a nut on the other end is 34mm thread length

Dave ESPI

I just busted my stock 4mm x 15mm pinion bolt 2 weeks ago. I hammered the throttle up and over a little knol and WHHIIZZZZZEEEEE ! and I draged the 'ja home on a lanyard.

I was running a HPI heat sinc inside the pinion, and the steel vented bell from Vertigo. Just a small piece of the tip of the bolt was sheared off in the endbell, and was removed with an EZ-OUT bit.

I think I'd rather bust a small piece than have an entire bolt through my bell housing. Two dollar bolt versus 40.00 bell..........

splcrazy

if my bolt snaps in two i can still remove both without any drilling , the piece in the bell is long enough to unscrew incase of a bolt snapping because of the extra thread length thats holding the nut

splcrazy

and i have a result , after doing the mod i took it out today ran it for maybe an hour and its snapped AGAIN this is the regular steel m5 bolt , its snapped right in the middle where the bell and pinion meet , the pinion was untouchable really hot , took it back home and put another m5 bolt in but this time a stainless bolt, im waiting for next weekend to test that bolt out, i think it will snap again lol , if it does ill try the steel high tensile then compare all three metals . Someone really needs to come up with a solution to this problem, and im only guessing that a whole redesign of the clutch bell keyway and pinion keyway needs to be modified , maybe a two bolt keyway bell and pinion , theres just too much stress on one bolt

Dave ESPI

Try a heat sinc insert with it Spl....

May help with cooling ?

da mad maori

do you have an inclosed clutch carrier?
are your bearings ok?

splcrazy

i have a heat sink but cant use it cos the heatsink hole is too small for the m5 bolt head , and the hole in the heatsink cant be drilled out bigger cos then the cooling fins just break off when trying do do so lol

splcrazy

its stock plastic clutch carrier and bearings are brand new , let me remind you all my engine is 7HP plus , but thats no reason cos less powerfull standard engines are still breaking pinion bolts , maybe i should geat an alloy clutch bell carrier to help take the heat away

splcrazy

what would be good is a clutch bell thats got some kind of keyway with a mahined thread and then the pinion could also have a thread that screws onto the bell then a nut on the pinion to tighten it all down just like a rc hex nut system that the baja uses on the rear wheels , something like that will be bulletproof and never snap off , if anyone has the turtle racing email we all need to tell them we need some ofther kind of system rather than the single bolt pinion to bell stock garbage lol