GRRRRR! Broken bolt on my RC300.

[JeRkY]

So the hardened M4 bolt that holds the seat collar to the frame on my RC300 has sheared, sub flush of the top of the hole.

Essentially means that the seatpost can not be fixed in place, the clamp still holds the post, but the clamp is not anchored to the frame so is able to spin 360 degrees and be lifted off the frame.

Looking at the bolt it looks to of had a fracture in it for some time as it shows signs of tarnish across most of its cross section.

Being set into soft aluminium the hole is wisely helicoiled by pace at the factory. The only solution I can see to remove the stub of the bolt is to drill the centre and use an easy out. Which sounds easy but on an 4mm dia bolt, sub flush in a blind hole means the potential for further damage is quite high.

My daily rider too! How frustrating!

So its time to strip the bike down and have one of the guys in the workshop mount it to the mill, rather than attempt to drill it at home with a black and decker!

 

[jamabikes]

if the little stub is not under tension then poss try a little jewlers screw driver and turn it out, or araldite another bolt onto the stub. wouldn't of thought the stub could be in there too tight.... f.l.w

 

[JeRkY]

There is no tension on the stub, however the surface has sheared in such a fashion that there is no where to get any grip using pressure & a small screw driver (I have attempted that route last night.).

And with the stub being sub flush by a reasonable amount, I would rather not risk a messy adhesive attempt, especially as the surface of the stub section does not look particularly receptive to adhesive.

Just been looking at left handed drills as a possible alternative to easy outs, as small easy outs have a horrible tendency to break if you are not careful, leaving you in deeper water.

I have decided to do it properly and shall strip the frame down next week and get it up on the mill.

It is a lot of hassle for the sake of a bolt costing probably costing 20 pence though.

 

[jamabikes]

good luck dude!

 

[rc200ti]

Have you ever had this happen before? Whatever the answer I think you've flagged up a useful replacement policy. I regularly check for tightness but have never considered replacing this particular bolt.
Thanks.

Rob

 

[JeRkY]

Nope never, and I doubt I'll see it again. I think judging from the way the bolt went, that it was a pre-exisitng fault in the bolt, that had been there since its manufacture.

Exposure to moisture had clearly gotten into it and coupled with the side loading the bolt would get over this time, this could have lead to further weakening over the 12 or so years it has been in there.

That said, to get a bolt with a fault in its structure would be a needle in the haystack type of event. So I am willing to say with some degree of certainty, this won't happen to you...but hey, no harm in checking.

 

[JeRkY]

By chance I have a spare RC300 frame, so as one is stripped, so shall the other be built.

 

[dbmtb]

By chance I have a spare RC300 frame, so as one is stripped, so shall the other be built.

Only Rob could write this.

 

[hamster]

It sounds like a fatigue crack in the bolt - typically part of it looks corroded on the inside of the crack.

IF the bolt hole runs straight through, then a small drill will often remove it. The spinning drill bit locks into the bolt and winds it out of the hole. This has worked for me with sheared dropout and tandem eccentric bolts

 

[JeRkY]

Sadly no, its a blind hole.