Help with GT RTS rocker play

[Kieran-b]

I have recently acquired a '92 RTS-1 and noticed a fair amount of play in the rocker pivot point despite allegedly having new bearings fitted.

After getting the tools out, I found that, yes, new bearings had been fitted and the bolt that went through the middle doesn' t look overly worn.


I read on a previous thread about inserting a very thin washer down each side of the bearing (good idea, as it would also stop them rubbing on the frame as can be seen above) so I have done that which has improved it a little.

Upon closer inspection, the cause is simply that the bolt diameter is smaller than the hole in the bearings - 7.5mm and 8mm hole.


To me, it seems that this is not the right bolt for the job and some sort of shoulder bolt with a longer unthreaded section would be better. However, the unthreaded section on all the bolts I seem to find is bigger than the threaded section. Seems like I would need an M8 thread and 8mm diameter unthreaded section, but all I can find is M8/10mm or M6/8mm.

So, I am thinking there is either a special part or a bit of play is normal and to be expected from a dated design?

 

[Tootyred]

You could buy a longer bolt, then cut off the thread, leaving enough to get the bolt on, but having smooth shaft through both mounts. The longer the bolt, the shorter the threaded section.

All bolts will be slightly smaller on the thead as they are cut from a blank shaft.

Measure the total distance, take that to a fastner shop and buy the closest you can.....then cut the thread off to just take the bolt.

Unless of course the play is side to side....then you may need a thin washer....

 

[markoc]

Hmmm. I'll try and grab the bolt out of the frame I have on the wall and get the vernier out - will also show what sort of bolt I have in mine. Doesn't look right to me as the cut thread is longer than needed. Could also be that the replacement bearing has the wrong diameter sleeve, which would also cause side/side wobble. Busy day today but bear with me...

 

[markoc]

Just popped it out, and my bolt looks very similar. Would have expected the shaft to be proportionately longer than the thread but it isn't (as in yours)

Check how much the bolt rattles around in the bearing itself, as it should be a reasonably tight fit...?

 

[Tootyred]

M8 bolts are designed to fit into an 8mm hole. So an m8 bolt will have about an 7.8 or 7.9mm shaft.

The thread will be smaller as its cut from the blank.

Here are 2 m8 bolts....just pick one where the shaft fills the bearing and the frame....then cut the tread off to nut length.

If its still moving, either its the wrong bearing, or it needs a sleeve .

Its bad practice to run bearings on the thread anyway, as it will always be too small and bearing to shaft should be snug fit.....if it can move round in the bearing, theres no point in the bearing....it might as well be a steel bush!

 

[novocaine]

have you tightened to the correct torque? there should be a nominal amount of play between the bolt and the bearing with the bearing held tight in place by the sides once at the right torque.

I have a recollection of them being crazy high but someone else maybe better place to say as I haven't touched an RTS or LTS in something like 20 years.

side note, bolt threads aren't cut, they are hobbed. a shit ton of pressure applied to a roller die to push the material out the way.

another side note: the correct bolt should have a shank 1-2 turns shorter than the gap between the outer flanges, on an m8x1.25 that's 2.5mm. looking at the wear on the thread I'd say you were about right.

 

[ishaw]

I can check the bolt I have on an inbuilt RTS I have. I certainly haven't got any play like you mention on my team frame.

 

[Kieran-b]

Thanks for the help/suggestions so far. The unthreaded section of the bolts that is there doesn't seem any larger in diameter than the the threaded part, but the examples in the photos from @Tootyred do look bigger, so a different bolt with a longer unthreaded section could solve the problem.

I was thinking something like this would be better, but as far as I can see the threaded section is always 2mm smaller than the shoulder. This is what led me to wonder if there is/was a specific part made for it.

 

[markoc]

Do you have a vernier gauge to measure the internal diameter of the hole in the bushing? Worth checking it’s not wider than 8mm for an M8 bolt. If it’s out then that’ll wiggle a little, and at the wheel it’ll feel a lot.

They do need a proper good tightening though as has already been said - and probably why the bolt is nutted rather than having a threaded side on the frame mount.

 

[Twozaskars]

As what most others said, I just buy a bolt based on the shoulder length then cut off the excess thread, although I do own a small lathe to do it nicely. That bolt you show has a flaw - self colour. That means it’s bare steel and will soon rust. The threaded section will be smaller in diameter than the shoulder but only by .2-3mm do hardly noticeable with the naked eye. As Novocaine says above - It is also about the entrapment of the bearing between the two parts it sits between, rather than the load placed entirely on the bolt.