A word of warning

[Colin Wilks]

Having been abroad for several weeks the RP had not been touched since the Cumbria Run in June. In preparation for a PWA7C Yorkshire Branch run out and barbecue at the weekend I was giving the car the once over last Friday.

Like most people relatively new to Sevening I try to pick up tips wherever I go and one of these was to always ensure the king pin cotters are tight. I put my 6" ring spanner on the nut, gave a gentle shove and the cotter pin instantly sheared off just behind the nut. 

I used my electronic torque wrench to check the torque on the other side and it read 24 ft/lbs. So, more than the 19 lbs I am advised is it for 1/4 and 5/16 nuts, but not by a lot.

Today has been spent removing the front suspension, which is now on the bench and ready to be stripped down in the morning. 

Am I cack handed or just unlucky? Probably a bit of both, but from now on I shall be using the torque wrench to "give it a nip".

[Howard Wright]

Hi Colin

Probably unlucky.  If the car is new to you, you won't know what the previous owner has done to it, nor what he has used!  Could be that the cotters are home made, low grade steel and have been tightened way beyond their yield strength. Also remember that if the cotter has been tightened up beyond yield it will relax over time so 24ft/lbs could well have been much more when first tightened.

I wouldn't give up on the idea of a six inch spanner, just check them regularly.

Cheers

Howard

[Andy Bennett]

Is not the random 'nipping up of nuts' almost certain to produce a similar random failure of said nuts, unless they are clearly loose for some reason, or have I missed sage advice to nip up these cotter pins, as I don't recall it having been said?

The only nuts I have regularly checked are wheel nuts, a follow up checking after a few hundred miles of any nuts loosened during any works and of course the staged checking of head stud nuts after changing head gasket.
Andy

[Chris KC]

I think that's basically a sound approach Andy, but it is generally considered advisable to check kingpin cotters now and then in order to avoid play developing in this frail and critical joint. The distinction which perhaps needs to be drawn is between ensuring they are tight and continually increasing their tightness - which will of course ultimately lead to failure.

20lbft is fine for a 5/16" BSF head nut but a bit much for 1/4" fixings in my humble opinion.

[Andy Bennett]

Thanks Chris
Never heard that one before so will add it in to my servicing list.

cheers
Andy

[Greig Smith]

Dad always me to always give the head of the cotter a clout with a decent sized hammer using a long thin drift to get in behind the backing plate & then to gently nip up the resultant looseness in the nut.

Relying on the little nut to pull the cotter in will result in stretching the threads, or what is termed 'necking' where the threaded portion stretches and ultimately snaps.

I'd have tried to whack the cotter out the axle with a small / thin pin punch before stripping the suspension, or cherished suppliers must have replacements, in a pinch an older bicycle shop would also have cotters lying around.

Aye
Greig

[Chris KC]

They won't come out that way Greig, one of the A7's little peculiarities.

[Greig Smith]

Ahh of course not Chris, I'd forgotten about that one, yes I stripped the front end down last time we changed cotters

G

[David Stepney]

Greig,

What you say is perfectly valid for taper cotters. Unfortunately, kingpin cotters are not taper cotters. They have a 'half-moon' cut into them which bears up against the circumference of the kingpin, preventing it from turning in the axle purely by friction. in order to remove the cotter, you hvae to take the kingpin out first.

The kingpin cotter only needs a good 'nip' for it to work. If it has come loose, then the nut will be loose too. I check mine during routine maintenance by applying a spanner to them and checking they don't move. if they do, then a nip is all that's required. No real pressure.

[Colin Wilks]

Page 176 of the Companion seems to provide a good recipe for fitting king pins:

"1. King pins must be a tight fit in the axle eyes"
"2. King pin cotters should be HT steel and must be kept tight"
"3. Bushes must be properly reamed in line with a parallel sided reamer"
"4. Vertical movement of the stub axles must be eliminated using thrust washers and a spacer if necessary"

Given regular greasing I think following these points should ensure the pins have little tendency to rotate in the axle.

David Stepney's advice about checking the cotter nuts don't move rather than giving them a nip is gold (and like all good advice, obvious when you think it through). When I got the car earlier this year the cotter nuts moved about a flat with little effort. They were coated in a thick layer of paint so I don't think had ever been tightened since installation, assuming the painting was done at the same time. My error last week was to think that another little nip wouldn't hurt. Lesson learnt!