5 replies to this topic

[ticktock]

I am refitting my water pump and have bought some new bolts - the short are flanged and the long are not. The on-line parts drawings show the long as flanged.

 

Can someone please tell me what the purpose of a flanged bolts is?  Is it for sealing against the leakage of coolant or are they used for some other reason?

 

Incidentally, the old bolts had flat washers - should I just use flat washers on my new long bolts.

 

Thanks in advance

[nicklouse]

No idea what you are on about with flanges.

Normal bolts with a spring washer is what I am normally supplied with and use.

[Swift_General]

No not for sealing - the gasket does that. The flanged bolt is supposed to be used without a washer, hence the flange spreads the clamping load as a washer would. You should see threadlock on the end of the bolt therefore. Personally I would use new spring washers to prevent against loosening. A plain washer is this situation would be pointless.

[Ethel]

The flanged bolts are common on A+ engines, it's just like a built in spring washer really. Some Austin-Rover bean counter will have decided it saved a bit of time & money on the assembly line.

[ticktock]

No not for sealing - the gasket does that. The flanged bolt is supposed to be used without a washer, hence the flange spreads the clamping load as a washer would. You should see threadlock on the end of the bolt therefore. Personally I would use new spring washers to prevent against loosening. A plain washer is this situation would be pointless.

 

 

The flanged bolts are common on A+ engines, it's just like a built in spring washer really. Some Austin-Rover bean counter will have decided it saved a bit of time & money on the assembly line.

 

 

Thanks all for your help with this.  

[tiger99]

It is not like a spring washer in some cases, but it is in many others, maybe most!

Those where the locking function is provided have radial "teeth" under the head which have a vertical (almost) edge and a sloping edge, so they can be done up easily but are difficult to remove, but only on relatively soft surfaces. A hardened washer would defeat the locking action as the teeth would not dig in. It is easy to tell by simple inspection whether you have this kind of bolt.
The other reason, which is possibly true in the vast majority of cases (in many instances, both reasons apply), is that the bolt is intended for robotic insertion, in which case the hexagon is commonly smaller than normal too. To determine if that is the case, see which socket fits. The older bolts were 5/16" and the head was 1/2" AF. Robotic insertion uses a hex at least one size smaller and maybe even metric.

If in doubt you can always replace by standard bolts (check whether thread is UNF or UNC) with ordinary split lockwashers, which worked perfectly well for many years, and avoid potential problems with tiny hexagons stripping.