snapped head bolt size?

[wickermonkey]

Are head bolts for different a-series engines the same size? I've got one snapped of in a 1275 marina engine.

[bmcecosse]

There was only ever one head bolt fitted - to the 1275 Cooper S engine (right beside the thermostat cover) , and indeed it is only 5/16" diameter and must only be torqued to 25 ft lbf., and then only after all the other nuts have been torqued. All the other head fixings are studs - 3/8" diameter. The later studs are better quality - identified with a 'Y' or perhaps a 'dimple' on the top end of the stud. These can be tightened to 50 ft lbf PROVIDED the threads are oiled - and the later flanged nuts are used. Earlier studs are only safe to 44 ft lbf. You must have been well above the correct torque to snap one - if they can be felt yielding then that's the warning to STOP.!!

[wickermonkey]

It wasn't me that did and not sure which one it is yet but will let you know at about half 6 when I get the minor. He had to remove W bolts to be able to fit some copper piping and when he did the second one up it snapped with ease, he said he hardly had even strayed to tighten it, probably weakened it taking it off

[wickermonkey]

Its one of the five that run along above the spark plugs, either the 3rd (from bulk) head or 5th

[bmcecosse]

Well -they should never be loosened - hopefully a new head gasket has been fitted when the new stud was installed??

[wickermonkey]

the stud wasnt (as far as in aware) just the nut on the top for the mounting bracket for the copper pipe, something for the brake servo i think.[frame][/frame]

[IslipMinor]

The pipe is the return water from the heater.

Is there any thread showing about the top of the head? Is the stud by any chance loose, and could be undone?

If there is nothing above the head, then obviously the head needs to be removed to replace the stud. When it's off I would look very carefully at the rest of the studs to see if any of them show signs of stretching (the diameter of the stud will be 'waisted', i.e. slightly smaller than 3/8").

[les]

I'd be surprised if you could actually see any 'waisting', would imagine a stud would break at the smallest diameter, ie thread. However it would be a good plan to replace them all if you get as far as taking the head off. Before you screw the stud/studs it's an idea to slightly countersink the tops of the threaded holes.

[bmcecosse]

I'm at a loss to understand how a snapped stud was fixed with a new nut........I suspect the thread in the nut was stripped - not snapped... But if it was loosened then you now have considerably increased risk of head gasket failure -especially as I would bet that new nut has only been 'nipped up' rather than fully torqued - for fear of it stripping again..... Why was it being messed about with in the first place ???

[wickermonkey]

Now i finally have the car and have been able to look at it in the light that pipe has been removed (as for why im not sure yet), so the bolt snapped when he was putting the nut (old not new)(neither was stripped) back on. It has broken 1 thread into the head so i have a broken stud with shaft and the thread plus nut. Hopefully i will get round to having a better look at it today

[bmcecosse]

What was being done to the car????? And who was doing it ????? You must not run the engine like this - you will need to remove the head and then fit a new stud. New head gasket of course - and may be a good idea to grind in the valves while you are in there. Whoever snapped the stud should really do this work for you foc.........

[les]

----or possibly not let him do it!

[wickermonkey]

It was broken by the previous owner and i purchased the car with the problem. I havnt had an answer back of him as to why he was removing the pipe but from looking on google i can see that some engines have the heater pipe running over the spark plugs and some seem to go into some sort of shut off/flow valve at the back of the engine

[bmcecosse]

PM sent with handy link. Don't worry - it's all very straightforward work.

[wickermonkey]

cheers for the link and info

[les]

When you get some more studs fitted, you may find that you have enough of the threaded end sticking above the cylinder head to fit the nuts as normal, THEN place the solid heater pipe over the studs ON TOP of the head nuts and secure with 2 thinner nuts. This way if you need to remove the pipe in future you won't have to touch the head nuts.

[chrisryder]

I'd be surprised if you could actually see any 'waisting'...

You could in my case! I just happened to inspect them before refitting and noticed this little doozey!
[frame][/frame]

[bmcecosse]

Hahahahaha - well spotted!

[les]

I'll consider myself surprised!!

[IslipMinor]

I'm glad I suggested looking.