cylinder head gasket

[john@theforge]

Hello,

Spotted a slight oil leak from the cylinder head on 1098 engine. More a seep than a leak really. Torqued it snapped a stud. New stud new gasket and all torqued down @40 as per haynes.

I know I need to redo after but to what torque and should it be done while engines is still hot?

Also I will need to check valve gaps.. Anything else?

Thanks in advance

John

[bmcecosse]

Torque to 44 ft lbf with oiled threads. But the stud should NOT have snapped at 40. Are you sure of the wrench?? You should be able to feel the stud yielding before it snaps.......and that's when to STOP. For years and years I didn't have a torque wrench - and used to just tighten to the yield point. The later studs with a dimple on top are much better - the even later ones have a Y (or maybe a T depending how you see it) on the top and are safe to 50 ft lbf when used with the later flanged nuts. Valve gaps 12 thou inlets and 15 thou exhausts.

[john@theforge]

Thanks Bmcecosse, I didn't have a torque wrench when I snapped the stud.Have got a lend of a calibrated one for the weekend. Re torque it hot or let it cool?

[bmcecosse]

I let it cool -but not completely stone cold.

[john@theforge]

Thanks again, fingers x'd

[IslipMinor]

Roy,

The last version of the official Minor BMC/BL Workshop Manual states that the head stud torque for a Minor is 40 lbf. ft, but does not state 'hot' or 'cold'. My understanding has always been that the final tighten is done 'hot', followed by the tappets.

Interestingly the Manual states the tappets are designed to operate with a gap of 0.012" COLD and also 'It must on no account be departed from'!! Then goes on to say they must be finally checked 'hot'. This is all in 1970.

The 'marked' or 'dimple' studs are usually found on 1275 engines and made from a different, higher tensile, material and are torqued to 50 lb. ft. Where does the 44 lbf. ft. figure come from?

Is the now 'oft quoted' 0.015" exhaust tappet clearance actually for the later unleaded heads fitted to the Mini? Or as a possible precaution for valve seat recession and the tappet clearance closing up? Will do no harm on a standard Minor leaded head, particularly as unleaded fuel burns hotter than leaded, so more 'seat' time could reduce the risk of the exhaust valve nipping the guide. Certainly worked for our 1380 after being converted to unleaded and nipped the new bronze exhaust valve guides and burnt out one valve. Changed the guide supplier and opened up the exhaust clearance by 0.003" - no more problems since.

If the tappets need adjusting every 2/3000 miles or so, maybe there should be a more permanent solution of unleaded exhaust valve seats and harder valves?

[bmcecosse]

The Cooper S engine used the same studs and nuts - and was specified at 44 ft lbf. That's what I always used (once I got a torque wrench!) and no problems. I tend to do with the engine warm - not roasting hot although I doubt it makes much odds because the head and the studs will expand at pretty much the same rate anyway - as will the push rods. So I can't say I have ever noticed much difference between hot and cold gap settings. 15 thou specified for all the later A series - seems a good precaution to give that small extra safety margin - the exhaust valve getting bl**dy hot and therefore expanding more than the nicely cooled inlet valve. i suspect inlets could probably be set to 5 thou - but haven't tried it! I doubt 'time on seat' is significantly changed........