Cylinder Head tightening.

[Trevor Wilks]

Pandah,

Hope you got what you needed from Tony Byford. If not, please be aware that there are no accurate torque figures given, as the nuts on the opposite side to the exhaust are inaccessible with a torque wrench. Bristol therefore supplied a special double ended ring spanner when new which was 1/4" Whitworth at both ends and had a bend in it to allow access to the rear nut on the non exhaust side. This allowed only a "one flat at a time" approach as described in the workshop manual, up to the limit in strength of the individual doing the job, or of the spanner !! In most cases the spanner wins and you get an evenly tight result by using the exact same length of spanner for all nuts.

Thanks in part to Geoff's advice, my 406 engine now seems to be working fine after 140 miles. Will wait and see whether I can tighten further at 500 miles.

Trevor

[Geoff Kingston]

At the moment have only workshop run the 85c Engine I bought from Bristol Cars but in view of this topic I asked Brian at Bristol Cars for his advice, he suggested 150 and 500 miles , in the past I have checked after the first run to full temp , at around 250 and 500 miles but this was with the gaskets available at the time.
I am lucky as I have the correct spanners, before the car is run on the road I will do a quick check, if any of the nuts pull up then they will all be done as per the book, a bit of a pain but worth it.
Geoff.

[Trevor Wilks]

My 406 has recently passed the 500 mile mark after its rebuild, I was able to tighten down the head by approx. half a flat at nuts 3,4,5&6 progressing to 3/4 of a flat by nuts 11,12,13 & 14. Nuts 1 & 2 hardly moved. Valve clearances have now been reset and engine has run well throughout having followed Geoff Dowdles advice below. I agree you really need an obstruction spanner similar to the one originally provided by Bristol to get at the nut nearest the bulkhead on the side opposite the exhausts.

Originally Posted by Trevor Wilks

Pandah,

Hope you got what you needed from Tony Byford. If not, please be aware that there are no accurate torque figures given, as the nuts on the opposite side to the exhaust are inaccessible with a torque wrench. Bristol therefore supplied a special double ended ring spanner when new which was 1/4" Whitworth at both ends and had a bend in it to allow access to the rear nut on the non exhaust side. This allowed only a "one flat at a time" approach as described in the workshop manual, up to the limit in strength of the individual doing the job, or of the spanner !! In most cases the spanner wins and you get an evenly tight result by using the exact same length of spanner for all nuts.

Thanks in part to Geoff's advice, my 406 engine now seems to be working fine after 140 miles. Will wait and see whether I can tighten further at 500 miles.

Trevor