I knew that the cylinder bolts on the inlet and exhaust sides were different lengths, but I hadn’t appreciated that the lengths of the exhaust side bolts on early DX engines are shorter than those on later DX and subsequent DX2 engines. It’s all about washers.
The cylinder head bolts on early DX engines were fitted without washers and so pressed directly against the cylinder head surface. The exhaust side cylinder head bolts on later DX engines and thereafter were used with a thick washer – presumably to minimise compression damage to the alloy head. The upshot is that the bolt is correspondingly a little longer to compensate for the length taken up by the washer. The parts books give the two lengths as 111.5mm up to July 1967 and 114.5mm thereafter, when a 3mm washer was also used.
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| Early (top) and Later (bottom) Exhaust side Cylinder Head Bolts |
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| Fitting the 3mm Washer Brings the 'Working' Length Back to 111.5mm |
Bolts on the inlet manifold side stayed at 160mm throughout and weren't used with washers. There was no need: they bolt to the head through the inlet rocker rail so the head already had something of a 'cushion' between them and the head.
Anyway, when my engines were stripped, several bolts on the exhaust side snapped on removal – and some of the rest were rusted and pitted. These exhaust side bolts are the ones most likely to fail (not only on removal but also on reassembly) and so are the ones most likely to be replaced.
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| Failed Exhaust Side Cylinder Head Bolt |
For this reason I bought lovely new replacement exhaust side cylinder head bolts. As I have written elsewhere – many of the reproduction parts are geared to DX2 engines – not DX. The replacement bolts I bought are 114.5mm long and so are a little longer than the ones originally fitted to the early DX engines. There is a risk that if I had gone ahead and used new, 114.5mm bolts on my DX engine without washers, the bolts could have ‘bottomed-out’ in the tapped holes of the block before they were sufficiently torqued:
- Leaving them at that point might have meant that the head gasket was not properly sealed - and failed down the line
- Continuing to try to torque the bolts when they had bottomed-out possibly risked the bolts snapping – causing quite a headache or:
- Continuing to try to torque the bolts when they had bottomed-out risked cracking the block – which would be even worse.
This may sound alarmist, but I found something that suggested i might not be crazy after all....
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| Thread from the "DS Club Deutschland" Forum |
'Pit' had leaks on his DX engine and attributed the problem to head skimming. He was trying to solve the problem with a marginally thicker, hand-made head gasket. As 'HGK' was suggesting, perhaps his bolts were bottoming-out.
It just goes to show what a little bit of research can unearth. In my case, and as I had a DX2 engine in bits as well, I was able to use the 3mm washers from that engine.
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| 114.5mm head bolt........with 3mm washer |
