Engine Rebuild (Part 5) - Exhaust Manifold Prep

The exhaust manifold has studs for a protective heat shield and also studs to hold the air cleaner on top. All these studs were quite badly pitted and rusted and the manifold itself looked very rusty. I decided to replace the studs and repaint the manifold.

Stud for Mounting Air Cleaner - 19 November 2017

I'm planning to use a high temperature manifold paint. It should really be cured at a high temperature - higher than the oven in the kitchen can produce. Alternatively you can cure the paint by running the engine. I think that's the way I'll have to go.

Where I'd expected to find studs between the manifold and downpipes, I found a couple of bolts.

Bolts Instead of Studs?

I'd already bought and fitted new studs to bolt the manifold to the cylinder head. In addition  I'd gone ahead and bought replacement manifold to down pipes studs, and studs for fixing the heat shields to the manifold.

New Studs and Nuts for the Refit

One Sunday afternoon in November 2017 I set to work trying to remove from the manifold, the rusty stumps they were going to replace.

Double-nutting did nothing. I just stripped the threads on four nuts. Tackling each stud, I had to use my biggest mole grips set as tight as possible to get any purchase on the studs.  They had to be repositioned copious times to maintain any grip and the threaded studs were  starting to shred.

With an insistent wiggling action I began to sense microscopic movement in a stud and blasted it with some Plus Gas. A little more wiggling, a little more Plus Gas and I could feel definite movement. Persevering in this way - lots of wiggling and Plus Gas - I was gradually able to great greater rotation on each stud and teased them all out this way. Well, most of them. One snapped and had to be drilled out.

Out With The Old, In With The New....

With all the studs removed, I put them back in again! Just loosely. I was sending the manifold off to be blasted and didn't want all the stud holes blocked up or the threads damaged. My workshop guy blasted the manifold and downpipes, then he gave them a squirt of WD40 to stop them rusting. 

I actually wanted them as grease-free as possible to give the high temperature paint I planned to use the best chance of adhering. Never mind. I think I will probably have him blast them again but leave them dry next time.

A Quick Word About..........Cylinder Head Bolts

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.

Early (top) and Later (bottom) Exhaust side Cylinder Head Bolts

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.

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....

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.

114.5mm head bolt........with 3mm washer

Engine Rebuild (Part 4) - Fitting The Valves

By mid September 2017, and after an initial clean up, I had been soaking my DX exhaust valves in Mek pretty much since mid August. This loosened some of the burnt on muck - but not nearly enough. In the end I had to resort to using my wire wheel to clean them up. I was very glad I did as it did a great job. I was very careful to avoid going too far up the shaft of each valve with the wheel as I did not want to introduce scratches.

At the end of September 2017 - while researching cylinder heads and valves -  I was lucky enough to find a set of NOS DX inlet valves for my 1968 car.

New Old Stock Inlet Valves - October 2017

These were the earlier 47mm diameter valves, BUT with the three groove cap and collar. They were only fitted for about 15 months between May 1967 and July 1968. Result! (See my other post on DX valves for more on this).

September and October were spent getting the cylinder head ready - including vapour blasting, skimming, fitting new valve guides and having the valve seats re-cut.

By mid November it was starting to come together: I  had my cylinder head, my valves ready and all other associated parts had been thoroughly cleaned and oiled. I was ready to go.

Underway - 12 November 2017

I spent an afternoon lapping the valves. This process was not nearly as long-winded as I thought it was going to be - possibly because half my valves were new and - more likely - because the all valve seats had been re-cut. The objective is to keep lapping until you have a solid, clean ring showing on valve and seat - meaning the surfaces are flush and a good gas seal. The tone of the grinding note changes as you reach that point. It was really quite satisfying. After lapping I carefully wiped up all traces of grinding paste.

With my new valve spring compressor, I was able to make quick work of re-fitting the valves.

Fitting The Valves - 12 November 2017

Compressing the Springs to Slip the Collars Around the Stem

Working methodically, I was soon done. I was very pleased with the results and finished the day by re-fitting the tappets. I couldn't resist sitting the head on the block and adding the push rods.

Valves and Pushrods - 14 November 2017