{"id":1662,"date":"2021-04-09T19:00:26","date_gmt":"2021-04-09T18:00:26","guid":{"rendered":"https:\/\/bxproject.co.uk\/blog\/?p=1662"},"modified":"2021-04-30T15:11:52","modified_gmt":"2021-04-30T14:11:52","slug":"citroen-bx-refurbishing-the-cylinder-head-parts","status":"publish","type":"post","link":"https:\/\/bxproject.co.uk\/blog\/citroen-bx-refurbishing-the-cylinder-head-parts\/","title":{"rendered":"Citro\u00ebn BX – Refurbishing The Cylinder Head Parts"},"content":{"rendered":"<\/span> 7<\/span> min. read<\/span><\/span>\n

Progress on the restoration of XPO continues<\/a> at a bimbling pace. After tearing down the engine block<\/a>, I’ve returned to the cylinder head. Having previously overhauled the cylinder head<\/a>, it was time to prepare the rest of the parts and maybe start putting some of the engine back together.<\/p>\n\n\n\n

Returning the Tappets to the Cylinder Head<\/h2>\n\n\n\n

To let air and fuel into the cylinder, before setting it on fire, the inlet and outlet valves in the top of the cylinder need to open at the right time. The opening of the valves is controlled by the rotation of the camshaft. As the cam lobes rotate, they push down on the springs allowing the valves to open. Between the wide cam lobes and the narrow valve stem is the tappet. These are often shimmed to take up some of the variations in manufacturing tolerances.<\/p>\n\n\n\n

\"Hydraulic
Hydraulic tappet break down as seen in the Citroen Workshop Manual<\/figcaption><\/figure>\n\n\n\n

The Mi16 engine uses hydraulic tappets which use oil pressure to auto-magically take up the gap between the camshaft lobe and the valve. Well, that’s how I understand it. The hydraulic tappets on this car are known to be sticking. This pretty much means they’re full of crud and need refurbishment to get the valve timing just right. To do this I’m using the guide from Taylor Engineering<\/a>, and the original Citroen workshop manual which can be found on the BX16v Forum.<\/a><\/p>\n\n\n\n

Dressing the buckets<\/h3>\n\n\n\n

The camshaft lobes are continually in contact with the top surface of the bucket, with movement lubricated by the engine oil. Over time the top of the buckets become warn in the middle, especially if the oil is not routinely changed. To make sure the buckets are serviceable before reassembly back into the cylinder head, they need to be dressed. <\/p>\n\n\n\n

\"Dressing
Dressing the hydraulic tappets<\/figcaption><\/figure>\n\n\n\n

Dressing the buckets mean rubbing the tops of the buckets down as flat as possible. As per the Taylor Engineering guide, I’m using a few grades of wet and dry (starting with 800) on a piece of glass in a figure 8 movement. In the picture above the left-hand tappet has been dressed, losing the scratches and rings. The even finish lets me know the top is not dished through excessive wear. Only another 15 to go!<\/p>\n\n\n\n

Priming the tappets<\/h3>\n\n\n\n

Continuing through the guide, the next step is to put the tappets back together. First the sleeve is topped up with oil, then the piston is placed into the sleeve and the ball spring depressed to let all the air out of the piston to only oil remains.<\/p>\n\n\n\n

\"Reassembling
Reassembling the hydraulic tappets<\/figcaption><\/figure>\n\n\n\n

The workshop manual states ‘refit both the piston and sleeve, exerting a pressure on the assembly to cancel the circlip’. This is an understatement akin to that of the Haynes manual. The reality is, rather a lot of force is needed to overcome the circlip, and some swear words, preferably in French. I managed to stop at a hammer though!<\/p>\n\n\n\n

Reassembly into the Cylinder Head<\/h3>\n\n\n\n

With the hydraulic tappets refurbished, it’s nearly time to start putting part together. However, before that, there is one last step in preparing the head. The camshafts sit in the journals in the head and once the engine is running they ‘float’ on a bed of oil, fed onto the top of the camshaft. I noticed when first taking the hydraulic tappets out of the cylinder head, that the journals were, in places, rather rough.<\/p>\n\n\n\n

\"Hydraulic
Hydraulic tappets back in the cylinder head<\/figcaption><\/figure>\n\n\n\n

I have a suspicion that previous aggressive removal of the hydraulic tappet may have caused the rough edges, or perhaps they weren’t removed in manufacture. Either way deburring is easy enough with a sharp edge. Then the journals are finished with an application of 800 then 1200grit wet and dry. Once the head is cleaned for one final time, the hydraulic tappets can be dropped back in. A drop of oil helps to aid slide them home, and avoid any oxidisation. <\/p>\n\n\n\n

Checking the relief valves<\/h2>\n\n\n\n

One thing that I did pick up on in the Citroen Workshop Manual was the presence of the pressure relief valves. The two valves sit at either end of the cylinder head, behind hex headed plugs. At first sight, they didn’t look too healthy.<\/p>\n\n\n\n

\"Pressure
Pressure relief valve in the cylinder head<\/figcaption><\/figure>\n\n\n\n

The manual states that the plastic valves should be removed by destruction (with a wood screw) and replaced with new ones. Well, they haven’t been available for a very long time, so I took a more careful approach.<\/p>\n\n\n\n

\"Cylinder
Cylinder head pressure relief valve assembly<\/figcaption><\/figure>\n\n\n\n

Once out, it’s clear the valve is actually in good condition and cleaner than it looked while in the head. The plastic valve has changed colour having been saturated in dirty oil. No amount of cleaning in the ultrasonic cleaner <\/a>will restore the original colour, so it goes back into the head and the cap is thread locked and tightened back up to the appropriate torque.<\/p>\n\n\n\n

Polishing my shaft(s)<\/h2>\n\n\n\n

Reinstalling the camshafts and the cam caps is the next step in rebuilding the cylinder head. The camshafts that came out of the cylinder head aren’t looking the greatest and need a bit of refurbishment. The lobes and the camshaft journals in contact with other metals, they need to be well polished to avoid wear and loss of horsepower.<\/p>\n\n\n\n

Poorly inlet shaft<\/h3>\n\n\n\n

The first shaft I take hold of is the one that drives the inlet valves. Initially, it just looks a bit dirty, but once the layer of built-up oil residue is removed, it’s clear the cam lobes aren’t happy. As can be seen in the picture below, the lobe tips are heavily pitted. It’s not something I’ve seen in a cylinder head before. The camshafts and especially the cam lobes are a very hard material, its not unusual to see their shape change due to wear, but pitting is definitely not a good sign.<\/p>\n\n\n\n

\"Damaged
Damaged cam lobes are unusually pitted<\/figcaption><\/figure>\n\n\n\n

It looks like the lobes have been left in water for a long time and rusted up. However, there is no evidence of pitting or corrosion anywhere else on the shaft. I do wonder if perhaps this damage is caused by high levels of friction between the cam lobe and a stuck hydraulic tappet. Or perhaps when the valves were previously damaged, they were so bent they couldn’t open. Either way, there is no chance of saving this camshaft, but fortunately, I have a spare!<\/p>\n\n\n\n

Polishing Method<\/h3>\n\n\n\n

With the damaged part swapped out for a better one, it’s time to get to polishing the shaft. I don’t want it getting away from me, so I’m taking a firm grasp of the cold steel and ratchet strapping it down. All smut aside, the method I’m using to get a shine on my shaft means it needs to be well secured.<\/p>\n\n\n\n