Engine Rebuild (Part 12) - Joining the Engine and Gearbox

With the clutch and distributor tower fitted, I could reunite the gearbox and engine halves.

The engine had been split before: back in 1999 to deal with gearbox input shaft that sheared as the result of a vicious clutch snatch. That was what took my car off the road for all these years. The solution back then was to fit an alternative gearbox from a low mileage car. As the car was never put back on the road after that surgery, the replacement gearbox never really had a road test and remains an unknown quantity. It probably only ran another 3 or 4 miles after it was put back together again.......before I pulled it all apart again in 2016.

Engine about to be split: 25 September 2016

With this engine build now well underway, I was getting closer to finding out if that gearbox was any good.

The procedure for refitting the gearbox doesn't seem to warrant a mention in manual 814, but is covered (succinctly) in step 18 of Operation DX.100-2 in Manual 518. The thrust bearing refit is covered by step 23 of Operation D.330-3 in section 2 of volume 2 of Manual 814.

I refitted the thrust bearing. my car has the type with the 'eye' that fits over a guide rod. It took me ages to work out that the retaining clips are meant to go through holes in the clutch fork.

Thrust bearing eye mounted on guide rod

Gearbox bolts come in all shapes and sizes. Some hold clips to secure hydraulic pipes – so it’s important that they go back in the right places. This is where earlier reference photos come in handy!

Reference photo - 25 September 2016

Before zinc plating the bolts, I laid them all out, to make sure they were all accounted for and to work out which went where. The 'anti-tamper' bolts had been replaced with normal hex heads.

Gerabox Bolts - All Accounted For

 I also numbered their positions on the bell housing. 

Working out Bolt Positions.....

When I built my engine trolley earlier in the month (see other post), I had taken account of the need to accommodate the gearbox on it as well as the engine: it would become the platform on which the rest of the engine build took place before re-fitting.

Lots of room for the gearbox....

With the engine now on the trolley, and the gearbox innards complete, all I had to do was swing the gearbox back into place. Simple. In fact it was simple, but just tricky for one person to do on their own. Alignment of the two halves was crucial. Strapping the gearbox to the crane to achieve a level lift was fiddly and I used blocks of wood strategically placed to pad out the strapping to give me ’level’. It was frustrating when, thinking everything was lined up, the two halves would not mate. More than once I pulled the halves apart convinced something was blocking the way.

Aligning the gearbox and engine

In reality, it was probably just a slight mis-alignment of the end of the gearbox input shaft to the splines on the clutch plate. After several attempts the gearbox suddenly slid into place. Pinching a corner together with no more than finger and thumb I was able to put one bolt in place by a couple of turns. I didn’t force it as I was concerned about exact alignment and the risk of stripping the threads on the aluminium bell housing.

Bolting the Gearbox to the Engine

Working around the engine I put more bolts in place (with some threadlock) and gradually tightened each a little to pull the gearbox into position (it has two locating lugs). When I was happy I blocked up the gearbox end and l released it from its sling…..

Reunited - August 2018

There are three bolts that hold the starter motor in place – these also serve to hold the engine and gearbox together and I would fit these in due course.

Engine Rebuild (Part 11) - Flywheel and Clutch

With the engine off the stand and now sitting on the trolley I had made  I could, at long last, refit the flywheel and clutch.

The Flywheel
As a 1968 car, my car has the 95 tooth flywheel and uses a starter with a 10 tooth pinion. (From October 1969 - so approximately 1970 model year - the flywheel then had 123 teeth and matched to a starter with a 9 tooth pinion). You can find out more about the change in flywheels in an earlier post HERE.

Back to business. With the retaining circlip removed, I had used a suitably sized socket to drift out the old flywheel bearing. I would fit a replacement later.

Using a socket to drift out the bearing

Anyway, fitting the flywheel was straightforward. The procedure (short and sweet) is covered in step 36 of Operation DX.100-3 and in step 36 of Operation D.100-3 in section 2 of volume 2 of Manual 814.

There is a lug on the flywheel that corresponds to a notch on the end of the crankshaft - so it stops you putting the flywheel on the wrong way round. I used a block of wood and some long bolts in the clutch pressure plate holes to hold the flywheel in place while I prepared to torque up the flywheel bolts.

Bracing the flywheel to tighten the bolts

BE WARNED that the instructions for tightening differ between Manuals: the earlier Manual  518 (dating from 1966) says to torque the bolts to between 5.9m.kg and 6.5m.kg. The later Manual 814 (from 1974) says that for bolts with a "spherical imprint on the screw head", they should be torqued to 9m.kg - so quite a difference. I judged that my bolts had the later spherical pattern and so went for the higher figure......

Has this got a "spherical imprint"?

With the flywheel fitted, I was able to fit a new flywheel bearing. The gearbox drive shaft will slot through the clutch plate and into this. The bearing is simply held in place with a circlip.

New Flywheel Bearing Fitted

You know that you can insert a pin into a little hole in the bell housing - and when it engages with a slot in the flywheel you can set the timing? Well if you ever wondered what that notch looks like, you can see it in the photo below. On my 1968 car, the notch in the 95 tooth flywheel gives 12 degrees before top dead centre of number one cylinder. The notch continued to give that mark for a while - even after the change to 123 teeth flywheels. However, from July 71 - so approximately the 1972 model year - the notch in 123 tooth flywheels changed to giving TDC - top dead centre. See my post of 1 October 2016 for more information.

Timing Notch in Flywheel

The corresponding hole where you insert the 'timing pin' is on the carburettor side of the engine - tucked away underneath the mounting point for the alternator.

Same view: the hole for the timing pin (centre in this photo) is beneath the alternator

The Clutch
If fitting the flywheel was straightforward, then fitting the clutch more of a head scratcher. I had agonised for weeks beforehand over the clutch disc and pressure plate. Mine is a three fingered clutch and, with the clutch off the car, rough measurement indicated that the three fingers were set at slightly different heights. Precise measurement with the clutch all bolted together on my bench confirmed it.

Even crude measurement showed the clutch fingers were at different heights

The difference was only a millimetre – but that might be crucial. Citroen specify heights for the fingers and the tolerance on these is a millimetre or more – but that does assume that all fingers will be set to the same height. Mindful of the ‘clutch snatch’ problem that led to my car being taken off the road back in 1998, I worried that this difference of finger height might mean that the clutch had not been releasing evenly and smoothly due to finger height? For peace of mind, I needed to sort those fingers out. 

Three problems: firstly Citroen give no correct finger height measurements with the clutch off the car – or more accurately they give no measurements that a home mechanic can make. They rely on the use of special Citroen jigs that mimic the clutch being fitted to the flywheel and operated.

Second problem, my car has an after-market ‘Valeo’ brand clutch that is (apparently) thicker than the Citroen originals - so any Factory set up measurements were not much use anyway. Darrin at Citroen Classics did give me a magic number that he used when checking the fit of Valeo clutches: with the plate clamped between flywheel and pressure plate - 35.2mm from the surface of the flange around the clutch plate centre, to the top edge of the clutch finger. That's pretty precise! At least I could use this measure to make sure all my clutch fingers were a consistent height, right?

Wrong: third problem, I could not release and adjust the nuts holding the fingers together! Not without ruining the bolts and nuts.

before i started hacking at nuts, I contacted a clutch specialised looking for replacements. He couldn't help me and simply advised instead, using very thin shim washers under strategic points of the pressure plate to give consistent finger heights. Trouble is that this would then take the flywheel and pressure plate surfaces out of parallel – something I judged to be just as important as consistent finger height. 

The alternative was to part exchange my clutch for a reconditioned one - but i could do without the expense of that. In the end I resolved to do nothing at that time and wait until the flywheel was fitted and then try it in situ on the car - and that time had now come........

The procedure for fitting the clutch is covered in step 37 of Operation DX.100-3 of Manual 518, and in step 37 of Operation D.100-3 in section 2 of volume 2 of Manual 814.

A key requirement is to fit the clutch disc centrally in the flywheel/ pressure plate sandwich, so that when engine and gearbox are reunited, the gearbox shaft can pass through the clutch disc and into the flywheel bearing. Citroen workshops use a special mandrel to get this alignment. The alternative (and since it's the gearbox shaft that needs to pass through the clutch) is to use a spare gearbox input shaft......Fate, as it often does, took a hand: reading of his gearbox rebuilding exploits, I contacted Badabec who very kindly lent me his worn and surplus gearbox input shaft to use as a clutch alignment tool. 

A spare input shaft can be used to align the clutch disc

I thoroughly cleaned the surface of the flywheel and clutch pressure plate using 'Mek' and did the same to both sides of the clutch disc.

With the engine off the stand and the flywheel fitted, I used the old input shaft as a mandrel to align the clutch disc to the flywheel.

Using  the input shaft to centre the clutch disc on the flywheel

With the clutch disc held centrally, I slipped the clutch pressure plate over the mandrel and orientated the pressure plate to line up the marks made when it was removed.

Chalk marks highlight the alignment of the two parts. Mandrel still in place

It was time to bolt up. The later Manual 814 updates on Manual 518 by advising you to replace the old-type clutch pressure plate bolts used on pre December 1969 cars with a later type (and presumably specification) of bolt. The distinction being the pattern on the heads.

Different Specs of Flywheel Bolts

My pressure plate bolts most definitely had chevron heads (like 'type 1'), and I didn’t have any of the updated bolts to use - so swapping up was not an option. I re-used my bolts (with serrated washers) and tightened to 2.9m.kg as per Manual 518 (not the torque in the later Manual 814). As I tightened, I checked to make sure that the clutch disc was still central and that mandrel was free to slide in and out of the bearing and splines of the clutch disc.

I Fitted the older 'type 1' clutch bolts..........

Taking a measurement of the finger heights again, I was surprised to find they all came up very close! Not the magic 35.2mm figure that Darrin had given to me, but all were about 34.8mm. While I didn’t know whether 34.8mm was a good or bad number, it was at least consistent for all three fingers - which had been my objective!


In the absence of any other information to the contrary, I resigned that there would be some clutch adjustment i could make to 'fine tune' the clutch once the car was running and decided my clutch was going to have to do - so left it at that.