Replacing/rebuilding the fan motor; fitting new brushes

 

My fan motor has developed an intermittent loud and embarrassing squeal. I assume this is a failed bearing. I would try to repair it but there is little if any information available and no  parts are listed. Replacement (pattern, non-Lucas) motors are available and relatively cheap, so I ordered one. The motor is mounted in a bracket and this is only attached to the car by 2 bolts and an electrical connection to the otter switch. I disconnected the connection at the clip joint and disconnected the battery in  case of accidental shorts. This "ought" to be an easy job. The recommended route is to remove the fan from the motor- detach the motor and then remove the front grill and remove the motor through this space. To remove the fan remove the top safety grill.

Unscrew the two bolts that secure the upper protection grill and remove it.

If you think you can remove the fan then do it at this stage. There are two access slots cut into the fan centre surround and one of these aligns with a small grub screw holding the fan hub to the motor shaft. 

New fan showing grub screw in fan boss opposite slot in fan "upstand"

Unscrew this and the fan should detach. This has to be tight to hold the fan securely, but it is also exposed to the elements and spray blown around by the fan itself. Faced with this problem you might perhaps have thought to use a decent, probably stainless steel for the grub screw. Maybe you'd have thought to use an Allen type to allow a reasonable force to be exerted?

As you've guessed BMC did none of this. Firstly they seem to have cast around for a suitable dairy product from which to make the screw, eventually settling on some form of hard cheese. If they ever thought of an Allen head, that thought didn't trouble them greatly and they seem to have dismissed it with ease. Consequently any attempt to remove this screw results in stripping the head. I note that it is recommended to use copaslip or similar when assembling this screw, but BMC didn't do that either. Consequently I have to remove the fan and motor as a unit so  unscrew the motor mounting bolts (2)

Remove the two bolts that secure the fan motor mounting bracket below the scuttle.

This creates problems. The motor/fan assembly cannot come out in front of the radiator because the radiator would need to be moved backwards. The radiator is mounted via a flange on each side which is bolted onto the front of the welded body side panels  (2 bolts each side). This flange prevents the radiator from moving backwards. I did try it and remove these bolts but predictably, even though the radiator bolts were removed and the hoses are flexible, the radiator can still not be moved backwards the mere inch or so necessary to make  removal of the motor/fan unit possible.

Radiator mounting. Note welded body panel steadied by means of 2 top stays that themselves are secured to the radiator mounting bolts. Note also that these bolts penetrate the flange on the side of the radiator so the rad cannot go towards the rear of the car even if unbolted. You can also see the ridge where the bottom tank meets the core and which will  be troublesome later.

I did remove the front grill panel (self tapping screws) but I can confirm that the fan plus motor cannot come out this way, although its quite possible the motor alone might. However for that you would need to be able to remove the fan.... Consequently the only way that is now possible is to drain the system and remove the radiator. Just see how a simple job has grown!! 

However, even this isn't  without its problems. The radiator bolts have already been removed as above. This only generates limited movement because the lower hose is thoughtfully and lovingly entwined with the fibreboard ducting and anti-roll bar.

Radiator bottom hose penetrates fibreboard ducting and passes beneath the antiroll bar underneath.

There's nothing for it but to disconnect the bottom hose (because the radiator was thoughtfully not provided with a drain tap) and drain the system. Then its a simple matter to lift the radiator upwards.... hang on.. what's this? The radiator has a ridge above the lower tank (just visible in the picture above in front of the fibreboard). This means the radiator has to be moved rearwards to clear the body at the front of the car before you can lift it up... but you cannot move it rearwards AND raise it because the bottom hose spigot fouls on the body and antiroll bar. A triumph of design! Just 0.5 cm more clearance would have made this simple. As it is you are forced to wrestle the large, heavy- and surprisingly delicate radiator out by twisting it and applying side forces at odd angles which I hope won't break the soldered seams. Eventually it came out and I may investigate cutting some of the body to make the job easier next time! The fan and motor can then at last be removed!

** Should add here that although I've been critical of the design here, on removing the rad, I did notice that it was distorted. The lower tank was flattened and the top tank bent into a curve. I was in two minds as  to what to do... new rad or repair, but having costed both I opted for repair (straighten tanks, new core) since they could fit a drain tap at the same time for about the same price as a new rad. The repairers recognised both the radiator as an MGB item- and the damage immediately. Apparently its very common and caused by jacking the car up on the rad... duuuh!!! Embarrassingly I think they thought I'd done it... honest guys, I'm an innocent man!

I had ordered a new motor but it was my intention to remove and re-use the fan. As the screwhead was stripped I tried to find an impact driver to use on the remnants. However the screw is too small for my impact hammer head whilst the obvious ridge around the fan prevents close access anyway. 

Fan and motor removed as a unit (still attached to mounting bracket). One of the grub screw access slots is visible allowing screwdriver access to the fan hub screw.

I was therefore forced to drill the screw out. Obviously the recess around the fan made drill access impossible and I had to enlarge the screw access slot in the plastic to do this. The screw did drill out fairly easily, although the fan would still not move.  I tried penetrating oil which didn't help it and neither did hammering.  The design of the fan prevented all means of holding the central boss in a vice so that the motor shaft could be driven out. The only means available was to hold the fan by hand. This had 2 effects; firstly the motor boss wouldn't move because the hammering force was absorbed by the fan, and secondly my fingers were injured when much of the force was dissipated there on the occasions that the hammer missed! Much swearing. After 4 hrs on this 20min job I gave up and cut the fan blades and central upstand off with an angle grinder. I could now grip the fan boss in a vice and tap the motor shaft out backwards. Once the boss was secure it came off very easily. I removed this remnant of the fan and also the washers and circlip beneath. All in all, this struggle shows me that it would have been impossible to remove the fan in position even if the grub screw hadn't failed. I think it highly unlikely anyone will get away without removing the rad for this job. Strangely a new fan costs more than a new motor- I can't understand that, but obviously I had to order one.

New fan came with a much meatier screw fitted instead of the grub screw. This was an M5 thread and probably different from the original. I decided that I could replace this with either an m5 Allen headed grub screw or a hex bolt. The grub screw was a little short so for the time being I've opted for the bolt. Not sure how this last (or the new meaty screw) will affect balance and vibration in use so I may revisit this if I have a problem. I tapered its end to help it locate on the motor drive shaft.

New fan screw as supplied and a hex bolt with tapered point. Ill try both and assess for vibration.

Even though I wont be reusing this motor I hate throwing anything away and wanted to see if it could be saved. My ham-fisted work with the angle grinder had shortened the motor drive shaft, but not so much that it was unusable. I decided therefore to investigate the source of the squeal and see if I could repair the motor. 

The motor is a Lucas type 9GM. There is a misprint in the Lucas manual and so the part number for the complete motor unit is either 78586 or  78568.

Fan motor exploded

The motor is held together by 2 long through bolts. At the front the nuts are thoughtfully recessed into the end cap  so you can't grip them with a spanner or socket, but you can jam them against the body of the motor with a screwdriver whilst you undo the bolt heads at the other end. 

Motor front cap. Note mouldings that prevent you gripping the through bolt nuts.

Rear of the motor fan unit showing the through bolts.

The front of the motor (fan end) then pulls off. The brush plate is attached to this end cap and comes away with it on the inside.

Looking inside the front end cap. Brush plate secured by 3 phillips screws.

The brush plate can be easily removed.

Brush plate removed

rear of brush plate

The brushes looked worn both in the sense that they were shorter than I'd expected, but also they had acquired a stepped profile where they've press on the commutator. I now realise that in fact they are not particularly short, but I don't think the stepped profile is correct. Unfortunately, I have nothing to compare them with so if anyone knows how these should look please let me know.

Brush close up... note stepped profile in the front

This profile suggested to me that the brushes have been riding on the raised section of the commutator (see below). I'm not sure, but it seems to me that they should run on the flat section where there is plenty of room, so perhaps the motor spindle has been moving fore and aft as it turns pulling the brushes too far back? This could explain the intermittent squeal.

The spindle commutator can then be pulled out of the motor body against the magnetism trying to retain it.

Commutator. Note fwd bushing land is a bit dirty as its the more exposed. The motor has no means of lubricating these bushes. Also the flat brush section is more than big enough to accommodate the brushes without them riding on the ridged section below it.

The commutator spins in two bushes, a blind bush pressed into the rear of the case, and a through bush held onto the front endcap by a star washer. 

Rear spindle bush- no play detected here.

Front spindle through-bush. Note the bush is held by a star washer which does permit some movement. There was little if any movement between the spindle and the bush itself.

This front bush did seem to have some movement but I think it was more to do with movement of the bush itself in the star washer than wear in the bush. I had expected ball bearings and I understand some upgraded motor versions do feature these (as does my new replacement in fact). In my case both bushes appeared in good condition. There was little play between shaft and rear bush and what was evident at the front appeared to result from movement of the whole bush against the star washer retaining it rather than between shaft and bush. I will strip this down and assess more thoroughly. The front bush is retained by the teeth of the star washer engaging with a groove in the bush. Closer examination revealed that the washer's teeth were uneven in length and many weren't "locking" into the groove. I think this is the origin of the to-and-fro movement that allowed the brushes to ride in an incorrect position. I should also add that the diagrams indicate a domed washer between 2 shims immediately above the floating bush outside the motor end cap (items 8 and two of 10 in the diagram above) and retained by a circlip (9). I suspect this is also a tensioning device that presses on the circlip and so pushes the bush into the motor and prevents fore and aft movement of the shaft. In my case only the circlip and one shim were present here.  Perhaps the others were  lost in a previous rebuild- or perhaps they've been made made obsolete by motor redesign? 

Bush retained by star washer. Note that several teeth no longer engage with the groove on the bush

I sought to secure the bush more firmly by fitting an external circlip in the bush groove against which the star washer could push. This secured the bush and test assembly showed that it also successfully limited the to and fro motion of the shaft. It also seems to have helped reposition the brushes although I won't know how effective this has been until I renew them.

Circlip in bush groove provides something firmer for the star washer teeth to press against.

However it still appeared that the brushes were worn and needed replacing. I suspect the source of the squeal may have been the brush bases rubbing on the commutator as it span rather than the motor bearings and the odd ridged wear suggests something of the sort. It would be nice to change the brushes but no spares are listed. In the past it was possible to change them, but only by replacing the entire brush plate rather than the actual brushes themselves. This brush plate is now obsolete, although it appears very similar if not identical, to the brush plate used in the Lucas wiper motor and which is still available. This often has an extra brush for 2 speed wipers but you can remove this and use the modified plate in the fan motor. If you are interested the part number is WKB102; however it costs around £20, and as new pattern motors are only a little more than that, replacing it would be unwarranted unless you were devoted to keeping everything original. 

The brushes themselves are mounted in copper seats in which they are a firm sliding fit and through which they make electrical contact. They are grooved on their sides to locate onto the brush plate. The copper seats themselves are spring mounted and permit the brushes to slide in and out along their grooves under spring pressure. Measuring the brushes showed that they are 8mm wide and 6mm thick on the grooved side, their length obviously depending on the extent of wear. Although generic grooved brushes are available, there are none of this size. However, this is a usual size for ungrooved brushes and 13.6mm  7.8x6.1 brushes are readily available. They fit for instance the 100mm Dewalt angle grinder. These are pretty cheap I got a bag of 20 for £5! However they need modification to fit into this motor and specifically they need to be grooved, cut to length and shaped. 

These brushes have a wire contact which the lucas motor doesn't use but it pulls out easily. 

I held the brushes gently in a vice and using a small file, filed a groove (app 1mm x 1mm) on each side.

Check that the brushes fit in the back plate and slide easily.

Without cutting the brushes are appx 2x as long as needed, and cannot retract enough to slip on the commutator. 

Without cutting the new brushes are far too long and press on the drive shaft, They can't retract far enough to contact the commutator.

I cut each appx in half using a hacksaw (gentle- no pressure needed). I used the half furthest from the wire contacts as this should be stronger. The old brushes slide sideways out of their copper seats and the new ones can be slipped in. This provides the electrical contact so they need to be a firm fit... but not so firm that they crack on insertion. I filed the ends with a half-round file before slipping the brush plate over the commutator and carrying out a final shaping using fine Emery cloth wrapped round the hub.

Replacement brushes inserted and shaped with half round file.

Reassembly was, as they say, the reverse of dismantling . I refitted the washer and circlip to the front end cap exactly as I had found it. I don't know whether the more complex "domed plus 2 washer" arrangement illustrated is actually needed. Its clear that the design of this motor has gone through several iterations and I suspect that the simpler arrangement I found is now the norm. 

Slipping one of the old brushes and its contact seat out if the brush plate

New brushes inserted.

Fog Lamps

 One of my rear fog lamps had snapped off and was hanging by the wire. I dont recall any incident that could account for this, but they are vulnerable hanging below the car and exposed to spray and weather. Mine was probably broken in the process of removing the car cover so  I'll need to be more careful in future.

My remaining fog lamp

 However this also underlies the main cause of the weakness as the need for corrosion resistance means that these lamps (Lucas 921) have plastic bodies. Some have a chrome-like finish, but are still plastic underneath. They tend to crack around the mounting point where they vibrate. This is compounded by what I'm calling bad design as well. The lights are mounted by a single captive bolt protruding through the back of the lamp. The stud then passes through the mounting bracket (rubber washer mount) and is secured with a nut and washers. This arrangement is fine for securing a new lamp, but the securing nut is exposed to the elements and its bound to corrode. It WILL weld itself solidly to the stud. This means that if you try to undo the nut, the whole lamp will simply rotate. The natural response to this is to hold the lamp as you unscrew the nut... DO NOT DO THIS. The bolt head is captive inside the lamp, but the lamp is plastic so its only weakly held between moulded plastic lugs inside the lamp body. Holding the lamp and then turning the nut means the whole bolt will rotate inside the lamp and its head will mash the plastic mouldings inside the case and probably crack it! 

Intact foglamp before removal- note the bulb contact wire (Gr/R) penetrating the case and the earth contact (top left) attached to the mounting bolt.

In my case the lamp had broken and was no longer attached to the body bracket - I cut the wires to release it- note the earth contact- from rear of fog lamp.

If you need to remove an old lamp (that is actually still mounted to the body) proceed as follows: Remove the 2 screws securing the reflector and remove it- care with rubber seal. Note the two rubber washers that cushion the screw holes.

Ease the green/black wire passing through the body of the lamp through its grommet and further into the lamp. You can then slip the white bulb holder forwards and out of its grooves. This is necessary before removing or fitting a bulb as there isn't enough room inside the lamp to do this. Remove the bulb.

Bulb holder slipped right off. Note rear bulb body contact below nut.

You will then have access to the bolt head in its moulded recess. There should be enough room to slip a small socket (1/4" drive) on an extension onto the nut, but as this is recessed it can be awkward. A slim box spanner might be more successful? In my case the rubber mounting washer behind the lamp had disintegrated and I could pull the remnants out. This gave the mounting bolt some movement and I could pop the bolt head up inside the lamp by pressing it in from the rear. Using a third hand grip the rear nut with a ring spanner and unscrew the bolt using the two spanners against each other. This is awkward, but should avoid damaging the lamp.  

Note the shake proof and flat washer fitted to the rear of the lamp and the electrical earthing wire. The bulb body contact inside the lamp will come out with the bolt, note how this should be fitted (protrusion forward and uppermost). One of my lamps also had a square copper reinforcing plate under this contact but I don't know if this should always be present.

Inside of lamp.. all fittings removed. Note moulded plastic lugs far too weak to to hold the bolt head

When refitting fit the lamp before replacing the bulb. Clean up the mounting bracket and treat it and the contacts to some dielectric grease. Put some corrosion-block or copper grease on the mounting threads. Use a new rubber washer and refit the lamp; the order is (from the car towards the lamp); Nut, shake-proof washer, flat washer, (mounting bracket), earth tag, rubber washer, (lamp body), internal contact, bolt head.  Fit a new bulb and slip the white holder onto its contacts. Pull the excess wire out of the lamp through the grommet.

Fog lamp refitted

Refit the red lens and don't forget the rubber seal and the two thin rubber washers on the screw holes.

Seat Recover

 My front seats have been grubby since I acquired the car, and despite my best efforts there's quite a bit of dog hair still stuck to them--- and I don't have a dog.

Probably the worst thing though is that the drivers seat in particular feels more like a hammock and it sags as you sink into it. I've ordered a new foam and diaphragm to try and tighten it all up but I'd not got around to dealing with it until my cleaning of the headliner meant that grubby, stained- and now bleached - seats were just going too far. Its time they had attention. I decided to remove the driver's seat and dismantle it for a rebuild. I'm starting with the driver's seat and hoping this is the only one I need to do.

Rhs Seat front runner mount and slider ratchet control. seen from footwell

Rear seat mounting bolt protruding through the weld nut viewed from under the car.

Drivers seat- photos better than it looks although bagginess of fabric is obvious. 

To remove the seats slide them all the way backwards and release the 11mm bolts that hold the runners to the car.

The front bolts screw into the chassis cross member and shouldn't be rusted in. The two bolts and their shake-proof washers are shown below.

Slide the seat all the way forward- note that the seat belt talk does obstruct the seat so you'll need to carefully feed it back beside the seat- compress the seat foam. You can also swivel the chair away from the stalk if the front bolts are out.

Inboard rear mountings remain hidden under the seat  so a bit fiddly.

Outboard mounting bolts visible

The rear bolts pass through weld nuts in the floor and protrude underneath the car. Clean  and oil the projecting threads before unscrewing the bolts.

 

Rear bolts removed, rusting section indicates thread protruding below the car.

Once 4 bolts removed the seat lifts out. The alloy running slides on the inboard (left) side may fall off whilst the outboard (right) side remains attached via the ratchet lever.

This reveals the wooden packing pieces beneath and the 4 metal bolt spacers in it 

The carpet around the base of the handbrake was a bit scrambled but brake lever and lever switch present. I de-fluffed them. Not sure what the contact is but it seems secure

Looking underneath the seat at the sliding rail rear...

.. and front with slide ratchet lever

I found there were 4 fabric clips per side.

... and another 4 across the back.

To separate the back support from the seat section unscrew the crosshead screws holding the plastic covers at the base of the back section. 

You'll need to compress the seat foam a little to remove the covers.

...and remove the covers

The nut inside the reclining joint isn't captive, so hold that with a spanner as you loosen the bolt. Note that there are two washers on this fastening- a smaller washer below the bolt head and a larger slip washer between the two sections of the seat.

 

Seat recline fastening- note washer sandwiched between the two seat lugs and one washer under the bolt head.

Fastener removed and reassembled to show both washers.

The seat fabric is secured with these vicious fabric clips. If you have any intention of reusing your cover then you must release these carefully. They have teeth that dig in to the fabric and if either clip or fabric is pulled before they are disengaged the fabric will tear. I lever up a free end with  fine screwdriver to raise and release the teeth. One the teeth are out of the fabric the clip can be slipped back to release the fabric. Start at one edge and then the fabric will be more easily slipped out from the subsequent clips once the teeth have been disengaged.

Carefully lever up the free end of the clip to pull the teeth out of the fabric before levering the clip back.

The seat-cover and foam can then be lifted off. I was surprised that my seat had webbing straps not a diaphragm but apparently this is period correct- diaphragms were phased out earlier. Looking at this seat there are only 4 cross straps- my replacement comes with 5. They are more closely spaced to the rear of the seat where it takes most weight.

The frame can be removed once all the clips are out.

Frame and webbing removed from foam

Once the foam is separated the cover should just peel off the foam. I noticed there are sections of hessian around the edges- presumably to reinforce it. I've found bits of this under the seat from time to time so its been falling apart for a while. I'm not sure how these should go  but I've ordered some hessian strip to replace the worn and vanished pieces.

Stray pieces of hessian under the seat.

Hessian reinforcement at the rear corners.

Peeling the cover off showed that it had been glued to the top of the foam. I peeled carefully to avoid tearing the cover and separated it from the foam.

Once clear, the glued areas showed up as dark areas on the foam 

.

Cover detached and will be gently hand washed before refitting.

Cover now free

There is some damage to the piping which I'll try to repair using an insert

two breaks in piping at the front of the seat cover.

I removed the webbing frame by pulling the hooks.

... and detached the runners at the cross head screws (3 per runner). Again these aren't weld nuts so you have to hold the upper nut as you unscrew the crosshead.

Note raised stop stud on the rear of the ratchet handle-side slider

This is not fitted to the other side

Detaching the slider strips.

Once removed the frame could be wire brushed and degreased

Prior to respraying in hampered black finish. This went on straight over the brushed rust and covered well v pleased with the effect.

The new "diaphragm" turned out to be webbing- apparently correct for the year. However it had obviously stretched so I decided to augment it by reusing both the 2 fore/aft webs and the front 2 cross webs (which stretch least) from the old seat support. This should give  bit of help in supporting my enormous bulk but I'll need to modify the frame to accept the extra straps.

New frame- I added the two front/rear straps each side of the two new ones.

I slipped the old front/rear straps, one either side of the 2 new ones, and then slid the 2 old seat straps up to the front.

I could then add the new webs behind them. The new webs come with a split and free hooks. You need to hook the new hook through the split and catch the wire frame with it. Sounds daft,  but don't forget to get all the hooks and strap seam facing the same way.

New strap slipped onto frame- note split in the end.

Hook to be slipped into the split in order to catch the wire frame in the smaller end.

Hook inserted.

I gave a lot of thought to how the webbing should be interwoven- or even if it should be interwoven at all! This is my final pattern but I suspect that there are dozens of ways to do this. I'm trying to support the new webs to spread the load, using the older webs to limit the stretch once the new ones have taken the weight.

Since I'm reusing 4 old straps in total I'll need new holes in the frame for their hooks. The seat frame already has 4 hooks at the front but will need 2 more at the rear and two on each side.

I drilled new holes (5mm)  on the back 60mm inboard from each of the existing holes. I also drilled two new holes in the rear frame cross member to accept the extra front/rear straps.

New holes drilled in seat frame

I could then restring the frame. This is a bit tricky as there's quite a bit of tension required.

Frame with extra holes to sides and rear- the corner holes were previously unused but now are fitted with the reused front/rear straps.

Using the existing but previously unused front corner holes gives a pleasing angle to the longitudinal straps. I suspect I should have added the reused seat cross straps at the rear not the front- but hey its done now and I've still got as much if not more support than original.

I had already washed the seat cover gently in Persil liquid detergent and allowed it to dry. I could now look at the damaged piping and any remaining dirt.

I repaired the piping using a nozzle tube from a WD40 spray. It needed to be rubbed with abrasive paper as it was rotated until to reduce the width to a tight sliding fit.  I could then slip one end into the break in the piping, trim it and insert the other end to hold the piping back together. It would obviously be better to use black not yellow tube, 🙄 and maybe glue it in. I reasoned the fit was quite tight and didn't want to risk glue stains on the seat so I left it unglued. We'll see how it goes.

Insert the WD40 spray tube and trim it

Use the inserted tube to fit across the split.

And push the broken piping back together.

At this stage the repair looks good. The seat was still stained- it looked like oily hands on the raised edges. I found I could remove this very satisfactorily using K2 Velor car upholstery cleaner- spray one, brush in, blot off- repeat. I found it to be quite effective.

Finally I found a small tear in the vinyl side panel facing the transmission tunnel. I think this is where the seatbelt stalk has been trapped. I patched it from the rear with a spare piece of vinyl.

Rebuilding the seat.

The old foam had split along the lines of the webbing frame on both sides. There are remnants of hessian attached to this seat- but having looked at various Youtube videos, there is no real explanation for it and hessian isn't described unless fitting foam over a steel "bedspread" type frame. However, hessian (US Burlap)  is used more generally in furniture  to protect foam from the webbing and metal hooks. I also found that older MGBs and Midgets featured a full hessian layer under the foam, presumably for the same purpose. This seems to have been reduced to short sections (as a cost cutting measure?) later on but the splits in my old foam suggest this isn't 100% effective. I decided to use some new hessian between the foam and the webbing frame.. 

Split in foam along the line of the webbing frame...

 and on the opposite side

I bought 1m of 3" Hessian strip and cut this into  strips along the sides of the foam.

I aligned the hessian strip to the foam edge, rotated it back...

... and then sprayed both the hessian upper surface and the foam exposed at the side. Allow the adhesive to flash off for 5 min...

... and then rotated the hessian back onto the glued area to fix it down.

I trimmed the strips to follow the edge of the foam. X

 and then sprayed both the hessian upper surface and the exposed foam at the side. Allow the adhesive to flash off for 5 min..

Strips of hessian stuck to foam base

The hessian now covers the metal hooks and frame wire.

I could then align the foam and refit the cover- I sprayed the foam in the pattern discussed above and then tried to attach the cover. This is the most difficult bit of the  whole operation because with this design there is no definite "seat" section in the cover to locate the cover onto the foam. It is important to locate the cover such that (in my case) the deckchair stripes are not only straight- but also that they will align with the stripes on the reclining back section of the chair. You also need to work out all the kinks and creases in the cover so that it sits flat on the foam when this is achieved. This is very difficult and really can't be done if the foam is glued as this prevents fine movements to align to foam after the cover has been applied to the foam. If I was doing this job again I wouldn't glue at this stage.

Finally, the cover needs to be secured to the seat frame tubes with the seat cover clips- these clips are the invention of the devil! Great care needs to be taken when fitting them. Firstly, its very important that the teeth grip the fabric only above the metal seat tubes where the fabric is supported and can be sandwiched between the tube and clip. If the clips are off the seat tube and engaged with unsupported fabric then they will puncture and rip it. Secondly, although the clips have teeth at both ends- it seems to me really important that only one end of the clip contacts the fabric and the other end should contact the bare metal of the tube. If both ends grip the fabric then it will not be possible to push the clip home against the seat frame tube because the teeth are trying to stretch the fabric between them. This means that the cover will need to be positioned/trimmed so that it doesn't fold all the way around the seat frame tubes. Positioned like this, the end in contact with the metal can slip around/over the seat tube and clip into place while the end embedded in the fabric need not move at all. If the seat cover is wrapped too far around the seat tube both ends of the clip will be gripping the fabric. 

This is all quite difficult to arrange, and if you get it wrong you may make additional holes in the seatcover as removing the clips to adjust is always a risk. The seat is then reassembled and refitted as the reverse of the dismantling.