Replacing Leaking Cam-Hub Outer O-Rings (Seals)
Part One
Part Two - Notes
Tools (Cam Pullers)
Cam Hub Diagram & Dimensions
Symptoms:
Oil leaks from the outside of the cam belt pulley or toothed sprocket. Oil collects on the lip of the holes in the cam belt plastic covers and in the round cam hub covers, eventually contaminating everything below including the cam belt itself.
Location:
On the outer side of the cam sprockets there are two round hubs about 5 mm or 1/4" thick, fixed with five small bolts and a large nut (and inside, a keyed spline). Between the two hubs there is a simple plastic o-ring to prevent oil loss. Over time it hardens and is squashed, and requires replacement (see diagram).
Relevant AR 164 (USA) 1991-93 Service Manual Pages:
00-45, 00-47 Valve clearance adjustment without removing timing belt covers. Shows detail of removing pulley support hub and seal (o-ring) behind.
01-40,01-41 Removal of camshaft pulley. Shows use of tools and two seals either side of the pulley. (I find the labelling of "oil-ring", "o-ring" and "seal" to be ambiguous throughout the manual, however the outer and easier seal is the one we're after. And to get to it we are going to remove only the outermost cam hub, leaving the hub behind it and the toothed pulley (sprocket) in place).
Parts required for this fix:
Two small plastic o-rings, costing less than a dollar each! One plastic cable tie. Perhaps silicone gasket cement.
Tools required for this fix:
Done by this method (the engine stays in the car and there's remarkably little disassembly) this is definitely a job requiring very specific tools. Don't attempt it without them. One of the tools, the cam hub puller, has to be specially made or an off-the-shelf puller adapted for this job. However, it's worth it! This is a great way to solve these oil leaks and if you're well prepared the job itself takes very little time.
1. Cam hub puller (see below)
2. Cam hub torque reactor (see below)
3. 41 mm socket to turn crankshaft (to set to TDC)
4. 22 mm ring-spanner/wrench (and socket if desired) long as possible
5. Torque wrench for re-torquing nuts and bolts
6. 11 mm ring-spanner/wrench for the small bolts
7. White corrector fluid/paint etc with a fine brush for marking position of the cam sprocket and cam belt (and a small mirror on a stalk might assist getting the paint to where you want it).
1. Cam hub puller. This is not the puller listed as an Alfa special tool. This specially-made puller is flat and will fit into the narrow space allowing access to the rear cam hub. (Thanks to Karl Maxon and Matthew Dooher for inspiration and basic design features).
The puller can be a modified off-the-shelf puller (see Karl Maxon's notes) or one specially made from mild steel plate (see Matthew Dooher's notes). The plate should be 10 mm or about half an inch thick, with a central threaded hole (eg 5/8" or 15 mm) for a broad, short bolt which provides the force to pull the hub off. Around this there are three holes large enough for 7 mm bolts to fit through with ease and some room for movement to align with the holes in the cam sprocket which the bolts screw into.
The puller can be round or triangular in shape (see diagram for measurements). Square causes some clearance challenges at the rear, but it may work.
The length of the bolts is critical to success and ease of operation. The central bolt should be the thickness of the plate plus 10 mm. A slightly tapered, rounded or pointed end will assist it centre into the end of the camshaft against which it will be applying force.
The three 7 mm attaching bolts fit into the existing threads in the cam sprocket and must have a shank length of 25-30 mm in excess of the thickness of the plate. Don't use shorter bolts. They should be long enough to use all the available thread in the sprocket, and anyway it's easier to shorten bolts than to lengthen them! The only difficulty with longer bolts is the lack of space at the rear to work in.
Click here to see Karl's and Matthew's harmonic balance pullers
(note in both that the fourth (vertical) slot is not necessary for this job - only the three equally-spaced slots)
For the hub dimensions (required to make a puller or a torque reactor) click here.
2. Cam Hub torque reactor.
Alfa special tool # 1.820.051.000 can be used if available. If not, a substitute will have to be made.
The torque reactor is fixed to the cam hub to prevent it turning when removing or refitting the large outer nut. Alfa's tool fits both the larger holes around the cam sprocket near its circumference and the cam hub's three holes through which the three 7 mm fixing bolts pass to screw into the sprocket. A makeshift item can take either course, however to gain access to the outer sprocket holes (a better option from a strength point of view) both upper plastic cam belt covers have to be removed. If you wish to work with the covers in place (as I have), the tool uses the three hub holes instead (not so much torque, but it should be adequate unless the nut is very hard to get off).
Some may find the Alfa tool is not long enough. The longer the handle the greater the torque and less effort required! For this reason I suggest making the torque reactor longer than Alfa's.
There are two possibilities for the design of the torque reactor. Most similar to Alfa's is to give the "business end" a similar shape to the puller plate. Much thinner steel plate can be used, perhaps 4 mm. (All the tools can be made from scrap readily available at metal shops). Tap three holes and bolt short 8 mm bolts through, then cut off the bolts so they extend 5 mm. When using the tool these studs protrude into the three holes in the cam hub referred to above.
An alternative instead of studs is to drill holes in the torque adaptor to be able to fit 7 mm bolts into any two (or more) of the holes through the hub and threaded into the sprocket. It takes a bit longer to use this tool with bolts but I feel more confident with it fixed firmly to the hub so it can't break free and allow the cams to move or the engine to back-up violently.
DISASSEMBLY
Caution!: place a rag below the hub to catch any falling bolts or washers. There are places where they can lodge below and be difficult to retrieve (and jam the cam belt on the crankshaft pulley, for example).
1. Raise the front right of the car, e.g. at the jacking point under the RH front door.
2. Remove the RH front wheel.
3. Remove the RH front inner (plastic) wheel valance cover (screws top, bottom right, bottom right under the front valance, and turn-clip centre bottom)
4. With the transmission in neutral, and using the 41mm socket, turn the crankshaft CLOCKWISE ONLY to TDC (see photo). Check that the TDC mark on the flywheel is now also in alignment. Re-engage the gearbox or "park" for autos.
5. At TDC, paint-mark the position of each cam sprocket and the cam belt (a long fine brush will be necessary to fully mark the rear cam sprocket.
6. With the "minimalist" approach described here, the cam belt covers, dog-bone etc DO NOT need to be removed, only the round plastic caps covering the cam hubs. Only if the cams move (ugghh!) or there is difficulty getting access to the hubs will you have to pull more off the engine. However, if all goes well there is no further disassembly, so now to the hubs...
7. DO ONE HUB AT A TIME, NOT BOTH. Complete the front (it's easier and you'll learn from it) before going on to the rear.
THE FRONT (OR LEFT HAND*) HUB.
(* Remember, the Alfa shop manual calls the front bank of cylinders the LH of the engine, as if viewed from the flywheel).
8. Remove the three 7 mm bolts from the front hub. You may leave the other two 7 mm bolts (further recessed) in place unless you find (in step 10) that you need an extra mm of clearance on the outer face of the hub to get a better grip on the big nut.
9. Fit the torque reactor with its studs extending into the three holes.
10. Undo the nut. It will take lots of effort (or it should if was tightened properly in the first place). DO NOT LET THE CAM MOVE. If you apply equal force on the nut (counterclockwise) and the torque reactor (clockwise) the cam should stay exactly where it is. Long handles on both these tools will make an easy job of this stage. Otherwise there will be a frustrating struggle.
11. When the nut is removed the cam's central spindle is exposed. Install the hub puller, making sure that, as you tighten the three bolts, the puller plate is parallel to the cam hub. Install the bolt with the most difficult access first (usually the bottom/rear one, for both hubs). With all three small bolts hand-tight, screw the central bolt into the plate and hand-tighten against the cam spindle, ensuring the plate is central. Readjust the three bolts to check again that the plate is parallel (so it will pull evenly on all three bolts).
12. Turn the central bolt into the cam spindle. When it's very tight proceed a half-turn at a time, it will "pop" suddenly (and maybe disconcertingly loudly!) and slacken as the hub loosens itself. When the hub has moved at least 5 mm you may remove the puller and if necessary prise the hub off with a screwdriver.
13. On the rear of the outer hub you'll see the old o-ring, hardened and squashed. Clean the hub and fit a new o-ring. Replace the hub, push it on by hand. Clean the threads of the cam spindle and large nut.
14. Refit the torque reactor and refit the large nut, torquing it to 97-117 Nm or 71.6-86.3 ft. lbs. Refit the three 7 mm bolts (with washers), careful not to over-torque these.
15. THE REAR (OR RIGHT HAND) HUB is approached in an identical way, except it is more difficult to gain access there than the front. Still, I have NOT found it necessary to remove the dog-bone, plastic cover, fuel line etc so try that UNLESS you can't get the access required. Just proceed slowly and patiently.
16. You may need to move a bundle of wiring/piping directly in front of the hub. Snipping the cable tie on the firewall side and unlocking a plastic clip permits the bundle to be moved a few centimetres, enough to put it out of the way as you work.
17. Access here is more cramped but the process should be the same as for the front hub. Smaller hands certainly help. Light the area well and use the wheel arch for access from the side/underneath.
DIFFICULTIES?
If the large nut or hub will not loosen it may be necessary to apply heat with a small blowtorch. I have no experience of this (it hasn't been necessary) but see Karl Maxon's notes for some cautions and advice. Also, replace any "rounded" nuts or bolts as these may spell trouble the next time they need to come off.
FINISHING AND TESTING
18. Replace the bundle of wiring/piping if moved while doing the rear hub. Replace the cable tie. Make sure the bundle is clear of the hub. Clean signs of the old oil leaks (I have used lots of hot water and detergent without apparent ill effect but keep all electrics dry). Start the engine and check just below the cam hubs for leaks. OK? Replace the round cam hub plastic covers and test drive, checking again for leaks some time later.
OTHER SOURCES OF OIL LEAKS AT THIS END OF THE CAMSHAFTS:
If oil is leaking from inside the cam sprocket the oil seal inside the head is probably responsible. The fix for this is not dealt with here, but this seal may be accessible without removing the engine from the car by using the above method (plus removing the top cam belt covers etc). (I'd like to hear from anyone who's done this).
It's much easier if oil is leaking from between the large nut and the cam outer hub. This leak will be evident if there is streaking of oil outward from the nut over the face of the hub. Remove the nut and smear silicone gasket cement between the nut and the hub before refitting. (On my car one hub leaked here because of pitting on the hub surface, but if both hub and nut are perfectly smooth this should not occur). Of course, you may have more than one source of leaking oil. On this side of the engine there are numerous other possibilities, notable the old-style oil-fed cam belt tensioner and the oil pump pulley.