[alfa] Fred and Herb on the detensioner (part one, second attempt, long)

["John Hertzman" <johnhertzman@xxxxxxxxxxxxx>]

--------------------------------(1990)
For quite a while I was sure the timing belt tensioner was a lousy idea and poorly designed. I'm not the only one who thought the V6 Alfa engine could run very nicely without that hydraulic unit until it was discovered that the belt could jump a notch or more during severe temperature changes. That is when I decided it was time to figure out why they fail and what could be done to make it reliable and not leak oil any more. Although I'm convinced that our modification of the tensioner will solve the oil leak troubles, this is not the only problem with the tensioner and it is still a potential source of real trouble after 30 or 40 thousand miles. But you should change the timing belt then anyway and when you change the belt it's time to check the tensioner.
 
First a brief description of the tensioner and how it is supposed to work:
 
The belt tensioner consists of a roller about 2 1/2 inches in diameter which is held against the belt by a combination of three springs. The roller is actually a double row sealed ball bearing which is mounted eccentrically on a pivot shaft. The roller assembly rotates about 200 on this pivot shaft and because of the eccentric action, the roller moves closer to or farther from the belt to increase or decrease the tension. When the engine is cold the springs exert maximum force on the eccentric linkage and the belt tension is high. When the engine is running the oil pressure acts on a piston which reduces part of the spring pressure and so reduces the belt tension. We have been told that Alfa did this to compensate for the expansion of the aluminum block. If one uses a fixed belt tension then as the block warms and expands the belt gets tighter. To cure this Alfa provided the infamous "detensioner The entire assembly of springs, roller and detensioner piston and cylinder is again eccentrically mounted on a hollow stud which goes into the block and supplies oil under pressure to the detensioner cylinder. The entire assembly is rotated about this shaft to provide the initial adjustment of the belt tension.
 
So it is now 40,000 miles and past time to change the belt. Good excuse to pull it apart and do some heavy thinking. One can't really see the oil leaking with the shrouds in place but it is possible to observe the leak with the shrouds off and cranking the engine rapidly with the plugs out, using the starter motor only. (Do not turn the ignition switch on!)
 
I found three things had gone wrong with my tensioner and Herb found the same thing in his Milano. The roller that the belt rides on turned freely enough (in sealed bearings) but the unit was frozen solid on its shaft with dry caked-up grease and varnish deposit and could not rotate to increase or decrease tension. The boot over the plunger shaft was torn off and oil was leaking past the seal located inside the sleeve - bushing. On both our cars the timing belts were much too loose; at the top, between the two cam pulleys, the belt deflected about 1/8 inch under modest pressure. This, of course, is because the tensioner was frozen on the pivot shaft.
 
The first thing we decided to attack was the U-shaped seal on the piston shaft which does not last long and defies any cure by replacement kits. That seal is inserted in a groove within the sleeve the piston shaft rides through. We found it to be rather flimsy and with little sealing power. I found a seal of just the right shaft size 8 mm, which uses a coil spring to squeeze the rubber around the shaft but the OD was too large. Convinced that this seal would do the job and out-last the original by tenfold, at least, we pressed out the sleeve and machined the inner hole to a press-fit size for the OD of the new seal. If you are interested in this mod we can provide details.
 
Next thing was to press out the roller from its shaft (it took a great deal of force) and then to clean it thoroughly of caked-up grease and rust. I'm afraid the wrong type grease is used at the factory where they are made.
 
If you have never removed and re-installed a belt tensioner before, be advised that the following tips will save you much grief. Rotate the engine till the "P mark on the crankshaft pulley lines up with the pointer and that the distributor rotor is in alignment with the notch at about 12 O' clock and that the timing marks on the cam pulleys line up with the pointers in the shrouds (pry off the two round covers) DISCONNECT THE NEGATIVE BATTERY CABLE ! After the radiator and coolant system is drained, remove the temperature gauge sensor and time delay sensor. Remove the (3) V belts and then the shrouds. You can also rotate the engine using flywheel nut and socket. I find this easier since you will want to rotate later on when the battery is not connected.
 
In order to remove the timing belt it is necessary to relieve the spring pressure and then rotate the entire assembly to move the roller away from the belt. To relieve the spring pressure, rotate the roller downward and insert Alfa tool A.2.0363 through the hole in the front spring plate and into the matching hole in the tensioner casting. (A number 9 wire drill can be used instead of the Alfa tool although it won't push the roller down quite as far). To rotate the roller use a pry bar between the end of the spring plate and the air conditioner bracket; put the bar directly under the end of the piston rod. If it is difficult to rotate the roller assembly on the pivot pin, the assembly is probably frozen on the pivot and needs work. Next, loosen the 13mm nut on the tensioner mounting stud and also the 13mm lock nut directly below it. The lock nut is out of sight behind the spring and can be reached with a 13mm deep socket. After loosening both nuts, rotate the entire tensioner clockwise as far as possible. Make sure all timing marks are aligned and remove the belt. After the belt is removed, remove the Alfa tool and remove two Allen screws holding the spring plate and let it hang. (Do not disengage the spring) With a 13mm socket, remove the two nuts and washers holding the unit to the engine. The spring behind the unit probably dropped to the floor. That will take some doing to replace it in its proper place) I'll tell you how later, Remove the tensioner unit from the car.
 
Now you are ready to install the various O" rings and seals from the kit. There are two O" rings (different sizes) which go on the hollow mounting stud and one thicker O" ring that goes in the backing plate (the backing plate should still be on the car). Clean everything up and install these O" rings. Now take the tensioner itself apart. Put the unit in a vise and remove the two Allen screws which hold the cylinder head. Hold the cylinder head so you don't lose the spring. Remove the "E" clip from the piston rod and disassemble the piston. Note how the boot and seals go together. The U shaped oil retainer seal can be pried out of its groove with a scriber but probably not without damage. Note that the U faces up toward the piston. When putting on the boot do not use all the parts shown in the diagram. These prevent the piston from fully retracting and ruin the boot. Just slip the upper end of the boot into the retaining groove, leave out the square cut rubber washer but slip on the cup washer and E clip. Next remove the roller. If it is frozen to the shaft you may have to use a vise as a press to get it off. Be careful not to damage the grease seals on the sealed bearing. Clean up the pivot shaft and the hole in the eccentric roller mount; if there is corrosion use 600 wet or dry paper and WD40. Use Moly grease on the shaft - the kind that goes in CV joints is suitable. Reassemble the roller on the pivot shaft using an "O" ring on each side. Make sure that when the retaining cap screw and washer which holds the roller assembly to the shaft is tight and that the assemble will rotate on the pivot shaft. We advise using the old "O" rings; new ones tend to make the roller assembly bind on the pivot shaft.
 
Putting the tensioner back on is easier if you do not mount the roller. This is the tricky part, at the base of the coil spring, wedge very narrow strips of tape between the spring and the housing to tightly hold it in the groove. Bull the top end out to about a 300 angle and slide the unit in place so the spring engages the back plate tab. Otherwise you will never be able to compress the spring enough to go under the tab of the back plate. Screw on the nuts and washers snugly. Install the new belt. Slip on the roller (make sure both "O" rings are in place) and bolt. Attach the spring loaded front plate.
 
You will find that you'll need every bit of slack you can get in order to slip the belt on the pulleys so rotate the unit clockwise and tighten the nuts. Compress the roller portion so the piston shaft is as far in as it will go. Leave the tool in place and then loosen the nuts so the back spring takes a set and then tighten. Now you can remove the Alfa tool and you're done.
 
Note from Herb. Try as I might I could not get enough slack to get the belt on using the factory procedure. So I removed the front spring plate and slipped the roller off the shaft. This gives plenty of clearance to get the belt on. After installing the belt (left side cam pulley, right side cam pulley and distributor) reassemble the roller and spring plate and reinstall the Alfa tool. Rotate the tensioner assembly counter clockwise until all the slack is out of the belt and tighten the two 13mm locknuts. Now turn the engine over by hand two complete revolutions to bed in the belt. Check to see if the belt is tight and that the timing marks are aligned. If necessary, loosen the lock nuts and repeat this step. Finally relieve the spring pressure and remove the Alfa tool.
 
Be extremely careful in timing the cams and distributor. If you do not take the cam covers off, the pointers in the shroud holes are accurate enough to set the timing by.
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