The MGA With An Attitude

At 02:30 PM 8/17/2007 -0600, Jim Franzen wrote:
>>"As I start to depress the clutch, I get a squeally/grindy sound. When I depress the clutch all the way, it gets really loud. Sounds like a bad throwout bearing."

The carbon faced release bearing makes no noise you can hear, unless it is worn away to have steel on steel contact.

This brash squealing sound with clutch released is a result of the clutch disk (driven disc) wobbling about violently (a small distance) while being energized by light contact with the flywheel and/or pressure plate (driving surfaces). It is a resonant vibration that starts small and increases in amplitude with continuing energy input from the surface contact. If you depress the clutch pedal quickly, before there is time to transfer much energy from the driving plates to the driven plate, it may not chatter at all. After engaging a gear, upon starting to let the pedal up, you may get this noise again. Letting the pedal up a little further to drag the clutch like you want to accelerate away should damp out the vibration and stop the noise, even while the clutch is still slipping before complete engagement

This odd movement of the driven disc is "allowed" by a small amount of working clearance in the splines. It can be slightly aggravated by worn splines giving larger than normal clearance (common with a rebuilt clutch disc). It can be greatly aggravated by a worn spigot bearing (the bronze bushing in the crankshaft) that will allow the gearbox input shaft to orbit at the front end. It can also be aggravated by contamination on the contact surfaces of the clutch disc (like burnt on oil for instance).

The first thing to try is cleaning of the friction surfaces. You can use a spray-on brake cleaner solvent. The older traditional type containing carbon-tetrachloride works best. Trichloro-ethane works as well (or trichloro anything). This is the stuff that wets the surface well and evaporates quickly). The newer enviro-friendly cleaners are not nearly as good. Those are the type that bead up without wetting the surface, immediately run off like water without cleaning anything, and take forever to evaporate. The better solvent is often cheaper as well.

Brake cleaner (or carburetor cleaner) commonly comes with a small plastic tube that can be inserted into the spray nozzle for spot application. You may be able to poke this small tube up through the bellhousing drain hole (where you normally find the loose split-pin. Be very careful not to accidentally spray this stuff in your eyes. Have a helper depress and hold down the clutch pedal (or block the pedal in the down position) to hold the pressure plate retracted. Spray the cleaner in between the driving plates and driven plate (ideally). Note that the only place you may have access to the edge of the driven plate is under the slightly relieved edge of the clutch cover. Rotate the flywheel 90 degrees and repeat. One or two seconds spray on each side of the driven plate at 90 degree intervals should suffice.

If you cannot get the spray tube in through the bellhousing drain hole, or you are not confident that the spray is going where desired (or if it doesn't stop the noise), you can remove the starter motor and apply the spray cleaner to the clutch disc through this aperture. With a little luck this spray cleaning of the clutch disc may eliminate the chatter without having to R&R the engine. Then it remains to be seen how long is stays quiet, or how long it takes to become contaminated again. If you have a badly worn spigot bushing, all bets are off.

>>" I just noticed that my rear valve cover nut came loose and I leaked a lot of oil down the rear of the engine." Could I have gotten oil into the bell housing?

Maybe, but it certainly can't be good. This is not very likely, because the bellhousing is a very tight fit against the engine rear plate. Furthermore, if oil did get in this way it would run down the back side of the rear plate without making contact with the flywheel. The problem is when oil comes into contact with the crankshaft and crankshaft flange, similar to when oil may leak past the crankshaft rear scroll seal. Then the oil can be thrown away violently in all directions from the front face of the flywheel. Oil thus spattering around inside the bellhousing can then get into the clutch friction surfaces. Oil on the friction disc is a common contributor to this problem.

>>"I pulled the engine once before. I guess I get to do it again."

Only as a last resort if spray cleaning doesn't work. You would have to pull the engine to replace the spigot bushing, or even to inspect the clutch disc or splines. With a little work you could disconnect the clutch slave pushrod and remove the rubber excluder boot around the release lever. This may give you some access for visual inspection of the clutch with a bright light. I have never bothered to R&R the engine just because of a chattering clutch disc. I rather train my throttle and clutch feet to defeat the chatter, or learn to tolerate it. Such is life when you need to determine your priorities.

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