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post #34 of (permalink) Old 09-14-2009, 03:34 AM
Alfisto Steve
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Thermal clutch spring device in mechanical tensioner

Here is my take on how the outer spring which is connected to the thermal clutch spring works to aid the inner spring on the Alfa 12v V6 mechanical tensioner # 60588421. Tech Service Bull 01.96.01 Alfa 164 TSB 01.96.01 says that " pointer will only line up ... when engine is stone cold". The bulletin does not says where pointer is when warm but thermal expansion is working here and thermal clutch spring is doing it's job.

SO just like oil fed tensioner mechanical tensioner is both a tensioner and DE tensioner.

Confused? Hope not just understand this tensioner really has THREE springs - inner coil spring, outer coil spring and thermal clutch spring.

Starting with the pointer right on the line of the reference mark with the engine cold. The pulley usually bounces a little when engine running. This is OK. Now as the engine warms up, the pointer begins to move lower, below the reference mark. When completely warm, radiator fan running, about 200 degrees on the gauge, the pointer is almost 1/2" vertical distance below the line on the mark. Now COLD the thermal clutch spring prevents the pointer from moving much below the reference pointer because thermal spring is now contracted pulling on outer spring and aiding inner spring to keep belt properly tensioned. THIS IS WHY IS IS IMPORTANT NOT TO OVER TENSION OUTER SPRING COLD so it won't break. Thermal clutch spring has to expand to prevent stretching out spring to the max.

If you notice under that round cover with reference mark on it for the pointer to be aligned with cold is this thermal expanson flat coil clutch spring that looks like the cooking coil on a electric stove. This flat coil spring is hooked to the infamous outer coil spring that aids inner coil spring to keep belt in proper tension (unless it is broken).

As engine expands due to heat this thermal spring expands to let pulley move so belt tension stays the same. This is why pointer goes below reference point when engine is hot. So the way I see it the thermal clutch spring allows belt tension to stay constant both hot and cold.

Hope that makes sense. Think of it as a dual purpose system of both expanding and contracting to prevent over tensioning and under tensioning of the timing belt.

So my take on this is that as long as tensioner installed properly cold with all three springs intact and pulley pivot point not binding timing belt should not become loose when engine contracts back to cold state AND cam timing pulleys should not jump time (slip under belt).

Further reference TSB's to install and tension belt/tensioner: Alfa 164 TSB 01.93.03 Alfa 164 TSB 01.93.04 REMEMBER TO USE SPECIAL TOOL (needlenose pliers to aid installing belt and setting tensioner pointer when using lifting lug on tensioner body).

Ciao, Alfisto Steve
Virginia Beach, VA
AROC 164 Tech Advisor

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Last edited by Alfisto Steve; 09-14-2009 at 04:45 AM.
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