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Andy Daley of Chi-Town Citroën in Chicago uses an innovative and surprisingly inexpensive SM chain tensioning solution that he has now performed on a few SM engines.
Andy points out that a fellow SM owner had discovered a primary chain tensioner made for a Mazda that is a near perfect fit for the MK2 primary chain tensioner.
Here’s what the tensioner looks like once modified with nylon m4 bolts so it’s not metal to metal. Bolts have a thin washer and a lock washer, and are assembled with blue Loctite. The head on the dowel is cut off to assure clearance.
The MK2 tensioners on most ’72 and later SM’s have a rubber pad on it that hardens in oil and must be replaced. Unfortunately the MK2 tensioners have gone from very expensive to now nearly unobtanium. MK1 tensioners are more readily available, which is fortunate since the Mazda tensioner does not work on the ’71 and early ’72 engines that use an MK1 tensioner because those tensioners are installed ‘backwards’ to an MK2 and the chain guide interferes with how the Mazda tensioner’s spring dowel works.
He also uses a curved nylon chain limiter for the primary chain (available from MIE Corporation at http://www.maseratinet.com//pc-18559-520-chain-guide-lower-merak.aspx.) The curved limiter is a direct fit, though cam timing is advanced slightly, so cam timing must be verified and adjusted if necessary.
Andy reports it was the late, great Andrew Brodie who discovered from a large Citroën dealer that the curved limiter was to be an update to the SM motor until SM production ceased. Like chain limiters in modern engines, a nylon curved limiter reduces resonate frequencies in the chain and reduces load on the tensioner.