free running or interference heads? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 02-27-2016, 03:14 PM   #1
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Default free running or interference heads?

1994 bonnie se 3.8 v-6 of course.no supercharger.i thought that it had a timing belt,but thanks to gates belt guide it doesn't list a timing belt but only a serpentine drive instead.i looked in the haynes manual and it lists chain and sprockets replacement procedure.ok so now i know that it doesn't have a timing belt.so does it have a free running motor or not?
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Old 02-27-2016, 04:38 PM   #2
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My guess? No.....why the questions? What is your problem?
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Old 02-27-2016, 10:48 PM   #3
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They are interference heads. Miss the timing, kiss the valves goodbye.
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Old 02-28-2016, 12:13 AM   #4
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It'* a chain for sure, but I don't recall any cases of a chain snapping in my history here.

If there is going to be an issue, it'* typically with the tensioner, that causes the chain to slap around. Even then those issues are pretty rare.

If it'* not giving you a reason to worry, then don't worry about it.
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Old 02-28-2016, 09:29 AM   #5
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Only 3.8 engine I ever ran into that jumped timing, was built in the late 80'*.....in their infinite wisdom, GM had plastic teeth(for noise) on their timing gears.....later, they went all metal........ran into one that sheared off, and jumped timing.....amazingly, the valves were ok....it bent the push rods......
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Old 02-28-2016, 11:51 AM   #6
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Only 3.8 engine I ever ran into that jumped timing, was built in the late 80'*.....in their infinite wisdom, GM had plastic teeth(for noise) on their timing gears.....later, they went all metal........ran into one that sheared off, and jumped timing.....amazingly, the valves were ok....it bent the push rods......
My 1987 Grand AM 3.0 did the same thing. Except the engine was running at about 3000RPM.
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Old 02-28-2016, 03:59 PM   #7
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I don't know what the rpm'* were on the 3.8, but in both cases you would think a valve would bend, rather than the push rod....my guy lucked out that all I had to do was remove the valve covers to replace push rods(in addition to the gears/chain/tensioner0......

The worst part of the job, was getting the front timing cover off......somehow those dowels were rusted and wouldn't let go.....then I pinched the gasket on the oil pan trying to get the front cover back on......
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Old 02-29-2016, 05:47 AM   #8
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Ooops, lol
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Old 03-01-2016, 12:59 AM   #9
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..........the engine was running at about 3000RPM.

1988 Le Mans.......was also running around 3k rpm.......she back fired thru the carb.......I pulled over, popped the hood, flames erupted.......volunteer fire fighters pull up 30 minutes later in a 1950 something GMC looking like circus clowns.......really (they were at a convention for children when the call came thru)
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