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[Main 9000 Bulletin Board | BBFAQ | Prev by Date | Next by Date | Post Followup ] Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos Interfering v. Non-Interfering Engines Like This Post: - Subscribe to Daily Digest for this Bulletin Board Posted by Bill Homer [Email] (#3427) [Profile/Gallery] (more from Bill Homer) on Wed, 23 Jun 2004 08:50:59 In Reply to: Re: Depends, Todd [Profile/Gallery] , Wed, 23 Jun 2004 06:38:15 Alert me when someone posts in this thread: Members do not see ads below this line. - Help Keep This Site Online - Signup

Engine valves open in two cases: 1. on the intake stroke as the piston is on its way down; and 2. on the exhaust stroke as the piston is on its way up. At the top limit of piston travel, the valves will be shut, i.e. the start of the intake stroke and the end of the exhaust stroke, if the valve timing is OK. Breaking a timing chain messes this up completely.

In an "interfering" engine, the valves open to the extent that they can hit the pistons if the timing is off. In a 'non-interfering" engine, the head is "deeper" and/or the valves may not travel as far, so they do not hit the piston tops. Most current engines, including the SAAB 9000 seem to be Interfering-type designs (perhaps they are more efficient or lower polluting?). The early VW Rabbit/Golf/Passat/Audi Fox engines of the 1970-80s were non-interfering - I fixed a friend's broken timing belt in a parking lot, no valve damage.

My guess is that redoing the timing chain is a waste of time on your car in its current condition. If you need a diagnostic check for insurance purposes, an alternative might be to pull the valve cover, set the camshafts to the indexed zero degree marks, then GENTLY set the crank to Top Dead Center (you may run into valves while doing this), and perform a leakdown test on cylinder 1. If it doesn't hold pressure, the valves are bent - of course, there is a chance that the cylinder 1 valves are OK, while others are bent. Sounds like the insurance company's rules are out of date.

posted by 129.188.33...

• Will broken chain total engine?, Todd , Wed, 23 Jun 2004 04:41:42
  • Maybe I just got real lucky, but ..., MikeC, Wed, 23 Jun 2004 19:25:06
    • I really don't understand how that could be, David, Thu, 24 Jun 2004 10:14:46
      • Well, I don't know ..., MikeC, Fri, 25 Jun 2004 05:35:47
  • Depends, Ari , Wed, 23 Jun 2004 05:53:53
    • Re: Depends, Todd , Wed, 23 Jun 2004 06:38:15
      • Interfering v. Non-Interfering Engines, Bill Homer , Wed, 23 Jun 2004 08:50:59 <-- Viewing This Message
  • yes the pistons will hit the valves, but it won't, David, Wed, 23 Jun 2004 05:07:51
    • Good point., Gene N , Wed, 23 Jun 2004 05:46:07
  • No, but..., Gene N , Wed, 23 Jun 2004 05:05:15

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• Prev by Date: Do a combination..., Joe98, Wed, 23 Jun 2004 08:49:46
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