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Old 01-16-2011, 05:18 PM
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"Interference" vs Non-Interference" Engines

I recently read a "Car Talk with Click and Clack" newspaper article regarding the preventive change of a timing belt on an "interference type" engine to avoid serious damage from a failed belt. According to the commentary, some engine designs permit the pistons to strike the valves if the cam shafts loose proper timing with the crank shaft in events where a belt jumps teeth or completely breaks.

In attempting to find out what engines have this interference type of design I found this site:

As I understand it, if the timing belt is not listed on this site for a given vehicle then the engine uses a timing chain and not a timing belt and is a non-interference design.

Can anyone tell me if some motors are built with timing chains which also have interference designs? From what I have been able to find so far, it appears that engines which use timing belts are all interference type motors and therefore, changing the timing belt at an appropriate maintenance interval such as 60K miles is advised to avoid lethal damage in the event the belt fails or skips teeth.

It seems possible to me that an engine could employ either a timing chain or a timing belt and still be either "interference" or "non-interference" depending on the design.

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Old 01-16-2011, 09:42 PM
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Chrysler 2.2-2.5 uses a timing belt and is non interference.

80's Ford Escort 4 banger is an interference motor
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Old 01-16-2011, 09:45 PM
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IIRC, all engines using a chain are interferance engines.
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Old 01-16-2011, 10:43 PM
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If the valve at max lift would strike the piston if the valve was held in and the crank spun is the issue. Not chain or not. Large lift and flat top or domed pistons could be interference. You are correct, there is no golden rule.

My stock 4.7L Porsche V8 engine was non-interference with a 9' long timing belt, until I went to a reduced base circle cam with more lift. Making cut outs deeper on the pistons would have solved the problem and also dropped compression. When I went with a 5.0L bottom end I ordered custom pistons with proper cut outs to once again be non-interference.
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Old 01-17-2011, 04:20 AM
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No engine is totally exempt from the possibility of bending valves, if it has poppet valves.

I have bent valves in a stock SBC that lunched the woodruff key of the crank timing gear at speed.

While there are some engines that will almost certainly bend valves if there's a chain/belt failure, it also depends on engine speed, engine design, mode of failure, etc. as to whether you'll hit a piston and valve together.

Last edited by cobalt327; 01-17-2011 at 04:25 AM.
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Old 01-17-2011, 05:18 AM
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valve damage

The old chevy 6 cyl engines would bend the pushrods when you lost teeth on the Fiber timing gear. the combustion chamber shape- valve angle resulted in a valve hitting straight on. We would take the pushrods to the anvil hammer on them then roll them across the table to get them straight. Some of the 427 Ford pistons had bumps on the top of the pistons to hit the center of the valve head when the engine was over revved and the valves floated... they were to keep from bending a valve. My brother floated the valves on the old Ford FE interceptor engine, dropped a valve, cracked the piston and it bent the crank.
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Old 01-17-2011, 05:44 AM
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Personally Known Benders
Chrysler 2.0 DOHC and SOHC
Chrysley 2.2 and 2.5
Honda 1.7
Hyundai Motors
Kia Motors
Nissan Sentra(chain) 3 Teeth off is the limit It will run
V6 3.1, 3.4, 3.8 Chevy
VW Motors, 1.8,1.9 DSL and 2.0 Gas
Chevy 2.4, 2.3 4Cyl
Ford ztec and 1.8 Escort GT

Personally Known Non Benders or often lucky
Chrysler 2.4DOHC (listed as a bender done 2 broken belts no problems)
Nissan 3.3LT (listed as a bender 1 belt no problems)
ALL TOYOTAS are free reving that I have ever seen (with Belts at least)
Honda 1.8 Prelude Early 90's and early 90's 1.5 Civics 80's civics can bend, 2.2 accords usually don't bend

Anyone else have personal experience... V8 porsche is good to know.
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Old 01-17-2011, 06:36 AM
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Interference vs Non-Interference Motors...

Thank you for all the responses on this subject. I eventually found this site which lists engines relative to interferene or non-interference:

I do not know if it is complete or covers older motors. If anyone makes comparisons on this site and finds issues, please post comments.

Thank you for your respsonses,
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