Advantage to interference valvetrain?

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JTK

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Is there any advantage to an interference engine over a non-interference? I can maybe see a smasher being more compact and higher HP, but what's the point? I could never figure out WHY a manufacturer would design an engine with a timing belt and then offer NO clearance should that belt break! Thanks Joel
 
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ya, me neither. I drive one everyday and it scares me that it will snap at anytime even though it has been replaced. could get a faulty new belt or someone who didn't put it on right
 
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JTK, you answered your own question, didn't you? "I can maybe see a smasher being more compact and higher HP". Well, add more fuel efficient due to lighter weight due to the compactness, and higher HP per unit displacement, and maybe we have it all covered?
 
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Yep, improved efficiency. Interference valve trains permit longer valve opening duration in a high compression design. But they don't suffer fools lightly. Some moron on one of the Edmunds boards was <i>bragging</i> earlier this week that his 2002 Accord with 172,000 miles on the clock was still on its original timing belt... I was tempted to post back that he ought to return the car to the dealer and ask for a check for the current trade-in value. If they asked why, he should tell the dealer because he's too stupid to own a car.
 
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Won't this timing belt as the weak link issue eventually go away? I thought I read on here somewhere that the Japanese minstry of whatever had recommended that manufacturers return to timing chains.
 
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Audi and Honda have gone back to chains on the 4 bangers in the A4 and the Accordk still interference but with a timing chain instead of belt, they put it in the rear onthe Audi to save space, don't know about the Honda.
 
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Allows higher compression which leads to slighly more torque & power. A belt is quieter and uses less HP than gears or chain. I have an interference engine with a timing belt. loved my 86 Saab with a roller chain running in oil. My thinking is a belt used in an interference engine is not the way to design the engine. Some manufactures are no going back to chain drive cams.
 
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If your 86 SAAB was a 900 like my 85, it also had a power transmission chain coupling the crankshaft with the transmission underneath the engine.
 

DJ

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Changing valvesprings is much easier if you can just bring the piston to TDC and let the valve fall .25" to the piston rather than having to deal with compressed air. Then again I am guessing most of you don't go around putting a hotter cam and therefore matching springs in your daily driver. I on the otherhand....................... [Wink]
 
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Our '00 Civic has a belt, the change interval is every 105k. The parts kit that Honda sells includes the belt, water pump, and the accessory belts. $450 including installation at an independent. I don't think that's too bad as maintenance goes. Maybe I'd feel otherwise if the car was having problems all the time, but the damned thing just runs like a top all the time. I wonder what % of timing belts break prior to the recommended change? I'm guessing it's extremely low, like 0.0001% or something. They do a good job designing the rest of the car, I'm sure they do a good job with the timing belt too. Not worth worrying about IMHO. jeff
 
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The problem with those is , the water pump impeller cracks and fails at about 65- 70k , so you have the whole thing apart anyway! Had my Ford do that, a Toyota and latest in the trend was my VW. That's the component that really gets me annoyed these days. my2c Jorge
 
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Greenjp is correct in that most of our vehicles are designed very well and a 450-600 timing belt replacement cost every 100,000 miles is not a finanical hardship. The real-world protential issues is that a water pump failure or idler pulley (s) failure or timeing belt tensioner failure or an oil leak will cause a belt problem. Yes, I agree; it rare but the potentional is there always.
 
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I predict the water pump maintenance being tied to the timing belt issue to also go away once they start using electric water pumps. This would also eliminate the thermostat. Belt-driven accessories in general should be on the way out.
 
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Another issue is low mileage cars that don't get to the belt change mileage in a reasonable amount of time. I had an 88 Supercharged MR-2 that at six years had not hit 60k miles, so I changed it and about 50k miles. I don't know what the time limits are if mileage is not reached, but it must be a consideration. A broken belt can be expensive.
 
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