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Old May 15th 05, 05:13 AM
jim beam
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FanJet wrote:
> "jim beam" > wrote in message
> ...
>
>>Elmo P. Shagnasty wrote:
>>
>>>In article >,
>>> (Jason) wrote:
>>>
>>>
>>>
>>>>>Ask him what happens if the timing chain breaks. Does the engine trash
>>>>>itself, or not? I think Toyota's are the non-interference type which
>>>>>don't trash themselves. At any rate, that's the important question. It
>>>>>doesn't matter if it's a belt or a chain. There's still chance for
>>>>>breaking, and there's still a requirement to change (although a chain
>>>>>*should* go much farther in theory).
>>>>
>>>>Great post. It's my opinion that a broken timing belt would in most cases
>>>>do less damage to an engine than a broken chain.
>>>
>>>
>>>That depends on whether the engine is an interference design or a
>>>non-interference design.
>>>
>>>It's not just the physical belt or chain whipping around in there; it's
>>>the pistons and valves you have to worry about.
>>>
>>>With Honda, the valves go down inside the combustion chamber. If the
>>>timing belt or chain breaks, the valves stay down there when the piston
>>>comes back up to top--and all hell breaks loose when they meet. That's
>>>called "interference".
>>>
>>>If the engine is designed, however, such that the valves don't go down
>>>inside the combustion chamber, but rather stay outside the combustion
>>>chamber, it doesn't matter what happens when the belt or chain breaks.
>>>The engine quits running, but a simple belt/chain replacement fixes the
>>>problem. No trashed engine to worry about.

>>
>>but you don't have the performance to worry about either - as a general
>>rule at any rate. in principle, a higher compression ratio and more
>>aggressive valve timing/higher lift cams both contribute to better
>>performance, but require "interference". so it's a trade-off. other
>>factors such as combustion chamber design, port/valve design, can help
>>produce a high compression non-interference engine, but what's good for
>>non-interference tends to be less good for chamber design, i.e.
>>efficiency, emissions, detonation tendency, etc. did i mention that it's
>>a trade-off?
>>
>>
>>>As far as the earlier comment regarding timing chains stretching, that
>>>happened to my brother's 92 Infiniti Q45. He had to replace both timing
>>>chains, at some unholy cost ($2700 comes to mind). It wasn't that they
>>>broke, but rather that they had stretched far enough out of spec.

>>
>>belts are good. people whine about cost of preventive maintenance, but
>>that's a function of dealer gouging, not design principle. it doesn't
>>take 4 hours to change a belt on a civic, regardless of what it says on
>>the invoice.

>
>
> Belts are certainly good for $dealerships$. Their replacement isn't
> preventive maintenance, it's scheduled maintenance - big difference. If
> Honda used a decent chain, the customer wouldn't need to deal with it. The
> Q45 issue was an anomaly. I'm sure there's the occasional Honda spun bearing
> or some other oddity. Maybe the customer ought to replace them every 80K.


if you drive some piece of v8 detroit iron with less than 40 bhp per
liter, you're not going to notice much difference with a bit of chain
stretch. and cam timing errors in excess of 10 degrees of crankshaft
are not unknown. belts don't stretch so they remain dead-on with timing
right up to replacement day. you want a high performance engine?

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