jim beam wrote:

> FanJet wrote:
>
>> "jim beam" > wrote in message
>> ...
>>
>>> 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?
>>
>>
>>
>> Sure. Try the Nissan VQ series (just one example). No belts, very high
>> performance. You repeatedly forget to mention the fact that engines
>> with chain driven cams also feature chain tensioners, preventing the
>> cam timing errors you're worried about.
>
> not so. chains /do/ have tensioners, but by definition, they are on the
> "slack" side of the chain and make absolutely no difference whatsoever
> to timing drift.
>
>> So, chain driven cams + decent normal maintenance = no problems.
>> Belts + decent normal maintenance = big $$ scheduled maintenance. Your
>> choice.
>
> sorry, belts came /from/ v. high performance applications & migrated
> /to/ stock vehicles. this is not to say that chains can't work in high
> performance vehicles, but with the mass of the chain, they're not suited
> for high revs.

Please don't tell the Porsche engineers - they've been racing the flat 6
which first appeared in 1963, when the 911 was first shown, for years.

There are few true givens in racing, e.g., for years there was a saying
"there's no substitute for cubic inches" until Porsche got heavily
involved in racing the 917 with Penske's crew. Their overwhelming
success caused the late Mark Donahue, IIRC, to quip "the only substitute
for cubic inches is cubic money".