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.

now, if you have a chain driven vehicle and can allow for drift caused
by wear, as i believe is done in some of the recent variable valve
timing engines like porsche, then sure, you can marry performance, revs
& longevity, at least in theory, but then again, if you're dropping 6
digits on a porsche, i really don't think the cost of the maintenance is
uppermost among your buying considerations.