View Single Post
  #7  
Old May 14th 05, 10:47 PM
jim beam
external usenet poster
 
Posts: n/a
Default

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.

Ads