Two Technical Questions

I know they make non-interference engines should a timing belt fail. But,
what is the reasoning for why anyone would design anything other than a
non-interference engine. There must be some advantage???

What makes it desirable to have a timing belt vs. a timing chain? I would
always think a chain would be the way to go, but some engines use
belts...that have to be replaced. What advantage would make someone choose
a belt???

On Thu, 5 May 2005 1810 -0400, "Prometheus7"
<david@nospammers-honeyhousedesigns.com> wrote:

>I know they make non-interference engines should a timing belt fail. But,
>what is the reasoning for why anyone would design anything other than a
>non-interference engine. There must be some advantage???
>

Easier to design and make. Slighty cheaper perhaps? In order for the
valves to be non-interference they have to clear the piston no matter
where the piston is--that is, if the valves stop full open, when the
pistion comes up to TDC, there must be some place for the valve to go
(dishes in the pistion face...) non-inteference also limits valve
lift, so that larger valves are needed (cost...) and with the
clearance for valves the compression ratio won't be as high.

>What makes it desirable to have a timing belt vs. a timing chain? I would
>always think a chain would be the way to go, but some engines use
>belts...that have to be replaced. What advantage would make someone choose
>a belt???
>

Cost. Noise. Reliability. A timing chain the length of the timing belt
in a modern OHC engine would be horrible. Even slight wear would throw
off valve timing. The chain would tend to slap around, and be really
nosiy. A chain that long presents reliabity issues...

Let me guess, you broke a timing belt on an interference engine and
trashed it? <g>