question re timing belt change for subaru legacy wagon 92, ASAP please?

wrote:
> All the 2.5L DOHC subie engines are interference. The 2.2L was non
> interference until 1996 at which point it is a bit hazy as to exactly
> when the interference design was brought in. Yes most SOHC engines are
> 2 or 3 valves per cylinder, but the subie went with 4. I admitt that I
> sure like the idea of a non interference engine, but with the DOHC it
> is a bit tough to pack everything in without utilizing an interference
> design. Regarding the use of DOHC arguments can go either way, but
> valve float can be minimized more easily in the DOHC design (as
> oppossed to using very stiff springs in the SOFC), valve placement and
> angle can be better optimized, and further the use of DOHC allows the
> spark plug to be centered in the combustion chamber which can improve
> flame propagation. Yes the difference could be quite small in the
> scheme of things unless you lean towards racing performance. The good
> news is that with the current timing belts that use curvilinear teeth,
> timing belts intervals have been upped to 100K, but even then as long
> as you have no oil or antifreeze leak issues your belt will probably
> hold out for a while yet. Regarding the valves issue indeed the
> original 2.2L engines had 16 valves, however, the cylinder was designed
> with clearance between the valves and piston. I do not believe there
> is any rule that 4 valves per cylinder indicates interference. The
> 1990 - 1994 engines are without a doubt non-interference type. If you
> had an outback with the 2.2L in 1995 you should be ok as well, but
> after that use caution. I spun my camshafts several times in my 1992
> Subaru Legacy AWD manual looking for the timing marks with no problems.
> If you are worried just change the belt ASAP and spin the cam shaft
> real carefully. Although to the untrained, the force of the valve
> springs could feel like some sort of interference.
>
thanks a lot, that's just the info I wanted. I have the exact same car
now, and I think I'm going to be very happy with it. OTOH, it did just
cost me $32 to fill up. (wondering if I should have just fixed the old
Kawasaki Ninja in the garage- would have been cheaper for commuting...)
thanks again for the details. I do appreciate it.
k w.

Ryan Underwood wrote:
> k wallace > writes:
>
>
>>Why would anyone use the interference design? It doesn't sound like it
>>increases performance. It just sounds like (from the bit of reading i've
>>done today) that you can make the engine physically smaller and get the
>>same power out of it. Is that right?
>
>
> I don't know what I'm talking about, but I would speculate that it allows you
> to get higher compression out of a shorter stroke or a smaller cylinder bore.
> The piston at TDC is flush with the top of the cylinder, so removing room in
> the cylinder head part of the combustion chamber increases the compression.
> And brings the valves closer to the piston.
>

pretty good guess... high compression is one reason, optimum combustion
chamber shape is another. Valve reliefs in the pistons aren't good for
either compression or efficient combustion.

nate

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k wallace > writes:

> what does running the radiator 'open loop' mean?

Shorthand for "let the engine warm up until the thermostat opens and water
starts circulating through the radiator".

k wallace > writes:

>Why would anyone use the interference design? It doesn't sound like it
>increases performance. It just sounds like (from the bit of reading i've
>done today) that you can make the engine physically smaller and get the
>same power out of it. Is that right?

I don't know what I'm talking about, but I would speculate that it allows you
to get higher compression out of a shorter stroke or a smaller cylinder bore.
The piston at TDC is flush with the top of the cylinder, so removing room in
the cylinder head part of the combustion chamber increases the compression.
And brings the valves closer to the piston.