My son's Mitsubishi Eclipse shed it's timing belt a few months ago and all sorts of mechanical mayhem ensued inside. Why they would not put some reliefs in the pistons to stop this calamity is beyond me, but I know many of the jap engines are like this (same thing happened to a neighbor's Maxima).
Now, I know the Triton engines use a chain, but are they "interference" fit? I mean, if the chain should derail, is the engine smoked, or do you just coast to the side of the road and put a new chain on (I know it is more complicated than that, but you get the idea)?
I ask because my son did have the belt changed out on time, but the crank pulley disintegrated about 6 months later. Same thing could happen to a chain setup.
__________________ 1991 F150 SC 4.9L ZF5 1991 SAE Bronco 5.0L E4OD 1993 F250 4x4 7.3L IDI NA E4OD
Can any of you engineer types enlighten me as to WHY a manufacturer would build an engine this way? Why can't they just put reliefs in the pistons to make room for the valves? I can see it, I suppose, with 4-valve engines since there is less room for all those valves, but our engines are 2-valve. Why is it necessary to have an interference fit in this case? This seems like a huge engineering snafu to me, but so many engines these days are as such, so it must be necessary, I just cannot understand why.
Somebody smarter than me clue me in please. [img]/ubbthreads/images/graemlins/shrug.gif[/img]
__________________ 1991 F150 SC 4.9L ZF5 1991 SAE Bronco 5.0L E4OD 1993 F250 4x4 7.3L IDI NA E4OD
The problem is that we all want the most HP out of our motors. To get the maximum compression and valve lift on a motor engineers are required to get the piston close to the valves. Nothing you can do about it. What they do to compensate for this is design a reliable chain drive so the possibility of breaking is reduced. I have not heard about any problems with the new modular engines (4.6l, 5.4l and 6.8l engines).
In the case of the belt driven imports it is recommended that the belts be changed at around 50k if I recall. I had an 85 Maxima and I changed it out. A $20 belt for 3 hours work but I knew what would happen it it broke.
Most people probably forget or don't know to change the belt. Could be because way back then it was $400 at the dealer to have it swapped. I think an oiled chain should last longer. As long as they didn't put plastic gears on them like the old Chevy timing gears. [img]/ubbthreads/images/graemlins/frown.gif[/img]
There were plenty of Fords around with plastic cam gears.
Probably still are ... the modular motors (according to pictures
in service manuals I've seen) have metal gears. I think the OHC
design basically requires it. Any misalignment of the gears from
the crank to the head would chew up plastic/teflon gears in
about 5 seconds [img]/ubbthreads/images/graemlins/smile.gif[/img]
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