I was just curious what a 302 that has been treated very well, can run before it dies. I give it a tune-up once a year and change the oil about 2500 miles. I have heard stories that some people get to about 250,000 miles with no problems, other than using a little oil. Any thoughts?

 

Your engine very well may run for 250K miles if you treat it well and above all else, keep the oil CLEAN. However, certain things will wear and require attention requardless of how well you maintain the engine. Things that will need changing after 100k are the timing chain and valve seals as well as all the obvious routine maintenance stuff. The chain will just stretch over time and have to be replaced and the seals will just get brittle and break apart. If you let the chain go then it could jump a tooth or break and cause real trouble. I actually have seen this happen (once). Bad valve seals will just make your engine burn a little oil.

 

>Your engine very well may run for
>250K miles if you treat it
>well and above all else, keep
>the oil CLEAN. However, certain things
>will wear and require attention requardless
>of how well you maintain the
>engine. Things that will need changing
>after 100k are the timing chain
>and valve seals as well as
>all the obvious routine maintenance stuff.
>The chain will just stretch over
>time and have to be replaced
>and the seals will just get
>brittle and break apart. If you
>let the chain go then it
>could jump a tooth or break
>and cause real trouble. I actually
>have seen this happen (once). Bad
>valve seals will just make your
>engine burn a little oil.



so how much is a timing chain, and the labor to install it, and how much is a valve job?

 

Not a valve job, just valve seals. Valve seals don't cost anything ($5) but can take 2 or 3 hours to install. The chain is $40-$70 and about 3-4 hours labor.

 

>Not a valve job, just valve seals.
>Valve seals don't cost anything ($5)
>but can take 2 or 3
>hours to install. The chain is
>$40-$70 and about 3-4 hours labor.
>


We have some company trucks that have well over 150k miles(351's,all highway) and they DO NOT burn oil, or smoke a tad when starting. Are you sure that they GO OUT at exactly 100k? I have a friend who has a 72 F-100 with a 360 and about 174k miles and his truck to this day doesnt use any oil or appear to smoke upon start-up. He claims that the seals are factory. So does this mean that highway miles arnt that hard on valve seals? I have about 76k miles on my 93. Does that mean that at 100k I will need to replace the timing chain? How do you tell if it needs to be replaced?

 

Typical valve seals on a factory engine are made of a fairly cheap black rubber type material. There is no wear per say on a valve seal. Valves seals are not really seals but rather deflectors. Their job is to deflect the oil draining off the rockers around the valve stem and not allow the oil to run down the stem and into the combustion chamber. What happens though is they get brittle from constant heating and cooling. Over time they tend to crack/break and leak(around the actual stem). A good after market seal can be obtained that is a teflon type material and will last forever. Keep in mind that a few leaking valve seals is by no means a catostrophic failure and in itself does not warrant replacing per say. Just because a seal is leaking the valve in question may have very tight clearances and not allow hardly any oil so seep by. Also on older engines, the oil flow up to the rockers tends to be very light due to dirt/debris build up. No, valve seals do not self destruct at 100k miles. Just a good rule of thumb if you are looking to keep your engine in good shape is to check the seals because they may need replacing. The chain is a little more difficult to check. You can rock the crank shaft back and forth with a big socket and breaker bar from the center bolt on the harmonic balancer. You need a gentle touch. The idea here is to see how much rotation you can get in the crank shaft without the cam moving. This gives you and idea how loose your chain is. If your engine is timed several degrees off of spec this is another indicator that the chain may be stretched.

 

>Typical valve seals on a factory engine
>are made of a fairly cheap
>black rubber type material. There is
>no wear per say on a
>valve seal. Valves seals are not
>really seals but rather deflectors. Their
>job is to deflect the oil
>draining off the rockers around the
>valve stem and not allow the
>oil to run down the stem
>and into the combustion chamber. What
>happens though is they get brittle
>from constant heating and cooling. Over
>time they tend to crack/break and
>leak(around the actual stem). A good
>after market seal can be obtained
>that is a teflon type material
>and will last forever. Keep in
>mind that a few leaking valve
>seals is by no means a
>catostrophic failure and in itself does
>not warrant replacing per say. Just
>because a seal is leaking the
>valve in question may have very
>tight clearances and not allow hardly
>any oil so seep by. Also
>on older engines, the oil flow
>up to the rockers tends to
>be very light due to dirt/debris
>build up. No, valve seals do
>not self destruct at 100k miles.
>Just a good rule of thumb
>if you are looking to keep
>your engine in good shape is
>to check the seals because they
>may need replacing. The chain is
>a little more difficult to check.
>You can rock the crank shaft
>back and forth with a big
>socket and breaker bar from the
>center bolt on the harmonic balancer.
>You need a gentle touch. The
>idea here is to see how
>much rotation you can get in
>the crank shaft without the cam
>moving. This gives you and idea
>how loose your chain is. If
>your engine is timed several degrees
>off of spec this is another
>indicator that the chain may be
>stretched.


I understand, I had my timing set at 12 degrees, so I dont believe I have any problems....yet.
Thanks for the info

 

How far off was it before setting it, and why did you set it? If it was off and it was never previously touched, it may be telling you something! About the actual time a timing chain lasts, would you rather replace chain ($40-$70) Or major engine damage from valve/piston collision. I'm not sure how tight clearances are in those engines,but I had an engine (Buick 3.8l) where the chain ripped all the teeth off the sprocket. I replaced the chain set, but the metal shavings were already throughout the engine and it blew about 2 months later. I guess it could be called cheap insurance.