Had a guy suggest that while I have the Chevy 4.8 (a '07 motor, believed to have around 60,000 miles or so on it) out and before I drop it into my truck (a 1972 C10), I should swap the rear main seal and valve stem seals. The rear main seal is pretty obvious now that he mentions it: If it leaks after the motor is in, I have to pull the transmission. So I put another one in.
The valve stem seals, I'm not so sure about. They look like it would be relatively time consuming to change, and I'm not sure there is a huge advantage to having the engine out of the truck to changing these out. What are the odds that these are bad, and am I wrong at guessing that they'd be no harder to change once the engine is installed?
If it helps, Dad's 03 Silvy has 190k miles on the engine, no smoke. Boss's 'burb is pushing 290k and in the same boat. If it was an old SBC, yeah, replace them.
Always easier to work on an engine when it is on the stand rather than in the vehicle. Esp. in todays vehicles where they bury the engine under the dash.
iceracer wrote:
Always easier to work on an engine when it is on the stand rather than in the vehicle. Esp. in todays vehicles where they bury the engine under the dash.
Except it's going in to a '72 C10 where you can climb in with the engine.....
I think that engine is probably junk. I'll take it off your your hands for free and I won't even charge you a disposal fee. 
If you do it buy the BEST valve seals you can buy. I did a set in a 2.8L Fiero motor with decent brand name valve seals and the new ones leaked worse than the old ones.. I guess something must have been wrong with the valve stem/guide but I wouldn't skimp here.
How long has the engine been out of a vehicle? I'd base it on that. If it was in a truck that was crashed in 07-08, and its been sitting in a warehouse for several years, I'd do the valve stem seals. If its something thats only been out of commission for a few months, no worries.
Are the stems visible in the ports oily?
Not sure how long it sat, but we just got a boroscope at the shop, and I'll have a look at the valve stems with it. (The manifolds are still on the motor, and boroscopes are fun.)
No doubt I would run it as is. Only 60k? I would not touch the rear main also.
The rear main, you may be as likely to cause a leak if you don't get it installed just right.
The valve seals, I would not touch. Have never, ever, ever seen a GenIII or GenIV with oil consumption issues of any kind.
Knurled wrote:
The rear main, you may be as likely to cause a leak if you don't get it installed just right.
The valve seals, I would not touch. Have never, ever, ever seen a GenIII or GenIV with oil consumption issues of any kind.
I have. My 06 LR4 consumes a 1/2 quart of oil every 7k miles. It's sitting at 74k miles right now so that means in 7 years it's consumed 5 and a 1/4 quarts of synthetic oil.
