• Mechanic A says it’s smoking and therefore the valve stem seals must be bad. He replaces all the seals and it still smokes. He scratches his headI take it you don’t have much knowledge about engines.
The late 80’s- early 90’s GM TBI engines are notorious for valve seal degradation and valve guide wear. Known fact.
No in 1991 Chevys still had o-ring seals. Unfortunately these guides aren’t machined for really nice umbrellas. The use of the umbrella can help along with the o-ring.If I'm not mistaken the valve seals are the umbrella type. That's a cheap easy fix. But as Astro and benjy stated, if the guides are wore then seals won't help.
I purchased the vehicle in about April 2015. The odometer broke in about April of 2016. I had put about 6k miles on it in a year. My driving habits are the same so I would guess current mileage to be about 130k. The truck runs great other than smoking burning a little oil!i believe if the seals are like the older V-8 they are a poor design O ring type, better ones are available but if the guides are loose they need reworking + having a machine shop install bronze guides + modern seals + a "valve job" while heads are off if you intend to keep your ride. knurling is a cheaper but short lived option. otherwise how is the engine + how many miles??
Actually, mechanic ”A” already diagnosed the issue. Valve guides.• Mechanic A says it’s smoking and therefore the valve stem seals must be bad. He replaces all the seals and it still smokes. He scratches his head
• Mechanic B says that under low vacuum conditions such as driving up a hill, crankcase pressure may be increased due to a clogged pcv valve or worn rings thus causing the engine to smoke like a banshee.
• Mechanic C says that during high vacuum conditions such as coasting down a hill, the high vacuum causes oil to be sucked past worn valve stem seals causing an accident behind the driver due to the smoke screen.
• Mechanic D says never to ASSUME anything and to start from scratch diagnosing for ALL possible causes before JUMPING TO CONCLUSIONS and broadcasting it like an idiot.
if you pull the heads odds are you will end up with oil consumption because the friction lock between the bores and the head will be broken and the torque when put back on will be different, resulting in out of round bores.
If you use the same exact head gasket, and clean threads, and torque carefully you might get by. But factory torques all of them at the same time, you can not duplicate that.
Put on the umbrella seal and it will be fine.
i’m assuming here....the engine had the factory o-ring valve seals that were worn. The engine smoked on start-up. The mechanic removed those and replaced with umbrella seals only. Without the factory type O-ring seals the engine now smokes more using more oil. Factory Chevy valve guide bosses aren’t machined for umbrellas. Sure there are the generic fit all umbrellas but they don’t seal. Installing the o-rings in conjunction with the umbrellas will ensure the best possible outcome for your engine. Note for proper o-ring installation.... compress valve spring with retainer and hold, install o-ring in its groove, fit the keepers in their grooves and then release spring and retainer. the o-ring seals the retainer to the top of valve stem so oil can,t run down the stem. This engine oils the rockers through the pushrods and pumps onto rocker arm and retainer. if nothing is sealing the retainer (no o-ring) oil will follow the stem down and be drawn into the guide and smoke...So, before replacing the umbrella seals, the truck only smoked on start-up. Now it seems to be smoking all of the time. What about replacing the umbrella seals would make it start smoking all of the time?
Actually, mechanic ”A” already diagnosed the issue. Valve guides.
Just about every post on this thread supplied somewhat LOGICAL alternatives to the valve guide diagnosis. Replace the valve seals.
There is no other common sense alternative to a 20 year old vehicle burning that much oil that has ready been diagnosed as valve guides. You can’t replace or repair the guides without exceeding the value of the vehicle. You can’t replace the rings without exceeding the value of the vehicle. And most importantly - aside from it already being diagnosed - is that valve seal failure on these vehicles is very common. The logical, and really only choice the guy has, is to replace the valve seals or scrap the vehicle...or drive it till it blows up.
Mechanics B-D provided some half decent modifications to a valve seal on this particular engine (umbrella and o-ring together).
So, instead of calling everyone idiots, why not just throw your PCV valve idea into the mix? Because at least a $5 dollar PCV valve would be a cheap alternative to a situation that money shouldn’t be thrown at.
I take it you don’t have much knowledge about engines.
So, before replacing the umbrella seals, the truck only smoked on start-up. Now it seems to be smoking all of the time. What about replacing the umbrella seals would make it start smoking all of the time?
I came to the conclusion that the valve guides were bad because he told us that a technician told him they were.@doublebase: Thank you for noticing my little joke regarding mechanics A through D (those who have taken and passed A8 and L1 will get it).
To answer your original question (IIRC it was to the effect of "what have you done to assist", before you edited your above quoted post). The answer is simple: to provoke some thought.
You state in your quote: "Actually, mechanic ”A” already diagnosed the issue. Valve guides". Please explain to everyone how you came to the conclusion that the engine has bad valve guides, especially since the OP originally stated in post #1:
"I replaced the valve stem seals ony (sic) 1991 K1500; 4.3 V6. The mechanic stated that the valve guides are bad"
"...The engine seems to be smoking as bad as before or worse"
As I've quoted @otis24 above "So, before replacing the umbrella seals, the truck only smoked on start-up"
This quote from the OP, was post #24. This is the only time it was mentioned when the engine smoked (originally), making it impossible to determine before this point exactly what was causing said smoke condition or when it occurred. @mk378 mentioned that "If it smokes worse when you floor the gas (while driving), and keeps smoking as long as you keep it floored, the problem is the rings" Given the information originally supplied by the OP in post #1, this line of thought a possibly correct cause, as low manifold vacuum and higher crankcase pressures under these conditions may contribute to a smoke condition.
Granted, my posts sometimes may seem a bit abrasive, but nothing personal against anyone here, there are obviously some very smart and experienced people here on the BITOG.
@stower17 quoted post above is simply ignorant. @doublebase, some fractured logic in yours, but don't take offense, a lot of "mechanics" wouldn't know a pcv valve may cause a smoke condition under the right circumstances, and I never mentioned anything about Mechanics B-D providing some half decent modifications to a valve seal on this particular engine in my little joke above that you quoted.
PS: @otis24, you're right for not trusting your "mechanic", who obviously didn't fix your issue, and then seemed (from what you've said, unless further testing was done that you haven't mentioned) to blame the guides when your vehicle smoked worse than before.
Here's something I found online, although you may want to find a more experienced mechanic for future repairs. Good luck with your 4.3, I've always loved those:
Hey guys, like the title says. I have much more smoke out of my 88 350 tbi. Replaced all the seals last weekend and thought it was fine. Now it smokes like I'm having a bbq! I'm thinking maybe the intake ones came loose off the guide and are riding on the valve? Won't be able to get back in it...www.gmt400.com
My apologies, I can completely understand how reading comprehension isn’t everyone’s forte. Next time I’ll try to talk slower so you can understand.@Hal-9000 my post isn’t ignorant. Everyone that has posted to this thread has given very solid advice. The only thing you’ve done is try to mock and discredit our recommendations. Blowing smoke on startup is always a sign of worn valve seals/and or valve guide wear. A cloud of blue smoke on acceleration after the engine has been idling for some time is also a sign of bad valve seals. Sure, it could be worn piston rings, but that would happen all the time during engine operation.