Anyone know anything about chevy engines?

I know it does'nt necessarily matter on the engine because it seems like a general thing, but still, I think it could be engine specific, so I'll give it a try! I'm not having any luck with the chevy forum, seems no one knows!

Okay so my brother has a 400 small block in his 70's GMC Sierra. My dad had the engine rebuilt about 10 years ago. Although the truck was rarely driven the whole 10 years.

Now, my brother has had the truck with the rebuilt engine for about 4 years.

A while back, he decided to give it a tune-up and we checked the timing and adjusted the carb as well. At the time we had the dist. advance hooked up and set the timing to 8 degrees BTDC.

It was running primo...

Today he brings it over and its crap. He never got around to changing the plug wires so we gave that a shot. No go...

I talked to 4 diff. people and one being a professional machinist that rebuilds engines and they all said to unhook the advance and time the igntion to 6-8 degrees BTDC. When I hook up the advance it goes to about 25 BTDC.

Now with that said, he said last night it just started to run like crap. I noticed the difference when I looked at it and it is not good.

IT seems like its running only on 4-6 cylinders cause its running rough and missing. I pulled 3 spark plugs out and they all were black and had oil on the threads... The plugs were brand new, not even a month old.

He took me down the block after we adjusted the timing accordingly and it makes a ping noise on acceleration. Although, you could open the throttle up in PARK and it wont ping on you.

I have no clue on whats going on and never experienced this before. He said his exhaust burns oil on startup and then goes a way. At idle it does'nt smoke, but when you accelerate, it gets a nice cloud going.

To me that sounds like valve seals or guides.

Could the valves need adjusted, or is it just time to rebuild the motor? I don't understand what could have caused this because the motor is pretty much new. I'd bet not even 10k miles on it.

BTW, my dads two cents on it is that partly the problem is the fact of the o-ring going out for the accel pump. I noticed also that there is a slight whistling noise at the carb when revved up. I presume it could be this faulty o-ring because I sprayed the base of the carb and there was no vacuum leak. All I can say is that it is a 4-barrel edelbrock.

does the dist. have a timing advance kit in it? I know that has been a fairly common thing done on older chevys, but over time the springs that control the weights in the timing advancer go soft throwing of the timing curve.

If it's pinging under a load the timing is too advaced.

Also smoke under a load is more likely to be rings. valve seals and guides smoke on deceleration.

If it has been sitting for 10 years and barely driven then the seals most likely went bad. I had the same motor in my 76 el camino. The white smoke is from the valve seals, i had the same thing. If i were you i would get the top end redone, including the carb

-mike

sounds like its time to rebuild the heads.... sounds like the valve seals or guides are leaking oil down onto the pistons causing it to through oil up onto the plugs (which will burn the oil onto the plug) which could be making it miss fire in the cylinders... also check the distributer (the dizzy and the points on the cap) it will look a little burnt but it if has build up on it that will cause a miss fire as well.. hope you guys figure it out.... also how old it that carb? open the butterflies and see what it looks like under them.... should be a little black but again if theres build up then i would rebuild the carb or buy a different one....

yeah I forgot about startup, that would be valve seals/guide related. but that wouldn't allow it to burn oil under acceleration.

but also think about how many times this motor has been dry started after sitting for long periods, and was the oil changed at least once a year with the truck not being used? assuming it was ran on occasion.

I should probably clarify some points...

1. The tune up we did was less than a month ago. The dist. cap, rotor, spark plugs and wires were changed out. It was all he could afford.

2. The only way it advances, to my thoughts is by vacuum. Not sure if that means if there is centrifugal weights in it... I hope its not a points ignition though.

When he brought it over he told me it was pinging BEFORE we adjusted the timing. So when the advance was hooked up and I adjusted the timing the first time it was at 8 BTDC. Now, I adjusted it again the right way, and it still pings. Just under a load. You can rev up the truck with it in Park and it won't ping.

It will smoke whether or not it is in park or drive. I notice it does'nt smoke at idle, but when you rev it, it shoots out black, and blue. But when it goes back down to idle it will only be blue, and will smoke more than when revved up..

My brother has been driving the truck for about 4 years without a tune up since we did it. It has ran fine since 4 days ago. It is not because it has been sitting or else it would have been doing it since the first time he started it.

3. I'm thinking about doing a compression test because I had a response from a guy in the chevy forums. Not too sure what good thats going to do as I dunno how you can determine if its rings or valves...

4. The carb is just as old as the engine. It was built to be a racing motor, but the guy went a diff. route and gave it to my dad. My dad said that he definitely needs to replace the accel. pump o-ring.

I cleaned the carb with carb cleaner, but did'nt tear the carb apart, so it probably needs cleaning since I'm sure it is gummy.

5. When my dad had it, it sat most of the time but he occasionally started it. I don't know about an oil change and whether or not its been changed, etc..

It seems like its got a multitude of problems all in one, but I can't figure out why it would all the sudden run so horrible? My brother said his wife drove it the night before he said it was worse. To me, the wicked with of the west blew his engine!

...same wife, that destroyed the mazda truck I got from him. You can see the comparison photos in my garage if you really wanna see what kind of damage she can cause! LOL!

the HEI distributors use vacuum advance, but there is weights under the rotor that still control it.


so when did it start to smoke?

the timing acting up and the ping could possibly be the dizzy cause i had a 90 model that i set the timing 6 or 7 times,changed plugs,wire,cap,and rotor and it would still skip and miss i changed the dizzy and it all went away and the smoking sounds like valve seals and guides to me

I know alot about SBC/BBC . Pinging is not a huge issue and can be caused by the timing , but numerous other things . How long has truck been pinging for ? Do you the difference between a ping and a slight knock ? Not trying to be a smartass with that question , just trying to make sure

I will answer the rest tomorrow morning sometime after I get to work . I will give you a couple of options you can try to get the causes .

From what he said, it started to blow smoke the day it was running crappy. Before it never smoked and ran fine... This only started 4 days ago.

The dist. has the coil inside the cap. I've never seen this type of ignition setup before...

I been told that if the dist. is working and its adavancing, its fine...

The trucks been smoking and pinging for 4 days. Hes not driving it now though until we figure this out...

I've heard a knock, but not a ping before. This does'nt sound like the knock I've heard before. Although, I'm not too experienced in determining the difference. He says its a ping, and I lean towards it being a ping, too..