1977 Vette/stock 350. When I bought my Vette last year, it had sat unused for nearly five years. Previous owner had inherited it and had no interest in driving it. I tuned it up as soon as I got it home, and it ran great. However, it does use a quart of oil every 300-400 miles. Only smokes a very little light blue smoke when you first start it up. After that, no smoke. I even had my wife drive it while I followed, just to make sure. It did have a small oil leak at the intake, behind the distributor. I removed the intake and resealed everything, and that fixed that. Last night I decided to do a compression check. It was getting late, so I only had time to check four cylinders. The four cylinders that I did check all read between 162-166 on my guage. I'm more familiar with outboard marine engines than car engines, but these seem like pretty good numbers on a 31 year old motor. If the other four cylinders have these numbers for compression, would it be safe to assume the rings are not worn out?? I'm just trying to figure out where the oil is going. The spark plugs do have some carbon build up, as if oil is getting to them. The guy at AutoZone mentioned valve guide seals as the possible oil burning culprit, because the car had sat up for a few years. Could bad valve guide seals cause it to lose a quart every 3-400 miles?? Also, is replacing the valve guide seals a hard job to do yourself, if it turns out to be the problem? Thanks for any help.
Kenny

 

Others will chime in, but here is a thresh hold screening...
Your compression numberrs looks good. Rule of thumb is no more than a 5% variance between highest and lowest readings. So if the other 4 cylinders come in about the same you are most likely OK. A leak down teat is more accurate and will tell what's really going on in the cylinders (do a search, thers are lot of posts on this subject). Start with the most obvious things first. My guess it's the valve seals. This is typical for small block Chevys. A 30 pluc yr old car with 30 plus yr old seals that are a rubber/silicone type od material. This is an easy fix, a few hours on a Saturday afternoon. Again doa search, there are tons of posts on this.
I would replace the seals, change the oil and drive the car for a few hundred miles to be sure the rings are not sticking or gunked up and see where the oil consumption is at that point. Most likely it will go away. If not. Then do a leak down test on the cylinders.
Best of luck and congrats on the Vette purchase. Mark

 

Change the valve stem seals. You can change the seals without removing the heads. You would need a valve spring compressor.And sparkplug fitting. If you have or can borrow a compressor.You need to fill the cylinder with compressed air to hold the valve up.

 

there's a good chance you won't find some of em because they've cracked off & washed away ... don't sweat this as OE seals're small & entirely rubber.

 

Yes, definitely change the valve seals and go from there.

 

Here's an update guys, I just finished checking the other four cylinders. All are between 160-165 except for the number 8 cylinder, back cylinder, passenger side. It's reading 140-142. Roughly 20lbs less than the other seven. Motor runs nice and smooth, no knocks, but obviously something not right with the one cylinder. What do you guys think?? Thanks,
Kenny

 

bump:

 

Since it doesn't burn oil [or doesn't appear to] after warm-up, it could be as simple as some carbon on the valves keeping them from sealing the chamber well. There are several techniques for getting any carbon deposits out of the compustion chambers. Some folks like to drizzle water into the carb when held at 2000-2500 rpm. That creates steam in the chamber and tends to dislodge carbon particles. Others [who have experience with it] claim that a product called Seafoam works similarly.
I would suggest that you try one of those methods to clear any potential deposit problem, then check #8 again. If it still shows low, it could be a ring problem... But I agree with the others; your symptoms point toward a valve seal problem for your oil burning at start-up.

 

Thanks for the advice. One other question. Will it do any harm to continue running the engine with the lower compression on the one cylinder, until I can replace the valve stem seals and investigate further the one cylinder? As I stated earlier, the engine runs nice and smooth, idles good, no knocks or misses. Thanks again.
Kenny

 

The only significant risk would be if one of the piston rings on #8 were damaged, but had not separated. If the ring were to fracture, it would do some damage to the cylinder wall. Try doing the carbon clean-out and the compression re-test; if it tests OK, your question becomes a moot point. If not, you make the call.

 

You can also squirt some oil into #8 and recheck the compression. If it goes up that indicates bad rings. If not then it could be a bad valve that's causing the low compression and bad seals causing the oil consumption.

 

i agree with this trick