gvcormack@watmum.UUCP (Gordon V. Cormack) (11/07/85)
Many, many people have posted articles to the effect that blue smoke on closing the throttle is a symptom of valve-guide wear, not ring wear. I think these statements are misleading. In my experience, the symptoms are exactly consistent with ring wear. There are a number of reasons why the smoke appears on closing the throttle. First, there is less fuel being burned, so that for a constant amount of oil getting into the cylinder, the oil-to-gas ratio is much higher. Second, the combustion is not nearly as complete, so the oil that gets in is not burned well. Third, as has been pointed out, the vacuum tends to draw more oil into the cylinder. This happens whether the leakage is at the rings or at the valve guides. I have not conducted a statistically valid survey (I am sure the other posters have not, either), but in my experience high oil consumption is almost ALWAYS caused by ring wear and almost NEVER caused by valve wear (5-0 on cars I have actually repaired). A couple of tests have been suggested. These tests can positively indicate ring wear, but if they are negative they indicate nothing. One test is the wet/dry compression. If your compression improves by adding a teaspoon of oil to the cylinder, the rings are certainly shot. A simpler test is to remove the oil filler while the engine is running. If puffs of partially burnt gas and exhaust come out, the rings are shot (there should be a slight vacuum, assuming your PCV system is working). I won't argue too strongly against replacing both the rings and the valve guides, but I think it is holding out false hope to suggest that fixing the valves alone is likely to cure heavy oil consumption. ASIDE: It has also been suggested that it is impossible to remove the oil pan on FWD cars. In the vast majority of cases, it is indeed possible, and is often easier than with RWD cars.
rls@ihu1g.UUCP (r.l. schieve) (11/11/85)
> Many, many people have posted articles to the effect that blue smoke > on closing the throttle is a symptom of valve-guide wear, not ring > wear. I think these statements are misleading. > > In my experience, the symptoms are exactly consistent with ring wear. ......... > I have not conducted a statistically valid survey (I am sure the other > posters have not, either), but in my experience high oil consumption > is almost ALWAYS caused by ring wear and almost NEVER caused by valve > wear (5-0 on cars I have actually repaired). ................ > I won't argue too strongly against replacing both the rings and the > valve guides, but I think it is holding out false hope to suggest > that fixing the valves alone is likely to cure heavy oil consumption. ............ One confusing part of the above article is whether valve guide wear or valve seal wear is being discussed. My own experiences, working with cars that are reasonably maintained, (oil changed regularly) is that rings are almost never the problem but valve SEALS very often are. Whenever my 1971 GTO started going through more than 1 quart of oil in 1000 miles, I knew it was time to replace the valve seals. One time I took the heads off thinking the valve guides were bad causing the seals to self destruct. The shop asked me why I bothered to bring the heads in as the valves were fine, just new seals needed. They recommended teflon seals for replacements. My 1980 Turbo Mustang, used to go through valve seals constantly due to the higher engine temperatures. The seals got brittle and cracked. The second set went bad so quickly that I let a mechanic convince me I had a cracked ring and I didn't recheck to valve seals until I had the engine disassembled. No cracked piston rings, but lots of cracked valve seals, and lots of cussing at the mechanic. The engine didn't even burn the oil, it got right past the seals directly into the exhaust manifold. 3 out of 4 exhaust port were wet with oil. My advice, try the valve seals first!!!!! Rick Schieve ...ihnp4!ihu1g!rls
ksbszabo@watvlsi.UUCP (Kevin Szabo) (11/12/85)
In article <728@ihu1g.UUCP> rls@ihu1g.UUCP (r.l. schieve) writes: >My own experiences, working >with cars that are reasonably maintained, (oil changed regularly) is >that rings are almost never the problem but valve SEALS very often >are. Whenever my 1971 GTO started going through more than 1 quart of >oil in 1000 miles, I knew it was time to replace the valve seals. I agree absolutely. I was in a situation that required the head to be removed. Just for kicks I lapped the valves and replaced the valve stem seals. Up to then I had been losing about 3/4 qt per 1000 miles. After the new seals the oil loss was unnoticable. I *had* thought my problem was uneven cylinder bore (the shop that rebuilt my engine said that this was a problem that would eventually crop up. I didn't rebore the cylinders 'cause it was a wee bit expensive for my student tastes). But, after 145,000 miles she's still going strong. Oh, yes, I forgot to mention the car. 1970 volvo 145-s, with B20 engine. Kevin -- Kevin Szabo' watmath!watvlsi!ksbszabo (U of W VLSI Group, Waterloo, Ont, Canada)