Motor is using about one quart of oil in about 100 miles. I did a compression test. I removed all the plugs and propped the carb open to WOT. This is what I measured:

CYL Reading
1 195
2 185
3 105
4 200
5 195
6 190
7 200
8 190

The motor has less than 5k miles since rebuild. All the plugs, even #3 cyl are burning clean with a light grayish color but oil on the threads. Checked the PVC valve and it isn't sucking oil, baffles are in place on valve covers. Previous owner had same problem but not as severe. I'm suspecting bad valve seals and improper installation of rings in #3 cyl. Definitely going to redo the heads but should I just replace the rings in #3 cyl? :confused: :confused:

 

Kinda hard to narrow down that problem until you actually dig into the block, but I would suspect valve seals, of course, once the heads are off, it wouldn't be much to redo the rings on #3 just for added security.

 

Did you try shooting some oil into #3? Believe if that raises the comp reading then you have bad rings, if it does not change it then look at the valves.

 

#3 is your problem, I would do a leak down test, it could be something simple like a valve seal or a leaking intake manifold.
...redvetracr

 

:withstupid:

 

Valve seals can not affect the compression reading. The only thing that can affect the compression test is bad/stuck rings, bent/burnt valves, a valve ajusted too tight or a head gasket. Compression does not start until after the valves are closed so anything upstream of the intake valve does not affect compression.

If you do a leak down test it will give you a direction to look. When you have air on the cylinder if you hear a hiss in the carb, it is a intake valve problem. If you hear a hiss in the exhaust, you have an exhaust valve problem. If you hear a hiss in the valve cover breather, you have a ring or head gasket problem. If you see bubbles in the radiatior you have a head gasket / cracked head or block problem. I doubt if it is a cracked head or block or you would be pushing out a lot of water with that much loss of compression. You will hear a small hiss in the intake, exhaust, and breather if everything is OK. But with that much compression loss one of those areas will be much more pronounced than the others.

If you do not have access to a leakdown tester you can buy just an adaptor to put air into the cylinder. Most parts houses have them for putting valve seals in. In this case you don't need a leakdown tester because you already know you have a problem in #3 cylinder. You just need a direction to look for the problem. With only 5K on the rebuild there is no need to tear the bottom end apart if all you have is a head gasket or valve problem. I would definately put air to that cylinder to narrow it down before I pulled it apart.

 

Hello

What type of compression tester did you use ?
A screw in type or just a push on type tester ?
With the push on type testers, you might not have seated the rubber nipple correctly onto the spark plug hole !
Would be too bad tearing all apart just to find out nothing is wrong. :crazy:

Good luck. Gunther

 

:iagree:

fyi, intake manifold gaskets have nothing to do with compression tests either, you can test compression without an intake at all.

:party: :leaving:


[Modified by mxzx turbine, 6:57 PM 12/27/2003]

 

I used a screw in type and did it three times. Each time the same results. Guess it's time for a leakdown, especially cyl#3.

 

I totally agree :) have done it many times myself.

 

Your "oil on the threads" finding might mean it is something a simple as valve cover gaskets. I know on my 427, a leaking valve cover gasket would cause the oil to run down into the wells where the sparkplugs sit and would get in the threads.

Also, check for blue smoke on acceleration and while coasting while in gear. Blue while accelerating might mean rings. Blue while coasting against the engine vacuum could mean bad seals.