Inliners International Forums General Discussion Engines Running lean on #5 cylinder?

I'm working on a 64 Nova with what I believe is a 230 according to the casting numbers-block 3850817, head 3824437. The bore is 3.905" so it looks to have been bored once. Compression was 120-125 psi in all cylinders before I took it apart. The piston in #5 looks to have a white residue like it's running lean. Why would only one cylinder be lean-bad valve stem seal?

Also, the exhaust valve in #2 is seated a lot lower than all the others. The rest are flush or above the level of the casting around it. Does that mean anything? Any observations would be appreciated.

This picture shows 3, 4, 5, & 6.

This shows the valves on #1 & 2

The white color could be considered , less oiled. Maybe the rest of the cylinders were getting excess oil past the rings or valves guides. Cylinder 5 is the only less oiled one.

Sounds like time for a overhaul of the head at the least. Maybe a rering if the bores look nice.

Cylinder 2 is a example of needing hardened exh seats.

Nice pics!

could be lean. My 230 had extremely worn valve guides and very low spring tension. #6 was leaking past the exhaust valve when running, leakdown test did not reveal it as the valve had time to "seat". I had hardened seats (1970 car, suspect 68 engine) but the valves still needed to be shimmed tighter, as if they had pounded into the seats. I also had two worn out cam lobes. You may have similar issues causing a difference in combustion

THE VALVE IS SUNK IN THE HEAD, COMMON WITH LEADED GAS ENGINES, YOU SHOULD HAVE HARDENED EXHAUST VALVE SEATS INSTALLED AND REPLACE ALL THE EXH. VALVES AT LEAST. # 5 CYLINDER IS PROBABLY DOING MOST OF THE WORK NOW AND HENCE RUNNING A LITTLE HOTTER. TIME FOR A REBUILD........ GO 250 IMO

I am going to throw out a general observation I have seen over the years. If you are running one carb. 5 and 6 and 1 and 2 will burn lean. No#3 and 4 will run rich. A two carb. set up will help relieve the problem and a carb. on each port will do the best. A manifold with equal length runners are suppose to take care of the problem. Don't really know. OK now everyone can start throwing the rocks. lol. Hud

MAKES SENCE HUD

Hud, that makes sense, but I think Tom is probably on the right track. When I inspected the plugs all of them looked sooty except #5 which was a perfect carmel brown-it didn't look lean at all. Up until very recently it had been running with a stock 1bbl Rochester. I put a 2bbl progressive Weber on not too long ago, but due to some exhaust and trans issues decided to pull things apart to inspect.

Anyone have a lead on a 250 in Arizona? Or possibly in So. Cal.? The car is a 64 Nova, 3.08 rear end, TH350, by the way.

it might even be a small water leak (equals a watered down mixture and a little steam cleaning, thus a lighter colored combustion chamber)

In the first photo - is that a drop of water on the edge of #5's bore at about 4 o'clock? The shot of the head shows more chunky crud in its chamber than in its neighbor.

Preacher, that is a drop of water on #5 but probably got there when I lifted the head off. The amount of 'chunky crud' is deceiving. Because it's black in the other cylinders it looks like there is less of it, but in fact there is probably less in #5 than the others.

Since you didn't know if this condition was occurring prior to swapping carbs, it was either doing it all along and you just didn't know it, or the new carb wasn't jetted correctly and caused the engine to be leaner than the OEM carb. You need to find the problem before rebuilding or it will likely be lean again on the restart and continue this cycle of damage.

The new carb was lean but I had a wideband O2 sensor that was used to get it close. If the carb was lean would that show up in only one cylinder though?

NO

I agree,it should'nt be the carb, nor the manifold because #6 aint the same, has to do with something downwind of the manifold-something different in that cylinder or combustion chamber than in #6. The gasket marks in the picture look pretty normal as best as we can see from the pictures. Could possibly be different sealing of the rings, or valves allowing one chamber to be more black or carboned with perhaps oil than the other. The condition of #5 dont seem too startling or extreme though. Do we know anything about the cylinder compression readings (too late now to check), but maybe when the head is back on record the readings just for record's sake.

Whoops, they were all 120-125 lbs like you stated--well, that beats me! Now after rereading the first post i'm confused -- if the block picture is really cyls 5 and six, and is the head shot really 1 and 2, OR are they the combustion chambers for the cyls (5 & 6)??

Here's another thought based on nothing. If #5 exhaust valve moved that far into the head the tension on spring was less. On the intake stroke it could have been pulled off the seat enough to allow some exhaust back into the cylinder creating a leaner hotter charge.

Preacher, the pictures are labelled correct: the engine shot is showing from left to right cylinders #3-4-5-6, the head shot is showing the combustion chambers from #1-2. #2 is the cylinder with the exhaust valve that is hammered into the head.

I think what I will do is take the engine out and do a more detailed tear down to try diagnose things better.

I AGREE SHOT

OK, I got it the valve that was letting the exhaust into #5 is in #2. Rebuild that sucker and make sure the the head and deck are flat.

ALSO HARD EXHAUST VALVE SEATS...............

Ok, I did some more probing. I've found that the a couple of the exhaust valves have a red residue like rust on them-#5 is the worst and #2 is next.

This is a picture of #4-5 exhaust valves


This is a picture of #2-3 exhaust valves


#1 & 6 exhaust valves are black with virtually no rust residue on them. #5 is the most "rusty". Also, as can possibly be seen in the photos #5 has the least carbon buildup.

What does the rusty residue mean? Does it spread anymore light on the previous pictures? Thanks for all the help guys.

Just so we're all on the same page, I will definitely be doing a valve job on this no matter what-bigger valves, screw in studs, roller rocker arms, etc. I wasn't planning on doing the bottom end but I will if it needs it. The car will not be raced, I just want a fun driver that can get out of its own way and get up the hills around northern AZ where I live.

THE BOTTOM IS JUST AS BAD AS THE HEAD, DO IT RIGHT OR LEAVE IT ALONE JMO
BOB

Ok, so you don't know what the red stuff is either I take it...

It reminds me of what engines that burned leaded fuel used to look like.

THE REASON THE VALVE ARE SUNK IN THE HEAD IS BECAUSE OF RUNNING UNLEADED FUEL IN A HEAD MADE FOR LEADED GAS. TO SOLVE THIS PROBLEM HE NEEDS TO INSTALL HARD VALVE SEATS IN THE EXHAUST VALVE SIDE OF THE HEAD.AS FAR AS SOME LOOK SUNK THE HEAD MIGHT BE JUNK