Rich in cylinders 1&2

[Texasdoc]

Any idea why this is happening?

I have been fighting this motor since building it a year ago. Performer RPM intake. Quick Fuel carb now but fought a holley EFI system for a year.

Why would cylinders 1&2 be rich while all the rest are normal/lean? They are on different sides of the intake plenum.

I can't tell if the picture is showing. Here is a link. https://www.dropbox.com/s/ta956l7f1oeoaok/Heads.jpg?dl=0

[keezling]

To be clear, are you saying same condition both EFI and carbed?

[Texasdoc]

I believe so, I never took the heads off with the efi, but had problems with it too. When I took these heads off today, I found 1&2 appear really rich while 3-8 look ok. My WBO2 that I have been using to help tune is on this side.

My problem with the EFI was that it kept fouling O2 sensors. The tail pipes are black. It won't idle at anything leaner than 13:1 measured on the sensor. I'm wondering if whatever is causing this is my problem.

[Texasdoc]

There was a little bit of oil in the intake plenum. After the broken springs fiasco, seeing the oil made me think I was having a problem with the valves, seats, or guides. I'm going to take the heads to the machine shop for inspection. Just can't figure out why one and two are so rich.

[undy]

Are you sure it's fuel, not oil?

[Texasdoc]

Good thought. I'm pretty sure it's oil in the intake. It's thick and sticky.

It may be oil in the cylinders instead of being rich (coming from the intake), but I don't know where that would come from either. I sealed the intake rocker studs, sealed the intake gasket (those looked good when taking off the intake). I have the adjustable PCV valve and the PCV catch can is mostly dry.

[undy]

I'd reuse the old head gasket and temporarily bolt/torque the head back on with valve train. I'd then do a compression check along with a leak down test too. Compare all 4 cylinder to one another. I would also pull the springs and the valves on 1 and 2 cylinder, inspecting the guides and seal for condition/clearances.

I really doubt it's a richness issue.

[Texasdoc]

I did a compression test two months ago and all were around 180 +/-. A leak down test showed one cylinder <5% (cylinder #7 that had the broken spring) and the rest <3% leak down.

So, either the intake gasket is pulling up oil into the runners from the lifter valley, the rocker studs are draining down from the top of the heads, or the valve guides/seals aren't working. I checked and replaced the intake gaskets a few months ago. I sealed the intake rocker studs when I installed them. So, unless I'm missing something, it must be the seals or guides.

I'll take the heads to the machine shop for inspection next week.

Any other thoughts? Am I missing something else?

[undy]

I'd key in on guides and seals, predominantly guides with excessive clearances. Leak down and compression tests don't always tell the whole story on oil control rings.

What's the history of the heads? New? reworked OEM?

[1795]

It could be the intake gasket or intake manifold. I had a Performer RPM that kept having oil leaks into #2 and would could the plug Tried to change gaskets twice, the second time we noticed that the intake manifold was a bad casting and would wobble side to side (lie a table in a diner) and when that gasket failed, ordered a new Performer RPM intake and it was square. Replaced it and 5,000 miles later everything was still running fine. No more fouled plugs or oil leaks.

[undy]

Originally Posted by 1795

It could be the intake gasket or intake manifold. I had a Performer RPM that kept having oil leaks into #2 and would could the plug Tried to change gaskets twice, the second time we noticed that the intake manifold was a bad casting and would wobble side to side (lie a table in a diner) and when that gasket failed, ordered a new Performer RPM intake and it was square. Replaced it and 5,000 miles later everything was still running fine. No more fouled plugs or oil leaks.

I agree, assuming you saved the intake gaskets, check for uniform imprinting on the gaskets, especially on #1 and #2 cylinder. Make sure you don't have a Fail-Pro print-o-seal.

[Texasdoc]

I'll check the gaskets - they were FelPro 1262 i got from AFR -recommended for these heads by AFR. Any specific SBF intake gaskets for use with AFR heads?

I'll also check the intake for wobbly-ness. I'll probably take it down to the machine shop too and have them mill it flat.

I will also check the angles on the block (and report those to the machine shop) to make sure the heads sit flat with the intake.

[1795]

Sounds like a sound approach. If the intake is a little off, much cheaper to machine it then to replace. A good idea to check everything to make sue that the fit is right.

[Texasdoc]

Originally Posted by undy

What's the history of the heads? New? reworked OEM?

See my other thread - high throttle miss.

I bought these new from Jegs. Apparently these were manufactured right around the time AFR switched spring manufacturers. AFR thinks I may have gotten a set that wasn't heat treated. We went over the geometry of the rockers and cam but didn't find anything amiss. I had two springs fail within 500 miles causing valve float and a high speed miss. I'm hoping it didn't do more damage - will see when the heads go to the machine shop.

[olddog]

I, too, suspect oil, rather than a rich cylinder. I'm not sure how an O2 sensor would would react to burning oil, but I expect it would report a richer burn.

A good carburetor, no matter how screwed up the intake runners, would get the same AFR to all cylinders. If one barrel was richer than the other, on a dual plane intake, then half the cylinders would be richer. It wouldn't explain two cylinders being rich.

The picture of the heads looks like oil carbon to me.

You want to make sure that the angle on the intake is correct. Also if the heads have been milled or the block was decked, the intake must be milled to match. In other words the intake may be wider than where the heads are setting.

Set the heads on the block with the old gaskets and torque them down then set the intake on with a gasket on one side and snug the bolts a little on the side with the gasket. Then measure the gap between the head and intake where the gasket is missing. Measure top of port to bottom of port on both ends. See if you are getting the same gap at all four places. Then move the gasket and bolts to the other side and repeat the gap check.

Check to make certain that the intake bolts are not bottoming out before they pull the intake tight. With the intake off screw the intake bolts (all of them) in by hand until they stop. Measure the distance from the head to the bolt head. Then measure the flange of the intake. I had this very issue, on a set of heads. In my case, I had the bolts torqued, and I could slide a 0.003" fealer gauge between the intake flange and the bolt head. Cylinders 1, 4, 5, & 8 were sucking in oil and the four end bolts were not pulling the intake down at all.

[Texasdoc]

All good recommendations. I eye-balled the intake and the gaskets but didn't see any specific abnormality. I will measure the intake against the heads at all four corners (top and bottom) and report that to my machinist. I remember he took off 0.006 off the block deck to square them.

I'll also check the depths of the holes in the head against the length of the intake bolts. May take 2 weeks for the turn around. Thanks for the recommendations!

[blykins]

My thoughts are the same as everyone else's. You're pulling in oil from somewhere.

This will also make it harder to tune the carb as the engine isn't as efficient as it should be, which would cause it to not produce the signal that it should.

If you're not using a PCV valve, then most likely you're sucking in oil. When you pull the intake manifold, you'll be able to see where it's coming from. Look for oil trails leading to/from the ports, indicating an area where oil is contaminating the intake gasket. Also look for oil on the heads of the valves, covering the inside of the port, or running down the valve stems.

If the port is oily, then the oil is probably coming from a failed gasket, or a PCV sucking in oil, etc. If the head of the valve is oily and you see traces of oil running down the stem, then you're most likely looking at a seal/guide issue.

[Texasdoc]

I have an adjustable PCV and the catch can is mostly empty. I did the measurements and the intake was mostly square - one corner was about .020 while the other 7 were less than .008.

The machine shop has the heads and intake. He is going to check the valves and guides and square the intake.

Brent, do you recommend using RTV on the bottom of the intake gasket to seal it from the lifter valley? I used RTV around the water ports but didn't apply any to the bottom of the gasket.

[blykins]

My guess is that your intake was not sitting square/flat and it was allowing oil to be sucked in. A .020" gap is a mile.

My SOP for intake gaskets is Dow Corning 732 in a caulk gun tube. I've been using it for over a year now and have fallen in love with it. On engines that are not going to see disassembly anytime soon, I will run a small bead around ALL ports, including air/water. I will then set the gaskets down and lay the intake down on the gaskets for a few hours. After I'm sure the gaskets are nice and glued down, I will pull the intake back off and lay another small bead around ALL ports, then lay my beads on the china walls. Dow Corning 732 is FE intake proof....so if it will seal and FE intake and oil pan, it will seal anything.

For gasket installation on engines that get freshened regularly, I glue the intake gaskets down in the same manner, but instead of silicone on top of the gaskets, I use a thin layer of white lithium grease.

[Texasdoc]

Excellent! That is the plan then.

This is why I love this site and recommend Brent to anyone needing anything. To have an engine builder give away his secrets for the benefit of all is outstanding.