427 Ford Blow-by

The port engine on our Commander 42 always had a blow-by problem, especially above 2000rpm. At WOT, the amount of smoke pouring out of the rocker arm cover vent was truly astounding. After doing a bit of checking around online, I learned that 427 Ford engines are known for blowing a hole in a port that runs through the intake manifold from #1 to #8 cylinder exhaust valve. The purpose of the port is to quickly heat up the carburetor when it’s cold outside—which tells me Chris Craft probably should have spec’ed out something else for marine use. When my port engine bent a pushrod in 2012, I decided I might as well tackle the intake manifold problem, too.

2020 Update: The same push rod bent again, as did the one for Cylinder 6. Both intakes. So I pulled both cylinder heads and found very sticky, nasty carbon goo on the intake valves and gumming up the intake valve stems. All eight valves had this problem, caused by the previous owners just not using the boat enough. The gas goes bad, then it causes all sorts of valve train and other problems. I cleaned the goo off the valves and valve guides, lapped the valves, installed new valve seals, then reassembled the top end As you'll see below, she runs great!

The work begins by stripping the top of the engine-the valve covers and carburetor come off easily enough. Next, drain the coolant entirely (there’s a drain valve on the side of the block opposite the starter), then remove the coolant reservoir. With the reservoir out of the way, access to the coolant circulating pump bolts is still not good; fortunately, there are only two of them. With the bolts out, pull the pump free of the block and remove the thermostat.

Next, note the installed position of the distributor rotor, then remove the distributor. It will be important to reinstall it in exactly the same position.

Next, remove the intake manifold bolts and loosen or remove the rocker arms, keeping track of which side of the engine the rocker arms came from.

Next, remove the pushrods, again, keeping track of the order in which you removed them. You’ll want each one to go back in the same hole. I think it’s odd that Ford decided to put the pushrods through the intake, but it’s a bit late to suggest alternatives.

Next, I broke the manifold gasket seal with a paint scraper in an area where the gasket mating surface isn’t critical. Tap it in a few spots and it breaks free.

The manifold is heavy, but not too much for one person. The underside of the manifold has a windage tray permanently attached to it. Clues that exhaust has been in the engine abound—there’s lots of particulates in the oily residue one normally finds inside an engine. I would have preferred to have the windage tray removable to help see if there is a hole in the exhaust port. I’m guessing Ford engineers didn’t foresee that particular failure in their engine’s future.

The windage tray in the lifter galley really gave additional clues that there was a significant exhaust leak into the crankcase. The particulates, iron oxide and products of combustion were abundant.

Et voila! The hole that was pouring exhaust into the crankcase! This really reflects poor engineering on Ford’s part. On the side that doesn’t have a hole, the material thickness in this area is around 1/8”, but only because the engineers opened up the port. They could have left it appropriately thick (i.e. as thick as the flange) so the wall would be as thick as they are in the cylinder heads and exhaust manifolds…don’t know what they were thinking.

Before opening the beast up, one theory for the bent pushrod was that boat engines don’t get run enough, gas goes bad and valve stems get varnished up. Sticky valves cause marginal pushrods to bend. In these pix, you can see extensive varnish build-up on the intake valves. It was a pushrod for an intake valve that bent, suggesting the theory was correct. I would have to remove the heads and do a valve job to clean off all the varnish. Instead, I just put a clean piece of cloth in each intake port behind the valve stem, then hit each one with carb cleaner, which removed the varnish quickly. Once the engine was back together, I ran some carb cleaner and Sea Foam through it.

After reassembling the engine with a section of stainless steel from a butter knife blocking off the exhaust crossover ports, the engine worked great! No more nasty smoke coming out of the valve cover breather, and the valves are all working properly now!

Fast forward to 2020, and I have TWO bent intake valve push rods on the same engine, and one of them is the one I replaced in 2012. Instead of just relying on Sea Foam and other magic sprays to degunk the valve stems, I decided to pull both heads and do it right, valve job and everything.

The two bent pushrods. Both were no longer in contact with the lifter or rocker arms. That gummy gas residue is tougher than steel.

I've been here before.

Major gummy gas residue on Cylinder 1.

Cylinder 6 is a bigger mess. That's it. Both heads have to come off.

Cylinder bores for 1-4 look good.

You can see that the head gasket had failed at the #4 combustion cylinder sealing ring. There's shiny metal where the ring was sealed well at the bottom of the picture. But on the left side, the shiny metal vanishes. This would explain a coolant loss issue I'd been dealing with.

Cylinder rings on #1 and #2 had also failed in spots. The seal had failed between cylinders and also between #1 and the coolant passage in the lower right corner. Good thing I decided to pull the heads and do this right.

Back home on the bench, I'm pulling valves. First thing I notice on Cylinder 1 is gummy goo around the intake valve guide.

Holy Cow! Check out the gummy carbon goo in the left picture at the valve seat for cylinder #1 when I pulled the valve! The picture on the right is after I'd scraped off the goo.

Cleaning the gummy carbon goo from the intake valves for cylinders 1~4.

Left pic: All the valves got lapped once the carbon had been removed.

Right pic: putting it all back together with new valve seals.

Pulling the outboard head was a bit more involved. It just didn't want to break loose. After bending the pipe trying to pull it up with a chainfall (left pic), I put rope in through the spark plug hole and rotated the crankshaft damper bolt until the crankshaft stopped moving (rope doesn't compress). Then I applied a bit of tension with the chainfall and bumped the damper bolt using a 3' breaker bar. Bumping is the key. Applying constant pressure only torques the bolt down tighter. Three bumps later, the head broke loose, as you can see in the right pic.

Whoa! So cylinder 6 was where the oil smoke was coming from. When the intake valve pushrod bent, the valve wouldn't open anymore. That created a lot of vacuum in that cylinder, so it was pulling oil down past the intake valve stem and guide. The bores all look fine.

I took the outboard head home and gave it the same valve job treatment as the inboard head.

Valve job done! Because of the tightness of the fit on the outboard side, I'm assembling the head and exhaust manifold log then will install them as a unit.

Cylinder head and exhaust manifold are ready for installation. I'm glad I have a chainfall hoist!

Lifters in, heads on and torqued, then I installed that 80 pound manifold, pushrods, and rocker arms.

By the way, blocking off the exhaust crossover ports back in 2012 really did wonders with keeping the windage tray clean. There was oil residue on it in 2020, but no hard particles like you can see up above when I first did that repair back in 2012.

I adjusted the valves, installed the covers and coolant system hoses and tubes, then came the carburetor and exhaust risers. Ready to test fire...

She runs like a champ! Very smooth idle. And shifting from neutral to forward or reverse only drops the RPMs by ~50 or so. Before, it'd drop 200 or more!