Advice on Rebuilding a Cylinder Head - 1949 Roadmaster 320

[Dan O]

I need to rebuild my head which is probably warped. The cylinder head that is - but you know mine is warped for getting into old car rebuilding.      I have it off and ready to send to a machine shop here in Houston.  I have an NOS gasket but that's it.  The engine ran alright without smoke and the cylinders are fairly free of gunk.  I think it has 90K miles on it. 

 

What all will I have to replace "as a matter of course"?  What is optional?  Any fancy machine shop tricks I should employ/pay for?  Should the valve springs be replaced or just tested and used?  Am I on a budget?  Not really for this job.  Why not do the whole engine while I am at it, you might ask.  Well, certain time and work space prevent that.

 

Also, any advice on choosing a machine shop in Houston will be appreciated.  I have been talking to the man at Super Heads who says he has done a few of these over the years.

Edited February 18, 2016 by Dan O (see edit history)

[DonMicheletti]

What makes you think the head is warped? Have you checked it with a straight edge?

 

What you should do is dependent on the measured condition of the valves, guides and if the head is flat or not. Also, the condition of the rocker arms and shaft have to be established.

 

You'll get lots of advise here from just lap the valves to replace everything!

 

Since you are not going to do the entire engine, you should be able to do just a valve grind.

As the saying goes, "never ask a barber if you need a haircut". A machine shop will probably advise you to change everything.

 

Step one is measure everything and compare against specifications and wear limits in the manual.

[NTX5467]

In consideration of the "design use" of the engine, not to forget that how it would have been done "back then" is now as antique and the engine is, BUT still applicable.

 

Valve springs will be checked for open and closed seat pressure.  Might just need a few shims, possibly.

There most certainly will be some valve guide wear.  Used to be that a shop would "knurl" the existing guides (which would include driving a specified-diameter tool into the knurled guide for sizing).  A more upscale method is to install bronze helicoil guide inserts. With a chrome stem on the valves, this combination is supposed to wear VERY well.

There will be some wear on the valve stems.  Just depends upon the area of the wear on the stem itself and the magnitude thereof.  Might be that used valves with the bronze helicoil guide inserts could have acceptable stem-guide clearance.  If the valves haven't been "cut" before and have enough "margin" left on the edge, they they can probably be "faced" and installed.  If too thin, then replacement is the only option.  Might check price of replacements for good measure.

 

The valve seats will need to be refreshed.  IF they might need to be "cut", then that could be problematic.  Just refacing should work, usually.  Key thing is that the seats have been cut too much with the result being the valve seat will be "sunk" too far from where it started from when new.

 

Make SURE they do the "surfacing" with a LATHE, not just run the head sealing surface over a "calibrated rotating rock" cutter.  With the lathe, the cuts will be much more even and accurate which can ensure that the minimum is cut that's needed to make everything "right".  Set-up in the machine is critical, though.

 

Of course, the first things would be to vat the head and such and check for cracks!  That would also mean new "freeze plugs" and such.

 

Might want to consider "port matching" the intake manifold ports to the manifold gasket.  Might not make much difference in performance, but it'll look nicer. "Visual horsepower" in many cases.

 

No fancy machine work really needed, just good and solid OEM-level stock things.  Anything that looks like it has "wear" needs to be looked at.  Pre-lube the valve stems upon installation.  Stock-type seals and gaskets should work fine.

 

When re-assembling to the block, be sure to use the correct torque sequence and values with a known-calibrated torque wrench. 

 

One thing I started doing a good while back on cork gaskets is to  get some hi-temp black silicone sealer.  Lay out the valve cover gasket on the bench, on some cardboard.  Apply a thin layer of the sealer to each side of the gasket.  Let it cure.  This will seal the gasket to keep it from wicking oil through it (prevents seeps on the fresh paint!).  ALSO makes removal, later on, much easier than if you use the time-honored "yellow gasket adhesive".  I also do the same "think coat" technique for thermostat housing gaskets and such, too.  It's worked well for me.

 

Please advise how things go.

 

NTX5467

Edited February 19, 2016 by NTX5467 (see edit history)

[smithbrother]

Lathe?, or do mean MILLING MACHINE.

Dale in Indy

[FLYER15015]

Dale,

I am sure he means a mill.

I don't want to be in the same block as that big old head swinging around in a 3 jaw chuck.

Mike in Colorado

[Barney Eaton]

I understood the valves would be surfaced on a lathe

The head would be done on a mill

[DonMicheletti]

Both the valves and seats would be ground. Any auto machine shop would have both these dedicated grinders.

 

You'd need a pretty big lathe to machine those heads on a lathe!!

 

I'd question whether they are flat or not first and not just go machining them.

[FLYER15015]

Yup, and if you really want to get down into the weeds, be sure and CC the head, just like the Pro Stockers do.

 

Then we can discuss "port matching" and polishing, to take proper advantage of that right angle intake manifold.

 

Mike in Colorado

[NTX5467]

Well, the "lathe" (as I'm calling it) is a sizeable piece of equipment.  The base is plenty big enough to secure a cylinder head to, even an inline 8 cylinder, where it is secured and leveled.  The round "cutting wheel" has individual cutter bits on it, which contact the work surface.  It turns somewhat slowly, as its arc travels from one end of the head to the other.

 

The "leveling" can be important as if the head is adjusted such that a larger cut is taken fron one side than the other, "angle milling" results, which on a V-8 cylinder head can decrease the combustion chamber volume rather quickly, BUT also can require the intake manifold surface to be cut appropriately for optimal sealing of the intake manifold.

 

This machine, which my machine shop operative surfaces heads with, has the "work" stationary as the cutter wheel moves.  NOT where the "work" moves as the ONE cutter makes the cut on the moving part.

 

Anybody still call an accelerator pedal a "footfeed"?

 

NTX5467

[FLYER15015]

Just to get our terminology right.

In a lathe, the work moves.

In a mill, the tool moves.

For the latter, think "Bridgeport".

I grew up in a machine shop at both J.I.Case, and John Deere.

Now I sell for a state of the art machine shop, with 5 axis CNC milling machines, that does a lot of automotive parts.

Mike in Colorado

Edited February 20, 2016 by FLYER15015 (see edit history)

[smithbrother]

YEP, you can call it a LATHE if you like, but it ain't.

NO lathe can MILL a cylinder head, PERIOD.

Ask your machine shop,

Dale in Indy

[60FlatTop]

Everything on that engine wore at about the same rate. The valve seats leak by some, the guides leak by some, the rings blow by some, the bearings are worn some. And apparently "ran alright and didn't smoke". Tighten that top end up and you will probably be known by your puffs of blue smoke coming out of the road draft pipe when you pull into an event. Watch for one at an event near you. I have two cars with completely rebuilt engines because the needed everything. The others have only had what was broken fixed. Actually one car has one repaired valve. When it came back from the machine shop that replaced the valve because in another life a piece of piston got wedged in and scratched it, I hand lapped the fresh machining to help duplicate the wear on the other 15 valves. My policy is just to fix what is broken or the balance of all the worn parts is disrupted.

 

BTW, I'd have the head blocked up in a surface grinder if I had to skim it. One with a big magnetic table. Reminding me of my days as a millwright  with old John the railroad yard holstler and mechanic. He'd grab his hammer and throw his tongue over his shoulder and run off to fit anything.

Bernie

[DonMicheletti]

Flat Top is right on. You cause more problems than you cure.

 

Having worked around steam locomotives, he is also right on with their mechanics!

[Bob Engle]

Most engine rebuild shops have access to a Blanchard grinder.  It has a flatbed to mount parts on and has a large (about 12" diameter) rotating head that has grindstones mounted in the head.  Most shops now use diamond stones. The flatbed has ways and the bed traverses under the rotating head.  By  the way the blanchard grinder is the best way to resurface a flywheel as it does not produce circular cuts like a lathe would do.

 

Bob Engle

[pont35cpe]

Dan O, once all your repairs are done and the head is torqued, when installing the rocker assembly be sure to seal the threads of the short bolts, otherwise oil will seep past the threads and puddle around the spark plugs.  It took me a long time to realize why oil was around the plugs and where it was coming from..   Good luck, Tom

[Dan O]

Thanks for all the interesting advice!  I would not even do this if I had not blown a head gasket.  I suppose it's warped.  We shall see when I am able to check it.  I do somethings myself, somethings I leave to my shade-tree mechanic.  , 

 

NOW, what is a good source for valves, springs etc if I need them?  I have not tried sourcing these except thru a simple Google search.  Any recommendations?

Edited February 23, 2016 by Dan O (see edit history)

[DonMicheletti]

If the '49 is like the '38's, be sure there is a sealed stud in the rear hole on the pushrod side. On the '38, the hole is tapped through to the water jacket. Removal of the stud allows access to the temperature gage bulb. If you put an unsealed bolt in there you'll get water in the oil since the water can get past the unsealed bolt and into the rocker are area and into the pan.