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Custom Cylinder head building.. What's Involved?

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This started out as just an update on one of our own Hybrid member’s custom N-42 race head that we are currently working on turned into an informational session for those of you who don’t know what’s involved or have never seen what goes into building a custom L-series cylinder head. This is not a complete, concise progress report, by far, but it does highlight a few key elements that go into custom cylinder head work.


Phil Reith, a member of this forum, was kind enough to allow us to photograph and document the progress of his cylinder head and make that progress public. Phil is having us build him a custom N-42 for his N/A road race project.


This N-42 head started its new life having another shop in Phil’s local region perform all the initial welding. The injector ports and injector mounting holes have all been welded in. The center exhaust ports have had the outlets welded to more closely mimic the outlet size and shape of the other exhaust ports and the chambers have been welded in as well. Then Phil shipped the head to us for us to wave our magic wand over it. Immediately, we started out rough shaping the chambers, and then we had any deficits of material filled in by Russ Meeks, a local hot rodder here in Portland who performs our aluminum cylinder head welding. Then we replaced all the valve guides and seats, and gave the chambers a final rough shaping. This is where most of the work lies in the chambers and exhaust ports. Many hours of grinding, carving, shaping, measuring, checking, and carving some more go into this. Then we removed the press-in oil galley plugs, drill and tap them for ¼” pipe plugs, being very sure the front galley plug does NOT stick out into the path of the timing chain. We then go inside that forward oil galley and slot it accordingly to make sure the new screw-in plug doesn’t block off the front cam tower oil feed. Then we re-tap and chamfer all threaded holes.


Today we just finished up with all the valve seat machine work including 4 and 5 angles on the valve seats. The valves themselves received a 30-degree back cut, and the heads of the exhaust valves have all been radiused as well. For valve-seat work, we only use Sunnen VSC seat cutters. Valve-seat cutting systems, like the Sunnen set up (there are other seat cutter systems used in other shops that are comparable) offer the highest quality and most consistent valve seat work available. The old hand held stone seat grinders are a thing of the past. The carbide cutters of these seat cutter systems have all three angles ground into them, with different valve face widths. For N/A engines, we use .040” intake seat widths, and .060” exhaust widths. We then set up the actual seat diameter as wide as we can, to the valves being used, without compromising valve face margins. This usually allows us to open up the ID of the seat itself using the Sunnen “bowl hog” cutter since the OE valve seats typically are slightly smaller than what is optimum for air flow. From an air flow standpoint, this is effectively like going to a slightly larger valve without the larger “valve head” shrouding the valve to the chamber wall. Of course this is a minor improvement, but every little bit helps. In the case of this custom N-42, the intake seat ID’s were opened up approx .5 mm more than OE, and being as the exhaust valves are 1mm larger, the effective seat opening is now approx 1.5mm larger than it used to be. We then go back after all the seats are cut and add the 4th and 5th angles, if space allows. Typical L-series heads receive at least 4 angles, sometimes there is room to get that 5th angle in. Each and every seat is EXACTLY the same width, diameter, and depth as the other corresponding intake and exhaust seats within the head, and all seats are concentric to the valve guides within .0005”. We use the Sunnen seat cutter system in conjunction with a bridge port style mill, and as such, we “dial in” and LOCK the cutter head to each and every seat exactly to the valve guide angle in both “X” and “Y” and then center up on the guide itself to within .0001” to maintain valve seat concentricity for 100% valve seal. Just to be sure that we have that 100% valve seal, each and every assembled cylinder head has its combustion chambers vacuum tested to verify 100% valve seal before the head goes out the door. If a valve doesn’t seal 100%, the head gets torn back down and a thorough inspection is performed to identify why that valve isn’t sealing and corrective action is taken. Then the valve seal is rechecked. The Bridge port mill does take a little longer to get the cutter set up to the valve seat as compared to the air float seat and guide machines using the same cutters, but the Bridgeport mill is more precise and more stable than the seat and guide machines. In my book, that extra time spent setting up on a Bridgeport is a small price to pay for a higher

quality valve job.


These pictures are of PReiths custom N-42 head during the seat cutting stage, (seat cutter can be seen in the pics hovering over an intake seat). The chambers will get a final surface prep, (they will look much nicer than this when done), the head will get a final surfacing, then the chambers will be CC’d to within less than ¼ CC of each other.













During the initial seat cutting on cylinder heads such as this, which are utilizing a big lift cam, we will cut only one intake and one exhaust seat. Then we install an intake and exhaust valve using our “soft” springs with the retainers and keepers that are to be ran in this head. Then we measure spring installed height, retainer-to-valve stem seal clearance, etc, and make note of anything that needs adjusting. Then we go back and cut the valve seats to the depth that offers the least compromise without having to sink the valve too deep into the head. This allows adequate retainer-to-stem seal clearance and installed spring height. We also use spring shims of varying thickness to help adjust spring-installed height in order to maintain correct seat pressure. There are also a couple other techniques we will use to achieve more retainer-to-seal clearance such as machining down

the under side of the retainers, but only up to within .010” of the keepers, no further, just as we did on this set up (see pics below). FWIW, the Fel-Pro Ford V-6 stem seals allow for considerably more retainer-to-seal clearance (the valve spring retainer “WILL” crash into the valve stem seal with big lift cams), and the Viton rubber is much more resistant to degradation over time vs. the OE style polycarbonate seals.



These pics show the retainers as originally sent to us, and then modified by removing .050” material from the bottoms allowing for another .050” clearance between the retainer and the valve stem seal. This also lightens the retainers just a smidge. Note, the shorter Viton Ford V-6 stem seal next to an OE style polycarbonate seal, height mic, various spring shims, etc.






We hope you all enjoyed this little peek into the world of custom cylinder head building…

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On a per quote basis,


Hahhahha But for you Cary?… I make vety vety special deal…


Hmmm.. what are up to Cary? I can’t imagine you’d let someone else do your L-series cylinder head work?!?!?!

You’re the type that does all his own work, especially really "creative" L-series port work….



Contact me off forum…

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Do you lap the valves?






With the cutters, some shops don’t lap as they feel there really is no need if the valves are sealing, (vacuum tested chambers). On all of our high performance head work, I do give the valves a quick lap. It doesn’t take long to do and this process also gives the builder a visual indication of the actual contact area between the valve and the seat itself.

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so, that is an N-42 head welded up beyond recognition, and now it looks more like a MN-47 head. Why not start with the MN-47 in the first place?



I guess the best answer to your question is, it would take less over all work to bring an N-42 to this level vs trying to do the same with an MN-47.


The MN-47 is a round port head. The round exhaust ports, (with the liners still intact), are excellent for mild race and hot street engines. Also of note, All the round port heads, (N-47, MN-47, and P-79), have a smaller intake port. At approx 1/2 “ into the port, the port takes on a “D” shape, this helps bias the port centerline which in turn helps to aim the incoming air flow toward the center of the cylinder. This is great, but for maximum effort high RPM breathing, that smaller port is a hindrance to overall flow. These “D” shaped intake ports compliment the round exhaust ports nicely for mild to hot street, and mild race applications. Especially for a street engine that is asked to have some civility at part throttle conditions like having to drive through town back and forth to work and in stop and go traffic on your way to your favorite bonsai back road. These "D" shaped intake ports and round exhaust ports found on the N-47, P-79, and MN-47, in my opinion, offers the best performance with the least compromise in around town drivability and low end and mid range torque.

The square exhaust ports of the N-42, E-88, and P-90, allow for considerable exhaust port alteration allowing the engine to breathe freer at the higher RPMS, though low rpm performance will suffer as a result. The Intake ports of these same heads are also larger than the intake ports in the N-47, MN-47 and P-79, so less carving.


In short, the N-42 offers more “all out” potential, but at the cost of low rpm and part throttle drivability. This same radical head on a street engine that is to be driven around town would be a poor choice. This N-42 works best at WOT and above 4000 RPM, where as the round port heads do their best, (depending on how they are set up and built), from as low as 1500 RPM up to 6500 and will have decent manners around town.


Here is a MN-47 in the "rough in" stage of chamber work. This MN-47 is going on Roger Waylands hot street L-28 powered 240 Z with an Electromotive L-7 cam and Triple Webers.



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Nice pics, nice look at what it takes. making it look like the old "peanut chamber" L16 head. i think the code was A87, not sure. but it looked like that from the factory. too bad the L6 never got heads like that. just gotta make your own. Ive got an N42 head, but it dont look like that! HA ha!


oh dear god, please, please tell me you dont plan on running those 4 prong plugs. bosch plugs are utter garbage, in my experience.

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Looks like my post was lost from yesteday. Paul has all the bases covered, I just wanted to add that the head was actually a carbureted N42, without the FI notches. That's not the reason I bought it, but it didn't hurt since I'm using it with triples anyways. It was the one for sale on John Coffey's web site (not the sunbelt engine).


Also, the final chamber volume after Paul finished it off was 37mm, which with flat tops at a zero deck height will yeild just under 12:1 or 11.9. Paul mentioned the OEM flat tops actually protrude about .022" above the deck, and if that's the case, the compression jumps to 12.5.

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"too bad the L6 never got heads like that."


Ahhhhh, Mack! Check out the FIA Homogolation Papers for the 240Z! You will find a head like that, FIA Homogolated, back in the early 70's.


Not that one ever made it to THESE shores, but then again, what good engine bit ever DOES?

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Nice pics' date=' nice look at what it takes. making it look like the old "peanut chamber" L16 head. i think the code was A87, not sure. but it looked like that from the factory. too bad the L6 never got heads like that. just gotta make your own. Ive got an N42 head, but it dont look like that! HA ha!


oh dear god, please, please tell me you dont plan on running those 4 prong plugs. bosch plugs are utter garbage, in my experience.[/quote']





Aren’t’ you running a Maxima N-47 on a flat top L-28 in your daily driver/work Z car? Are you running the OE EFI, carbs, or aftermarket EFI on it?



Yeah, I haven’t seen one of those peanut L-4 heads in some time. I think the last one to come through our shop was some 4-5 years ago. In fact, I think the last one I built was when we built Mark Warners L-2.2 that powered his Bug Eye Sprite, Ron Tyler and myself built the custom tubular EFI intake as well. Dave Lum ended up with that engine some time after that and then sold it to someone back in either SC or NC currently running around in a 510.











That multi electrode is actually an old NGK that I still have laying around from the early 90’s, BP6EQ13, that I used to run in my old L-28 back in the day :) That plug is no longer in production. I don’t have any first hand experience with the Bosch Platinum’s though I have heard they tend to foul easy if the mixture isn’t be spot on, but as long as the mixture is spot on, I guess they work great, again no first hand experience here. We are currently taking a long hard look at carrying BRISK spark plugs for various applications including the L-series engines and the SBC. We will be testing few of their offerings before we commit to carrying them. So far, everything we have found on the Brisk spark plugs, (unbiased that is), has been positive…




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Here are some more shots of the valve train set up on Phils N-42.


The first picture shows the rocker adjuster bushings being installed and cylinder # 2 with its valves installed using the soft springs. The exhaust valve has a .190” “test” lash pad installed. What we are doing with Phils head here in these pics is setting up the cam wipe pattern on the rockers. Our goal is to bring the wipe pattern to the rear, or the pivot end of the rocker wiping pad by juggling lash pad thicknesses and then fine tuning that by grinding the tips of the valve stems themselves if need be. In the 2nd picture you can see the exhaust valve all set up ready to check the cam wiping pattern. We start out with the Cam manufactures suggested lash pad thickness and then go from there, (we have on hand, one each, of Nissans different lash pad thickness available just for this operation). If the wipe pattern isn’t exactly where we want it, we try either a thinner or thicker lash pad, depending on which end of the rocker the wipe pattern shows up. Then we apply another thin coat of the non drying Prussian Blue to the rocker surface, reset the cold valve lash again, and check the wipe pattern once more. When using the valve seat cutting systems, as mentioned above, the valve seat depths are very consistent and in most instances, we will use only one, sometimes two, lash pad thicknesses depending on whether we had to sink the exhaust or intake valve valves for one reason or another, or in the case of Phils N-42 here, we turned down the +3mm exhaust valves down to +1mm and left a thicker than original valve margin, which in turn alters the installed height, we will then have to use different lash pad thickness for those respective valves. After verifying each and every valve for lash pad thickness, we then engrave each rocker to mark its installation location, as can be seen in the 3rd pic, cylinder #6 Intake and Exhaust rocker, (6I and 6E). This also helps expedite future tear downs as the rockers are now marked for their respective cam lobe. Also, with large cams that have very aggressive opening and closing ramps such as Phils here, the wiping pattern will tend to cover most of the rocker surface as compared to a stock or mild camshaft, which means it is even that much more critical to make absolutely sure that the cam is not riding beyond the rocker pad surface on either end.



Remember, lash pads come in .010” increments. Now for the budget DIYer who may only do this once or twice in his life, there really is no need to purchase one of every lash pad for doing this, though you will need at least one solid lash pad, not the OE .120” that has dish in the bottom. Any how, you can use snippets of old feeler gauges stacked under the solid lash pad to simulate thicker lash pads. Get that extra set of feeler gauges from either a yard sale or just buy an extra set from the local hardware store or Sears, they are CHEAP! Using Aviation tin snips, snip a few pieces of .010”. You can snip some of the .020” as well, just don’t get it confused with .010” when doing your measurements. If you think it you might get them confused, then just use as many .010” pieces as it takes. Snip them small enough to fit inside the retainer on top of the valve under a solid type lash pad, (not the stock dished style lash pad). You will use these scrap pieces of feeler gauge to simulate thicker lash pads. I.e. a .160” lash pad with two pieces of .010” gauge underneath is equivalent to a .180” lash pad.. You get the idea.










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Paul, I was curious about your valve seat cutter. Does the pilot that runs through the guide have a taper? For concenticity, does the cutter rely on the tip or the entire length of the valve guide to locate itself?


Reason I am asking is during my porting job, I ground down the exhaust valve guides flush to the floor?/ceiling? in an attempt to get more flow. The exhaust bowls now have a smoother ramp down out to the port. I was told that I would need new valve guides installed since the cutter needs a flat guide top for a tapered pilot to work.

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Paul' date=' I was curious about your valve seat cutter. Does the pilot that runs through the guide have a taper? For concenticity, does the cutter rely on the tip or the entire length of the valve guide to locate itself?


Reason I am asking is during my porting job, I ground down the exhaust valve guides flush to the floor?/ceiling? in an attempt to get more flow. The exhaust bowls now have a smoother ramp down out to the port. I was told that I would need new valve guides installed since the cutter needs a flat guide top for a tapered pilot to work.[/quote']






Great question. The Sunnen Seat Cutters use a tapered pilot and as such, the pilot should not seat all the way down in the guide, (you can breathe a sigh of relief that, yes, your seats can be cut with no issues, unless, your valve guides are WAY short now?!). In fact, only the upper half of the pilot itself is tapered which keeps the tight fit in the guide during the cutting operation. In short, if your guides aren’t too short now, (chances are they are fine), then you did NO harm in cutting down your valve guides from the stand point of being able to cut your seats. The down side to shortened valve guides is accelerated valve stem and valve guide wear, and depending on how much shorter they are now, this is only minimal and won’t impact your project any more than any other high performance modification made to the engine package.


This picture shows a few of the components used with the Sunnen Seat Cutter system including our Exhaust seat cutter, (.060” seat width), the cutter body, bounce spring, and two pilots, one of which has an old Datsun L-series valve guide on it and the pilot is sticking through it at the optimum depth.










Now, when installing new “valve seats”, we DO need a flat shoulder perpendicular to the valve guide, for the pilot of that cutting system to rest on, just like “someone” told you, but no worries mate. Being as there are some OE Iron heads that don’t have a square shoulder to use, (just like your cut down valve guides), we have a cutter that allows us to cut a square shoulder just for these pilots. The picture below shows some of the tooling used for replacing valve seats including that cutter. All the goodies at the top of the pic are the following parts mocked up, consisting of the cutter itself used to remove to the old seat and cut the pocket for the new seat, the adjustable arbor that sets the depth at which we cut into the head itself, the Pilot with an old Datsun valve guide on it, and the bucket which clamps the pilot into the head. Below that is a bare pilot, (note the squared off shoulder circled in green), and below that is the Spot Face cutter which cuts a square shoulder in the head for the pilot to rest on. Of course, this leaves a nice little flat spot around the valve guide itself, but you can always go back in and blend that in if you so desire. Speaking of which, I’ve never had to use that spot face cutter on the Import .315” guides before, only on the Iron heads, Ford, Chev, Chrysler, .342” etc. I had better make sure we have a pilot for that spot face cutter that fits the smaller Datsun Valve guides for heads like yours... :-)



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