Modifying 4.3 cylinder heads, with pictures, Step 1,

[brokenwrench]

Flipped the heads over today and spent a few minutes at lunch time doing more machining. This machining is done on a 45 year old vertical mill that I bought for $200, The head is set up in a jig so that the spring seats are level and perpendicular to the machining head. This same machining can be done with a drill press or hand drill. The first picture is simply the work area painted to highlight the areas to be machined. Click to enlarge picture.

This first cut is done to shorten and narrow the cast tower that supports the valve guide. These cutters can be bought from Comp Cams, and numerous other valve trains specialty suppliers. A pilot goes down the valve guide (11/32) to centre the cutter then it is feed downward. This allows a higher lift cam without the retainer hitting the valve guide tower. It also allows an inner spring (dual spring) versus the factory single spring setup. Click to enlarge picture.

This photo below is of the valve spring seats cut down and cut wider to host a "bigger" valve spring. This allows more seat pressure necessary for a higher lift cam. The seat is cut to 1.440 inches in this example. These is the partner head of the pair in the above examples. Click to enlarge picture.

Here is a picture that demonstrates why these heads leak at the intake manifold gasket. The erosion is dramatic, this is from mismatching of the intake manifold versus the head, I cut these open to match them. I will repair this with epoxy and machine it smooth, after it is opened. Click to enlarge picture.

The machining bits can be bought in various combinations of cutting, some do two procedures at once, all said and done, these are now cut for top quality "positive" valve seals, a wider spring, more seat pressure and a dual spring. And the guide towers are shortened for a higher lift cam.

All these cuts are 0.020 short of finished height, this is because when I replace the valve guides a more precise cut can be made as there will be less clearance in the valve guide.

[doyoulikeithere]

Wow, this is an excellent write up.
Thank You
Excellent pix too!!
Will you need to use shims under the bigger springs?
I've heard the meat is a bit thin in that area...

[brokenwrench]

Wow, this is an excellent write up.
Thank You
Excellent pix too!!
Will you need to use shims under the bigger springs?
I've heard the meat is a bit thin in that area...

Thanks again:

I too have heard that but I have a cylinder head (4.3) cut into slices and it is not thin at all. I think with reasonable spring pressures there is no concern. This cut is small compared to springs out there, it however still touches the perimeter wall that supports the valve cover in some places. If you look you can see how the factory perimeter casting is close to the perimeter wall at one end and not at the other. You can also see how not all the cuts are concentric and some are missing a little meat on the outside. If you think of the pure physics of pressure, equal to force over area, a shim does not increase the load bearing area. Some tout their benefits as to better heat distribution under the spring, historically shims were used to prop up spring pressure on rebuilds, there is a company that made their entire name on this, let me think, ....."VSI", "Valve Spring Insert", started like 75 plus years ago. They still push their product. Sometimes it is unavoidable if you get a head that has been serviced several times the valves can be recessed into the heads and the installed height of the spring is too tall so shims make it up. This is why you should be very careful buying rebuilt heads from the local autoparts emporium. Sometimes the only new parts are the valve seals, some places are still knurling guides. There are of course factory limits on wear for springs, valves, guides, and you can be sure some unethical rebuilders let even that slide. But would you want a head that had parts that were at their service limit and at the maximum tolerances before the waste can? I can buy a rebuilt head (4.3) for $189, if I was in a pinch I would buy them for the castings and throw away the moving parts. But I might end up with some heads where some guy named Armstrong leaned on the downfeed handle too much and set the valves too deep into the head, then you have to put 12 new seat inserts in.

There is an interesting pattern to the casting of this head, if you look at the threaded holes for the rocker arm studs you can see that some of them are off-centre and some are not, then look at the valve seats I machined and you can see the corresponding casting shift reflected on those seats, two threaded rocker arm stud towers are perfectly centered and have perfectly round machined valve spring seats, the other (4) are all offset, the valve spring seats are incomplete and the threaded holes are offset in the tower. This is because the $40 per hour union guy setting the machine cast sand plugs in the mold set them in incorrectly. I have seen how it is done, the sand plugs are CNC designed and are perfect, the go together like Lego®. Only carelessness would give an imperfect outcome. This is why "back in the day" one guys 69 302 DZ Camaro would rev to 10 grand and go like stink and another guys would be a dog, when you add up all of these imperfections, it can make a profound difference item to item.

Next, ...., not sure, see what work is lined up

[brokenwrench]

Like the writeup.

The pictures look good, keep em coming. How much additional horsepower will the reconditioned heads add to a stock 4.3?

Good question, if I have time I will do a dyno swap with a pair of bone stock heads, if you look at aftermarket heads made by the big boys, RHS, World Products, Edelbrock, some of their dyno tests done by independent sources show 40 HP plus just by bolting on the heads with no other changes (SBC 350). This goes up dramatically with different cam and carburetor. There is no doubt that bigger valves and modified ports will make proportionately more power with a "bigger" cam, more compression and carburetor modifications. These heads would increase performance on a bone stocker, if you wanted more torque with a bone stocker I would not increase the intake valve diameter and would only do work in the exhaust port. On the V8 brother to the 4.3, there are articles in major "hot rod" magazines that show about 35 HP increase (V8).

If you have a high mileage motor with worn out heads, you have already lost a lot of power, even putting new rebuild stock heads on gives you a wake up call, like refurbishing your front disc brakes, you slowly forget how they used to work, so you make some very small upgrades and you think you have build a track car and have discovered the secrets to performance brakes. When I get some guy with no experience and lots of money who wants to spend $1500 on a "Brembo" rear brake package so that he can stop quicker I try and talk him into putting new shoes on his front brakes to restore factory performance. This often works.

[brokenwrench]

First my apologies about getting this done so slowly, once again life is interfering with pleasure. I am awaiting a "Black Beauty" reamer as my 11/32 valve guide reamer selection is at the end of its service life and I have promised to get new ones before I do another 11/32 valve stem diameter head. Have been waiting about 10 days for them and they are supposed to come "before the weekend". Anyway's, I am doing this whole procedure not in the usual order. These pictures today are taken after I have done a 5 degree top cut on what will be a five angle valve job. There are several advantages to doing this on this particular head, the primary one is that the roof of the combustion chamber is relatively flat and I can save a lot of time by cutting and polishing the roof this way rather than laborious grinding and sanding with a die grinder. There is also a benefit to creating a transition area for gas flow.

Almost all cast heads have a machining recess immediately near the valve seat and this is the most difficult to get at with a die grinder as once you hit the valve seat it has to be cut again. With a machined cut I can entirely control this. Using a tool bit also allows very precise control and consistency. I have cut these heads now within 0.001 inch of each other for depth below the "fire deck". When I cut the valve seat to enlarge it for a 1.60 inch valve, I get a perfect transition area. Note that the cut is now the entire circumference above the valve seat compared to the first cut in the first photo set I posted. The finish is nice enough to call it final, note that there are still casting defects in the metal. Since these are "innies" not "outies" there is no risk of "hot spots" and detonation, particularily with the final compression ration of 9.87:1

Hopefully I can get my new reamers and do the guides this weekend.

[doyoulikeithere]

Hey Bud, No rush!
Curious though, did your black beauty reamer arrive yet? Looking forward to the next installment in this saga.
These heads look great so far.
Thanks for sharing.

[oldsmoker]

Fabulous write-up.

I served my time as a toolmaker in England and hence spent many, many hours machining on different equipment.

I have to say, seeing freshly machined faces get me kinda aroused!...i have no clue about engine building/re-building but this is some cool stuff going on here, id love to pull my old lump out, take it apart and rebuild it some day.

thanks for the high quality pictures, that stuff is like p@rn for me!

[1Gary]

This O/P has done some really nice work on these heads.I have been debating with myself if in the name of just getting along I was going to withhold info about porting.For the benefit of the forum here is the post.

Back in the 80's with hand porting flow bench tests and dyno pulls where critical in porting.The flow bench part of that is still very important even today.Thing is duplication is almost impossible with "hand porting". Now that is a statement not limited to from side to side,but almost cylinder to cylinder.That hand porting did very as much as 10%.When you consider just a 4.3's output that 10% is alot.

Since then the advent of the 5 probe coordinate measure machine or CMM to create a program for a port has change the game alot because that program is transfer to a CNC machine and it has a duplication of 1/2% or less.So as Tony McAfee of Dart Machine stated you might gain in a less than programed CNC port job(pretty much a hand port job),but there are real possibilities that you would end up losing output.

The foundation of this is based on hrs and hrs of flow bench tests.Also need to remember not all ports on a head are alike.Example is the end ones on a head might flow completely different than the center one.Question is,isn't that the point of porting in the first place??.So to have the ability to build a program in three "D" then transfer it for machining is really important.The fact of un-shrouding a port is a good thing,but without having the R & D port to port "could" end up with a situation of uneven cylinders.Then adding in bigger valves might compound that.Also when you consider the limited material the OEM heads allow,where you do the work and what you do as exactly the same is a multiplying factor.

The last thing I was thinking about is having a SCR in the high 9's with cast iron heads and today's gas might mean with a knock sensor it is pulling out timing.Normally the ragged edge of SCR is 9.5.For me anyways,I don't think of my Astro and the use of the highest price gas in the same thought.

Again guys this is just a on balance post to the other side of this topic.Brokenwrench does nice work........................it is just there is more to that to consider.