What should be done to a 351 CJ head?

[scgamecock]

When I pull the heads off what modifications should I do to get the most out of my 1972 351 CJ heads?  

I will definitely do screw in studs and guide plates for a .600 lift cam

What porting\polishing?

Gasket match both intake and exhaust?

Stainless one piece valves??  What brand?

Larger valves? What size?

Bee hive or cam matched springs?

Gasket match head gasket? Polish?

What else?

 

[c9zx]

Assuming you are doing a street build with stock stroke, remove the hump in the roof of the exhaust port and smooth the area around the upper bolt boss at the exhaust ports, use a narrow and long piece of coarse emory cloth to smooth the short turn radius of the intake and exhaust ports just above the seats. Don't try to reshape the short turns. Stay off of the seats. Don't remove a lot of material with a burr bit, "First, do no harm". If you use a die grinder turn the pressure down so you can control the speed and motion of the burr bit (Buckeye Carbide). Don't waste time trying to polish anything, it is just marketing for head porters and actually harms the intake mixture. Don't waste time port matching the intake. It is actually a good thing if the intake manifold is a bit smaller than the head ports, helps reduce revision at higher RPM. Use valves that are undercut and swirl polished (Ex. Ferrea 6000). Have a good 5 angle valve job done by a race machine shop, not the local parts house machine shop. Bee Hive/Conical springs are attractive because they reduce weight in motion making the valve easier to control at high RPM. The down side, compared to a dual spring, there is no second spring to keep the valve in place if one spring breaks. This has happened to me 3 times over the years so I use dual springs. It come down to personal choice.

 

[c9zx]

The 72 CJ heads already have the big valves, no need to go larger. Use quality valves like Ferrea or Manley. If the budget permits use the race valves (Ferrea 6000 series). Don't polish anything, waste of time and hurts the stability of the intake fuel mixture. Don't remove a lot of material, you don't need more volume, especially on the intakes. If you get out the die grinder and burr bits out, turn the pressure way down so you can control the speed and motion of the bit. All I will suggest using the burr bit on is the roof of the exhaust port to remove the "bump" and the transition to the upper bolt boss on the exhaust. Good burr bits are available from Buckeye Carbide. If you are not VERY familiar with what does and doesn't work on 351C 4V short turn radius don't touch them with a burr bit. I've seen several heads ruined by overnight head porters. If you want to improve short turn radius flow use a long and narrow piece of 50 grit emory cloth run through the port and work it back and forth until the radius is smoothed, STAY OFF OF THE SEATS! Don't waste time port matching. The port of the intake manifold being just smaller than the head port actually helps reduce reversion at high RPM. Have a quality valve job done by a race machine shop, not the local NAPA store. Bee hive/conical springs are attractive because they reduce weight in motion and make the valves easier to control at high RPM. The downside, compared to a dual spring, is there is no second spring to save the engine if one spring breaks. This has happened to me three times over the years. So, I use dual springs. If you want it to be close to optimal get a custom cam and lifters from someone like Mike Jones Cams. It is worth the extra money.  Chuck

 

[Don C]

+1 on what Chuck said. Additionally make sure you have hardened valve seats or have them installed. Make sure the head and block surfaces are within flatness specs. Do not polish the head and block surfaces. OEM soft surface head gaskets need a certain amount of roughness to seal. The head gasket manufacturer will specify the roughness average surface that should be used. Lay the gaskets on the block and make sure all of the openings are correct and that none of the coolant holes or oil drain holes are blocked.

 

[scgamecock]

I am thinking of just bringing them the bare heads and then assemble them myself.  The machine shop has to do the surfacing of the heads and machining for screw in studs.

Is it worth doing some things as a cost savings or better off let them do everything?

What does the machine shop have to do compared to what I can do?  

What constitutes a 3 angle valve job?

 

[c9zx]

The machine shop should clean and mag the heads, check/replace valve guides, machine the guides for viton seals, check spring pressures set proper installed spring height for closed and open pressures, surface the head, and do the valve job. Pick the right shop and let them do it all. Three different angles are ground on to the seat and the valve to promote better flow. Chuck

http://johnmaherracing.com/tech-talk/3-angle-valve-job/

 

[Ron Tanzi]

Good advice from everyone. The most important of all is to replace the valves being that the OE Ford intake valves are 2 piece induction welded and can fail catastrophically. New bronze valve guides are also a must.

 

[Omie01]

Just a couple side notes: I took my heads to a reputable head shop and they made one mistake. There is a step where the spring centers on, if you switch over to double springs, this step has to be removed. My head shop did not do this, which would have caused spring bind on the inner spring, luckily my engine builder caught this and did the necessary work. Whew!! Almost destroyed my engine!! So make sure the head shop removes this step, also, if you have bronze guides installed, remember to ask if they gave them proper clearance, cast iron  and bronze do not expand evenly so the guides have to have a little extra clearance to allow for the bronze expanding. if not done right the valve will get stuck in the guide. I also have learned that on a mild build bronze guides are not really necessary. Good luck!!

 

[Ron Tanzi]

Just a couple side notes: I took my heads to a reputable head shop and they made one mistake. There is a step where the spring centers on, if you switch over to double springs, this step has to be removed. My head shop did not do this, which would have caused spring bind on the inner spring, luckily my engine builder caught this and did the necessary work. Whew!! Almost destroyed my engine!! So make sure the head shop removes this step, also, if you have bronze guides installed, remember to ask if they gave them proper clearance, cast iron  and bronze do not expand evenly so the guides have to have a little extra clearance to allow for the bronze expanding. if not done right the valve will get stuck in the guide. I also have learned that on a mild build bronze guides are not really necessary. Good luck!!

Hi Omie01, I suggested the bronze guide inserts in terms of longevity. When I did an "economy" rebuild on my 72 351 2V in 1995 the parts store machine shop knurled my guides (half assed repair) but it worked for about 30K miles. When I pulled the intake manifold the intake valves heads were covered in oil crust. Upon further examination the valve guides were horrendously loose. I did second engine build in 2002 with more funds available and I built it hopefully for the last time.



Best, Ron

 

[rotorr22]

Just a couple side notes: I took my heads to a reputable head shop and they made one mistake. There is a step where the spring centers on, if you switch over to double springs, this step has to be removed. My head shop did not do this, which would have caused spring bind on the inner spring, luckily my engine builder caught this and did the necessary work. Whew!! Almost destroyed my engine!! So make sure the head shop removes this step, also, if you have bronze guides installed, remember to ask if they gave them proper clearance, cast iron  and bronze do not expand evenly so the guides have to have a little extra clearance to allow for the bronze expanding. if not done right the valve will get stuck in the guide. I also have learned that on a mild build bronze guides are not really necessary. Good luck!!

Hi Omie01, I suggested the bronze guide inserts in terms of longevity. When I did an "economy" rebuild on my 72 351 2V in 1995 the parts store machine shop knurled my guides (half assed repair) but it worked for about 30K miles. When I pulled the intake manifold the intake valves heads were covered in oil crust. Upon further examination the valve guides were horrendously loose. I did second engine build in 2002 with more funds available and I built it hopefully for the last time.



Best, Ron

 

[rotorr22]

Most Cleveland's back in the day (70's) would have worn guides by 40K miles. The knurled guides didn't last but a fraction of that.

I often wondered if it was just bad geometry, bad rocker design or both.

 

[Ron Tanzi]

As far as I can tell the valve geometry causes a great deal of side load on the guides, this side loading can be alleviated somewhat by the use of roller tipped rockers. This fact also led me to use the best guides available.

Ron