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OT Cylinder Heads

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  • OT Cylinder Heads

    Maybe you guys can give me some advice here.

    I've got a 400cid small block chevy. I tore the heads off the other day and found a puddle of oil in cylinder 8. I figured its most likely due to a leaky valve seal/worn valve guide. I still need to check the cylinder bore for out of round, excessive wear, and taper.

    I pulled the valve and found alot of oil on the stem and face of both valves, although it was worst on the exhaust which had a stock umbrella style seal. I measured the stem for wear and found it to be .3719" or .3721". They must be fairly new ... the engine was "rebuilt" but recently its been smoking quite a bit and i'm tearing it apart for storage until i can throw it in a rat rod so i wanted to have a look-see to figure out what i'd need to buy to turn it into a performance engine.

    Pulled the valves on cylinder 1. Measured for a stem diameter of .3409 or .3410. Again no noticeable wear, but why the difference in stem diameters!??

    Second, how difficult is it to drill out the guides for bronze inserts and how difficult would it be to drill steam holes in a new cast iron head? (Set-up i will obviously have to figure out myself based on my machines, but what about tooling? Do i need carbide for the cast-iron?)

    Also, does anyone have any specs or suggestions on determining whether or not i can re-use my valve springs, valves, and rocker arms? My heads are 333882 which are notorious for poor flow and cracking, so if my springs and valves are good, i wouldn't mind dropping 500 bucks for a set of new bare cast iron heads that flow better. I would then need to drill the steam holes of course.

    In regards to the above, what kind of heads should i be looking for? I want the biggest engine i can and still run on low octance fuel. That being said, some options are the torquer II's from world which are pretty mild improvement over stock or the mowtown classics from world which have 200cc intake runners and 2.08"/1.6" valves. Would that be too big for the 400 to live in the low rpm band?


  • #2
    The steam holes you can drill with a hand drill.400sb are not a high rpm motor with the stock crank,all factory cranks are cast.You should limit your rpm's to the 5500-6000 range.That being said,heads with 194 intakes should be fine for the street.

    Putting in false guides or guide liners takes some special tooling,none of it to be had very cheap.If your just doing 1 set of heads,take them to a shop and have them installed.

    Your different stem diameters are either a .030 over valve stem(common practice with big rebuilders or it is a sodium exhaust valve(truck head)with small intake valves.11/32(.3437)is the stock size of passenger car guides,3/8(.373) stock HD truck exhaust valve.The clearance for the valve stem should be ground into the stems,.001-.002 or thereabouts.

    You can drill cast iron with hss,cuts like butter.

    If the rockers don't have smiles in the valve end and the balls and seats show no signs of galling,then you can use them over.

    If it were my car and I was thinking of buying bare castings,I would cough up the other $200.00 and get the heads complete.Like you said,882 are not the best casting number to start performance work with...and don't forget about the rocker studs pulling out of those heads too.
    Last edited by Steeltoe; 05-30-2007, 02:53 PM.


    • #3
      sounds like some one did the over size valve stem trick. i would look for a set of 441 heads like said have them bronze walled. and use the .343 stock size stems.

      do not use the 2.08 or even the 2.02 intake valves they will kill low end. do put in the 1.60 exhaust valves.

      one other thing with the 400 over heating is a problem. the way to fix it is to drill and tap the rear of the manifold where it blocks off the water jacket in the heads and connect them the the front crossover. that makes if a full flow colling system.


      • #4
        Thanks guys! Just for the record, this will be for a non-street application. Soley to use up money ... or have fun ... funny how those seem to go hand-in-hand.

        As a side note, i posted this same question on a hot-rodding forum. I've gotten more replies on that forum, but i've got loads more useful info from you two! Thanks alot. Tons of great information here - it always impresses me.


        • #5
          Fasttrack, if guides are bad enough to leave puddles of oil in the cylinder the valve should really flop around in them, it should not be hard to spot. Regarding the smoking, guides with moderate wear, and or bad seals will usually give you a big puff of smoke on start up and then not smoke much after that. If tearing down anyway look for a holed or cracked piston, that can put oil in cylinder and even back up through the intake. If you are going to build a runner and want to run on low octane, seriously consider aftermarket aluminum heads before buying new castiron, you might even score a set used if you have time to look. I have been away from it along time, but I don't remember an umbrella seal on a smallblock, unless it was one with the teflon insert installed later.

          Hotrod published an interesting article a few yrs. ago on how they thought the smallblock should have been built. I am a little fuzzy on it, but I think they used aluminum 305 heads on a 400(might have been 350). They pulled over 400 hp on 87 octane with a mild cam and carb, and no detonation problems. Anyway it was an interesting read.


          • #6
            If you have the money,aluminum is the way to go.You can get a extra ratio point with alum over cast,all thing being equal.One more thing about drilling steam holes.You need to look at some 400 heads BEFORE drilling.The holes are 2 different sizes and one of them is at an angle so it hits the water jacket.

            I second looking at the pistons.The valve would almost have to be missing for a pool of oil to be on the back of the valves from the guide.The only time I have seen that much oil come down a guide was when the drainback holes in the head got plugged and the head would fill up with oil.Sounds more like oil in the pcv system then anything else.


            • #7
              If this is for a non-street application, I wouldn't bother drilling the steam holes. They are there to evacuate steam pockets at low rpm because the 400 has siamesed cylinder walls. They are also prone to develop cracks from the steam hole to the head bolt hole on the intake side.

              The only real way to determine if you can reuse valve springs is to have them checked on a valve spring checker. There is a spec at installed height and a spec at maximum lift. Most G.M. springs are shot by the time the heads need rebuilding. DO NOT try to increase the valve spring pressure on weak springs by using spring shims. You are asking for coil bind if you do and I don't even want to think about all the things that will break if that happens! Shims are used ONLY to correct installed height problems. Valve springs should be considered consumable and new ones installed when the heads are rebuilt.

              Just my $.02

              Last edited by 3jaw; 05-31-2007, 04:50 PM.
              "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill


              • #8
                Yeah hadn't thought about the advantages other than weight that aluminum heads offer...

                I've torn the whole thing apart now and the only problem with the pistons i found was the number 6 cylinder has a broken ring. Number eight was fine - bore checked out too. It was a little bit worn, but not horrible. This had been sitting for some time before i took the heads off and found a puddle of oil. SO... what do you guys think?