Nailhead professionals, I was disassembling my 401 and found some light marks on the pistons left there by the intake valves. The rod bearings are good, no loose rods, wrist pins are good, so the only things I can think of is overrevving of the engine, weak springs, or a bad timing chain to get the valves to contact the piston. Pushrods are straight and I don't have any broken springs. What are the normal clearances for valve to piston on a 401? Last question, what brand of head gasket do you recomend? The originals where the very thin steel gaskets. I know the Feldpro blue are going to be double the thickness. I guess this would cure my piston contact problems, however, my compression would suffer. What do you think would be best? Thanks Doug
Definitely stick with the factory style gaskets--you will loose alot of compression going to the new style. Engine could have had a sticky valve at some point in its life if it sat a long time without running, and when it was started up, the valve hit the piston and left the marks.
I agree. The modern gasket will lower compression to about 9.2...not much need for domed pistons at that rate, ha? But don't forget, if it is a driver you could use 87 octane..Steve
I have to disagree with you Brian on the head gaskets. Unless you are planning on always running super premium, I'd opt for the thicker head gaskets. This is a matter of personal choice, but my own experience is that even with the thicker gaskets, 93 octane almost pings with my timing set to specs so I backed it off a few degrees. I'd hate to think of what would happen if I used the thinner gaskets. I'd rather waste a few HP than take a chance on cracking a piston. :bglasses:
Re: Pinging To Nailheadina67, I noted your comment about pinging...and also see that you're running dual quads. My 401 with dual quads used to ping all the time (on hard acceleration that is) on 93 gas. To compensate, I used to retard the timing. I ultimately discovered that the way too lean factory secondaries were the culprit. This problem was made worse if you used high flowing air filters (like K&N's) instead of the factory breather which was so restrictive it was hard to get TOO lean. Increasing the secondaries from .092 to .098 all around improved the A/F ratio, eliminated pinging and improved the 1/4 time substantially. May not be applicable to you...just thought I would pass along the experience.
2x4 I think theres alot of cheap gas out there, what would you think of running two 650's on a dual quad the original carters? Also is ther a difference in the 401/425 cam single and dual set-up?
Very little difference between factory single 4bbl and x engine cams... The pinging in a non original 2 x 4 car might well be that the correct distributor was never part of the changeover. That's what makes the big difference. Don't have it and the timing'll never be "rite". Different weight and springs. See pic..LX setup un the right. Steve
When I had mine dyno'd it smoked a lot at high speed........I thought it was running too rich.........maybe it was the air cleaner? The jets are all stock and the float level was OK but after that I lowered them just a little. Never went back for a second run. Carmen set up the distributor for the dual quads as far as I know it's the correct curve. Thanks for the photos, I'll check to see what I have. :bglasses:
In response to the original post, I think the problem is most likely bad valvesprings. Easiest way to check would be to bring the springs to a local performance engine builder, and have them check the spring rates@installed height and max lift. I am not sure of the specs off the top of my head, perhaps someone could chime in with that info. It is also possible that your valve seats have sunk slightly into the heads, which would raise the valves enough to affect your spring pressure.
:3gears: Doug, If all the pistons have an "eyebrow" in them, I would suspect over revving and weak valve springs. If just a couple have the marks, I would suspect that the engine lost a timing chain at one time. If you know the history of how the engine was used, you could backtrack the cause that way. Hard to say what caused a prblem in a 40 year old engine if you don't know the engine. Good luck on the rebuild. Tim
Doug, I rebuilt my first nailhead when I was 17, and installed an Isky 'Super Magnum 310' cam. The instructions from Isky specified a minimum of 0.100" , and a desired clearance of 0.125". Isky further states if valve float does occur, it's the exhaust valve that is more likely to make contact with the piston.... You can get steel head gaskets and valve springs from Carmen Faso, or good replacement hp inner springs from Isky, and stock outers from Sealed Power (NAPA). With this cam, I had to have the forged 10.25:1 CR TRW pistons notched for valve clearance. Deck clearance was around 0.045", and I used composition head gaskets (about 0.040"?). I never computed the compression ratio, but the car still runs 13.40's :grin: I always wondered how much more power I could get out of it with deck and quench specs set to the minumum?????
Great info amd the factory specs Walt, Tim, Artie and the entire gang, Great insight, I was hoping that you would feel the ideas or thought I had might be in the right direction. The weak springs and any sunken valves might be the culprit along with a really bad chain and sprocket. The chain is REALLY streched. I do think that the exhaust valve would be the likely valve to strike with a bad chain as timing is late. The specs on the springs are: Outer @ 1.60 inches is 42 lbs and the inner is 25.5 lbs @ 1.69 inches. Thanks everyone, its always fun to talk about these engines Doug :3gears:
I think I have encountered a little valve float on my '55 264. Last night I wound it out a little, perhaps a little too much, and managed to bend the #1 cylinder exhaust valve and pushrod :shock: :ball: ou: ! You think a professional auto technician (A.K.A. -mechanic) would know better. The odd thing is that everything else looks fine. It also seemed to be a delayed reaction--I didn't hear/feel anything until I had slowed down, and had gone another 1/4 mile. One minute, she's idling good, the next, rough,and noisy. I have less than 200 miles on the engine, that I rebuilt "sparing no expense" as it were, just four years ago. New guides,valves,hardened exhaust seats, etc. I guess I need a tachometer, or need to have some of the lead removed from my right foot - Zach.
Zach, Sounds like someone was out having fun! :3gears: At first glance I would suspect that the #1 exhaust valve did float and cause the problem. It could also have been the lifter that pumped up and caused the damage. If you installed new hardened seats, did you check the installed height of the valve stem? If the valves are too tall, the lvalve train geometry could be off, and could lead to things like valve float and bent push rods and such. One other possibility is that the valve guide to valve stem clearance is too tight. As the exhaust valves heat up, they can actually seize in the guide if there is too little clearance. Did you replace the valve springs or shim them to proper tension? Hope you get this sorted out, not fun pulling the heads this soon after a rebuild! Take Care, Tim
I've been running a Nailhead since I was a teenager.......about 30 years. I've revved them up until the valves floated many times and never had a catastrophic failure, although once I swear the lifters had pumped up. After I drove another 1/2 mile or so it smoothed out.....good thing b/c we were about 5 hours from home. :laugh: Before I pulled out my last motor, I tried to explode it and couldn't. (the lifter bores were worn and it needed to be bored 60 over). I held it to the floor in L1 for until I ran out of road, she was revving around 6,500 RPM's. :Brow: I think if something was gonna let loose that would have been the time. If the clearances in a motor are all correct and it has good oil pressure, an occasional romping shouldn't hurt anything. .......I suspect Zach has tight valve guides. Carmen sells heavier inner and outer springs, that's what I used....stock springs I had would never rev past around 5,500 RPM's. There's nothing up there, so it is not necessary to rev that high, but heavier springs are always better. :bglasses:
Uh, tim63riv: My professional machinist handled all the valve job formalities. I have done business with him for ten years, and trust his work completely. He is familiar with Nailheads too. I'm afraid I'm not "weenie" enough to go back and check a fellow professionals work. No blind trust here: just respect for another Man's work.----Zach. P.S.- I may take the head to him and get him to double check the valve-to-guide clearance,etc. before I reinstall it just for the heck of it.
