labrat Posted May 3, 2001 Share Posted May 3, 2001 I noticed on one of the heads the valve looked recessed about 1/4 in into its seat. Is this just because the cam is not there to offset the valve spring, or is there something wrong with the head? Or is the valve possibly too small? I've never seen anything like this. Sorry about all the questions at once, but i'm elbow deep here and have to get this thing back together. Thanks for the help! Bill I'm on my way! Quote Link to comment Share on other sites More sharing options...
DavyZ Posted May 3, 2001 Share Posted May 3, 2001 Sometimes valves become recessed just do to wear. I can't remember if you have the camel hump heads or not. If they are, they probably still have the valve guides and valve seat made for leaded gasoline. I may be misdiagnosing your problem but bear with me: With today's unleaded gas, you'll find that the exhaust valves tend to wear right into the head. On intake valves, they get lubricated by the fuel, so there is usually no problem, but not so with the exhaust valves. Lifters, pushrods, and valves rotate as the engine runs. It is the friction of the valve as it rotates against the seat that causes the wear; the valve actually grinds away the seat until it sinks deep into the head. Eventually the valves will be seating so deeply in the head that major problems will result. The stem height (the distance from the spring seat to the tip of the valve stem) will become so great that the geometry will be thrown off and spring pressure will decrease. The seats will become so sunken that flow will be affected. If not corrected in time, the heads may crack or the seats may become unrepairable. The best method to prevent this problem is to convert the heads to accept unleaded gasoline. A machine shop has to install hardened exhaust seats to prevent this from happening again. If this is an intake valve, I'd be very curious to see if all of the valves are not doing exactly the same thing. David Quote Link to comment Share on other sites More sharing options...
Kevin Shasteen Posted May 3, 2001 Share Posted May 3, 2001 Ditto to what David said; and....if you dont know the history of the heads-then you dont know how many times a valve job has been done on those particular valves. You dont know how many times the heads have been milled. If you dont know the above mentioned-then I'ld be leary about putting those heads on my engine till a competant mahine shop checked them out. You definately want to confirm your heads are not warped; definately want to confirm the valve's edges are not knife edged; definately want to confirm your valve springs are not worn out to the point they are not keeping your valves on the seats when they are suppose to. All of those variables are something I'ld want cleared up prior to putting any cyl.heads on an engine. Sorry to be a doom & gloomer but engines are like computers; the output is only as good as the input. Kevin, (Yea,Still an Inliner) Quote Link to comment Share on other sites More sharing options...
Modern Motorsports Ltd Posted May 3, 2001 Share Posted May 3, 2001 quote: Originally posted by labrat: I noticed on one of the heads the valve looked recessed about 1/4 in into its seat. Is this just because the cam is not there to offset the valve spring, or is there something wrong with the head? Unless it's simply a worn valve seat in an old set of heads (which I doubt but could be possible), it's had a major valve job or three in its day and as you say that valve is recessed which you do NOT want at all. Just not worth playing with unless you're on quite a budget as you don't want to put any money into them anyhow. Just won't flow as it should and once it's recessed etc (and if only one of them is) geometries can get quite altered as well. I paid $20 for a 'vaccuum test' to have my RPM heads tested when I swapped them from my 327 to my 350. The machine shop that was testing my valve springs REALLY wanted to lap in my valves and I was VERY much against it and was so relieved when I found out they could vaccuum test them to see if they were still sealing well (I killed the valvesprings/fatigued fast on overrevs , edelbrock heads aren't known for great OE valvesprings anyhow). $20 and I found out all valves were sealing 100%. Avoid recessed valves if possible Bill. Quote Link to comment Share on other sites More sharing options...
DavyZ Posted May 3, 2001 Share Posted May 3, 2001 Yeah, Kevin is right about taking them to a machine shop to get looked at. If only one valve is 1/4" recessed, it may not be a problem, but at least call a machine shop and get their opinion. David [ May 02, 2001: Message edited by: DavyZ ] Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted May 3, 2001 Share Posted May 3, 2001 the valve seat is worn.most have have replacable seats-time for the machine shop.but before you spend too much on rebuild a set of old heads you might be better off getting a new set from summit or some of the chevy factory perf heads.i had the v6 heads done on my ford ranger and spent $400 in a hurry.2 seats were sunk 3/8 of an inch-they are flame hardened at factory and some times it doesnt get done. Quote Link to comment Share on other sites More sharing options...
RPMS Posted May 3, 2001 Share Posted May 3, 2001 If just one seat was worn, what are the chances that some yahoo put in a heavy duty replacement spring on that one valve sometime in the past? Scott Ferguson 1974 260Z - 305 engine coming apart AGAIN this weekend Quote Link to comment Share on other sites More sharing options...
labrat Posted May 3, 2001 Author Share Posted May 3, 2001 it is just one exhaust valve that's recessed like that, and they are going to a machine shop, i just liked the idea of knowing what was up before i got there. But unfortunately, i am on a serious budget, and super hi performance is not a necessity, just reliability. Thanks for the input! You guys are great! Bill PS, they are the camel hump heads and quite old (1966) Quote Link to comment Share on other sites More sharing options...
Guest JAMIE T Posted May 4, 2001 Share Posted May 4, 2001 If those heads have been on a running engine in the last 20 years, they have been used with unleaded fuel and beating the heck out of the seats. If this is to be a driver and use unleaded fuel, I would recommend scoring a set of later heads, anything after '76 or so... You could easily sell those double humps to a restorer. A little clean-up port work in the bowl area and a 3-angle valve job and the later heads will flow as well as those double humps. If this seems like a lot of trouble, it is. I have a set of 492 castings(64cc chamber, good ports)in the garage and thats where they will set until someone wants them. Its expensive to have old heads converted to hardened seats. I just scored a 327 with World Products Torquer heads(2.02, 1.60, 64cc chambers) for $500. These heads are basicaly big valve double hump replacements. They have hardened seats and all of the other good stuff. The machine shop you take the heads to can fill you in on the cost of hardened seats for your heads, and/or maybe find you some later heads. Good Luck. Jamie, Ferrari 250GTO Project: Deathstar Quote Link to comment Share on other sites More sharing options...
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