flathead valve problems???

john mullen

john mullen

Senior Member
I have a newly rebuilt 8rt with everything new in the valve train with NOS ford stock cam, new aftermarket springs, guides, keepers, retainers, valve locks and ss valves.
After debugging I did a 400 mile road trip break in run and developed a miss on # 6 cyl. it got worse as I went along. After returning home I did a compleat comp check found that the # 6 cyl shows only 30 lbs. The rest all checked at 110 lbs.. all the plugs look perfect and looking at the ex valves through the plug holes they all have a nice clean brown color inc # 6.
while driving under load there is no miss ,under steady cruse there is a slight flutter and off gas a more pronounced flutter.
Has anyone had a similar valve problem .I'm thinking maybe a broken spring or a valve lock fell out or lifter adjustment came loose.. I will pull the intake sometime next week when I get time but just wondered if this has happened to anyone else...
 
Hey thanks Mart, I don't think this is a stuck valve as I fit each and every one at + - .002 to.0025. loose in my op. what do you think? I'll know more next week when I can pull the intake but at least I will have some idea as to what to look for. thank you
 
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did you lap the valves in?? I know of 3 engines that have had problems with the after market horseshoe clip being to soft
 
52 merc, I did lap the valves. I use a special guide I made up with very tight valve stem clearance .0015 and lap first with cource compound then wash up. Then lap with fine. I use a valve lap tool that rotates the valve 1/2 turn then reverse 1/2 turn. I spent a very long time doing the valve setup getting it just rite. I'm stil thinking something came undone ..
 
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my guess is even tho you lapped the valves one has stuck open, if its an intake the engine will blurp or back fire out the carb, if its an exhause valve hang a shop towel over the tail pipe, if the valve is stuck the towel will be sucked into the ex pipe, pull plug and squirt marvel mystery oil on the valves and stems and turn engine over with starter, squirt some more and let engine set all night, 4 to 6 oz of mmo in 10 gallons of gas is good for lubing the intake valve
 
ford3, the tail pipe shows as you say and air blown into the plug hole with the piston at tdc on firing stroke leaks air out the tail pipe. I have done the mmo and will let it sit as you say. I will let you know what happens .I will delay the teardown until I try this fix. Thank you
 
we had this problem and it was a lifter adjustment came lose hope that's not what happed to you. my friend listing to my tale pipe and diagnosed it as lazy valve .
 
pulled the intake and found the valve adjustment just as they were set on install. so I pulled the head and found #6 ex valve not seating itself. I dismantled the valve assy and cleaned it all up. I touched up the seat to freshen it up only to find it was also the same as built. I put the valve into the valve grinder and found a warped valve.???? how this happened I do not know. I started checking The color on all the other valves and you can see a hot spot right where the plug fires. the valves are not self rotating type. I wonder if the heat from the initial firing was getting hot enough to warp a valve. you can see the hot spots through the plug holes on all 8 ex valves. anyone ever have this problem before.????
 
What clearances are you using, and which method for setting clearance (i.e., are you using that old Ford method of setting multiple valves when #X and #Y are open)?

I saw exactly what you describe on my engine, but I didn't have adequate clearances. Valves were not seating when hot.
 
ross f-1,
I set the valves at .014 in .016 ex cold as per Vanpelt specs ..( Stock ford nos cam) The valves were set properly when built and were still set as built when torn down for this repair. There are no tight valves
 
I ended up taking all the valves out after finding the #6 intake also warped. I reground both # 6 valves and re laped all 16 over. all seats seemed to be good except #6 and they were not hurt but I did re cut them just to be sure I re adjusted and put it all back together ...runs great now.... I just cant wrap my head around how those two valves got warped, no contact with the head, no overheating and no suspicious markings from anything going through the engine.
 
I've heard of a guy doing a compression test and repeatedly finding bent exhaust valves... due to the extension of the compression tester end into the space the exhaust valve needed to be in when open...
Karl
 
Karl Wolf said:
I've heard of a guy doing a compression test and repeatedly finding bent exhaust valves... due to the extension of the compression tester end into the space the exhaust valve needed to be in when open...
Karl
Click to expand...

That would almost be funny if it weren't so sad!
 
Karl Wolf, I could see that happening with the screw in type compression gauge as they do have threads for the long reach type plugs . I use the old skool hand held unit myself.. I'm hoping it is not poor materials. I'm going to do another long road trip soon and we will find out what happens. I put about 50 mils on it today and it seams ok so fare.
 
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