Hello John! It was suggested that the problem with low compression was the camshaft.I would much rather pull the heads than get into pulling the bottom end apart.With many members input I think the cause has been found!I will be asking for input again when I take it apart as far as head gaskets etc to use when reassembling.Thanks!

  

Mark:

Though there is some variation in lifts (did you notice if exhausts typically differed from intakes, could be the cam was made with more lift on one) I don't feel it is enough to cause your rough idle.  You have already diagnosed the problem, low compression on some cylinders.  Looks like a valve job is in order.  To convert cam lift to valve lift, multiply cam lift by your rocker arm ratio.  If you still have the original rockers, that would be 1.43.

John - "The Hoosier Hurricane"

I got a basic depth gauge at the hardware store.Measures in 1/32 inch plus a nice conversion table on the back.I went one valve at a time and I think I was very accurate in measuring spring height with valve open and closed.Not much difference between any of the cylinders I don't think but you can maybe tell me how these look to you.All were between 11/32(.343) and 13/32(.406).This is the difference between spring height  valve open and spring height valve closed.I definetely did not see a great difference between any of the cylinders.The Ford manual lists lift at the cam as .259 intake and .257 exhaust.I don't know how to convert that to lift at the valve.Does this look like a "flat" cam to you or do the heads simply need a valve job?The one cylinder which has a compression reading of 100 is measuring the same at the valves as the ones with 60-70.Thanks 

  

Mark, yes there is an old set of directions in Clymers ford handbook, i found it and says, with # 1 cyl on compression you can adjust 3,6,8 intake and exhaust, 7 intake, 4 exhaust. then rotate engine to # 6 on compression and adjust 1,2,5 then 7ex ,4in. Personally i cant see it and do them individually, then start engine and slip feeler guage under each rocker and feel the ease or slip of the guage and nip up or loosen any that dont feel right. Thats only my view if it helps. good luck

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

For a compression test, warm up the engine to operating temperature, pull all the sparkplugs, with a fully charged battery and the carb throttle plate WIDE OPEN. And use a know good gage. My 57 312 has 155 to 165 PSI. Pete

fMark:

There are probably more than one valve fully open at at time, but I haven't researched it.  I would probably use a remote starter button, hold the gauge against each spring down the line and bump it over until the "leg" touches the head, then go to the next one.

John - "The Hoosier Hurricane"

Hello Bill! I had an idea that the y-block should be around 125 when doing a compression test.The Ford shop manual says 155-160 which seems very high with a "low" compression 8.4 rating.My question is can other valves be checked in other cylinders when working on another cylinder?Saves continually turning motor to check all valves. Thanks for your input

  

Mark, generally most good engines at cranking speed show compression around 125 lb/". Obviousley when doing comp test you have the carb throttle plates in the open position! just rotating engine 1/4 of a turn at a time will bring each cyl to TDC. Keep on going. best regards bill.

  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Thanks for the suggestion John.Question.If I am checking one valve on one cylinder is there a corresponding valve somewhere else I can check at the same time? Or if I have one cylinder at TDC with both valves closed can I check others at that time instead of turning motor over and over?I was just looking in my shop manual and the compression according to the book is supposed to be 155-160.Does that sound correct in your experience?

  

The compression test I did in the spring had me between 100 and 115 on all cylinders. Thats not what I envisioned when the motor was built, and this engine builder believes in tight cylinders. It's almost as if rings never fully seated. Gary

       

Gary, 55 Vicky, St. Germain, Wisconsin