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BILLBEN Member
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TOTAL VALVE JOB RESULTED IN ZERO COMPRESSION ON CYLS1&2, 60 LBS ON 3&4 ALL NEW VALVES, GASKETS, ETC...AM I MISSING SOMETHING OBVIOUS, OR JUST STUPID? BILL |
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Brett Gibson JH5 20497 Member
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Take your cams off so all the valves are closed and see if you have compression then, if you do then your valves are not adjusted right, if you dont its in your cylinders..... |
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Jensen Healey Super Moderator 
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Sounds like your valve timing is way off or your valves are poorly adjusted. Check that the cam sprocket marks line up at TDC. If that seems ok, remove the cam covers and check the valve adjustment. The valve adjustment on this engine is very difficult to get right. Follow the instructions in the manual. Kurt |
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Esprit2 Member
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Bill. Was nothing else done?... just a valve job? A good compression engine became a no compression engine after nothing but a valve job? To do a proper compression test, the engine should be brought up to full normal operating temperature then shut down, remove all spark plugs except for the cylinder you are testing, hold the throttles wide open and crank the engine at a speed of at least 200 rpm. Failure to do any of those steps will result in low readings. If the engine isn't operational, that makes reaching full operating temperature impractical. The test will result in low compression readings, but you'll just have to live with it for now. Cylinder to cylinder variations are more important for the moment than absolute pressures. If the starter and/or battery are tired, they may not be capable of spinning the engine at 200 rpm. As above, carry on with the test, but the readings will be low. Wide open throttle is not negotiable. A closed throttle test tells you very little. I find it curious that 1 & 2 are low while 3 & 4 are still low, but at least have a reading. I'm wondering if you did the compression test with closed throttles (no air gets in, so very low pressures across the board), and if the carbs are not balanced? (the front carb is more closed than the rear carb? ). Strombergs or Dellorts? Imbalanced Dellortos will result in a distinct difference between the 1-2 pressures and the 3-4 pressures. With Strombergs the balance tube in the intake manifold will mask carb imbalance at low rpm. If carb balance and test methods are not issues, then... Check the cam pulleys to be sure they are installed properly. .. the appropriate side of the pulley facing forward for each cam, and the correct timing marks aligned (some pulleys have multiple sets of marks). With the crank set to TDC, the timing dot next to the IN mark on the front of the INtake cam pulley should align with the dot next to the EX mark on the front of the EXhaust cam pulley. The teeth the dots are on should align face to face, or be off by less than a tooth width (the belt can only be moved on the pulley in whole tooth increments). If the proper dots are on the centerline between drawn through pulleys, but on far opposite sides of the pulleys, then turn the engine through one more revolution and back to TDC. Now the proper timing dots should align. If they are off by more than a whole tooth increment, then re-time the cams. Check the valve clearances. Did you re-shim the valves? It's almost a lead pipe certainty that they would have to be re-shimmed after a valve job. If you have negative clearances on any cylinders, those valves will not seal and pressures will be low to non-existant. Shim all valves to the high end of their ranges. .005" - .007" for intakes and .010" - .012" for exhausts. The clearances tend to close up with wear, so starting at the top will give the most miles before the job valves must be re-shimmed. High or low within range won't significantly affect the compression pressures. Good luck, Tim Engel |
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Dan (Florida) Member
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Remember,when grinding valves and seats the valves sink deeper into the head reducing the clearance to the cam. If enough is removed the cam will hold the valve open. The valve grind should have included grinding a bit off of the stem to maintain a gap with the cam. hth Dan |
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Esprit2 Member
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True, grinding/ lapping the valves will result in them receding into the head, getting closer to the cam, and closing up the clearances. Proper clearances will always go away during the process. And the machinist should check the valve stem height and grind it to keep it within spec. However, no machinist is going to try to hold valve clearances by grinding valve stems. It's just not practical. The total range is just too narrow (0.002"). The only reasonable way to adjust clearances is by shimming during final assembly. Every time the cam carriers come off the engine, the first step should be to check the valve clearances. Then take the time to adjust the shims when the carrier goes back on. In the case of a valve job, all clearance settings will be lost during the process. In that case, reassembly will require several trials. First assemble the cam carriers to the head using thinner shims... something on the order of .010" thinner than what was in there before. Then measure the clearances that result to get a base line, calculate what shims are required to bring the clearances into spec, then R&R with the new shims. Measure again and adjust again if necessary. Regards, Tim Engel |
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Jon Plowe Member
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I you have a 'leak down test', where compressed air is forced into each cylinder a TDC and the rate of leak is measured, it can tell you whether it's the valves, rings or both. Escaping back out the carbs means inlet valves, out exhaust means exhaust valves, crank breather means rings. Might save pulling a block and/or head apart uneccessarily. Jon |
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