GraniteBayBob Posted October 6, 2017 Share Posted October 6, 2017 New pistons, rings and valves. Honed piston walls. Reassembled and did compression test. Would like to know what kind of pressure to expect while hand cranking. Got 22+- psi on all four cylinders dry but wet I started to get different results. Two squirts of oil: 30 30 26 28 Two more squirts: 40 35 35 37 again this is hand cranking, because the starter only makes 1/2 rotation at a time. When cranking there seems to be a lot of resistance on bottom part of rotation. Question is all of this normal or should I be getting different results? What should I expect? Link to comment Share on other sites More sharing options...
Spinneyhill Posted October 6, 2017 Share Posted October 6, 2017 On the starter it takes about three compressions on my Dodge 8 to come up to full compression pressure. Link to comment Share on other sites More sharing options...
viv w Posted October 6, 2017 Share Posted October 6, 2017 Hi, If all the spark plugs are out of the head, the starter should be able to spin the motor more than half a turn. If not, I would say something is wrong. I did a Chrysler 50 some years ago, it was very tight and once started would run a few minutes and tighten up and then stop. I thought it was the pistons too tight and it was partially siezing, as it warmed up. I eventually found the problem. I had a new distributor right angle drive (the diecast one) cast in aluminum and the engineering firm that did the machining and assembly , had put this unit together DRY, with no lubricant. It was enough to stop the engine dead when it tightened up, and I was surprised it did not break. I suggest you check this drive unit, to make sure it turns freely and is well lubricated. It could be that the diecast metal on your unit has started to distort, causing the shaft to bind. Viv. Link to comment Share on other sites More sharing options...
GraniteBayBob Posted October 6, 2017 Author Share Posted October 6, 2017 (edited) Thanks for the input. I did have all the plugs removed when trying to crank and getting the difficulty completing a full revolution. Pulled the head last night to check cylinder walls. Specs diameter 3.6285 (3 5/8), had a difference on one cylinder of 3.6335. This with caliper at top of cylinder, I'll have to get the tool for checking lower down in the cylinder. I did replace fiber cam gear with an aluminum gear. Will take a look at that also. Today's engines are higher compression but what should I be getting? The tool from Harbor Freight does not hold the pressure when under 30 pounds. The little valve stem gadget will not seat at low pressure. Edited October 6, 2017 by GraniteBayBob (see edit history) Link to comment Share on other sites More sharing options...
Spinneyhill Posted October 6, 2017 Share Posted October 6, 2017 Nominal compression ratio is 4.7:1. Guess volumetric efficiency as 72%. Then compression pressure (gauge) should be about 14.7 * 0.72 * 4.71.3 - 14.7 = 64 p.s.i. So your compression should be around 64 p.s.i., perhaps a little less if the volumetric efficiency is less than 72%. Link to comment Share on other sites More sharing options...
GraniteBayBob Posted October 7, 2017 Author Share Posted October 7, 2017 (edited) Thanks you Spinneyhill for your help. With heads off could crank easily with even force.So rechecked cam/timing gear and verified TDC also reset tappets. Did all that when I had the engine out and it was much easier. I'll put heads back on recheck compression and try to start. Fingers crossed. Edited October 7, 2017 by GraniteBayBob (see edit history) Link to comment Share on other sites More sharing options...
Spinneyhill Posted October 7, 2017 Share Posted October 7, 2017 A dumb question: has the head had a fair bit planed off? A valve might be hitting it? Link to comment Share on other sites More sharing options...
GraniteBayBob Posted October 7, 2017 Author Share Posted October 7, 2017 No, the head has not been planed. I only cleaned it up. Good news I got it running (3 times) but only about 10 seconds. It was chocked and did't run long enough to make adjustments. Then it acted like it wasn't getting spark. I felt the coil and it was very warm. Should it get warm? Has voltage on both + and - side, it only has no voltage it seems like when points close; is this correct? Would like to get answers to this before trying to start again. Thanks. Link to comment Share on other sites More sharing options...
Guest Posted October 8, 2017 Share Posted October 8, 2017 There should be no current flowing when the points are open. When they are closed the current flows and sets up a magnetic field in the coil, when they open the field collapses creating a momentary high tension current that can jump the spark plug gap. Link to comment Share on other sites More sharing options...
GraniteBayBob Posted October 8, 2017 Author Share Posted October 8, 2017 One question: on a positive ground 6 volt system the lead from the ignition switch to the coil, should it be connected to the positive or negative side of the coil? Or does it make a difference? Link to comment Share on other sites More sharing options...
maok Posted October 8, 2017 Share Posted October 8, 2017 Think of it this way. Where does the other side of the coil go to? The points contact then to ground/earth. Link to comment Share on other sites More sharing options...
Rusty_OToole Posted October 8, 2017 Share Posted October 8, 2017 (edited) On a positive ground car the positive side of the coil should connect to the points. The negative side to power. Yes the coil will get quite warm when in use, this is normal. Edited October 8, 2017 by Rusty_OToole (see edit history) Link to comment Share on other sites More sharing options...
GraniteBayBob Posted October 8, 2017 Author Share Posted October 8, 2017 (edited) That's good to know, but in this case the ground is connected to the positive side of the battery; so I'm still not sure about the lead from coil to ignition the switch were the negative is coming from. In some cases the negative is not always ground/earth or vice versa. Maybe I'm over thinking this thing. P.S. Thank you Rust_OToole, That is what I was thinking. Missed your post b4 sending this. Edited October 8, 2017 by GraniteBayBob (see edit history) Link to comment Share on other sites More sharing options...
maok Posted October 9, 2017 Share Posted October 9, 2017 On 9/10/2017 at 3:15 AM, GraniteBayBob said: That's good to know, but in this case the ground is connected to the positive side of the battery; so I'm still not sure about the lead from coil to ignition the switch were the negative is coming from. In some cases the negative is not always ground/earth or vice versa. Maybe I'm over thinking this thing. P.S. Thank you Rust_OToole, That is what I was thinking. Missed your post b4 sending this. Yep, you're over thinking it. Which I usually do as well. Link to comment Share on other sites More sharing options...
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