rags Posted May 1, 2011 Share Posted May 1, 2011 I friend of mine has been having trouble starting his 3.1 liter track car. It has always been troublesome to start but at the beginning of last season, it just wouldn't start. I volunteered to take a look at it so he trailered the car to my house. Since I did not build the motor, I started from scratch. Cam timing is set to spec, Ignition is set to 8 degrees BTDC, Mikuni's have fuel and are jetted properly for the motor. What I did find troublesome is the 105lbs of cylinder pressure but since they were all the same, figured it was due to the cam overlap. I have a nice spark which will jump an inch gap but the motor refuses to start. You can hear some of the cylinders fire and try to start the motor but it never catches enough to start completely. When the engine is cranked with a fully charged battery, to me the engine is just not cranking fast enough. Also, when doing the compression test with all of the plugs out, the engine also does not spin as freely as I think it should. Is it possible that this bottom end was just assembled too tightly? The owner said he has always had the same hard start condition since day one. It just seemed to get worse until eventually it wouldn't start at all. Any suggestions? Joe Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 2, 2011 Share Posted May 2, 2011 Carburetion? Cranking Vacuum? Has he ever tried starting the car by spraying quick-start? If the car fires off and runs till the priming is gone---which is common in low-vacuum carburetted setups, it's a matter of getting more fuel to keep it fired off. As long as you crank around 250 rpms that's more than fast enough. In reality you really only have to get one cylinder up to compression kickover with a good gasoline charge in it and standing on a ratchet is enough cranking speed to start an L6 when cold with adequate fuel. And after warmed and primed with good F/A in the cylinder, the same applies. It only takes one to fire to get it started, the essense of the old hand-cranked startup. If it's cranking, but not catching consider the vacuum is low and 'priming' in a more efficient manner may be the way to go. Quote Link to comment Share on other sites More sharing options...
rags Posted May 2, 2011 Author Share Posted May 2, 2011 Tony, I tried spraying starting fluid and I get the same result! The spray will ignite but not enough to start. Let go of the starter and the motor stops turning. I know it's burning because I can see exhaust at the tail pipe. Quote Link to comment Share on other sites More sharing options...
josh817 Posted May 2, 2011 Share Posted May 2, 2011 (edited) Perhaps have someone spraying into the carb while you crank with the throttle cracked/fully open. My dad does this a lot on the cars he has at his shop and once they're fired up he will continue spraying into different throats so each cylinder gets a bit. By continuously spraying some carb fluid into the throat you're essentially "fuel injecting" it so a lack of vacuum to pull fuel from the jets would be resolved. What Tony said about lack of vacuum coincides with what you say is a lot of overlap in the cam. Oh and also if the bottom end was too tight it would have worn itself loose, down to specs where its "happy". I've learned that. Edited May 2, 2011 by josh817 Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 2, 2011 Share Posted May 2, 2011 (edited) Joe, I would take the plugs out again and turn it over by hand with a wrench on the crank pulley. Compare what it feels like to a known good engine. I am thinking spun bearings or a bound up cam if it's turning too tightly. A side note...old fuel? My car fired up and ran with three cracked pistons and a heap of coolant in one cylinder. Edited May 2, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
inZane 240 Posted May 2, 2011 Share Posted May 2, 2011 I had a similar problem. Problem was due to insufficient grounding. Quote Link to comment Share on other sites More sharing options...
PalmettoZ Posted May 2, 2011 Share Posted May 2, 2011 (edited) Hey- 105 lbs of cylinder pressure sounds really low. Something is wrong there. My 3.1 that I built last year that had a 306 degree duration and .530" lift camshaft had 200 psi per cylinder. I had Mikuni carbs on it at time as well. Start with the basics and double check the distributor rotor position and cam timing again. I think your cam timing is way off. Even if the bearings were too tight, the cylinder pressure should be higher than that. Also double check your spark plug wire positions and make sure that they are correct to each cylinder. Scott Edited May 2, 2011 by PalmettoZ Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 2, 2011 Share Posted May 2, 2011 If it's turning over really slow the compression test may be moot. Quote Link to comment Share on other sites More sharing options...
rags Posted May 2, 2011 Author Share Posted May 2, 2011 Does anyone have an idea of how much torque it takes to turn a motor from the crank bolt with all of the plugs out? I'm thinking this should be my first test to see if there is something obvious going on. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 2, 2011 Share Posted May 2, 2011 Does anyone have an idea of how much torque it takes to turn a motor from the crank bolt with all of the plugs out? I'm thinking this should be my first test to see if there is something obvious going on. Are you sure the plugs aren't fouled? So far your description sounds more like fouled plugs, especially considering Tony's comments and the fact that starting fluid didn't help. Maybe try a fresh set of plugs before you start doing more complicated tests.. Quote Link to comment Share on other sites More sharing options...
rags Posted May 2, 2011 Author Share Posted May 2, 2011 Tim, Plugs i took out were not fouled. To be sure, I put in a new set and the same thing happened, plugs fire but she won't start. I feel like I've tried all of the obvious things and also verified all of the easy things which is why I'm now grasping at straws. Joe Quote Link to comment Share on other sites More sharing options...
josh817 Posted May 2, 2011 Share Posted May 2, 2011 The torque is going to be different with each motor because of valve spring rates. Maybe try a totally different model of plugs. Not to sound like a fool but we had an MG in the shop a couple weeks ago that needed a tune up. Changed the plugs to the ones we have always used. Car started up and ran that morning. Couple hours later, the owner came to pick it up and the car would not start at all. Dad tried everything except changing the plugs because they were brand new, still looked new, had worked for him before, etc. I changed them to a totally different heat and I think I went to a resistor-less plug and it started right up no problem. Quote Link to comment Share on other sites More sharing options...
rags Posted May 2, 2011 Author Share Posted May 2, 2011 I'll try anything. Any brand plug and part number recommendations? I know what I'd use but would rather compare notes from others. Joe Quote Link to comment Share on other sites More sharing options...
SHO-Z Posted May 2, 2011 Share Posted May 2, 2011 It almost sounds like the timing is 180 out. Was the car running when it was parked? If the car has been sitting for a long time check the inside of the distributor cap for moisture. If all else fails and the car was running when parked put a tow strap on it and try starting it by poping the clutch in 2 or 3rd gear. It also could be bad gas. Drain the tank and flush out all of the fuel in the lines and carbs. My Z sat for almost a year and the went bad. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted May 2, 2011 Share Posted May 2, 2011 (edited) Joe, how slow does it crank with a full charge on the battery? Does it turn "steady and slow" or does it lump over "fast-slow, fast-slow" like a high compression motor. If it's mostly steady slow in both cases, with the plugs in AND the plugs out, then there is some internal resistance to spinning that is greater than the resistance from the compression. I still think you should be able to "feel" if the engine is too tight by putting a wrench on the balancer bolt. If it's tight enough to slow the starter down, then you will feel it. I can turn my motor over a little with just two firm hands on the pulley; with the plugs in it. It's much easier to turn by hand with the plugs out. What accessories are driven by the engine... Alternator, A/C, pumps? Are they free spinning? Is the starter good? Might want to drop the pan and have a look. Does it have a magnetic drain plug you can inspect? Edited May 2, 2011 by cygnusx1 Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 3, 2011 Share Posted May 3, 2011 (edited) Joe, If the motor has run good in the past, then something has gone awry since then. If you have checked: TDC with respect to the timing tab, cam timing, ignition timing, spark, and fuel, there is something else causing this. Since the motor doesn't turn easily (with the plugs out I am assuming), and compression is low, I think it is time to tear it down. Is this "Shotgun" Jimmies car? Pete Edited May 3, 2011 by z-ya Quote Link to comment Share on other sites More sharing options...
rags Posted May 3, 2011 Author Share Posted May 3, 2011 Yeah Pete, this is Jimmy's car. Plugs out and difficult to turn, cylinder pressure low. I asked if the motor was ever easy to start and he said "no, always difficult". I'm with you, I think it's time to tear it down Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 3, 2011 Share Posted May 3, 2011 Yeah Pete, this is Jimmy's car. Plugs out and difficult to turn, cylinder pressure low. I asked if the motor was ever easy to start and he said "no, always difficult". I'm with you, I think it's time to tear it down The term "shotgun" coming from how often that car backfires. LOUD backfires... I'd be willing to bet that the camshaft timing has always been off, and after all those backfires, the damage has finally been done. Take it apart for sure. Pete Quote Link to comment Share on other sites More sharing options...
steve260z Posted May 4, 2011 Share Posted May 4, 2011 Have you verified tdc by looking at the piston through the spark plug hole, then the cam lobe position then the distributor position.? Tried new distributor cap and wires. I'd do all that plus new gas plus any other above issues and certainly get advice on the carbs before taking apart. It just sure seems much more likely than the bottom end being too tight. When he put the motor together he must have turned the bottom end himself with ease. Quote Link to comment Share on other sites More sharing options...
theramz Posted May 9, 2011 Share Posted May 9, 2011 If the cam is retarded it would explain the low compression and the backfiring. The piston would be on the way up before the intake valve closes. Backfiring is from unburned fuel in the exhaust. The slow turn could also be from a weak starter/connection. Quote Link to comment Share on other sites More sharing options...
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