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Hot!No start

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Fordrulz
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2019/04/09 20:21:07 (permalink)
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No start

Hi. I have a mighty merc wood splitter with a 5hp tecumseh enduro engine that won't start. Spark is good. Cleaned carb would fire but not run, won't run when fuel is put in spark plug hole, would fire off starter fluid once or twice real quick. Plug seemed dry. Replaced carb and same results. Carb does prime. Replaced cracked vacuum hose from valve cover to carb. Checked valve movement and it is good. Checked flywheel key way it is good. Fuel is clean and fresh. Kind of stumped at this point any help would be appreciated. Thanks.

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    Mikel1
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    Re: No start 2019/04/09 21:33:10 (permalink)
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    Not unnormal for there to be a crack from vac hose to carb, happens over the years. Any idea of the compression? We need fuel, spark, timing and compression to run
    Fordrulz
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    Re: No start 2019/04/10 06:33:07 (permalink)
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    Got spark, going to check compression tonight. Have good fuel to carb. Not sure if it is reaching the plug though. Not sure on the timing. My initial thought is was the cracked vac hose but vac is still fairly week at the carb so maybe it is not pumping the fuel like it should due to low compression????
    AVB
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    Re: No start 2019/04/10 08:18:20 (permalink)
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    Normally as long as the flywheel is intact the timing will be fine as the valve timing is mechanically gear driven and only gets off if someone had the engine apart.
     
    As for hose you replaced it is a PCV vent line to feed cylinder blow-by into the carburetor so it can been recycled.
     
    As for doing a compression test it is fairly useless on these engines due the ACR function. What you need to do is a leak down test instead. Since this an OHV engine (fairly sure it is) I would disable the valves by removing the push rods before doing the leak down test. This way you can check the cylinder condition from TDC to BDC. With the age of these Tecumseh engines I suspect it be worn tapered at near BDC and is losing most it cylinder seal. This leak down test will also test the valves sealing as if one is sealing you will air escaping from the intake or exhaust depending which valve is the culprit. It also test the head gasket sealing.
     
    It is not possible to do the above TDC to BDC test on L-head engines as you can not disable the valve train.
     
    My most recent OHH50 which I worked on had only a 10% leakage at TDC but when I got halfway to BDC it was over 60% with the maximum allowable leakage rate of 20% though some Briggs engines it is 40%; way too much in my opinion. I torn the engine down just to verify the diagnosis and confirmed the non-invasive test results.
     
    Rebuilding the engine is not recommend due lack of parts as there is probably no OS piston available. Your best option is to find a suitable replacement engine. This will require some modifications to get the hydraulic pump to mount up properly. I suspect that you will have a Lovejoy coupler setup. Depending on the current crankshaft length it might require the shorting of the new engine's crankshaft or the shorting of the couple housing.
     
    Abbreviations used:
    PCV = Positive Crankcase Vent
    TDC = Top Dead Center
    BDC = Bottom Dead Center
    OHV = Over Head Valve
    ACR = Automatic Compression Release
    OS = Over Sized
    post edited by AVB - 2019/04/10 09:12:26
    Mikel1
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    Re: No start 2019/04/10 09:54:53 (permalink)
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    Yeah leak down tester would be great if he has one and an air compressor.
    AVB
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    Re: No start 2019/04/10 10:13:38 (permalink)
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    I do assume repair techs have the basic small engine shop tools. Things like hand tools, air compressor, and the basic test equipment. However many DIYers don't but this equipment it makes the troubleshooting much harder and more of a guessing game. Having experience does help somewhat but is not much of a substitute for actual knowing what is going on which these tests will indicate without tearing down the equipment.
     
    Harbor Freight has a nice leak down tester for $50, $40 if you have a 20% discount coupon. It uses much less air pressure to test. 10-15 psi vs the 100 psi many other testers use. This allow you hand the flywheel and rotate it through out the cylinder stroke. With 100 psi this impossible to do as it quite dangerous due the torque generated. With HFT tester just remember to reset it zero input before putting it away as you can damage the gauges if you forget and apply to much initial pressure.
    Mikel1
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    Re: No start 2019/04/10 11:39:59 (permalink)
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    True.
    Not sure I understand the 10-15 psi, unless your referring to the guage numbers.
    AVB
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    Re: No start 2019/04/10 13:30:03 (permalink)
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    Mikel1
    True.
    Not sure I understand the 10-15 psi, unless your referring to the guage numbers.

    Yes it is the regulated input pressure with leakage percentage gauge at set position before applying to the cylinder. The line input pressure can up to 125 PSI. Even the homemade leak down test set I have made and use for 6 yrs uses a pressure regulator but I have a commercially made one for the last 4 yrs. Basically the other testers use two 100+ psi gauges with a .140" orifice [metering section]. It is the second [percentage] gauge that is marked in percentages instead PSI on the commercial sets but if you use a regulator, 2 regular 100+ gauges with the orifice between the two gauges, the first one is set at 100 psi and the second would read 80 psi for a 20% leakage, 70 psi for a 30% leakage, and so forth.
     
    Does this makes sense now?
    Fordrulz
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    Re: No start 2019/04/10 16:58:47 (permalink)
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    So I did a compression test it has 0psi. Did a leak down test with the rockers removed so the valves were closed set gauge to 70psi on left gauge and the gauge on the right rear 10psi with it hooked to engine and I feel air out the carb it doesn't change mush depending on where the piston is.
    AVB
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    Re: No start 2019/04/10 17:12:36 (permalink)
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    Then you have a problem with the intake valve, valve guide, or seat. This will require removing the head for further investigation.
    Mikel1
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    Re: No start 2019/04/10 18:59:17 (permalink)
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    AVB
    Mikel1
    True.
    Not sure I understand the 10-15 psi, unless your referring to the guage numbers.

    Yes it is the regulated input pressure with leakage percentage gauge at set position before applying to the cylinder. The line input pressure can up to 125 PSI. Even the homemade leak down test set I have made and use for 6 yrs uses a pressure regulator but I have a commercially made one for the last 4 yrs. Basically the other testers use two 100+ psi gauges with a .140" orifice [metering section]. It is the second [percentage] gauge that is marked in percentages instead PSI on the commercial sets but if you use a regulator, 2 regular 100+ gauges with the orifice between the two gauges, the first one is set at 100 psi and the second would read 80 psi for a 20% leakage, 70 psi for a 30% leakage, and so forth.
     
    Does this makes sense now?

    Yeah I see what your saying, I was thinking it was input psi to
    output psi and that tool pressure at air compressor could be dropped to compensate. Sorry for the delay was busy and was cutting grass.
    Mikel1
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    Re: No start 2019/04/10 19:03:31 (permalink)
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    Fordrulz
    So I did a compression test it has 0psi. Did a leak down test with the rockers removed so the valves were closed set gauge to 70psi on left gauge and the gauge on the right rear 10psi with it hooked to engine and I feel air out the carb it doesn't change mush depending on where the piston is.

    Sorry we high jacked your thread😂. Compression test and ldt were both together. Let us know what you find
    Fordrulz
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    Re: No start 2019/04/10 19:21:53 (permalink)
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    Pulled the cyl head and the valves look good and so does the seat. I noticed very small movements in the pushrod maybe 1/4inch or so. Does that sound like enough? Might have a camshaft issue??
    Fordrulz
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    Re: No start 2019/04/10 19:28:33 (permalink)
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    Got spark, going to check compression tonight. Have good fuel to carb. Not sure if it is reaching the plug though. Not sure on the timing. My initial thought is was the cracked vac hose but vac is still fairly week at the carb so maybe it is not pumping the fuel like it should due to low compression????
    Fordrulz
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    Re: No start 2019/04/10 19:32:19 (permalink)
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    I removed the head and cheked the valves, seats, guides and pushrod they all look good. I noticed the pushrods only move 1/4 inch or so when spinning engine is this enough to operate the valves or is there a possible cam issue??
    Mikel1
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    Re: No start 2019/04/14 18:11:03 (permalink)
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    That much leakage on ldt and everything is good?🤔
    Fordrulz
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    Re: No start 2019/04/15 18:02:03 (permalink)
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    Think its timing or in the cyl wall??
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