Question about 1979 Harley Davidson XLS 1000

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Low oil pressure at rocker box

My 79 xls has low? pressure at the rocker box when hot. cold with 50w hd oil has 40 psi then when warm(after 5 min running) drops to 0. at 3500 rpm hot has approximatley 1 psi. is this normal or should i look for worn rocker bushings or weak pump? anyone please help cause i haven't had a clear answer from anyone!! thanx

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  • 79ironhead May 02, 2009

    my oil is circulating and have oil to both rocker boxes when cranking. i haven't had problems with wet sumping. i did put 2 guages on, 1 at pump and 1 at rear rocker box, and started cold. about 38-40 degrees. upon startup had 100+ at pump(pegged my guage) and 45 at rockers. engine at 1800rpms. warm after running 5-7 minutes had 1-4 at pump and 0-1 at rocker with 50 w oil and new filter. i also have vacuum in the oil tank when running. when i pull out the dipstick the engine drops in rpm, about 75-125 rpms, and runs uneven. it doesn't smoke and isn't oily in the pipes. when revved warm to 3500rpms pressure at pump is 6-10 and at the rocker is 0-3. is there anything i can check or is it just that way?

  • 79ironhead May 02, 2009

    this was all with the air filter off the bike

  • 79ironhead May 05, 2009

    all tests were done with air filter installed and does have breather hose from cam cover by generator to air cleaner. carb is kehin(?) original. and engine is bored 0.020" over and has about 10k on upper rebuild. 29k on bike. also have dual open 2" drag pipes for exhaust. went on little ride sunday(2nd) and had 0 pressure at rockers at 65mph and engine at 3100rpms. had no noise or problems but am worried about no pressure.

  • Mel Jacobson
    Mel Jacobson May 11, 2010

    I dont know what the problem is ... but no ..... your pressure should never drop below 5 ,, I'd start by checking all yer lines for blockage.... check and make sure the oil is circulating to the tank.. let me know

  • Anonymous Mar 22, 2014

    oil spitting out of rocker box pushrod tube hole

  • Anonymous Mar 23, 2014

    Pressure is good at idle but drops to 0 when ridding? Thanks!



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The Ironhead Sportys have a tendency to do this when the Gerotor Gear Set is worn. These are the thin set of drive gears in the oil pump. HD Part # 26492-75. Do you have a problem WET SUMPING? This is when the oil drains from the reservoir into the crank case if the bike sits for a period of time and when you attempt to start it pukes oil from the breather tube. If so you need to check these gears. Gerotor Gear Sets inner/outer clearance should be .000 the shaft should have a clearance of .0005 and the feed gear height in the pump should be .011. Normal operating pressure when hot should be 4 psi at idle and 10-20 psi at 3500 rpm. The pumps generally have issues before the rocker bushings.

Posted on May 01, 2009

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  • smitty368 May 02, 2009

    There are 3 lines connected to the oil tank. One connects to the lower left inside under the battery box (near the drain plug) and is the feed line connecting to the rear of the pump, the second line connects to the upper left inside just above the battery box and is the return line connecting to the front of the pump, filter output or oil cooler return (depending on your setup), the third is connected to the top right under the seat and is a vent line that connects to the right side crank case just in front of the main sprocket (you have to remove the sprocket cover to get a good look at it). There is a forth line in this though, on the front of your cam cover (right side) you have either a down tube for venting or a breather hose connected to the back plate of your carburetor. I mention both as some early “79” models had the "78" style down tube. If you look at the generator bump on the front of the cam cover you will see the "flats" for both, the down tube would connected to the 6 o'clock position flat and goes to ground and the breather hose would connect to the 9/10 o'clock position a connects to the carb. If you have the down tube there shouldn't be a noticeable vacuum in the oil tank, if you have the breather tube the carb creates a vacuum through the hose to the crank case and to the oil tank through the vent line. The vacuum will vary depending on how clean your air filter is. The dirtier the filter the more air it will draw through the Crank Case & Open Oil Tank. You might consider removing your air filter, replace the filter cover, start the bike and see if there is a significant change. If so change the filter. If you are running a K&N style oil dressed filter this also increases the resistance the filter creates increasing the draw through the oil tank when opened. With a dirty filter or oil dressed filter the reason the bike’s rpm changes is when you open the oil tank while running you change it from a “sealed” system to an open system effecting the way the bike is breathing and with the increased air flow the air/fuel mixture will be enriched causing the rpm change. The vacuum is not a real issue, but be sure to check your filter.

    As to oil, I live in Cleveland and run 60w oil year round. If you are in a warmer climate than Cleveland consider moving up to 60w. I also add 6 - 8 oz of Lucas Heavy Duty Oil Stabilizer to prevent dry starts and help with oil viscosity break down. The Lucas doesn’t help with wet sumping when the Gerotor gears get worn though.

    Sorry about the length of this post, I’m just trying to be complete.

  • smitty368 May 03, 2009

    What carb does your bike have? Is your bike using the breather hose attached to the air filter backing plate? What type exhaust do you have the 2 into 1 or dual single?

  • smitty368 May 10, 2009

    All seems correct with the carb set-up, hoses and pipes so my concerns go back to the gerotor gears in the pump. Try an oil change to the 60w with a few oz of the Lucas. If that fixes the problem then the gear are most likely worn but not worn out. If it doesn't fix the problem then the chances are the only cheap fix is to rebuild the pump. But this is still cheaper than the heads.

    Good Luck



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