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Old 05-09-2011, 09:13 PM   #1 (permalink)
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Evo Oil Pressure

I just put an oil pressure gauge on my '98 Road King. The bike has 11,400 miles on it. The pressure gauge registers about 11lbs at a hot idle and jumps to 20 lbs. with a quick throttle twist.

This seems low to me. The bike runs great.

Thanks
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Old 05-09-2011, 09:16 PM   #2 (permalink)
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Nope. Perfectly normal. Repair Manual gives specs of 7-35 psi range. Evo doesn't need oil pressure so much as oil presence. Only the tappets rely on high pressure, and the passages up the pushrods, into and through the rocker shafts. That's it....

Mine runs 23 highway (hot) and 15 idle. On really HOT days, I'll see 18 highway and 8-9 at idle.
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Old 05-10-2011, 05:55 AM   #3 (permalink)
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The Evo doesn't have a crankcase. For the oil to run back to the tank it would have to run up hill, when you shut the engine off the oil stays right where its at. I don't know about S&S pumps, but the stock one has a filter screen in it. Its located right on top of the pump. It should be cleaned, their is a spring around the screen that we used to stretch a little bit to boost the oil pressure. Maybe S&S has the same on their pumps. Hope that helps.
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Old 05-10-2011, 06:31 PM   #4 (permalink)
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Quote:
Originally Posted by santaclara View Post
...their is a spring around the screen that we used to stretch a little bit to boost the oil pressure.
The spring isn't at the oil screen, (oil screen is in the boock) it's under a cap on the oil pump that covers the oil pressure relief valve.

The increased spring pressure raises the amount of oil pressure needed to lift the slide and allow oil to the bottom end. This results in increase oil pressure to the top end at idle.

What it does is forces all the oil to the lifters and the top end.

When the amount of oil directed to the lifters cannot pass through the lifters and the top end, it builds up pressure and raises the slide allowing oil to flow to the connecting rod bearings.

In a hot motor at idle, the oil flows through the top end and doesn't build enough pressure to lift the slide, thus depriving your bottom end from receiving oil.

The stock spring was designed to balance the needs of the top and bottom end oiling requirements. In the good ole' days, people would remove the stock spring and stretch it. Then your guess was as good as anyones as to when it opened.

The spring is used to compensate for other problems. As mentioned above, rocker arm bushings, lifters, pump body scoring, worn pump gears and lifter blocks are more than likely the cause.

I don't recommend simply stretching the spring.............
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Old 05-10-2011, 09:29 PM   #5 (permalink)
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Thanks for the info, Dave.

I know it's probably also normal to hear a tapping while cruising along. I assume it's the valves tapping. Should I hear this or does it indicate the top end is being starved for oil? Thanks.
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Old 05-10-2011, 09:32 PM   #6 (permalink)
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You may have a weak lifter. (Tappet) The front exhaust tappet is the most common to go, as it's angle and distance from the pump. HD recommends replacement at 25K. Excessive pinion/cam gear lash can cause the same noise.....

Make sure it's not an exhaust leak at the pipe/head too. They can be deceiving.
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