Thread: track test problems

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Sorry for the long story but might be nessacary for a proper answer.

O.K. heres the senareo. When I first recieved the nitro harley it had no oil pressure, I removed the pump and discovered the o-ring seal was missing on top the pump. I replaced the seal and immediately got oil pressure. If youve followed this bike in step weve also had old fuel problems and also ironed that out. We went for a practice session at the track Sunday All seemed good. We warmed the motor up on alcohol as I was advised on here, then again on 94% nitromethane.

Now heres the problem, on the nitro warm up we had a solid 145 LBS oil pressure. He racked the throttle a few times to run in the clutch and then the oil pressure dropped to 90 LBS and stayed there. The bike was shut off and cooled for about 30 minutes. He was hessitant about the drop in pressure, so we fired it back up. It held at 90 LBS for a couple minutes then dropped to 45 LBS.

We shut it down and blew out all 9 of the oil lines one at a time, cleaned the resivoir, changed the oil, and started it again. The pressure went up again to 120 LBS, after a minute it dropped to 45LBS, then another 30 seconds back to 90 LBS, twenty seconds later back to 40 LBS, then 30 seconds later we were at ZERO. Well I pulled the pump again, The seal had a tear in it but I dont think enough to cause that or if it had anything to do with it to begin with. We cleaned out the system again and just cranked it over, not starting it. Still NO OIL pressure.

This leads to my previous leak down question posted earlier. We are hearing that if the rings are bad there will be NO OIL PRESSURE. That I dont get because it is a mechanical pump ran by the crank gear, and it blasts oil from spinning the shaft, but it will not fill the line to the gauge. I would think it would show some pressure at least, Is this true or will bad rings cause absolute ZERO oil pressure in this situation, and can both cylinders go bad within a few minutes to cause that? It did not sound odd or make any strange noises either.

Originally Posted by DennyW

Right off the top, it sounds like a pressure relief not working properly to me, or a clogged pickup screen.

Thats my thought sort of, I will have it on my bench tomorrow for a complete teardown. Ive read where one model like this has a checkball as well. Its got 3 ports for suction, one from a line at rear, and two from internally inside the case. I dont know still cofused on the bad rings suggestion though.

heres a like pump picture. and ya its 560.00 for a new one. But that would beat a complete teardow of the top end.

Don't see where the rings would have anything to do with it.....


What kind of oil pump is that, Moon???? Looks like there must be seals in between the stack plates, sounds like one of them could be bad.... Another thing could be that the scavenge lines, either the threads or around the hoses are sucking air.... Had that problem on an old pan/shovel many years ago.....

Is there a pressure relief spring behind that Allen plug on the left side?????

Is the oil pressure gauge "Direct Mounted" to the engine? If so take it off and shake it to see (hear) if it has shaken the internals apart.

We have had this problem several times on our VW drag motors due to vibration. Several gauges would not even last the weekend before erratic readings. The cure for us was to take the direct gauge (or sender) and place a short piece of -3AN stainless hose between the engine case and the direct gauge (or sender) to isolate it on the car body.

Also sounds like you have a relief valve problem. Are you using a filter with a valve?

Originally Posted by Dave Severson

Don't see where the rings would have anything to do with it.....


What kind of oil pump is that, Moon???? Looks like there must be seals in between the stack plates, sounds like one of them could be bad.... Another thing could be that the scavenge lines, either the threads or around the hoses are sucking air.... Had that problem on an old pan/shovel many years ago.....

Dave, The pump is a company called zipper, they make alot of aftermarket stuff for these fueler bikes. I will split it this afternoon and check the seals between the layers. all the lines pushing and pulling are new Earls AN fittings, as far as the allen screw, I dont know whats behind it yet.,

Denny, the O-ring went somewhere, and from where it came at top it had to pass through the pump now that you got me thinking about that.

John, the vibration idea is a good thought. It is mounted on a rubber pad directly in front of the motor. I'll move it to the rear of the bike as far away as I can. The rider cant see it anyway, its solely for the crew to look at. I'll set it on the ground off the bike for a test. But this damn thing vibrates so bad with 94% nitromethane. It litteraly walks on the stand 4 feet across the ground on warmup with 2 people holding it down. Thanks everyone for your thoughts I will post what I find in that pump tonight,

Some of the crud from the seals could be in the gauge or the passage leading to it.

I just tore every piece of the pump apart, It is spotless. Now I guess I will bang my head against a wall. I will mock up a bench test with an oil can and spin it with a drill and install another gauge ive got laying around. Then if it still wont work, It Looks like its time for a leakdown test next.

I still agree with your first thought that a "leak down" problem should not have much to do with a low oil pressure problem.

It's got to be either in one of two areas. 1) you have an actual "oil pressure" problem. And you have already checked and eliminated the oil pump so maybe you have a scavange pump oil problem and the pump is sucking air, which is then causing the erratic oil pressure readings.

Or 2) you only have a problem with the "indicated oil pressure". You would need to hook-up a quality test gauge "not mounted to the vibrating vehicle" and see if you get the same original pressure results. Whenever I have found the cause of one of these difficult to diagnose problems, it always turned out to be something simple, or dumb. Hang in there.

Just some ideas

thanks for the insight john. About thursday we will get togther, build it back up and lay my liquid filled gauge from my mustang on the floor and spin it over. Until then its just time to give it a break for a day or two.

if you are suspecting the rings in the cyl,jugs, it has nothing to do with oil pressure.sounds like an obstruction or pressure relief problem.