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Post-rebuild bearing care: proper way to prime? Is idling bad? - Engine/Ancilliaries - The Lotus Forums Jump to content
ESPREE

Post-rebuild bearing care: proper way to prime? Is idling bad?

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So my 1999 V8 is just about at the end of its 3rd rebuild in about a year's time (see other threads for details), and I'm trying to learn as much as I can about the best post-rebuild process so that I can talk to my mechanic somewhat knowledgeably. I am really hoping that I never have to hear the sound of rattling bearings again!

Once you have rebuilt an engine, putting assembly lube in all the bearings, what is the right way to "prime" the engine to get the oil everywhere before actually starting it?

The Lotus manual suggests removing the spark for a few cranks until pressure is up, and then you are good.

But do you have to use some kind of hand pump to get the oil in everywhere first?

I am also wondering if proper oil pressure can exist at very low RPMs, like what is shown here from my second rebuild:

They were flushing the oil, testing for leaks, and making sure everything was good, but I wonder if doing this might have caused more bearing wear if there was not enough oil pressure. I don't know how they were making the engine turn. Is this a normal (good) thing to do?

Finally, once the engine is in the car and running, is it bad to let it idle in the shop for a long period? They had done this for many hours to again make sure there were no leaks and everything was working well, but I remember hearing that you should avoid extended periods of idling after a rebuild. Does that mean you should start driving it right away?

Thanks for any thoughts.

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Priming without a spark is merely to get some pressure before running at idle rpm (and above). Not a lot of difference to doing this after an oil change to when doing it after a rebuild (hopefully everything's been liberally coated during the build). Low (i.e. idle) rpm on first start is generally avoided when bedding in new cams and/or piston rings. I personally wouldn't run any engine at cranking speeds for a prolonged periods due to the lack of oil pressure.

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mention: to undo the relays for the fuel-pumps/injectors

..as trying to start without sparkplug-leads still means that fuel is injected, and gets into the combustion chamber -unburnd !

You can ask you'r workshop to fit an 'overrun pipe' from one side of the oil-cooler port to the other on the oil-filter. As with this you do not need to fill in so much oil ...the oil gets into the right working temperature faster, and the way the oil has to go is shorter at least. The initial pressure on 'starter -crank-rpm' is all the engine sees every day of its life, so that's why every oil-pump is designed to offer an basic pressure even under low rpm. Of course, an engine that was stopped after it has runed there still is some oil in the bearing, making the next 'start-crank' less risky in terms of wear (that's why you fit the new parts with this assemply-grease to have something between the surfaces from first time on)

*as a note: the sound in your video, and the speed the clutch/crank-pulley show indicates a notable slow crank ?! Think without sparkplug (as such with no compression) it should crank with a much faster spinn ! ..so the guess is there was something on the crank that was not calibrated with the right dimension. Are you shure that the bearing shells were clamped the right way, and *plastigage-strips* used to verify ??

Edited by Günter

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Hi Derek and Gunter,

Thanks for the info.

mention: to undo the relays for the fuel-pumps/injectors

..as trying to start without sparkplug-leads still means that fuel is injected, and gets into the combustion chamber -unburnd !

Yes - good thought. It's odd that the service manual says "the engine should be cranked with the ignition disabled until oil pressure is registered on the gauge", because you are right that fuel will be injected and then left unburnt!

You can ask you'r workshop to fit an 'overrun pipe' from one side of the oil-cooler port to the other on the oil-filter.

Yes, I believe this is the setup he had when the engine was in the video - there was a short bypass oil tube instead of the long run to the oil coolers.

*as a note: the sound in your video, and the speed the clutch/crank-pulley show indicates a notable slow crank ?! Think without sparkplug (as such with no compression) it should crank with a much faster spinn ! ..so the guess is there was something on the crank that was not calibrated with the right dimension. Are you shure that the bearing shells were clamped the right way, and *plastigage-strips* used to verify ??

Well that video was from the second rebuild and I am not sure. I know at least for the current build (#3) that all of the measurements and tolerances are supposed to be checked and rechecked by the machine shop, even with the bearings in place for good measure.

But wouldn't the speed of that test setup depend too on whatever power source is driving it? I have no idea if that was compressed air or a electric motor of some kind - maybe the speed is variable.

So you think that test setup in general is an ok thing to do - i.e. there is enough oil pressure at that very low speed to keep the new bearings properly lubricated?

Edited by ESPREE

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the *tincan*-sound on the rear, near the clutch was from the starter turning the flywheel and as such crank the engine

(and think you can actually see the starter there on the flyweehl, top side with the dog-gear spinning ?)

if you hit the flywheel with an screwdriver it makes those 'cristall'-bell sounds you can hear in nearly all videos of starting 918 engines, as the flywheel actl like a bell


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to name the things if I see them, that's what I call integrity..

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It is a bit misleading of the manual to refer to disabling the 'ignition', disabling the fuel pump is better and usually the easiest thing to do.

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