rebuilt motor, low oil pressure - Honda Prelude Forum

berkshire40 · 10-25-2005, 10:59 AM

okay so I rebuilt my engine. same rods/rings/pistons, new crank/bearings (yes I checked the clearances), new cams, new valve springs & retainers, cam gears, etc...

i have a low oil pressure problem, when the car is warm the red oil light comes on gradually at idle only.

i just bought an oil pressure gauge but havent hooked it up yet. the car obviously has low oil pressure. how do i increase it? i am told i can take off the oil pan and adjust the relief valve in the oil pump.

is this true? anyone done it before?

thanks

71dsp · 10-25-2005, 11:05 AM

The only way to adjust the relief valve in the oil pump is to shim it, and it shouldn't have any shims in it to begin with, so shimming the pump is only going to mask your problems. Did you install all of the oil control orifices correctly? IIRC, there is one in the block and two in the head. Have you checked for leaks?

The oil pressure light switch comes on at about 7.5 PSIG, and the sending unit sits right after the output from the oil pump, so if that light is coming on, that's very bad news. I assume you reinstalled the balance shafts?

I wouldn't run the engine for any period of time with oil pressure that low. The cams won't be getting enough oil and that will probably cause some damage to the cams and valve rockers.

Install the gauge and see what the oil pressure actually is. It might be a faulty sending unit. I'd also install the gauge in the head to see what pressure you're seeing at the head.

On my car, hot idle is about 25 PSI in the head, but runs to around 100 PSI as I get close to 8k RPMs.

berkshire40 · 10-25-2005, 11:18 AM

dont worry i know better lol...
the car is parked until i get this straightened out but keep in mind im a motor building newb.

yes i replaced the oil control orfaces, i was especially concerned about the one in the bearing cap cradle because previously the motor had issues with the main bearings.

there is a small leak by the distributor, im gonna fix that up (new o-ring, some more sealant) and see if it solves my pressure issues.

thanks for the help

McLude · 10-25-2005, 01:19 PM

It may still be your main bearings. My car had the exact same problem. The oil light would kind of flicker. We heard a very light tapping that almost sounded like a valve, but with a stethescope we heard it coming from the block. Thought it was a rod bearing, but when we ripped apart the block, the main bearings were totally scored and I had a coppermine for a block.

71dsp · 10-25-2005, 02:53 PM

Quote:

Originally Posted by berkshire40

there is a small leak by the distributor, im gonna fix that up (new o-ring, some more sealant) and see if it solves my pressure issues.

That o-ring has nothing to do with oil pressure. The head is open to the bottom end, and is not (or should not be) pressurized, and the o-ring just keeps oil from leaking out around the distributor. There are no oil passages around or behind the distributor that the o-ring seals.

berkshire40 · 10-26-2005, 07:52 AM

Quote:

Originally Posted by Agent BB6-T

It may still be your main bearings.

my main bearings AND crank are 100% brand new OEM honda. i got the color of the bearings from the stampings on the block, crank, and rods. also verified the oil clearances with a plastigauge.

71dsp, you're right, the distributor should not affect the oil pressure but it was a problem i had to fix anyways.

i also had the alternator belt too tight.

not sure what else to do besides shim the oil release valve. i could take off the valve cover and clean out the two orfaces in the head?

i was also told running thicker oil can help.

any thoughts?

thanks for the input.

edit: 71dsp, in answer to your first post, the balance shafts are in with new seals on the gear, belt, everything. i would have removed them if i could do it over (Which im sure i will eventually)

71dsp · 10-26-2005, 09:53 AM

I would put an oil pressure gauge on the bottom end and on the head and see what the numbers look like before I did anything else.

McLude · 10-26-2005, 10:24 AM

Quote:

Originally Posted by berkshire40

my main bearings AND crank are 100% brand new OEM honda. i got the color of the bearings from the stampings on the block, crank, and rods. also verified the oil clearances with a plastigauge.

71dsp, you're right, the distributor should not affect the oil pressure but it was a problem i had to fix anyways.

i also had the alternator belt too tight.

not sure what else to do besides shim the oil release valve. i could take off the valve cover and clean out the two orfaces in the head?

i was also told running thicker oil can help.

any thoughts?

thanks for the input.

edit: 71dsp, in answer to your first post, the balance shafts are in with new seals on the gear, belt, everything. i would have removed them if i could do it over (Which im sure i will eventually)

ALL of my bearings were also brand new OEM HONDA as well. It was a complete rebuild all the way. My crank was balanced, micropolished, and journal sized. The bearings just wore out because of low oil pressure, not because they were old. It doesnt matter how new your bearings are. I'm not saying I'm right. I just had the same symptoms on a fully rebuild brand new motor. I hope you're not having the same problem I had, but I wouldnt be suprised. Let us know what you find out.

71dsp · 10-26-2005, 10:32 AM

I would assume that you used PLENTY of assembly lube on the bearings, crank, cams, rockers, etc. Right??

berkshire40 · 10-26-2005, 11:12 AM

yes, i went through almost two tubes (1 was the smaller crower tube that came with the cams)

my bad, i thought you were assuming my bearings werent new. i havent driven on them very much yet so hopefully they havent worn very much. like i said the car isnt going anywhere til i figure out a way to increase the pressure all around.

i plan on hooking up the gauge tonight. ill have to search where to hook it up on the head though, im guessing its near the pressure switch somewhere.

thanks again

71dsp · 10-26-2005, 11:29 AM

On the passenger's side, near the back of the head by the coil. There is a BSPT plug that can be removed.

berkshire40 · 10-28-2005, 12:23 AM

OK finally. after buying the wrong fittings for my gauge, i went to summit and bought a stainless steel line hookup and got the thing installed right. also put some thicker oil in. one question: do i really have to ground the wire for the gauge by the sending unit? i havent checked the pressure yet but when i started it up cold it was like 60 psi which seemed a bit much. ill get it warm tomorrow and get some more readings, i just want to make sure i have the gauge hooked up right so they are accurate.

thanks

71dsp · 10-28-2005, 04:45 AM

You don't have to ground the wire for the stock sending unit. It's a ground sensing unit. Grounding it out will just make the light come on.

60 PSI cold is fine. Mine is close to 80 PSI cold.

berkshire40 · 10-28-2005, 06:49 AM

i was talking about the ground wire for the gauge. i have it in the head so no need to T for the stock sending unit.

berkshire40 · 10-28-2005, 07:24 AM

okay, so i let it run longer and its not good. im getting pretty low pressure in the head (under 5 psi at idle when warm). i have very good pressure at higher RPM though. should i move on and check it in the block or dont even bother? im not quite sure what to do next...it seems like the problem is ONLY at idle (<1100 RPM).

it seems like when i drop down to idle it hovers at about 10psi for a bit, then drops down more for some reason.

thanks

71dsp · 10-28-2005, 09:13 AM

I'd check pressure at the stock sending unit location too. It's the main feed into the engine block, and if it's low, the pressure throughout the entire engine is low. Just pull the stock sending unit (you don't have to ground it or anything), and use a BSPT adapter to install an oil pressure gauge in the stock location.

When hot, I get 25 PSI steadily at idle. I'd say there's a problem. I'd at least pull the valve cover and see what the oil control orifices look like under the caps. If they're clogged or whatnot, that could be the problem. Hopefully it's not the oil control orifice in the block!!

71dsp · 10-28-2005, 09:14 AM

By the way, what's good pressure at higher RPMs? Mine is like 80 PSI right off idle!! Well, maybe not 80, but close to 70. Almost 100 PSI by 4 or 5k RPMs.

berkshire40 · 10-28-2005, 09:22 AM

yeah i was around 80...it was way up there i was suprised. may have even hit 90 if i remember correctly around 3-4k

i will check the pressure in the block as well.

the oil control orifice in the block is located under the middle main bearing cap correct? I replaced the o-ring for this orifice and cleaned it....should be fine!

im frustrated to say the least. thanks so much for the help, ill let you know what #s i come up with

71dsp · 10-28-2005, 09:48 AM

Sorry, I said the wrong thing. I meant to ask if you checked all 3 oil control orifices in the head. There isn't one in the block, IIRC. There's just an o-ring in the girdle.

nuro · 10-28-2005, 10:07 AM

holy crap billy your car is done?! where's the thread i want to see all the pics and what you're running!