No oil pressure?! WTF. Help!

[dtw]

Brand new rebuild on Tim's 2.4. Oil bypass mod, correct springs and pistons, moving freely in their bores, SC oil pump, everything carefully put together. We fired it up and got 20psi, cold. Depending on the weather, my new 2.4 gets 40-60psi, cold. Changes in RPM do nothing - we goosed it up to 3k rpm, the pressure just stays dead, 15-20 psi, no change.

Gauges are ruled out. Tryed new sender, tried new gauge, tried wiring the gauge directly to the sender in the back of the car, tried two different mechanical gauges. Harbor Freight special and a brand-new Snap-On. All gauges read dead nuts - 20 psi or less. Often hovering around 15 psi.

Called the local wrench this afternoon and he confirmed our worst fears - only thing he could think of if the bypass pistons were in good shape, was an oil seal left off the pump. Even though we were 100% sure the oil seals were in place, we ripped the engine back out of the car and tore it apart. All oil seals were in place - the engine looked perfect upon disassembly. Thermostat was oriented what I believe to be correctly - the "cold" position was directing oil back towards the oil pressure sender, not out to the cooler. The bearings haven't even been scuffed up yet - they still look they came out of the box 5 minutes ago.

What's going on in here?? Could there be some kind of blocked passage? Need some ideas here.

[thunderdenton]

I am not an expert... That being said i just rebuild an engine and started it yesterday.

The oil pressure never came up because of the assembly lube...

Don't know if you are having the same problem, but after the first oil change the pressure came up.

Thunder Denton

[Wayne 962]

Despite the fact that it appears like it can be inserted backwards, the thermostat only goes in one way (the studs are offset slightly). For future people here, I would recommend waiting and getting a few more opinions before tearing down the engine.

Check the piston bore of the oil pressure piston. Sometimes the plugs in the case become loose and interfere with the proper movement of these.

Did you have the case flattened and remachined (can create large clearances if the case is bowed?). If you suspect this, then one solution would be to bolt the case together and use a dial-bore gauge to check.

Any noticeable leaks?

My tech editor (for the book) says that sometimes they run low (2-3%), but after running for about 20 minutes, it came up to higher oil pressure. He thinks the problem that time was maybe something screwy with the Carrera chain tensioners.

The engine should have 60-100 lbs of pressure when starting up.

Are you measuring back by the thermostat (higher oil pressure) or at the front of the engine (near the chain tensioners)?

-Wayne

[dtw]

-No major leaks
-No case resurfacing, std bearings, we're going to put the dial bore gauge on the case tomorrow
-Measuring at the thermostat area (2.4L)

Sorry for brief response wife's yelling at me to go to church - but keep the thoughts coming. Should we just run it for 20? Sounds scary at 15-20lbs of pressure.

[Wayne 962]

Dialbore the case - there could be excessive bowing/clearances that is just bleeding off oil pressure.

Piston squirters in this case? (should be).

-Wayne

[Tyson Schmidt]

Measure the seated depth of the bypass pistons. I've seen them not fuuly seat, yet still move freely in the bore. Once it was on a case that had the galley plugs removed and replaced, and the epoxy stuck ever so slightly into the path of the piston. The piston moved up and fine, but the epoxy kept it from seating completely. I checked the depth with a caliper, and compared it to another engine. that's how i found the problem.

[Tim Walsh]

This case does have piston squirters which tested out just fine with air.

Tyson,
That's the first logical explination I've heard yet. I'm taking the case to the machine shop this morning so I'll have that checked then.

[BK911]

I had the same problem with an eninge that had the oil bypass mod done incorrectly.

[dtw]

Update:
Had a local wrench and Dave Brown of Speedwerks look over the case this morning. Findings:
-Scavenge pipe to the oil pump was loose in the pump body, pipe could conceivably have been sucking air and aerating the oil.
-Squeezeout of 574 into the mains caused a noticeable plug of dried sealant between bearing halves, possibly causing a bad bearing clearance.
-Gunk buildup in the lower bypass bore went unnoticed somehow. Possible that the piston was not seating and pressure was being lost (Tyson - you may be our lucky winner).
-BK - we thought the same thing about the bypass after all the "easy" culprits had been eliminated. We checked it on the bench and the passages appeared to be clear and drilled properly. Machinist re-examined as well and found no issues.

As we've seen these three items that escaped the build, we're going to correct them and rebuild tomorrow. If that doesn't work, someone may be able to get a brown 911 with low oil pressure real cheap from Tim. He's downstairs in the garage right now sorting through the case.

Build Theory
Brown had some choice words about a few of our build-up techniques. He claims that the application of 574 to the main webs is a no-no, for the exact reasons we noted above. Argues that it should have no impact on the case torque-down, which is the popular argument here in favor of applying orange goop to all mating surfaces (which I have been a proponent of as well). He felt our issue was timely, as he was just in the midst of working on an engine rebuilt by a DIY guy - the 574 had actually caked up in a through-bolt hole, blocked the main bearing feed to that journal, and starved/roasted a bearing.

Another one was the rod-bolt/loctite argument- he really went nuts when, upon complaining of the torque required to break the a rod nut loose, he learned that they had been loctited. Actually both the local mechanic and the race shop were astounded this was done and both vehemently argued against. Dave Brown's explanation was quite technical.

[Doug Zielke]

Thanks for mentioning the comments of Dave Brown.
Very interesting to have the views of another professional mechanic.

[davidl]

Hello there.

I'll bet serious money you have a bent and battered case.

The presence of significant Loctite between the webs makes this almost certain IMHO.

I'd want it bore guaged and checked for alignment..

Kind regards
David

[Tim Walsh]

While we were at the machine shop we wanted the crank and case checked out. Both came out just fine. The case has had a line hone run through it but is still std.

[davidl]

I'm afraid I'm not convonced about this line hone thing..

No-one can convonce me you can remove enough metal with a line hone to make a case straight without skimming the case halves to keep the bore to size..

Can anyone explain where I'm wrong on this?

I've seen some very "creative" use of bore guages over theyears..



Kind regards
David

[Tim Walsh]

David,
I'm sorry but I'm still going to disagree with you on this one. My machinist is a well respected race mechanic who's built hundreds of motors, knows what works and what doesn't. I personally watched him check the case and the crank and both came out just fine without any funny business. When the case came back the webs weren't so much as honed as they were "scratched", the hone had JUST BARELY touched the main webs.

[davidl]

Fair enough, Tim.

I'm not impugning him.

If No metal was removed, I would seriusly ask why it was necessary to hone it at all ?
And had any metal been removed, would he then have skimmed it to bring it back to size?

Just agin logic IMHO..

Also, why did RTV remain between the webs after torquing?
It should virtually all have squeezed out..barely a diaphenous, holey, almost undetectable veil, remaining on most eninges I've seen where it was used on the webs....



Kind regards
David

[Tim Walsh]

David,
I'm not sure why he ran the hone since I bought the case from a friend (dtw) and wasn't around when the case was actually prepped.

I'm not sure exactly what happened there. I followed the instructions in the rebuild book to the T. I'm slightly confused though in the book where it says there should be loctite up to but not on the bearings and yet a page or 2 later it says there should be "significant squeeze out" so what happens at the bearing to that squeeze out at the bearing? In my case it left little chunks by the bearings.

[dtw]

Originally posted by davidl
Hello there.

I'll bet serious money you have a bent and battered case.

The presence of significant Loctite between the webs makes this almost certain IMHO.

I'd want it bore guaged and checked for alignment..

Kind regards
David

The case has been repeatedly checked with the dial bore gauge. I have been present for each of the tests (the original check, the check after the hone, and the sanity check yesterday), and there is no "creative usage" as you call it- the bore is dead nuts straight and true. The case deck was examined for flatness/warpage with zero problems.

This case had a hone run through it due to a very slight ovality condition, not case warpage; the crank began beating the bore after the mains started to go away. The shop was able to clean up the ovality and still stay inside a standard bearing size. In fact, the shop was quite pleased to report that the case had no measurable runout on the major axis.

I'm not trying to bark at you here, I am actually pretty sensitive to the use of a hone to clean up twisted cases. Fortunately I haven't run into a twisted case yet- when I do, I will bite the bullet and get one of the west coast gurus to properly repair it.

The squeezeout into the bearings was present all the way down; we undoubtedly applied too much Loctite. We will likely be admonished for "not doing it right" but the race shops opinion was, it's not necessary to place loctite on the webs in the first place.

There's a big Worldpac distribution center here in town so we often enjoy same-day delivery of parts - I'm going to bolt the bottom end back together today if all goes well. We began cleaning parts last night after a bonzai late night run to Wally World for cleaning supplies. BTW if someone was wondering if Wally World still sells guns, that's an affirmative...and they've got a nice selection of bore brushes too.

[davidl]

Hope you don't mind me coming back about this...

I'm also sceptical about this business of honing.

Hoing is an operation primarily intended to create the rrequired surface finish.
Which is perfect from the factory on every case i have seen..

If ovality was present in the case bores, does this not imply that the transverse axis diameter of the bores was over spec?

Surely, then, what honing will do is put both the transverse axis and the vertical axis over spec.?..and make them the same?

BTW I do not put RTV on the case webs, but I do not think it would cause any problem provided it does not block anything.

And will be virtually undetectably thin on a healthy block after torquing...

Kind regards
David

[Tim Walsh]

First of all the standard "spec" is actually a range of numbers so just because the bore is oval doesn't mean if it's "bored out" it will automaticly be out of spec.

I don't belive there is a "funnish" on the main journals it's just bare magnesium.

[davidl]

Hello, Tim.

I'm sorry if I have offended you..most definitely not my intent.

But I am trying to help you, and hopefully others, and enhance my knowledge too if possible...

Yes there is tolerance to the bearing housing... it is a nominal 62mm, maximum 0.019mm over.
This is very tight indeed, less than 0.8 of one thousandth of an inch, on diameter.

All surfaces have a finish, the term includes the appearance under magnification, the roughness, shape of the asperities, any compaction etc.
Hones are not designed to, and do NOT correct ovalisation.... they simply follow the surface which exists.

In my opinion the tolerance is so tight that any ovalisation would be out of spec, or not worth correcting anyway.

And if your wrench tells you different, refer him to any standard text...

Kind regards
David