KJF69

Thanks guys for all the Hayes reports in the archives.
Boots are shaking now. Just over a week back, dropped in a 13B Street 1 Port engine from you know who. Oh yeah, 88 Rx non turbo GXL.

My mechanic at Malcom's Auto Electric in Corvallis, OR (who has been great by the way) has two issues with this rebuild.

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One ~ Low oil preasure at idle. Hayes says 10lbs is normal at idle. (There is supposidly installed an eccentric shaft mod for oil flow.. ask me & I'll look it up)

Two ~ Compression is ~90lbs cold and ~80 warm on the Re-manuf. engine.
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My first trip out, I put 500 miles on it right away. Looking to resolve the low compression. And demystify the "Break in Period"

To my surprise, warm, I the stock oil gage reads so low, we're spooked. The needle sits very low.
Malcom's confirmed the oil preasure is indeed that low -- ruling out any sensor or wiring issues.

Ok guys --- your turn --- Lets say I leave the car idle for an hour parked with oil preasure like that?

Oh, and what is "normal"? I've never witnessed a "normal oil preasure idle" recommendation.


"Break In Period" I'm really not fond of the use of "break".
Getting close to $6000 on this rebuild ride.

Here's the scoop. Hayes informed us at 500 miles the engine will have better compression. Drove the 500 miles, same compression readings. The new gospel is it will improve at 1500 miles.
Give me your break in opinions, guys....

Oh, and great list, btw. I used to be on the Rx mailing list in 93-96 or so, when it started getting shuffled between servers. And got lots of advice replacing the engine in my 82 Rx.




[B]

tesla042

Before I replaced my oil pressure sender, it was reading ~25-30 at idle on the stock guage.. Now, with the new one, it reads REAL low...like 10 or so.. Scared the hell out of me.. But, I figured that either

(a) The new one is off, and the pressure is what the old one read
(b) The old one was off, and the new one is right...

Either way, the car runs real well... I often let it warm up by idling for 10-15 minutes in the morning... no bad side effects.. but I also am curious if this is "too low" or something.. I wish i had a mechanical guage to see what it really is at....

-Tesla

Wankel7

KJF69 - I have an atkins rebuild and it runs about 14 psi at idle and 55-60 at 3000 rpm. I guess the main question for you is this.

What is you oil pressure at 3000 rpm warmed up? Should be 64PSI - 70 something.

James

KJF69

Tesla & James,

Thanks for the replies.

To your question James,

At cold-->warm & running ~2-3000 RPM I see oil pressure no less than 30lbs and more like 60ish.

When I drive on the highway in 5th gear ~2700 RPM (now at operating temp) I see readings in the 30's.
Only on sudden acceleration do I see pressure jump to 60ish. Which then settles down.

Again at warm idle, we're talking very low on the gauge.

What do you guys think?
The mechanic told me flow is more important than pressure -- which I believe.
Any real sure fire ways to measure oil flow in an Rx?

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All readings taken in the cockpit with stock gauge and new OEM pressure sending unit.
---

-KJF

niner

im kinda wondering the same thing.
ive only got about 1500 miles on my new motor and i put a racing oil pressure regulator in-which i kind of regret now-
but at idle it will sometimes drop to almost nothing and it sometimes takes a sec to build pressure when motor speed is up.
ive started using premix just to be a little safer. oh yeah, but when im flooring it the pressure is usually almost off the scale according to the stock guage
...maybe thats not too good either though

copandengr

Flow is equally as important as pressure. Think of it this way; The oil pump puts out an equal amount of oil for each pump revolution. This is because the oil pump is a gear type and therefore a constant VOLUME pump. Now, think of the various places in the engine that the oil has to go. There are a lot of small diameter oil passages, plus the very small clearances between the e-shaft and the plain bearings.

The slower the engine speed, the lower the oil pressure because the oil FLOW is not great enough to meet much resistance. Sorta like a major city street at 2:00AM on a weekday night. Now speed up the engine and the increased volume starts to meet resistance because it has to take the same route, like the same city street at rush hour. This is where oil pressure comes from.

Pressure has very little to do with the protection the oil offers to the engine. Of much more concern is the oil's chemical shear strength. Shear strength is the point where the long chain polymer molecules begin to break down and become short molecules. This thins the oil to the point where it becomes too "runny or light" to offer protection to the plain bearings in the engine. As long as there is an intact thin film of oil separating the e-shaft from the plain bearings there is no danger of wear at all. Modern oils are light years ahead of what was available only a few years ago. Resistance to molecular shearing is why synthetic oils are vastly superior to dino juice.

Rotary engines are much easier on the plain bearings than piston engines are because of the fact they contain only rotating mass. A piston engine encounters tremendous pressures on the rod and main bearings every time the piston changes direction. Rotaries are much less likely to shear the oil molecules than a piston engine is. This is also why you never hear of an e-shaft failure in a rotary.

I know we all like to see high oil pressures because it makes us feel good. The thing is simply that a rotary does not need the oil pressure that a recip does because a rotary is not trying to tear itself apart with each revolution of the e-shaft. Nothing in your rotary is going boing boing. It simply goes hmmmmm.

I know this is a long post, but 10 psi hot at idle would not alarm me assuming the pressure at 3,000rom is near 60PSI.

Scott 89t2

how did you put the 500 miles on it? if it was highway then you can restart your break in period. you need to constantly change the rpm. shift, speed up, slow down, shift. etc....

my pressure is around 15psi at idle. and 60 at 3000 on my autometer.

KJF69

Thanks copandengr and Scott.

Great advise.
Copandengr -- Great insight... shouldn't your reply be put on a FAQ somewhere? Very usefull.

Scott, about the "break in"... you suggest I go back to city driving, starts stops, etc. to get myself up to 1500 miles?
I always that was harder on an engine's seals than highway drivng. Harder in a sence, that it would cause added stress in a way that might not benifit a new motor (or the seals, at least).

Anything you might add to your previous post?

-KJF

turboren

"Rotary engines are much easier on the plain bearings than piston engines are because of the fact they contain only rotating mass. A piston engine encounters tremendous pressures on the rod and main bearings every time the piston changes direction. Rotaries are much less likely to shear the oil molecules than a piston engine is. This is also why you never hear of an e-shaft failure in a rotary. "

Well, that, and they're so damn beefy. If piston engines had journals of similar size, they'd be much less likely to break. Of course, they'd be a LOT harder to accelerate, but they'd be super-effective as a braking assist.

Anyway, you can make a mechanical (tester) gauge in one of two ways:

1) Expensive:Go to automotive supplier and buy a mechanical gauge (Autometer, VDO, etc) and adapter.

2) Cheap: Go to local hardware store and buy:
a. water pressure gauge, reads 0-100 psi
b. 1/8" npt-to-hose-barb adaptors (2)
c. hose
d. brass pipe, 2-3", with 1/8" npt threads
e. teflon tape

Plug'n'play. The only difficult part is getting the US-threaded pipe to fit into the metric-threaded hole in the engine. For this I used a metric pipe-thread die, which I happened to have. If you don't have one, a friend who knows a friend who has a buddy who works at a machine shop can probably cut it for you. I wouldn't recommend buying one (die), as it's not used very often. Alternately, you can use an adaptor from one of the automotive gauge manufacturers and plug it into your cheapie gauge setup.

I got fancy with mine and used quick disconnects to make installation and removal a snap. All told, I think I spent about $12.

I used this to determine whether I had good pressure or not. I found one engine had an inaccurate gauge, while another actually did have low oil pressure (about 4psi at idle, 40 psi at 3k). It won't tell you which one (gauge or sender) is malfunctioning, just if you have good pressure or not.

Of course, you SHOULD get the gauge calibrated, but as long as it's within about 5% accurate (most are from the factory), you should be good.

Ren