Low pressure at idle after rebuild
 

Hi pelican people,

I am rebuilding, by myself, my 3.6l engine from my 1990 c2. This is my first rebuild. I am running into a pressure problem that puzzling me and direct me into splitting the case again, which is the last thing I want to do. I used mobile 1 15w50 al the time.

The problem is I have low pressure at idle , around 0.75 bar on the dash gauge, but soon i am give higher rpm the pressure goes up roughly 1 bar / 1000 rpm. Before tearing the engine apart everthing was normal, i had to open the engine because two head studs bolts had undo.

Things I have performed and changed:

-I followed Wayne's book method of assembly.
-Case was hot bath clean, clean by me afterward until you can heat on/in it.
-All parts were cleaned using varsol and brake cleaner when possible.
-During dessambly everthing, I mean everthing, was pictured, put in bag and labeled in order to help me during assembly.
-I measured, crankshaft, connecting rods, case, rocker arms, rocker arm's shaft and everthing was in specs. ( i am a machinist, therefore know how to use properly measuring tool).
-Installed new crankshaft, connetcing rod, intermidate shaft bearing that a compared with old one before installed and were all similar within a 0.001" ( accuracy of my vernier)
-Used vector reinz gasket set with green pump seal and blue case thru bold o-ring.
-Everthing was torque using porsche factory manual.
-New nut was used on the case perimeter and used 574 to seal the case.
-The pump was remove from the case, empty from the oil by gravity, placed in a box until reassembly.
-New 102 mm J/E piston with Mahle cylinder, new matching Gotzie ring.
-Reground cam shaft to 993 supersport specification.
-993 H/E with rerouted scavenging line in A/N 16 and a Setrab ( m22 to #16 A/N) fitting in the case.
-Complete head work done by a locale porsche experimented shop.
- RS fan hub.
- Supertec head stub hardware, ARP connecting rod bolt.
- New custom Steve Wong chip.

This is where I think things can be wrong:
- Pressure sender deffective, which I eliminate because reading are similar using the old one.
- Oil pressure relief pistons in the case, I took them out in everthing was according to manual.
- RS hub, which make the alternator run slower, combined with a worn alternator could not generate enough voltage at idle.this is my next thing to do, I will check the pressure with a manual gauge from the case directly to eliminate this one.
- Setrab fitting or A/N line causing problem.
- Pump sealing ring wrong or pinched during installed.

I need some advices or comments to make this work. Thanks in advance.

Here a few pictures to help, sorry for the order:
Also note that number on piston does not match firing order was for weight measurement only.

http://forums.pelicanparts.com/uploa...1364550097.jpg
http://forums.pelicanparts.com/uploa...1364550143.jpg

http://forums.pelicanparts.com/uploa...1364550179.jpg
http://forums.pelicanparts.com/uploa...1364550229.jpg
http://forums.pelicanparts.com/uploa...1364550420.jpg
http://forums.pelicanparts.com/uploa...1364550464.jpg
http://forums.pelicanparts.com/uploa...1364550524.jpg
http://forums.pelicanparts.com/uploa...1364550570.jpg
http://forums.pelicanparts.com/uploa...1364550618.jpg
http://forums.pelicanparts.com/uploa...1364550665.jpg

KISS.....Verify the reading !
2 -if all clearances are correct..it has to be in the pressure management section

I had similar problem, years ago, and pulled it back apart and o-ring for the oil pump had slipped out during case assembly.

Sounds like you've considered a lot of the potential sources already. Only thing I can add is recently a guy on the forums had a similar problem. Turns out the paper towel he used to plug the pump inlet while working on the engine was still in there! Yikes. Disaster averted.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/720161-prime-oil-rebuilt-engine.html

I just went through a similar problem with my rebuild.

When you put the rod bearings in did you check for proper clearance?

When you installed the tensioners in the chain housings did you confirm the oil hole is pointing toward the cap on both sides (i.e., away from the chain). You can confirm this by removing the cap. Also, confirm you put the right tensioner on the right side, left on left side as they are different (both of these errors are common during rebuilds, ask me how I know). Check your pictures, maybe you have a shot of these after install.

Be careful as to how long you run the engine. I am assuming you have not done the break-in procedure (2000 to 2500 RPM for 20 minutes). If you run the engine at idle for too long it can potentially screw up the camshaft/rocker break-in. Run the engine as little as possible before you solve this.

Check the oil pressure with a manual dial gauge. While it is unlikely that BOTH of your senders are bad, it is possible.

When you removed the rockers did you clean out the oil holes? Sometimes these can get blocked.

This can be discouraging. Keep at and you will eventually find the problem. Good luck.

http://forums.pelicanparts.com/uploa...1364586405.jpg

A - Left-hand chain tensioner. Oil supply hole hole points up.

B - Right-hand chain tensioner. Oil supply hole hole points down.

Note

The spring retainers are additionally marked with „oben" (top) and „unten links" (bottom left) or „unten rechts" (bottom right).

Here is a diagram of the oil system. Solid lines represent oil under pressure. I found this helpful in understanding how the oil system works.

http://forums.pelicanparts.com/uploa...1364586713.gif

A couple more things:

1. Check the 2 oil hoses that go to/from the engine to the oil tank. Sometimes these can get crushed or maybe a rag was left in there, both of which would cause pressure problems. This is a tough one - perhaps do this last because you will have to drain the oil. But if you get to the point of tearing it down again, you'll have to do this anyway. Hopefully not.

2. Did you do anything with the lines to the oil cooler. If so, check for blockages after doing 1, above.

3. Confirm the oil hoses from the oil tank are going to the correct spots as per the diagram above. Check to make sure connections are tight.

4. Check the vacuum hoses - all tight?

Guys,

Thanks for the good hints. The diagram is really helpfull to understand potential problem.

- First, yes I have done the initial break in, where pressure was at a solid 2.5 bar at 2000 Rpm. Keep this for 10 min. Then shot the engine and let it cold for a day. Change the oil. Then start the engine when notice the low pressure at idle.
- I am almost 100 % sure chain tensioner piston were install correctly, with the hole pointing toward the cap, however will double check.
- the hoses are in correct location
- cooler line was left untouched.
- rocker arm holes and tube where clean extensively, varsol, breakckeaner, air, etc.
- vaccum hose are all tigth.
- rod bearing clearance was check using platigauge and was within spec.

Based on everyone comment i will check the pressure with a manual gauge. Then if pressure still low will look if I forgot something in the pump inlet. If problem remain, will tear the engine...

Thanks to all, help is really appreciated.

Pat

Let us know what you find!

So was I. That is, until I went in there and looked. Sure enough, I had it in there upside-down!

1 bar / 1000 rpm is what I have always heard. At idle .75 bar would be pretty close to 1 bar /1000rpm.

Is that .75 when the engine is cold or after it warms up?

Every 993 engine I've ever seen idles at 3Bar and hits 5 bar almost immediately at like 2000 RPM. 1bar/1000 RPM should be the min for an early engine oil pump IMO.

I'd verify with a mechanical gauge or known good setup first. You don't want to be chasing a ghost.

Guys,

First tanks again for you help and support this is really helpfull to diagnose this problem.

I did check the oil pressure reading with a manual gauge and reading from car ( oil sender) and manual are same.
I did also look in the pump inlet: everything is clear.
Lines are also all clear.
Only the chain tensioner remain left to check, but I run out of time...family was back and I had to stop for the night.

I notice two things however, nut at the front of the engine ( flywheel) is oily and the oil color was unusual which is weird for oil with not even 1 hrs of running. ( like if foaming).

Unfortunately I did not took pictures this time.

Peppy:
The 0.75 bar is at warm temp. I got 1 bar when cold. Before the rebuild I had solid 2.5 bar at idle warm.

Green993:
You are right, in situation like this everything can be questioned, therefore my next step, is to check the chain tensioner.
Then if they are good, the next step is the tear the engine apart. Something is telling me that one if the O-ring in the case as not seated properly. Something I did not mentionned, is that the breather cap gasket was leaking after the initial startup, which after thougth, could be related to pressure in the case.

Again many thanks,

Pat

Guys,

I did check the chain tensionner an they were installed properly.
However did find the problem, teared oumpm seal ring:

http://forums.pelicanparts.com/uploa...1364935236.jpg

Most likely badly seated when joining the cases half; lesson learned here. I will investigated a bit further just un case something else append. On the positive side engine did not suffer from low oil pressure, everything is good.

Pat

Well glad you found the problem. Sorry to see you had to open the case but obviously that's what was needed.

On the oil pump, i'd recommend changing out the mounting nuts to an all-metal locknut instead of the nylock type. Nylon is not too good when submerged in oil. Or you could use the locking tab plates.

OHHH Uhh where is the rest of it ?

I need to trace the pieces. I kept the oil filters, most likely in there. However, i need to make sure no holes are blocked, the came tower appeared to be free of debris, but i need to triple check this.

KTL:

The mounting nut for the pump are the all metal lock nut. I personally don't like to use nylon lock when oil or heat is involve.


Pat

The good news is No Damage , right ?
If i remember right i put some silicone grease around the pump sealing rings to hold them in place.....and prayed while I dropped the other case 1/2 on......

Well, you identified the problem very quickly. It looks like you are good to go with a new seal and finding the debris. I will be doing this soon (case mating). There's got to be a better way than prayer. Maybe using a boroscope right up until the last 1/4 inch to ensure the seal?

When you closed it up do you remember how you did it. I think we can all learn from this lesson. Thank you.

Gents,

Based on Green993 oil diagram the chance are that the ring got pushed out from the pump into the case, then been catched at the pump screen or in the oil filter; cannot assume all debris get there but a close examination of the pump and filter will reveal this for sure. Since debris are "rubber" they when thru the pump being compressed with minimal effort, without creating dommage. My only fear is if some debris when into the crank and blocked one if the connecting rod oil passage, I guess I need to take the connecting rod off as well and clean the crank... :(

Will investigate and post what I found later on.

Pat

Thats the pressure side of the pump, youre right to look to the crank.
Bruce

Yep that seal should not be ingested by the pump. Scavenge screen would avoid any large chunks being sent to the thermostat and oil filter. But I agree that there's opportunity for smaller bits to be sent to the crank. Crankshaft is the first place the oil goes after leaving that pump port.

Also check your camshaft housings for debris in the spray bars. Can't take any chances there either.

So....how do it happen?..

It would be interesting to note any differences in height between the old (i.e. if you still have them) and new seals.

Of the 4,349,872 different things I worried about before being able to start my rebuild, this particular issue was one of them... Did those oil pump seals seat right? As afterburn already suggested, I used some Dow Corning silicone grease to improve the odds of them staying in place. Still, there was an element of worry until I was able to finally start the thing.

It is great that you found the issue and that there is no damage. It sounds like you are doing the appropriate next steps and making sure all narrow passages, e.g. crankshaft galleys, are clear of debris.

FWIW my oil pressure on start up is 3.5 bar at 1200 rpm (high idle for a cold 3.2). After the engine starts to warm and the idle drops to 800 rpm, the oil pressure is just slightly less, maybe 3.3 or 3.4 bar). When warm, this oil pressure is about 2.2 / 2.3 bar at idle. This is the gauge reading and I have a new oil sender. This is for a stock 3.2 build (except for Euro p's & c's and longevity upgrades like Supertec head studs and ARP rod bolts). It is obviously different than your motor, but I would not expect the idle oil pressures to be that different.

Looks like you did a thorough job and this is just a temporary delay.

Little update,

After removing everthing from the case ( pump and crankshaft) I found all the debris, especially the big one, but also the smaller one. I open both filters that I used and found one debris in the one of the filters. I can even rebuild the seal from all the parts I found!

My theory on what append is that the seal did not saddle properly, got pinched and when the pressure build up the seal just burst in the case. I don't think the seal quality can be questionned here, more the builder experience. However, I did kept the old seal I will compare dimensions between the new and the old one.

Next is to clean everything and assemble this engine properly, this time with the help of a friend to mate the halfs.

Pat

Good job Pat. Thanks for sharing the lesson.

Little update:

After a extensive week of cleaning, inspection and assembly of the engine, I got back in the car today and I start it, pressure is good, 2 bar at idle warm and 5 bar at 2250rpm. and the engine runs without leaks ( for now !), few things worth to be mentionned:

1) For the second sealing, I used the Supertec method of sealing, ( four glue), and I am really pleased with the result.
2) the New #8 bearing was 0.002" bigger then the original on the outside diameter, which made the the case's halfs not joining properly the first time at the #8 bearing area, I decide to install the old one the secound time, much nicer fit now.
3) MUCH, MUCH, MUCH easier to put the case 's half together when you are two persons, especially when it is your first time ( now my second).
4) I used good quality o-ring assembly grease, this sured help to seat the pumps sealing rings
5) finally, always investigate until the problem is resolve, I had to do the job twice, but i am really pleased that I found this problem. Low oil pressure in a Porsche engine is not a good thing.

Pat

Nice job sticking with it and going back in to fix it properly.

What o-ring grease did you use?

I think I will be assembling my case at least 2 times, just to get some practice in. I will make sure to organize all the tools and all the hardware in one spot so that if I have anything left over, it should be obvious.

Have to think about sequence too. Doing a practice run or two helps sort out and develop a good and efficient sequence.

Thanks again and glad you found the problem.

AlfonsoR sorry I don't know how to quote, here your answer:

I used "MOLYKOTE® 55 O-RING GREASE" mixed with 15/50 motor oil in a 50/50 volume proportion just to make it more fluid. I used this also for the case thru bolt o-ring, this really make them slip in place, but also will make the o-ring sit properly when you tigth the bolts and the washer push on them. O-ring needs to be able to move.

Practice is a good idea, also make sure you count everything before you start, my kit came with two extra case thru bolt o-ring.

For my assembly, I had all the tools ready on the table, organized and cleaned with break cleaner. I also wrote the torque values on a post-it and had the Porsche manual at the torquing sequence page. Having a extra person to drop and position the one half and give you the hardware really helps. This part of the assembly need to be well thougth out before doing it. I am not sure how the pros are doing this, but this work for me.

Pat

Thanks for posting your problem Pat, hopefully it will save others (and me) from having the same issue. See you on Ottawa's horrible roads soon - we hope!

I went through similar anxiety after closing up my case. I found a "bonus" oil pump seal. Rather than pull the case apart I borrowed a boroscope and ran all the orifices. I was able to see the seal positions internally, save one as I recall. I was able to scope the outside of the oil pump to look for problems as well. A boneyard engine I tore down had a a bent calcified oil pump seal which might have resulted in its failure.

A boroscope might have been able to look at this seal by going in through the pressure relief piston hole.

Pat, Great news. Glad you stuck thru to the end. Thanks for posting advice as I will be doing this shortly.

Pelican friends,
Another rebuild with low oil pressure. This is and '86 3.5l, running very good pressure before rebuild. I had a ring go bad (not enough ring end gap on turbo motor) so I rebuilt the entire motor. Nickies, JE pistons, bearings, new cams eveything. I flushed EVERYTHING including oil lines to front cooler, all case galleries, rocker oiler tubes also. This is my 9th 911 rebuild and never had this problem. When oil hot (about 95C I wanted to open front cooler thermostat since it was empty after flushing) and at idle I get oil light coming on and also <1bar pressure on gage. Since both light sender and gage are showing low pressure I'm pretty sure is not the gage (but I have bought a new sender anyway). I used to get about 1.5bar prior to rebuild under same conditions. When I run without plugs on starter and cold, oil pressure momentarily (1-2secs) goes to 3 bar then drops down to ~1 bar. I've also checked both pressure relief assemblies and all looks good/free movement etc. Am running Brad Penn 30W break-in oil so expecting somewhat lower oil pressure but not to the point where the oil sender light comes on.

I used Carl Reinz gaskets and thinking either one of the greens seals did not seat properly or per some other posts some of these brand of seals was off spec interms of seal height. Does anyone know what the spec height should be on "good" ring seals for the oil pump.

Either way motor is coming apart again since I want to make sure I did not damage my new bearings during 20 min break in :(

Don’t be so quick to assume the worst. A 3.6 has higher oil pressure at hot idle than your engine. If you consult the owners manual for older 911s they will tell you it’s not unusual to have almost zero indicated hot oil pressure. One time I spun my race car and knocked the throttle pushrod off the bell crank. The engine started but would only run at idle due to the throttle disconnect. The oil pressure was at zero as far as I could tell and it worried me. Once I connected the throttle again I found the oil pressure was fine as soon as I came off idle.

Put in the correct oil and drive the car normally. If there’s a problem you’ll find out soon enough, but I bet it’s fine.

Low oil pressure at idle
 

For what it's worth, from the world of NASCAR and 750 hp 358 ci 9000 rpm pushrod motors. The newer tight clearance motors that run on 0-30 racing oil see like 6 to 8 psi of oil pressure for every thousand rpms. Old school guys like me want to see 25-30 psi at idle and 50 psi at 8500 rpm and it just don't happen anymore. I realize their not Porsche flat 6's but fresh thinking and oil technology are newer and different/better. When I ran the Ford NASCAR D3 motor on the chassis dyno at Rousch-Yates the lower oil pressure scared me and they said, you'll get used to it it won't blow up that is all it needs. Excess oil pressure just raises oil temperature. That thing was at 250 oil temp all day on the mat at Daytona. That wasn't my stuff, I drove someone else's car in the ARCA 200 at Daytona in 2016. My car is older, has a Chev SB2-2 NASCAR motor that is not tight clearance. That uses VR1 20/50 and has the higher oil pressure that I was used to. I don't see oil temps over 210 and at Pocono where you hang it at 8400 for a while on 2 straightaways. When we open up the Peterson reusable mesh canister filter nothing in it so we just assume all is well. That motor will go 500 miles from rebuild and get valve springs and then another 500 miles and get rebuilt again. Max time before going back inside it will be like 1100-1200 miles to be safe.

Howdy everyone,
My story is very similar to this post, just finished a 3.2 build, and I noted some clattering right after breakin when I revved the engine to 3000 RPM. This is my 9th 911 motor rebuild and follow Wayne Dempsey's guide religiously. So motor came right back out and now disassembling and carefully observing EVERYTHING. No valve interference (checked again for Dempsey's book) or evidence of anything hitting the pistons.

I am just about ready to now split the case. I did notice when pulling the large case bolts that on two of the bolts there was quite of build up loctite 574 right in the middle of the bolt where the case halves meet. This could have blocked the oil flow around bolt bores. These serve as important oil flow paths feeding the bearings. The 911 motor thread from this forum is clear on using 574 on the bearing webs but in my case I used to much causing to ooze out into the bolt bores possibly causing severe oil starvation to the crank bearings.

This is an really important consideration in my view and should be included in the engine sealing thread NOT TO USE TOO MUCH LOCTITE 574 in this application. It probably already says this but needs to be in BOLD CAPITAL font. Best case if this is the problem I will see only minor bearing damage when I finally split the cases tonight. Worst case will be crankshaft damage and off to the machine shop.

I'll update this thread. Oddly I will be relieved if this the problem as I have checked everything else and so far still scratching my head.
Andy

hi there
yes another too much of 574 loctite used story...as i have mentioned in another thread here is how i do it on 911 engines on more then 30 times.Once my friend in LA did the same mistake and had an oil leak next to the inter shaft....too much of 574....
Ivan
https://www.youtube.com/watch?v=IandhtwG5no

same technique goes for assembly of camshaft housings to cylinder heads.
https://www.youtube.com/watch?v=STWf7WnC4xo