Engine test out of car

Bob Ashlock · 06-02-2010, 06:15 PM

Hi, this is my first post in quite a long time. I recently picked up a used 911T engine (1970 vintage) with little prior history (other than the owner claimed it was 'rebuilt' and ran well before it was removed from a wrecked car about 4 years ago). I want to first run compression testing and start it up where it sits on a pallet my garage floor as a kind of 'sanity check'. In the future I may decide to put this engine in '66 912, but for now I would just like to make some initial determination as to whether the engine will run, sounds reasonable, etc. The only major obstacle is figuring out how to connect some type of temporary oil tank to connect the big oil lines to as I don't even want to crank this thing over for compression testing without being sure the bearings are getting oil. Has anyone attempted this trick before, or is the only reasonable way to go out and get the oil tank (that I'm going to eventually need anyway)? Thanks for some advice! -- Bob

sc_rufctr · 06-04-2010, 06:19 AM

What you need is an engine test stand. There are threads about building your own.
The oil tank is straight forward. Most use a stock oil tank mounted on the stand.

It's a lot easier than it sounds.

Here's one for sale... FS Hot Engine Test Stand

Here's a good thread with some pictures... plans for a six motor test stand

Here's the search I did. Lots of good threads and details... Pelican Parts Technical BBS - Search Results

Bob Ashlock · 06-04-2010, 02:03 PM

Thanks Peter, those are some impressive setups. I'll probably do something a little more basic, since this is a one-off kind of test. Since I made this post, I've picked up an oil tank and hoses, and will be able to rig up a basic test-bed. --Bob

sc_rufctr · 06-05-2010, 04:34 AM

Post some pics of yours when you're done.

Simple is good. As long as it holds the engine securely you really can't go wrong.
Just one word of caution. Make sure you mount the oil tank relative to the engine in a similar position as it would be in the car.

Bob Ashlock · 10:20 AM

Peter, thanks for the tip on the oil tank location. I had indeed figured that out, but it's better to be "safe than sorry". Here's another "911 newbie" kind of question... when the engine is NOT running, does all the oil in the tank eventually work its way back down into the crankcase, and then most gets pumped back up into the tank when the engine is running? I'm having a little trouble visualizing how the dry-sump system stays "in balance" (i.e., enough oil in the engine to always be picked up by the pressure-pump. Is it that there is a certain level the oil reaches in the crankcase area where it begins being picked up by the other section of the pump that sends it up to the tank? --Bob

Walt Fricke · 06-05-2010, 07:42 PM

Bob

All the engine needs is enough oil in the tank so that the pressure side of the pump always has oil it can suck in/gravity can push in. If the pickup inside the bottom of the engine sucks air from time to time, that isn't going to matter (leaving aside issues of aerating the oil and so on).

And pretty much all of the oil the pressure side is pumping into the engine is squirting out of the bearings and piston oilers and the oil pressure setting system (a spring loaded piston that leaks off excess pressure into the case) at the same rate. It has to, as it has nowhere else to go.

I think you may be still a bit stuck on wet sump systems, where an oil pickup issue means an instant problem.

How the oil in the tank goes into the case when the engine isn't running is a bit of a mystery to some of us. The oil level in the tank is significantly higher than the pump intake, so there is always some pressure there. The pump shafts don't have seals on them, so oil that is in the pressure intake side of the pump can work its way to the front end of the pump and seep out. And into the scavange side, and out. And it can migrate around the pump gears. Now you have gravity pressure of a sort allowing it to access other areas of seep. For the pressure fed parts of the engine that means pretty far up before it goes down, so I kind of discount that. But the secondary oil overpressure relief piston is much lower down. It doesn't have seals or rings, so oil ought to be able to seep past it, given enough time.

For these, or other reasons, after a 911 has sat for a long time there can be quite a bit of oil in the bottom of the case. If you drain oil when the engine is hot shortly after driving, a lot less comes from the case than if you have let it sit for some days before changing.

None of which matters for your engine test stand, though perhaps it wouldn't be helpful to mount the oil tank way high up.

Walt

Bob Ashlock · 06-06-2010, 08:19 AM

Hi Walt, thanks for the explanation. As I studied this a bit more, I came to the same understanding and conclusions... i.e., that the return line from the tank to the pump MUST always have oil available so the pump can maintain pressure to the engine bearings, etc, but the scavenge side of the pump merely stays busy "cleaning house" (so to speak) returning any oil from the sump back up to the tank such that only a minimal amount of oil builds up in the sump while the engine is running.

al lkosmal · 06-06-2010, 09:41 AM

Bob.
Several years ago I bought this engine stand at Costco. (see video below) It is designed for V8s, but I adapted it for 911 engines using an old bellhousing, starter, engine hangers, oil tank, etc. It does come in handy. I am now using an Innovate LM-1 with LMA-3 sensor input adaptor with my laptop as the display. This allows you to bring in the Lambda sensor for air/fuel mix, tach input, MAP, temp, oil pressure, etc. Nice little tuning device.

YouTube - 71E engine start1

Regards,

Al

PS: the leak down test is your friend.

Bob Ashlock · 07-03-2010, 08:38 PM

Here's an update to testing the used 911T engine I recently required. Photos show my "poor-man's test lab". I built this "roll-around" cradle from scrap materials I had laying around the garage. The engine hangs from its front mounts as it would in the car, and can be raised up enough to easily have access underneath. The oil tank is on it's own separate "roll-around" platform, connected to the engine with the oil lines. A home-made gas tank (old paint thinner can) gravity-feeds the carburetors. A small yard tractor battery easily turns this engine over. A basic "control panel" interfaces to the engine harness to start and run, confirm alternator charging, etc. A screw-on oil gauge was used to confirm pressure before ignition and first start-up. This is definitely the way to check out an old engine with no history and clean everything up nice before putting it into the car. I have been able to resolve many issues, fix some oil leaks and check out the carbs. The oil gauge was showing 100 psi at high rpms. This was suspicious, and I found someone had stuffed a washer under the pressure relief spring! Anyway, it's kind of fun to go out to the garage and throw a switch and listen to it run.