Lizard928

So the question is, does anyone know how many Ft Lbs it takes to rotate the 928 S4 motor with all plugs out etc.?

TIA

blown 87

That is a loaded question, a lot of things can change that figure.

New engine that has never been ran is going to be a lot higher than a high mileage motor.

to many things to affect that to be of any use for a diagnostic figure.

mark kibort

about 50 ftlbs if I was going to guess, and it fluctuates for all the compression strokes. there is one that is greatest during one part of one revolution. maybe up to 75ftlbs. (on a stroker), on a stock S4, maybe only 50ftlbs is a peak. (all a guess on my part based on the amount of strength it seems to take to rotate the motor)

IcemanG17

too many variables...the age-condition of the engine, if accessories are attached..how long the engine sat...& so on.....but they do take a fair amount of oomph to rotate

Lizard928

MK,

I have a motor that felt like it takes 60-70 ft lbs to turn it over with NO plugs in it once hot.

After sitting for around 1 hour, no plugs in, flex plate disconnected it took over 45 ft lbs to turn it.
Motor currently has .010" end play on it. Checked with vernier caliper and dial indicater.

mark kibort

Sorry, I was referring to with plugs in. no plugs, it turns with about 20 ftlbs. if you are trying to spin a "plugless" engine and it takes 50ft-lbs, you have some issues going on there

mark kibort

I didnt notice any difference between my new engine that never ran and old engines. with no plugs, they all kind of "feel" the same.

ptuomov

I don't think those numbers make any sense for rotating an engine with all the plugs out. Or am I losing my mind, or given superpowers in my right index finger?

ptuomov

For a new motor that one has just put together, it better be really low. I ***-umed that this is what this was about.

Lizard928

Thanks guys,
Just confirming what I already knew.
Sometimes it helps just to hear others say yup, somethings up.

Odd thing is that it seems to only get this way once the motor is hot.

Compression test shows within 3PSI on all cylinders (200 on my guage), with the engine hot.
Leakdown tester isnt the best, but showed a couple cylinders at 20% leakdown, the rest at 55%.
All was coming by the rings, nothing by the valves. As well with 120PSI in the cylinders, it didnt matter where in the cycle it was, the engine would not turn with all plugs out and 120 PSI being pumped in....

Will be cutting open the oil filter today. And trying to beg, borrow, cheat, or steal a borescope to try to get a peak in the bottom end before pulling off the pan.
I will also pop off/remove the timing belt to ensure that it isnt something in the top end causing this issue....

AO

Bummer.

I'm not as well versed on some of this stuff, so let me ask a question or two to see if I have this right.

I assume this is looking like a bearing problem. Generally the increased friction when hot is similar, if not exactly, related to a bad thrust bearing. However, the crank end play, is within spec. So does this point to a bad rod bearing, or something else?

I suppose a bad/siezing water pump could also explain the difficulty. Taking the TB off and spinning the WP by hand should identify if it's suspect or not.

Am I missing anything here? What about the Torque Tube or Torque Converter? They're tied to the crank...

(It's fun to play armchair mechanic. All the fun, none of the mess.)

Lizard928

Andrew,

I disconnected the flex plate via the 6 bolts which hold it to the flywheel for all tests. To ensure that it was not part of the problem. (incidently, the clamp needs to be replaced).

It is difficult to say right now what the exact issue is. But I believe it is a bad bearing. My hunch is a spun main. But I really hope that I am wrong, and that it is simply a bad WP or tensioner bearing etc.

AO

Got it... Makes me feel good to know that I am actually understanding this stuff.

Keep us informed as you get down to the root cause.

dr bob

Colin--

It's unlikely that a water pump or tensioner roller would cause 50 lbs/ft of drag.

The combination of only-when-hot with lots of leakdown would steer me towards pistons and rings sticking. The .010" endplay is not quite panic time. What does the oil look like? Any metal in the filter?


For those playing along at home, the "breakaway" torque is the only meaningful measurement available for tasks like this. It is an indication of "stiction" plus friction. After that, a friction-only measurement might be helpful except that the speed of rotation needs to be measurable and consistent; with eight pistons/rods/bearings and the valve gear all dynamic during rotation, the torque requirement at any given speed would be all over the place in a single revolution.

mark kibort

Yep, when scots mystery motor siezed on lap 10 of the 2nd day of its existance, it was really hard to turn over. it go easier with every turn, but it was a bearing issue. cooked! this was with plugs in however, but yes, if the motor is turning over that hard with plugs out, it will more than likely be a bearing. I hope not, but you will soon see.