Engine Vibration.

[Bob Cowan]

I'm on a 6 day road trip, and developed an engine problem. The car was running great - smooth, even, good mileage, not even warm. We came down out of the mountain pass, and parked in a small town for lunch. After lunch, I got back on the roadway. When I hit the gas to get into traffic, suddenly things changed.

The engine developed a significant vibration, and ran poorly. I pulled over when I could, and checked things out. It had a significant engine vibration around 2300 rpm's, and would not run well at all above that.

It was clearly missing on one cylinder, and We tracked it down to cylinder #3 by unplugging injectors. Spark is great - a good 1" bright blue spark. After messing with the injector plug, I got that cylinder to work again. So it's a bad injector that needs to be replaced.

BUT.... the vibration remains. it starts around 2300, and fades off around 2700. Anything above or below that and it runs great - smooth, even, sounds good, good, and decent fuel economy. But, the vibration is significant.

These are the things I'v tried that did not help:
-- Removing the fan belt
-- Tightened the balancr bolt
-- tightened the pulley bolts
-- tightened
-- swapping spark plugs
-- checked the ohms on the cables
-- Swapped injector plugs/wires (batch fired).
-- Checked compression - finger test only, it is getting some compression
-- visually inspected all the springs and valve train
-- Adjusting the clutch cable.
--

It is clearly engine related. It's easily reproducable in the parking lot. If I run the car up to 3,500 rpm's, push in the clutch and let it roll, it resolves. It's rpm related.

Doesn't matter what gear it's in, and is not related to clutch actuation.

Any thoughts?

[Geoff H]

Any chance the balancer has moved?

[Gordon Levy]

A chunk of piston may be missing

[snapperlr]

Is the internal balance neutral on the build?

You could also drain the oil real quick just to look for anything unusual.

[Don Payne]

Originally Posted by Gordon Levy

A chunk of piston may be missing

That is just a wrong thought man.

[Big-Foot]

You swapped spark plugs... Between holes or you swapped old for new?

If just swapped holes, I'm thinkng that you may have just glazed a plug or two by running that cylinder too lean. I did that once on one of my cars and it exhibited the exact same symptoms...

[Bob Cowan]

Originally Posted by Geoff H

Any chance the balancer has moved?

I doubt it. It's a high quality SFI balancer. The pulley and the toothed trigger wheel still match up.

Originally Posted by Gordon Levy

A chunk of piston may be missing

I hate to say it, but that's what I was thinking. I'm afraid the injector failed, the cylinder went lean, and burned the piston.

Yikes; not again. This is getting expensive.

[Gordon Levy]

Going by your discription it's my best guess. A fluoroscope will tell you a bunch.

[trevor]

something broke off your pressure plate and/or disk throwing the engine out of balance.

Years ago, my engine had a bad vibration like yours....then the backside of the crank snapped off. I think my failure was a very rare occurance.

[Big-Foot]

From my past experiences, if it went lean enough to torch a piston, it torched the spark plug electrode too. If you don't have access to a borescope, buy a compression tester that will give you a better idea of cylinder condition.

Good luck and hope you make it home without further difficulties..

[trevor]

randy has a good point. The ground strap usually burns away with a piston burning lean condition.

[Mustang Man]

SFI dampers don't have a rubber insert and weight ring to move like a stock one, but they usually have a bolt on weight on the back. Check to make sure the weight isn't loose or came off. Also, what kind/type of clutch are you running? I've een vibrations like this when a good portion of clutch disc broke off...

HTH...
Mark

[Bob Cowan]

Originally Posted by Big-Foot

From my past experiences, if it went lean enough to torch a piston, it torched the spark plug electrode too. ..

Good point. I pulled all the spark plugs, and they all look pretty good - and all look the same.

Originally Posted by Mustang Man

SFI dampers don't have a rubber insert and weight ring to move like a stock one, but they usually have a bolt on weight on the back. Check to make sure the weight isn't loose or came off. Also, what kind/type of clutch are you running? I've een vibrations like this when a good portion of clutch disc broke off...

HTH...
Mark

The engine is internally balanced, and there's no balance weight on the balancer or flywheel.

I was thinking of the clutch, too. Maybe a piece of the clutch or pressure plate broke off. Or lost a bolt. Clutch operation feels exactly the same as it always has - smooth and even.

When I get home, The first thing I'll do is a compression test. Then use a bore scope to look in the cylinders and in the bellhousing.

[Bob Cowan]

I made it home OK. When I started the car this morning, it seemed to be a little rough. When I tried to drive down the road, it ran very poorly. I had to pull over and shut it down.

I started trouble shooting by hooking up the lap top, and checking the program. All seemed to be good there. Then checked the spark, and that was good. It sounded like only 1-2 cylinders were firing on the right. The left bank seemed to be fine, though.

Pulled the spark plugs, and they were fuel fouled. Cleaned them with a flame and a wire brush, and got the car running. After it warmed up, it seemed to run OK. Not great. But OK.

That vibration was still there, though. Not better or worse, but there. If I kept the rpm's around 2000, it seemed fairly smooth.

When I got home, I cleaned things up and got to work. The first thing was a compression check. All 8 cylinders were well within spec, and within a few pounds of each other. I didn't do a leak down test for a variety of reasons.

Because that bank of cylinders was a problem, I started by pulling the right head. No matter what, I wanted to look in there and make sure all was OK. Other than running rich, I don't see anything bad. The head, block, pistons and gasket all looked fine.







Internally, everything seems to be fine. I'll take the injectors to a shop tomorrow and have them tested. I'll also test all the wiring harnesses and connections.

[Bob Cowan]

Now for the vibration. I couldn't find anything in the engine to explain it. So, following my diagnostic plan, I used my trusty See Snake to inspect inside the bellhousing. This is what I found in there.

Originally Posted by trevor

something broke off your pressure plate and/or disk throwing the engine out of balance.

Originally Posted by Bob Cowan

I was thinking of the clutch, too. Maybe a piece of the clutch or pressure plate broke off. Or lost a bolt. Clutch operation feels exactly the same as it always has - smooth and even.

This is a Centerforce pressure plate. Fortunately, it didn't explode. So, the clutch has to come out. I'v done this from under the car before, and it was a real nightmare. I think I'll just pull the engine out and do it right.

And while I'm at it.......

[Big-Foot]

Very lucky Bob!

While you're at it, toss in a new set of spark plugs!

[BigLeo69]

cleaning a spark plug with a wire brush and a flame?

explain

i always use a tooth brush no metal brushes, and have found it to be less of a hassle just to throw new plugs in.

and i am with u right there easier to yank the drive train out and throw her on an engine support

[Bob Cowan]

Originally Posted by BigLeo69

cleaning a spark plug with a wire brush and a flame?

explain

Once they're covered in raw fuel, they won't fire. A light flame will burn off the fuel without damaging the plug. Then use a soft bristle wire brush to get all the soot and crud off.

[Bob Taylor]

Nice cltch-oscopy !! is it possible that the clutch damage was caused by the misfire ? Thats roughly a 75hp im balance. Bob

[Bob Cowan]

Originally Posted by Bob Taylor

Nice cltch-oscopy !! is it possible that the clutch damage was caused by the misfire ? Thats roughly a 75hp im balance. Bob

Yeah, that's very possible. They both magically appeared at the exactly the same time. That's the real reason I pulled that head off. I wanted a good look in there before doing much of anything else.

Since I'm pulling the motor anyway, I'll probably pull off the other head just to see what's in there, too.

[ROADRACER83]

Is it just me or do those Centerforce clutches seem to be defect prone. Every time I read about them on this forum or others, there seems to be a broken pressure plate, a diaphragm broken or a centrifugal weight coming off and making it a bad day for someone. Maybe just the bad ones are commented on, but I sure wouldn't buy one based on what I have read.

Ron

[Bob Cowan]

I'v been using these clutches for a quite a few years. This is the only failure I'v seen. I admit, I beat up on the car pretty hard. But I think it should have held up better over the last 3 years.

I'll replace it with another Centerforce, only because I have one sitting in the garage. But the enxt time I overhaul the engine (this winter), I replace it with something else. Maybe a Spec clutch.

I took the engine out yesterday, and took some pictures. I'll post those tonight when I get home.

[Big-Foot]

Bob, I suggest you take a good look at RAM clutches.. I've been using them for a number of years now with absolutely no complaints..

[Erik W. Treves]

I had a Ram HD clutch on mine until this last rebuild....went with spec 3+ this time....I like this one much more...not so grabby, and it is actually easier on the leg.

[Bob Cowan]

Ram HD and Spec 3 are right at the top of my list. The one thing I'v always liked about the Centerforce is how street friendly it is. Pedal effort is low, and it's really smooth and predictable in traffic. No chatter, no grabbing, no lurching.

Of course, if it doesn't last.......

Here are some pictures I took once I got the engine out of the car.





3 other bolt holes had cracks similar to this one. And the rest had evidence of fatigue.




Here's a shot of the pressure plate from directly above. Can you see the problem?



Take a look at how the finger weights are sitting.

Also, noticed that this is a Valeo clutch hat. Not a big deal, lots of companies use Valeo - and Weber. The product description for the Centerforce states, "These clutch-and-disc sets are designed for engines producing high horsepower and big torque outputs. "

But if you go to the Valeo web site, you'll find a picture of this clutch hat under the "Heavy Duty" section. http://www.valeoclutches.com/Product...Clutch+Kits/52 Valeo lists a 15% increase in holding force.

If you want to see a heavy duty version, you have to look under the Performance section. Interestingly enough, the description of the Valeo DF Pro clutch sounds exactly like the Centerforce Dual Friction.

[Rod]

Hi Bob:

Did you check the bell housing alignment to your engine when you installed it? I believe its referred to as "run out and off set" and is a measurement of the miss-alignment of the pilot bearing to the input shaft on the transmission caused by the position of the alignment posts and line-boring the crankshaft. I understand the solution is to replace the original alignment posts with offset posts.

Reason why I ask is I am having similar vibration issues with my new engine and original Tremec. I've spent weeks checking compression, spark plugs, plug wires, fuel delivery, timing, timing advance, valve lash, piston height and any other other wild and bizzare possibilities that came to mind. After reading your thread I thought there might be some similarity to your and my problem.

From looking at your photo of your pressure plate I wonder if your bell housing alignment might be out and this caused the failure of the metal around the bolt holes?

I found a couple of videos showing the measurement technique to determine run out and offset.

How to Dial In a Bellhousing - YouTube

How to Dial In a Bellhousing - YouTube

and this one

Bellhousing Alignment With Offset Dowels - YouTube

Bellhousing Alignment With Offset Dowels - YouTube

I'm no expert and am hoping a real one might be able to confirm this miss-alignment as a possible cause of my vibration?

[Bob Cowan]

I doubt that's the problem. I'v been using this same bellhousing and pins for years. The alignment was good during the initial build, and I don't expect it would change. Not a bad thought, though - maybe it's time I rechecked them.

The biggest problem with a mis-aligned bellhousing is that the trans input shaft is not lined up with crank shaft. It shouldn't put any significant strain on the pressure plate.

Unfortunately, tracking down an engine vibration can be difficult in the garage. You can eliminate a lot of stuff, but when it gets down to the big things like a flywheel or crankshaft, you need a machine shop.

You can eliminate the bellhousing fairly easily though. Pull the transmission out, bot the rear of the bellhousing to something solid, and run the engine. If the vibration is still there, it's not the bellhousing or transmission.

[Bob Taylor]

clutch looks like it got warm around the fracture point and the fingers are uneven due to the break ?? No? Bob

[Big-Foot]

The centerforce weights are not actually tight on the fingers and you can move them. They actually reposition themselves in what is supposed to be a perfect balance - although I've always been skeptical.

When you install the pressure plate, do you observe the one revolution per bolt in a cross side tightening sequence? (like tightening a wheel or cylinder head) If not, there is additional stress introduced to the hat during installation.
Not saying that's what caused this though. I would certainly want centerforce to know about the problem. If nothing else, you may get a free replacement which you can sell to help offset the cost of that pressure plate you really want.

[ROADRACER83]

Bob and all:

That is just a classic case of fatigue failure caused by a crappy die that had very sharp radius curves in that bolt area making for stress raisers right where you dont' want them. Probably aided by poorly heat treated or the wrong alloy steel. That area near the bolt and the adjacent pin is where all the loads are concentrated fron the pressure plate. Those steel straps allow the shoe to move fore and aft but they also carry the torque load into the area next to the bolt. The fact that other cracks are starting is an indication that that pressure plate was a defect just waiting to happen. That has nothing to do with the bell housing alignment or the weights.

Ron