Cam walks - thrust control?

[fyrebird68]

What keeps the 3.4 cam from moving front-to-back? I think the occasional noise I hear is the cam bumping into the block.

New Cloyes timing set reduced the amount of motion but there is still some.

On most motors I have seen in the past there was a thrust washer or clip to control this movement. I don't see anything to prevent this motion on the 3.4 cam.

Also, is there a timing chain guide available for Cloyes set that will fit the 3.4 block?

[60dgrzbelow0]

If the block was re-built and imperfectly align bored for spun bearings or... if the crankshaft and camshaft have imperfect sets of bearings installed ...particularly at the very front of the engine block.. the distance between the center-line of the of the camshaft and the center-line of the crankshaft might be reduced... and make for some slight slack even with a new Timing Chain Set. If the main thrust bearing on the third journal of your crankshaft is badly worn...that would allow the crankshaft to walk back and forth and become the likely offender on a high mileage engine. Have a look at this image... it shows a concavity in the Cam Cover plate that is in line with the oil gallery that pressurizes behind the end of the camshaft as the Oil Pump Drive is turning. Since liquids are incompressible...no matter how much lateral pressure is placed from the camshaft attempting to walk to the rear... the oil pressure in-dwelling will repel it in a frictionless manner. Also, most Timing Chain sets do not exhibit very much flexibility along the limb of the chain (at least they don't show this tendency when brand new) and when the chain is aligned and tightly mated between the Camshaft Gear and the Crankshaft Gear... there is little chance for much horizontal camshaft movement. In rare cases, an improperly secured camshaft Gear (not torqued and sans Thread-Locker on the three bolts) will cause the gear to move off the nose of the camshaft between the bolts and the camshaft nose and contact the Timing Cover inside, sometimes catastrophically.

There is one other force involved here and that is imposed by the torque and driving motions that occur between the helical gear at the rear of the camshaft and the helical mate on the Oil Pump Drive. Generically, as engine RPM increases and the rotational forces increase along the length of the camshaft, where these two gears meet, they'll resist each other in such a manner as to make them want to separate or get closer to one another depending upon whether the engine is rotating clockwise or counter-clockwise. The bronze thrust bearing in the top of the GM 60* V6 OPD absorbs this force and likewise, the hex shaft at the bottom where it plugs into bottom helical gear and then down inside the Oil Pump will also flex a bit and resist this torque pressure while turning. But hopefully, as the RPM increases, all of these forces somehow become self-cancelling and the camshaft remains rotating in a steady state while the cam lobes move eccentrically, lifting and lowering the hydraulic tappets and behaving itself without trying to escape either through the front or the back of the engine block. Please have a look at my camshaft rear cover to illustrate the design.

http://s557.photobucket.com/albums/ss19/60dgrzbelow0/CLOYESTRUEROLLERTIMINGSET/?action=view&current=CAMSHAFTBOLTASSEMBLIES_1.jpg

As for the Timing Chain Damper... here is the one I ordered ...but just know that the extruded metal around upper mounting hole in the back of this item will need grinding off if you are installing the damper on a 93-95 60* 3.4L L-32 Engine.

http://s557.photobucket.com/albums/ss19/60dgrzbelow0/GM34LNEWENGINEPARTS/?action=view&current=TIMINGSETCHAINGUIDE.jpg

http://s557.photobucket.com/albums/ss19/60dgrzbelow0/CLOYESTRUEROLLERTIMINGSET/?action=view&current=TIMINGCHAINDAMPERSET.jpg

On the next occasion you have to remove the Timing Chain Cover...you might examine the inside of it for signs of either chain slap or contact directly with the camshaft to determine if there are problems at the front of the engine as described above.

[fyrebird68]

Ironman,

thank you for the very thoughtful answer. The motor in question is a rebuilt short block, so it has new rod and mains and (supposedly) new cam and bearings. Also has a new Cloyes timing chain set.So I'm looking for anything either inherent in the motor design or in my improper assembly that could cause it to move.

I was not able to open the photobucket pics - don't know why. If you could tell me the part number and your source for the timing chain damper I can locate one that way.

Rods and mains I checked when looking for my clunk, cam I did not. My next project is to go through the top end of the motor - rebuilt or not - to see what i can see. I'll keep you posted.

[60dgrzbelow0]

Fyrebird... You're quite welcome...I've snagged the three images from the photobucket and attached them below (part numbers on original box are displayed). I was wondering if you could explain what the motor was doing leading up to the presentation of the sound...Were you Idling the engine in Park/Neutral and then heard the sound when you engaged the Drive setting on the Transmission? If not...were you either accelerating... or decelerating when the noise occurred? If you can narrow the band of engine operations and circumstances down...it might be easier to diagnose the problem. Please remember that just aft of the back of the engine...you have either a heavy flywheel for a manual tranny or a flex plate for the auto flavoured tranny and these can be improperly bolted on as well... so if the bolts that hold either of these two rotating masses get loose...the clunking noise might occur there...as well as via any of the three bolts coming loose from there positions holding the torque converter to the flex plate. So diagnosing noises that are being REFERRED from one errant component to other areas or places to be heard can make pinpointing the actual problem difficult. Don't leave off having a look at the Harmonic Balancer to determine if the outer heavy race is trying to walk off the inner section of the HB.

I'm paraphrasing here from Sir Arthur Conan Doyle, author of the fiction detective stories about Sherlock Holmes:

"When you have logically eliminated all the variables that are possible... then the impossible thing that is left...however improbable... is the answer to the problem..."

PS... Are we to understand that at present... this engine has NO Timing Chain Dampner installed or when you discovered this problem? " Hmmmmmm...Watson... The Game ...is Afoot!"

[fyrebird68]

A little background: this 3.4 pr V6 motor is installed in a Fiero GT, replacing the 2.8 V6. Heads had a recent overhaul. I used intake, heads, water pump, etc from the 2.8. Timing chain is a Cloyes roller set. New lifters, pushrods and rockers. No radical parts - mostly stock spec.

Short block was purchased from a block refurbisher in Arkansas. Billed as "cleaned and bored, with new cam and bearings, refurbished crank, new rods and main bearings." (I had some issues with them, so I am not sure of the quality of the work. I can go into detail if you're interested.)

I checked the rod and main bearing clearances and assembled the block and it runs fine. I had a slight knock but I went through the break-in period. After the 1000 mi. oil change I got the noise. Oil looked like crap, but I was expecting some dirt from the new build. Not metallic so much as very sludgy.

The noise is intermittent at idle. I can get it consistently at certain rpms (around 1500-2000 rpm) with or without load. It is very noticeable under acceleration and not heard under deceleration. The sound is definitely in the block, as opposed to flywheel or balancer.

Since my first post I had a mechanic friend take a listen. He does not feel the sound is heavy enough to be rod/main bearings, nor is it present at other rpms like main bearings would be. He suggested I go through the top end of the motor closely, looking for a stuck lifter or something like that.

I began thinking about the cam because when I assembled the block I noticed a lot of play in the cam (~3/4") while installing the timing set. I was able to push it back toward the block and get a "clunk". Once I got everything together (heads, etc.) the play went away due to distributor gear and the spring pressure on the cam. I didn't think any more of it.

That's how I got to this point.

My question regarding the timing chain dampner is because I used the one from the 2.8. Not a good fit, but I modified it. I thought maybe the chain could be slapping against it. Worth a try, especially since I have to open the motor up again.

Once again, I appreciate your time and expertise. I am a novice engine builder so I have the nagging feeling I am doing something wrong or just overlooking something obvious.

Bob T.


PS I am a big Holmes fan.

[60dgrzbelow0]

Okay... Well Done on your follow up description of actions... and this raises some critical questions:

1. Prior to starting the engine after you built the short block and installed all the necessaries... DID YOU PRE-OIL THIS ENGINE?
2. At the IP (Initial Point) of the first start up...DID YOU FOLLOW PROPER NEW CAMSHAFT/ENGINE BREAK IN PROCEDURES?
3. If you followed any Engine Break-In Procedures...did they include using the proper Engine Break-In Lubricants such as Valvoline Racing Oil with ZDDP or Royal Purple Engine Break-In Oil
4. Did you also include a bottle of Special Hydraulic Lifter Flat Tappet Camshaft Break-in Additives in your motor oil?

RSVP... But a heads up that camshaft damage in the absence of a YES answer to each of the above listed questions may lead to the conclusion that the camshaft was damaged (wiped lobes...ruined lifters, etc) Which..if you are still working on the engine can still be dealt with. Sherlock would insist that you remove the in-dwelling Oil Filter...cut it open inside a plastic bucket of Kerosene and after swishing it around ...use a magnet to see if anything Ferrous glomms onto the magnet out of all that "dark oil" mung... You might try to sweep a magnet thoroughly attached to a flexible wire inside the bottom of the crankcase via the oil drain hole and see if anything gets picked up there as well... if it does.. find a way to pull the oil pans and get all that metal crap out of there... and this may well turn out to be the source of all the racket inside your engine...

[fyrebird68]

1. Prior to starting the engine after you built the short block and installed all the necessaries... DID YOU PRE-OIL THIS ENGINE? ---- YES
2. At the IP (Initial Point) of the first start up...DID YOU FOLLOW PROPER NEW CAMSHAFT/ENGINE BREAK IN PROCEDURES? ---- YES
3. If you followed any Engine Break-In Procedures...did they include using the proper Engine Break-In Lubricants such as Valvoline Racing Oil with ZDDP or Royal Purple Engine Break-In Oil ---- MAYBE. I used cam assembly pre-lube, but regular oil for break-in.
4. Did you also include a bottle of Special Hydraulic Lifter Flat Tappet Camshaft Break-in Additives in your motor oil? ---- MAYBE. I added STP, primarily for its high ZDDP content.

The car seems to run fine - lots of power and torque. Wouldn't a missing cam lobe cause a noticeable decrease in performance?
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Due to the, ah, unique configuration of the Fiero engine bay I'll be removing the motor to get to the oil pan and intake to inspect the valve train. (I've gotten pretty good at it, actually - only a few hours from car to stand.)

I promised my wife I would finish my current bathroom remodel project before I touch another car, so it's a couple of weeks out. I will post as soon as I get out of drywall hell. Thanks again for the thorough and patient responses. I'll be back....

[geoffinbc]

On a flat tappet cam the cam is held in place by the lifters, and in the case of out motor, the distributor gear.

Lifters on a flat tappet cam sit slightly forward and the lifter foot has a radius on the bottom and the lobe has a taper. The spring pressure on the lifter acting against this tapered interface forces the cam back.

A roller cam needs a thrust plate or thrust button to keep the cam in check because the rollers and lobes are flat.