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Old 12-14-2005, 01:01 AM
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Engine valvetrain tap

Hey guys,

I've been a member for almost two years here but I couldn't successfully log in under what I thought was my old username and I usually browse without loggin in....I frequently search out this board when I have engine related questions....Unfortunately, I couldn't find what I was looking for this time...I appreciate any advice or opinions in advance and sorry for the long post...

I have what I believe to be a valve train tapping that is proving to be very tough to diagnose....I've searched the archives here for possible answers, but I still can't figure it out....The engine is a turbocharged 4.3 liter V6....the block is a 1995 marine balance shaft block...The block is four bolted (2 center mains) using Diamond Racing billet caps-All except for the oil pump cap....Stock 4.3 crank, eagle h-beam rods, JE Extreme duty forged pistons, 2000 model vortec heads with manley stainless valves (2.02 intake-1.60 exhaust) LT1 springs, one piece chromoly pushrods, isky guide plates, comp cams .500" lift and 206/210 duration @ .050 with a 112 lobe center, comp cams 875-12 roller hyd. lifters, crane 1.52 full roller rockers...ok, that covers the basic build....now on to my tapping issue...

I built this motor about a year ago and it was running fine using SRP's (JE made street pistons) for around 2500 miles....I over boosted a few times and cracked the ringlands on a couple of the SRP's and ended up with bad blow by....so I pulled the motor, visually inspected everything and replaced the pistons with the JE's...Being that the JE's are racier pistons, it is my understanding that they clearance out looser than the SRP's...we ended up with .0065 clearance when we honed out the cylinders....the spec sheet recommended .006 to .007 when used for forced induction apps...no unusual tapping before the engine came out for the JE install....we recently reassembled the engine, installed it, primed the oil pump then started her up....The tapping was coming from the driver's side valve cover so I pulled both valve covers and used a stethoscope and started checking around...the sound is very evident when you listen in on the #3 cylinder intake rocker stud....none of the rest make suck a loud noise....sounded kinda like tapping a sheet metal valve cover with a 3/8's open end wrench....I used a timing light to see the frequency of the knock and it knocks exactly with the timing light...if I put the stethoscope on the side of the block or anywhere else such as an intake bolt, the sound is just not there....

So here's what I've tried so far before yanking the motor:

Pulled the lower intake, replaced all the comp lifters with brand new gm hyd roller lifters....replace the one piece push rods with an older set of stockers, replaced the rockers with the comp stamped steel roller tip rockers (not roller fulcrum type)....put the intake back on and fired her up...noise was still there....no change....so I compressed air into the #3 cylinder, removed both springs and associated hardware, checked the valves for freedom of movement, replaced the springs, retainers and seals with new ones (i had the remains of a V8 set) and fired her up again....tapping is still there.....

The only way I've managed to reduce the sound is if I start the truck, wad up a shop rag, place it over the push rod end of the suspect rocker/valve and apply around 60 lbs. of force to it with my thumb...that greatly reduces the tap...now in order to virtually eliminate the noise is when I back the polylock of the suspect valve to zero lash or looser while the engine is running...the tapping goes away....I used a local reputable engine builder/machinist this time around and I have this noise now....He came by a few times to help me diagnose this and he claims to have never experienced any noise like this one and he is stumped....he told me to pull the engine....I spent a ton of time installing this engine and would like to avoid pulling it again if I really dont have to...All of the turbo plumbing and electronic stuff is a real pia to undo.....The noise doesn't sound like piston slap and I have plenty of oil pressure and oil flow....Does this sound like it could be a bad cam?? I have recorded 3 sound clips and can post them is anyone is interested in hearing them...the noise is evident in the clips but not like being there in person listening to it....what do you think??

thanks,

serv

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Old 12-14-2005, 02:01 AM
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This is a real stretch but would the number 3 hole be the former residence of one of the collapsed ring lands? If so, it may have aquired a partical molten material in the valve seat area that didnt make noise with the original piston. Can you look at the old number 3 and determine if any valve to piston contact occured. Was the number 3 ex valve misteriously out of adjustment after the overboost? Was the valve grind and valve shape checked (valve tulipped?) while it was torn down? Have you thrown a leakdown gauge at it yet? Were valve to piston clearances checked on all holes? Were the valve reliefs checked against actual valve location? Your ex valve may not be in the same location as it was when you first installed it. I am having difficulty understanding how an overboost would collapse a ring land unless there wasn't any timing taken out of it and at that point I'd say it was severe detonation that collapsed the ring lands not boost. The damaging, hammering effects of severe detonation are often not limited to the rotating assembly. J&E did supply you with new pins right?
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Old 12-14-2005, 03:01 AM
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Quote:
Originally Posted by 56Maynard
This is a real stretch but would the number 3 hole be the former residence of one of the collapsed ring lands?
yes it was....

Quote:
Originally Posted by 56Maynard
Can you look at the old number 3 and determine if any valve to piston contact occured.
We did not find any evidence of piston to valve contact....I have pictures of one of them with the cracked piece in place then after removing the broken piece

Quote:
Originally Posted by 56Maynard
Was the number 3 ex valve misteriously out of adjustment after the overboost? Was the valve grind and valve shape checked (valve tulipped?)
I don't believe so on the adjustment....I do the half turn after zero lash on this motor....as for the valve grind check, we didn't tear the heads down...the man that built them only gave them a good visual check....we did check the valves for freedom of movement when we replaced the springs....even twirled them on their seat to see if there was any resistance to them on the seat...it's the best we could do with the heads on....




Quote:
Originally Posted by 56Maynard
Have you thrown a leakdown gauge at it yet?
no, we have not...your questions are opening my eyes and make perfect sense....



Quote:
Originally Posted by 56Maynard
Were valve to piston clearances checked on all holes?
no...these are dished pistons....could the clearances have changed? the heads are running the exact same valves as before....




Quote:
Originally Posted by 56Maynard
I am having difficulty understanding how an overboost would collapse a ring land unless there wasn't any timing taken out of it and at that point I'd say it was severe detonation that collapsed the ring lands not boost. The damaging, hammering effects of severe detonation are often not limited to the rotating assembly.
well, in order to keep my story short, I didnt go into the high timing that this motor may have experienced....I didn't want to turn anyone off from reading too long of a post....I had electronically disabled the knock retard during these runs...that caused the motor to experience higher timing at that boost level than if it would've corrected for if it sensed deto...my reason for disabling this was a false knock condition that I have been chasing since building up this motor.....the stock knock sensor location of my truck is on the very rear of the motor and I believe it picks up false knock from the noisier aftermarket valvetrain....my knock sensor has always reported false knock under light/no loads and pulls timing when there's no way the motor is experiencing detonation....My next project is to relocate and install two knock sensors on either side of the block to help minimize and or correct the false knock.....




Quote:
Originally Posted by 56Maynard
J&E did supply you with new pins right?
yes they did....


Why is it that the tapping sound goes away when I put pressure on the pushrod side of the rocker? Am I possibly deadening/muffling the sound with the rag? Are you focusing on valves because of the fact that the noise goes away at zero lash or looser while the engine is running?

thanks you very much for taking the time to help me with this issue....should I pull the motor just yet? My builder says he wants to do a COMPLETE teardown/inspection of everything....at no charge of course other than the bearings and gaskets....thanks again....

Last edited by sy733; 12-17-2005 at 04:33 AM. Reason: added pics
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Old 12-14-2005, 09:58 AM
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Your welcome but I dont know that I helped anything. Yeah, my thought was that the rag and pressure might be deadening the tap. The reason the valves are suspect, is that the severe hammering hammers and heats in both directions or, against the rotating assembly and the head.

Given that the whole valve train had been changed except the valves, I was entertaining the thought of maybe the valve (under intense heat) grew within the guide and began to bind in the guide limiting the valve's ability to close and subsequently being bent a little on impact. But all of this theory has been eliminated. This same heat could cause a valve to begin tulipping or the face collapsing under the heat and beginning to pull back through the seat with spring pressure. Are the valve stems still at the same height all the way across when the rockers are off? Was the cam inspected? Were the valve faces covered with a real light grayish deposit?
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Old 12-14-2005, 10:40 AM
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Quote:
Originally Posted by sy733
Hey guys,

now in order to virtually eliminate the noise is when I back the polylock of the suspect valve to zero lash or looser while the engine is running...the tapping goes away....

..what do you think??

thanks,

serv
This is what really is bothering me. Something is wrong here.
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Old 12-14-2005, 10:48 AM
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If the tapping goes away when you push down on the rocker or loosen the rocker, I think of two things. 1. You are lowering the amount that the valve is lifted. 2. by removing lifter preload, you are allowing the valve to seat a little harder. If the valve is bent just a bit, or the seats aren't exactly concentric for some reason, what you could be hearing is a bit of exhuast pushing past the valve at max cylinder pressure. You said it occured at the same frequency as your timing light, so it's a possiblility. Or, the shape of the dish on your JE is a bit different than the SRP. Could be that the extra couple thousands of lift from the lifter preload is causing the valve to kiss the piston at some point.

Another possibility I just thought of: If the cam could have somehow gotten a ding/dent in it, that the roller goes in giving extra slack, and then gives a tap when when it takes the slack back up. That would be easy enough to check.
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Old 12-14-2005, 01:06 PM
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Thanks guys....so this is what I'm thinking should be my next moves...

1. Measure valve stem heights with a dial indicator...
2. Use the same dial indicator to check cam lobes by measuring the travel of each rocker...
3. If the above checks out, remove suspect head and take them to the builder?


As you can tell, I'm trying to avoid pulling the motor again...I will pull it, but if this is in the head, I'd rather pull only the heads...Even R&R'ing the heads while in the truck (gmcsyclone) is a bear of a job....or would that be cutting corners? should I just yank the motor and be done with it?

Whats the best way to check for a tulipped valve? visually? or is there a measurement procedure?


thanks again for your time gentlemen....

serv
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Old 12-14-2005, 01:28 PM
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I had a 396 bbc that sounded the same way. A ticking lifter/rocker was driving we crasy. The engine had good pressure and oil flow. The ticking seemed to get louder as the engine warmed up. So, I pulled the engine, slapping in a 454, and tore down the 396 (nice to have two engines). It turned out to be a rod bearing eaten doen to the copper. I'm still not sure why the lifter/rocker arm was ticking, but the rod bearing was killed.
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Old 12-14-2005, 01:37 PM
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Quote:
Originally Posted by xntrik
This is what really is bothering me. Something is wrong here.
Yeah that struck me the same way. Makes ya kinda want to ask if the lobe is ok. The cam is already being called on to lift against increased spring pressures and against boost, now if you factor in the hammering effect of detonation against those lobes, could a piece of that lobe failed? I dunno but its worth pondering and looking at.
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Old 12-14-2005, 01:39 PM
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Yeah, I think I'd pull those heads for inspection and if they and the cam check out, you'll have to pull the motor.
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Old 12-14-2005, 02:54 PM
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valve train tap

i had the same problem with my 64 327 vette. the previous owner took the pressed in rocker studs out, drilled and tapped the holes to accept the 7/16 threaded studs. this is all fine and good. however, this guy must have used a twist bit and a hand drill. the car had a lifter tap when i found it, but had all the required ncrs goodies and was in good restore-able condition so i bought it. on the way home the noise got worse and then the #3 intake rocker stud broke, that rocker arm fell between the #3 exhaust rocker arm and valve cover blah blah blah you can figure the rest. anyway, i discovered that the center line through the push rod, rocker stud and center line of the valve was off by as much as 1/4 inch. because it was off so much and the push rod guide holes in the head were so badly worn, the rocker arm was riding at an angle on the valve until the valve stem wore at an angle, and the rocker arm slid off. close your ears for the next part, i know it was wrong but i took a die grinder and flattened the tip of the valve and replaced the broken parts. i adjusted all the valves, zero lash running, zero lash one turn, ect. ect. the noise would not go away. i pushed on the vale, rocker arm and push rod which made it stop. i put the cover on and drove it. the same thing happened again after @ 1500 mile's later. at that point i started the Restoration. the engine is the original so i planned on saving it. i discovered the problem while just starring at the heads one night. i re drilled the rocker stud holes to the factory spec. angle using a bridgeport and installed heli coils. i didn't go radical with the build, basically just zeroed out the wear. i opened up the push rod guide holes in the heads and used self aligning stamped rockers. it runs like a raped ape, with no tics or knocks. you said you have guide plates on the heads, so you definitely have hex head base screw in rockers studs. check for minute gaps between the base of the hex portion and guide plate, the drill may have went in at an angle. sorry for being so long winded, good luck. jim

Last edited by corvette jim; 12-14-2005 at 03:00 PM.
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Old 12-14-2005, 04:18 PM
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valve tap

If you can almost eliminate the noise with the shop rag and pressure on the push-rod side of the rocker I would think that your lifter itself is bad. The lifter may be bleeding down and causing the tap. Try giving the valve more adjustment and see if that helps. However, I would still check clearances in the stem and cam. Steve
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Old 12-14-2005, 10:26 PM
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update

update:


Is it typical for hydraulic roller lifters to bleed down? I'm going to assume Yes...These are brand new federal mogul lifters that I installed just last week in an effort to rule out a bad set of comp roller hyd lifters... I'm trying to measure lift of the cam right now, valve per valve measuring from each valve retainer with a dial indicator....so far, every valve that I've measured on the driver's side is bleeding down at a rate of about .001" per second after setting each one to full lift...Is this typical? I even cranked the starter enough to get oil out of all the pushrods and I'm getting the same results....The lifters appeared to be bleeding down well over .150" before I gave up and moved on to the next valve....kinda makes it hard to measure my cam lobes with this going on....

TIA again guys....
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Old 12-14-2005, 10:30 PM
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Quote:
Originally Posted by sy733

1. Measure valve stem heights with a dial indicator...
2. Use the same dial indicator to check cam lobes by measuring the travel of each rocker...
3. If the above checks out, remove suspect head and take them to the builder?

so far, I found that I wont be able to try option #1 with my dial indicator....#2 isn't working out for me either because of the bleeding down of the hyd lifters...I guess it's time for option #3 now....time to pull the heads now...

serv
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Old 12-15-2005, 01:22 AM
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thanks.......

Last edited by sy733; 12-17-2005 at 04:32 AM.
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