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My 93 having a mysterious tapping or knocking under acceleration that comes and goes

dbrannon79

dbrannon79

I'm getting there!
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Seguin, TX
Guys. I have been noticing a mysterious tapping or light knock while using acceleration that seems to come and go randomly. When it starts happening I just let off the go pedal and get back into it and it seems to go away. Might have mentioned it before in another thread but today I decided to go ahead and tear into the top end thinking about the plastic rocker retainers not to mention I need to do valve cover gaskets anyway.

So I got it tore down and pulled the passenger side valve cover off. preliminary inspection the retainers are all in place and nothing appears to stick out like a sore thumb. I feel the rockers and three out of the four rockers on the forward bank I can move slightly by hand. I go to try rotating the push rods with my fingers and those three i am able to turn but they get stiff and then loosen as I rotate them. One gets stiff then try to wiggle the rocker and it’s now tight, rotating that push rod more till it’s looser and the rocker will wiggle!


What do yall make of that??

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Pulled the one that was doing this and used my straight edge. Confirmed it’s not bent.

How critical is the wear on the rocker to shaft or the wear on the ends where it contacts the valve?

Here’s a pic notice the wear pattern where they contact the valves. The second and fourth you can see and feel the impressions

image.jpg
 
Remember this is the same engine that I had pulled the oil pump drive off to fix an oil leak and found the hex shaft with so much wear on it that it was about to “slip” like a rounded off bolt in the drive!
I was afraid I’d find other things that would show lots of wear.
 
No bent push rods, retainers are intact. Don’t think there is much of anything I can do about the wear. Still have the driver’s side valve cover to pull and inspect but I’m thinking of just verifying retainers are intact and slapping it all back together. Was gonna do the bolt mod in place of the retainers but with the condition of this engine I don’t think there’s any point in doing the bold mod for the rockers unless others disagree.

I feel like the engine is gonna fail before these plastic retainers do!
 
For me, its a 'while I'm in here' thing. I'd do the bolt mod because you don't know when you're going to either 'do things right' or one of those old plastic retainers is going to decide your next course of action for you. Bolts will cost you what 15 - 20 bucks? Cheap insurance and you can re-use them on the next engine...or not.
 
Paveltolz said:
For me, its a 'while I'm in here' thing. I'd do the bolt mod because you don't know when you're going to either 'do things right' or one of those old plastic retainers is going to decide your next course of action for you. Bolts will cost you what 15 - 20 bucks? Cheap insurance and you can re-use them on the next engine...or not.
Click to expand...
Yeah your right, who am I kidding here LOL. considering home depot is within walking distance to my house I might as well go get some hardware. I already did this to the 95 way back with good results.

16ea 1/4"x3/4" grade 8 bolts, 32ea 1/4" flat washers (doubled up on each) that should be right at 3/4" diameter, and 16 nuts along with a tube of red lock tite. I remember doing this to the 95 and couldn't find any steel lock nuts, I will look and see if they have any.

I pulled one of the retainers out and didn't break it. the lower area of the rocker has some wear but there's not much I can do about that.

pulled off the drivers side valve cover and all looks good there too, still no smoking gun as to why I am hearing what I think sounds like a lifter randomly collapsing under load. I somehow doubt that is what I am hearing though, oil pressure stays in the 40's under load and only drops to around 20 sitting at a stop when warm. I'm sure once I get it back together again, later some miles down the road it will rear it's head, get louder and more consistent so I can be under the hood to hear it. or see a rod fly LOL.
 
Big T said:
Just install the new plastic retainers. This things were not designed for the bolt mod. Although the bolt mod looks cool, there is no evidence that the mod is better than the plastic retainers.
Click to expand...
I have some of the plastic retainers. Had one bust when trying to get it installed.
Said, no way these things is going into My enjun.
IIRC, they are Mahl brand, spelling might be offt. 😹
Anyone wants whats left ofum, let me know.
 
Wear on the entire valve train... weak lifters, ware on rockers, ware on valve tips, ware on valve seats, week springs....

It all loosens the preload on the lifter, say new preload is .050" new .. now you may have .020", the wore out lifter doesn't stay pumped up as well...

The fact you stated it goes away when you vary the load on the motor points to lifters as the main culprit transferring the lack of preload to the rockers...

Get the picture...
 
Went fourth with the bolts nuts and washers. Need to get it back together by Sunday night. Can’t get replacement plastic retainers that quick!

I think Chris is right. Everything has a lot of wear and this engine is half way through its last leg already and near working on hopes n dreams. I just wanted to open it up to make sure it wasn’t something simple. I remember when one of the rocker shaft bolts backed out of the head on my 95 while we were 150 miles from home!! I got lucky then being able to drive it home before it really tore anything apart!

Got the rocker assemblies finished and installed. Torqued down. Cleaning up the valve covers now and checking with a straight edge.

Picked up a can of the right stuff sealant. Funny thing was the passenger side cover was glued on with sealant but the driver side had a gasket and no sealant. That made for easier clean up, had to use my wire wheel on the drill to get all the sealant off the passenger side.
 
A little late to the party but…
When you have a noise like a tick,knock, etc. it is usually coming from one location/ cylinder. Not that the other 7 couldn’t be doing it or be right behind it but identifying where it is coming from before opening up is almost always the best action.
Mess with applying load/ rpm while sitting still to cause it and kill cylinders one at a time to narrow the search.

Those rockers have enough wear on them and most likely the valve does as well that it could be friction between them generating the gap and causing the noise.

If you haven’t put the rockers back on yet- don’t.
Consider pulling all 8 glows, and use the starter via push button to crank the engine freely and apply pressure to rockers one at a time while cranking to recreate the sound.

Did you do the stethoscope test to try locating sound if it is along side of block/ oil pan/ valve covers?
 
Will L. said:
A little late to the party but…
When you have a noise like a tick,knock, etc. it is usually coming from one location/ cylinder. Not that the other 7 couldn’t be doing it or be right behind it but identifying where it is coming from before opening up is almost always the best action.
Mess with applying load/ rpm while sitting still to cause it and kill cylinders one at a time to narrow the search.

Those rockers have enough wear on them and most likely the valve does as well that it could be friction between them generating the gap and causing the noise.

If you haven’t put the rockers back on yet- don’t.
Consider pulling all 8 glows, and use the starter via push button to crank the engine freely and apply pressure to rockers one at a time while cranking to recreate the sound.

Did you do the stethoscope test to try locating sound if it is along side of block/ oil pan/ valve covers?
Click to expand...
Already mostly put back together. Lacking the intake and other stuff. I’ve tried to get it to make the noise while parked but it won’t do it.

I can say that when I do hear it while driving down the road the it’s rhythmic enough to know it’s only one cylinder making the sound. At times it also seems a bit too loud to be a lifter tick but more like a knock. Even revving it in park it seems fine so that kinda throws out it being a rod and I would think that a piston pin or slap would be constant rather than it coming and going.
 
Heck. Could it be an injector? How loud can they get? I do have plans to finish setting up some of those old injectors and install them on this engine at some point. Just haven’t gotten around to that. Now that the weather is warmer I need to get back at that!
 
Here’s the state of affairs. Valve covers are back on and sealed using the right stuff. IP lines back in place but loose at the injectors, even replaced the inlet fuel hose that lives underneath the intake.

Will continue on in the morning. I’m pooped for the evening lol. It’s 11pm and I’m going inside for the night haha.

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