1996 Collector Edition Corvette

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wxo
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Re: 1996 Collector Edition Corvette

Post by wxo »

New plan:

I spoke with MostMint yesterday and we talked about finding the source of this screeching noise. Is it the new timing chain and sprockets or something else like the water pump drive gear bearing again? The noise is especially difficult to pinpoint because it sounds like it is coming from the front of the engine, but access is covered up by the Opti-Spark distributor which attaches to the timing cover and then the Opti is further covered by the water pump. One thought that came out of the discussion was how to spin the engine to recreate the noise without it's being covered up by starter noise. I think removing all the spark plugs might just quiet the starter noise enough to listen for the source of the noise. Anyway, it's worth a try. I might even be able to spin the engine with the timing cover off which would be ideal.

Obviously, I will be inspecting the inside of the timing cover very closely for witness marks and metal particles. I might even bite the bullet and remove the intake to look for a trail of metal particles leading to the oil pan.
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wxo
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Re: 1996 Collector Edition Corvette

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In anticipation of a third foray into Silvia's timing case, Maverick came by and we removed all the spark plugs to allow the starter to more freely spin the LT4. Maverick encouraged me to post a photo of the plugs as they are now.
Silvia plugs.jpg
Keep in mind that the condition of the plugs reflects the tune done by Jeff Creech in February of this year.
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wxo
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Re: 1996 Collector Edition Corvette

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Latest news: With the objective to look for a trail of steel particles on the way to the oil pan, I removed the intake manifold yesterday. Maverick came over this afternoon and we closely examined the lifter gallery. The major finding was the water pump driveshaft bearing looked good. No steel particles anywhere near it. In addition, we could identify no steel particles of significance on the floor of the lifter gallery. This leads me to believe that the bad water pump driveshaft bearing was the current and original source of the steel particles we found in the oil pan.

So what about the noise, you ask. Well, through a hole in the front wall of the engine block, and using a light, we could see the teeth of the gear that drives the water pump drive shaft. We could also see a wear pattern on the teeth. This appears to be evidence that the noise may possibly be simply wearing in between the two gears. Maverick feels that the wear is excessive given the short running time; hence the noise.

So the plan now is shelve the third major teardown for the time being and reinstall the intake and plugs and run the engine long enough to see what happens with the noise. At least get it warmed to operating temp, but maybe more depending upon what it sounds like. I feel fairly confident that the noise and the metal particles are distinct issues. This gives me additional confidence that running the engine is not generating any additional metal chips. This is what this latest course of action hopes to prove. If this action doesn't resolve the problem, I plan to go back to the original timing set and chain.
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wxo
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Re: 1996 Collector Edition Corvette

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I had a good day in the garage today. I took my time cleaning all the gasket surfaces and installed the intake and hooked up most of the do-dads. I'll finish up the intake do-dads tomorrow and start with installing those pesky spark plugs. If all goes well, we should have another startup soon. :D
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wxo
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Re: 1996 Collector Edition Corvette

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I got a late start to my work on Silvia today, but I got all the vacuum hoses and connectors routed and connected and started on the spark plugs. I decided to install the worse one first, #8. Standing with my back to the engine I reached down with my right hand holding the plug. I had a small piece of hose on it to help screw it in when it is in place. I was having difficulty moving it around with the few fingers that would work in the tight space and, wouldn't you know it, I dropped it! Worse yet, it didn't make it to the floor. You may remember the last time this happened and I had to remove the starter to get to it. That's what I'm facing again. I decided to install and torque all the rest of the plugs and leave the starter removal and #8 for Monday. This is a bit disappointing, but so be it. Maybe I'll start it on Monday.
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wxo
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Re: 1996 Collector Edition Corvette

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Maverick came over and we started the LT4 this afternoon. To net it all down, the noise is still there. It would vary in intensity, but never go away. In fact it is pointing directly at the new Cloyes timing set. We could hear a definite gear noise above the other when raising the rpms. It sounds like I have a gear cam drive rather than the chain and sprockets. I'm convinced the source of the gear noise is the interaction of the gear on the water pump drive and that of the large gear on timing chain sprocket. At this point it appears I have no alternative but to dig back in and install the old timing set.
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wxo
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Re: 1996 Collector Edition Corvette

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I started another deep dive into the LT4 today. Antifreeze and oil are completely drained, starter is off in preparation for taking the oil pan down again. I had a couple of notable surprises. Oil drained from the oil pan and filter was noticeably free of the larger glistening particles and there were none on the magnetic oil drain plug. I cut open the oil filter and examined it for metal particles. They were relatively few and far between, and they were smaller, but at this point, not very worrisome. I'm looking forward to seeing what is in the bottom of the oil pan. Maybe next week.
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wxo
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Re: 1996 Collector Edition Corvette

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I removed the throttle body and water pump yesterday and got the oil pan off this afternoon. It has fine, visible particles in the bottom, some of which are attracted to a magnet. Next, I plan to set the engine on TDC and start working my way back down to the timing case. This is not fun.
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wxo
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Re: 1996 Collector Edition Corvette

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I finally dug myself down to the timing case yesterday. I see nothing obvious that could cause the ruckus we are hearing. There are no witness marks to be seen. There is no debris inside the timing case. The water pump gear spins smoothly and quietly. I plan to do more in-depth inspection of the area so this report is just preliminary. I still plan to go back to the old timing chain and sprockets, but it would be nice to see some evidence of the cause of the noise. Maybe Maverick can come over this afternoon to get a second set of eyes and thoughts on the situation.

In addition, I think it would be prudent to change the spark plug wires again. They are recently new, but are getting beat up by repeated pulling and manhandling during this crusade, especially the boots connecting to the Opti-Spark. I'm seeing some scarring and splits on the boots. I don't need future mysterious ignition anomalies emanating from places that are so difficult to access as this is.
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wxo
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Re: 1996 Collector Edition Corvette

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Today, Maverick and I studied, under magnification, both gears that drive the water pump drive shaft. The large gear on the back of the cam sprocket showed an abnormal wear pattern. The wear was only about 50% across each tooth indicating an alignment problem between the two gears. This could explain the gear whine I mentioned in my previous post. The original noise, different from the whine, was also evident on the last test run, but I've seen nothing that can satisfactorily explain it's source. A damaged bearing on the WP drive shaft would explain it, but that's not the case this time. The bearing feels smooth and tight. So, now what? I looked at the old cam sprocket gear just to get some perspective. It has a nice, full tooth wear pattern on each tooth as it should. This is more evidence that there is something wrong with this timing set from Cloyes. It also tells me to go back to the original timing set in hopes that it will fix all this.
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wxo
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Re: 1996 Collector Edition Corvette

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I have completed the first step toward my objective of starting the LT4 without the water pump. The old timing set is installed. The first thing I had to do was to go back and exchange the Cloyes gear on the water pump drive shaft for the original gear.
IMG_4104small.jpg
This time I did not send it out to the machine shop. I used my bench vise. It was very difficult to move the gear on the shaft using the vise, but with some effort I was able to remove the Cloyes gear and get the original gear back in place. I wasn't sure exactly where to position the gear on the shaft because there is no locating shoulder. I looked at some pictures online to get a sense of what a brand new assembly looks like. Next, I pressed the shaft in place and then installed the sprockets and chain. Looking over my handywork, I noticed that the gear on the drive shaft was not centered on the cam sprocket drive gear. I had to take everything apart again and press the gear on the shaft a little more. Putting everything back together again, I see that the two gears are positioned exactly where I want them. Step one done. Next, I'm waiting for new timing case gasket coming Friday. I also ordered some magnets for the oil filter as extra insurance to help keep any metal particles out of the engine.
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