I Found Out What Made My Engine Knock - Team Camaro Tech
Engine General Engine Discussion.

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post #1 of 12 (permalink) Old Aug 25th, 02, 04:38 PM Thread Starter
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As some of you may have already read in a post that I started here a week or so ago, my 400 small block started knocking last weekend. I got the engine out this weekend and this is what I found. The number three rod bearing was gone, but it didn't spin. I guess that is why there was just a slight knock. Here are some pics of the bearings. None of them looked good, but the number three rod bearing was, by far, the worst. The mains didn't even look good.
http://cards.webshots.com/c32640113nksyos http://cards.webshots.com/c32640120rtbybo http://cards.webshots.com/c32640138ourlrv http://cards.webshots.com/c32640153wkfefv http://cards.webshots.com/c32640166dvrjqz

So, what do you guys thing happened here? The engine was never low on oil that I know of. I do autocross it on a regular basis. Could oil starvation have occurred?

I think that everything was too tight when I put it together. I plastigaged everything. All of the bearing clearances were right on the lower end of the tolerance.

I am going to get the crank turned tomorrow. It will probably be .010" under on mains and rods. What do I need to do the prevent this from happening again? Also, do I need to have the rods reconditioned again? None of the bearings spun. They were just excessively worn. Is there anything else that needs to be replaced in this engine? Is there anything else that I need to look at?
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post #2 of 12 (permalink) Old Aug 26th, 02, 04:37 AM
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i wouldnt turn the crank unless necessary if it can be polished an the oil holes chamfered do so an use better bearings H race bearings. if you didnt have a windage tray get the milodon stripper an the correct main studs to place it correctly. contact milodon i dont remember the part # for the longer studs arp not long enough also a moroso pan with trap door will help alot i also used the moroso oil pump an pick up that raises the oil pressure with rpms instead of having huge oil pressure all the time. let me know if you need help making the stripper fit no one makes a stripper just for a 400.
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post #3 of 12 (permalink) Old Aug 26th, 02, 06:01 AM
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How old was the motor and rebuild? Who did the work on the crank and rods?

I had the same experience and it my case it was poor quality work on the rod journals and crank. The motor was still virtually new (<400 miles) and I had a local shop check the parts after disassembly. Everything was off just a little, the rod journals weren't flat (very slight side-to-side taper) and the finish was too rough. A rough finish won't allow the bearing to transfer heat correctly into the block and rod and the excess heat can cause problems with the oil film which leads to a quick death. The taper also changes the clearances across the bearing face.

I had everything done again locally and thay showed me their work (proudly) when they were done. The motor is holding up great this time around.
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post #4 of 12 (permalink) Old Aug 26th, 02, 06:20 AM
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You might want to pay more attention to the oil pressure gauge during hot laps. If you suspect running the pan dry, you could run a quart or two over the full mark on the dipstick with no problems at the track. Just another thing to consider.

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post #5 of 12 (permalink) Old Aug 26th, 02, 06:32 AM Thread Starter
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I rebuilt the motor almost exactly a year ago. It probably has 5000 miles on it. I had the crank polished and the rods reconditioned by a local shop that came highly recommended. I used Clevite .001" undersized bearings and like I said before, all main and rod bearing clearances were right on the tight side of the tolerance. I thought that I did everything right. I did use a Melling high volume oil pump only because it came with the kit that I bought. Is is possible that I pumped the oil pan dry and starved the engine of oil? I am going to put a stock pump back in it this time around.

When Autocrossing, I don't look at the gauge, but I do have the idiot light hooked up too. I have never seen it come on while making a run. Are stock oil pans really bad when cornering?

[This message has been edited by Cameron (edited 08-26-2002).]
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post #6 of 12 (permalink) Old Aug 26th, 02, 08:32 AM
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It is possible to expose the pickup during autocross events. The stock Z/28 Trans/am road racing setup would run into that problem once in a while when running hard. The Chevy recomendation was to run the sump a quart or two over full if you were loosing pressure on hot laps. Yes, it can happen with even the best stock racing pieces.

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post #7 of 12 (permalink) Old Aug 26th, 02, 08:33 AM
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From looking at your photos, it appears the clearances at the bearings may have been a little tight. From what I can gleen from the pictures, it appears the majority of wear is on the non-oil fed side of the mains and rods. This leads me to believe they may have been a little tight. There is the possibility of improper or out-of-round journals, but this should show on both bearings, equally. Was just in your neck of the woods at the horse park. Nice place if you like low horsepower figures and nice horses (it's a daughter thing).
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post #8 of 12 (permalink) Old Aug 26th, 02, 09:07 AM Thread Starter
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I just got back from my machinist's shop. We have determined that the engine was probably starved of oil during the Autocross events. The combination of a high volume oil pump and a stock oil pan were just too much. Everything on the crank checked out just a little under factory specs with no taper. That is why I used the .001" under bearings. Does this sound like a reasonable explanation?
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post #9 of 12 (permalink) Old Aug 26th, 02, 03:03 PM
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He, He!! Those bearings look better then the bearings I took out of my 260 Ford Fairlane S/W engine I did a shade-tree to in the early '80's!! I just put stock bearings back in her and kept on going...

BUT, I NEVER hammmered on the old sucker!! I drove the old car for years and years... Real easy...

And to this day, I miss the old car, it would hold a 4' x 8' sheet of plywood in the back with the rear seat down.. pdq67

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post #10 of 12 (permalink) Old Aug 26th, 02, 05:08 PM
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Get your crank checked out by a good shop for sizing, taper and finish. Have it polished while its out if good. Stay with stock crank if possible. With stock size journals you can mix and match std., .001 U/S and .001 O/S bearings. With undersize journals you have to depend on machine work for correct clearances and take what you get as long as they fall into range of specs. It's a lot faster and cheaper to vary specs with bearings than machine work.

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post #11 of 12 (permalink) Old Aug 26th, 02, 05:34 PM Thread Starter
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That's what I thought when I was disassembling the engine. This thing looks like it has 150,000 miles on it.

My machinist has the crank right now. It is going to have to be ground .010", .010". This time around, I'm going to install a stock oil pump and an oil pan with some baffles to keep oil near the pickup. Hopefully, this will keep this problem from happening again.
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post #12 of 12 (permalink) Old Aug 26th, 02, 07:36 PM
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If the main bearing got smeared like that and the oil hole is restricted, then oil would have a difficult time entering the crank and traveling to the rod bearing.

Make sure to check the cam bearings too!

If you have hydraulic lifters that are anti-pumpup type, those really fill the valve covers with oil.
If solid lifters, use the orifice type lifter, not the std "piddle valve" type.

I found a corvette six quart pan that fit my Camaro that helped, it had a trap door on it too.

Check my web page for First Gen Camaro suspension info:
David's Motorsports page
First Gen Suspension Page
67 RS 327 original owner. 69 Camaro Vintage Racer, 65 Lola T-70 Chev SB Can-Am Vintage Racer
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