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Rod knock?

  
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Rod knock?

 
YeshuaisLord YeshuaisLord
New User | Posts: 1 | Joined: 03/11
Posted: 03/04/11
04:46 AM

I have a 1961 chevy Bel Air with a frankenstein 327 block. It has 1970-80 350 heads on it, block is 1968 and intake is off a 1965. I bought it last March of 2010 because I liked the idea of the 327 block in it and I wanted a classic. I have a pretty big family so I wanted a 4 door. So this works out good. My problem is  I have a knock. Now I have changed the oil in it and put racing oil in it 50w. That didn't help. I checked the old oil and old filter for any metal shaving and there was nothing in it but oil. I pulled the plug wires out 1 at a time and it kept knocking. I gave it a tune-up  ran premium gas also. Is it a main bearing? Any ideas or help would really be appreciated. Thanks

Don't junk'em, Rebuild'em Cool  

Pontiacman2 Pontiacman2
Moderator | Posts: 8956 | Joined: 09/08
Posted: 03/04/11
05:14 AM

With out hearing it for myself I would say it is most likely a rod or main bearing that will cause it to knock.
Could you post a video of it?  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

tuffnuff tuffnuff
Moderator | Posts: 7827 | Joined: 12/09
Posted: 03/04/11
12:14 PM

+1
Could also be a fuel pump knock or loose bolts on flexplate/converter.
With a bearing going out.,. the oil pressure would be very low at idle.

Grin  
When The Flag Drops.,.

tuffnuff

The Bull ***t Stops.,.
tuffnuff

P. Engineer, Engine Builder

Pontiacman2 Pontiacman2
Moderator | Posts: 8956 | Joined: 09/08
Posted: 03/04/11
02:02 PM

+1 on the oil pressure thing.  
Pontiacman2
Pontiacman2

Professional Hi-performance engine builder

chevelle83 chevelle83
Addict | Posts: 2280 | Joined: 11/09
Posted: 03/04/11
08:56 PM

I have had BOTH flexplate,,,, and torque converter bolts come loose and sound just like a bottom end knock.

 does it change with the transmission in gear vs neutral.  usually rod knock will get quieter with a slight load on it at idle.  

zman123 zman123
Enthusiast | Posts: 531 | Joined: 06/08
Posted: 04/25/13
08:00 PM

I know this an OLD thread but I'm researching knocks. I did 4 dyno pulls yesterday (to 6000 RPM) drove it home on the freeway, drove around town no problems. Today, I'm warming it up to go for a ride (check my thread from a couple of weeks ago on MSD Atomic injection install it will give you all the specs on the engine) 60 PSI oil pressure, no noise at all until it gets to 190 degrees then I start getting a knock. I let it cool down while I go to town in another vehicle and start it back up when I get back 30 min. later, no noise at all until it gets up to operating temp. I have not checked rockers or flex plate yet but i'm hoping to find something that sounds like a rod knock but isn't. Engine only has about 6000 miles on it. holds the 60 PSI. Knock is 1200-2000 rpm, didn't take it any higher. Got a simple answer for me that ISN'T a rod knock?? Thanks, Z  

68scott385 68scott385
Guru | Posts: 1990 | Joined: 10/09
Posted: 04/25/13
08:41 PM

I've had header gasket leaks sound like bottom end death rattles.  
68scott385 68scott385 68scott385

zman123 zman123
Enthusiast | Posts: 531 | Joined: 06/08
Posted: 04/25/13
09:01 PM

I'm hoping I found it, loose cast aluminum valve cover hitting a rocker arm. let you know tomorrow. Z  

redneckjoe69 redneckjoe69
Addict | Posts: 2337 | Joined: 03/10
Posted: 04/26/13
02:08 AM

hope its something easy Z.        if thats not it, a mechanics stethaspcope or a long piece of vacuum hose could help narrow down the area of noise.

   do you have an air/fuel ratio gauge to make sure that atomic fire isnt running lean on ya?   same motor?  

     i saw a guy with big block mustang finishing off the motor.  sounded great.  he put the stock valvecovers on and started it up.  you could hear the rockers hitting the covers instantly, lol.   it left lil dings all down the covers. Grin

   ive heard badly worn/stretched timing chains sound like rod knocks too.   usually puts little metal particles in the oil from rubbing the cover.

   hows the timing?   maybe back it down a few?   how did you make out on the dyno?  

zman123 zman123
Enthusiast | Posts: 531 | Joined: 06/08
Posted: 04/26/13
06:29 AM

First, the Atomic unit controls the A/F mixture, I set the perameters so it's ok. I took the valve cover off and there were marks on the inside from the rocker(s) hitting it. It was almost loose enough to wiggle. the dyno was a little dissapointing. I ran it just to get a baseline for some work I'm going to do so we didn't do any tuning at all. The second part of the Atomic injection install is to mod the distributor and lock it so the MSD computer can control the timing. After I do that it's back to the dyno for tuning. (good thing the school has one I can use whenever I need to. They installed it when they built the new shop 2 years ago)  

Dave632 Dave632
Addict | Posts: 2217 | Joined: 07/08
Posted: 04/26/13
03:25 PM

Remember rear wheel dyno's can indicate anywhere from 20-30% loss due to the drive train. An engine test I saw where a BB Chevy made 700hp at the flywheel. When installed and tested on a chassis dyno it dropped to 496 for about a 30% loss. This car did have a high stall converter and heavy duty drive train components which all eat power.  
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zman123 zman123
Enthusiast | Posts: 531 | Joined: 06/08
Posted: 04/26/13
07:18 PM

Yeah, I knew that. still was disapointing. It made 425 on the engine dyno last year when I built it. 300 wednesday on a Mustang chassis dyno. I was about 300 lbs too light on the weight we entered too, I suppose that would make a little difference. Next time I put it on the dyno I'll fill the tank with ethanol free gas(and maybe a can of octane boost too!)  

Dave632 Dave632
Addict | Posts: 2217 | Joined: 07/08
Posted: 04/27/13
08:44 AM

If you have a high stall converter and heavy duty drive train parts that could be right on the money. 30% taken off of 425 comes in right about at 300.
One of my 632s, the one in the 68 Camaro I had, pulled 606 na on a rear wheel dyno.
This motor was hooked to a high stall converter, HD glide, and the big Dana 60, 9 & 3/4" rear which surely takes some extra HP to turn. I figure I was losing at least 30% on that setup or maybe more.
I remember one of the magazines changing a wimpy Chevy 7.5 rear assembly for a Ford 9" and losing 3 tenths in ET and 5 mph in trap speed in the 1/8th. The trap speed shows how much hp is lost when going to heavy rotating drive train parts.  
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zman123 zman123
Enthusiast | Posts: 531 | Joined: 06/08
Posted: 05/03/13
06:21 AM

OK, after several days of trying to figure out what the noise is, adjusting valves, doing a cylinder balance test and listening to it with a stethascope I think I have decided it's a bad lifter(or 2). I listened to the engine running on a lift yesterday and got very little noise from the front and rear mains but more noise listening from the top, I'm ALMOST positive it's a bad exhaust lifter on #8. Banging noise sounds like it is being transmitted through the cam. Anyway, I ordered new lifters from Comp this morning. (I'd rather pull an intake than an engine anyway) I'll keep you posted. Oh yeah, the lifters in the engine now are NOT Comp lifters. The cam in the engine is a Comp XR270HR. Z  

Dave632 Dave632
Addict | Posts: 2217 | Joined: 07/08
Posted: 05/03/13
09:24 AM

Lifters are usually consistent, thru different rpms, with their sound and are a higher pitch when compared to a rod knock or the deeper sound of a main knock.  
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