Strange rattle at front of the engine

Discussion in 'Street/strip 400/430/455' started by Jim Blackwood, Jul 17, 2021.

  1. Jim Blackwood

    Jim Blackwood Well-Known Member

    '71 455
    Oil pressure is good, doesn't sound like rods or mains. Very uneven rattle at idle that goes away at speed and slacks off as the engine warms up. Could it be the water pump?

    Jim
     
  2. 73 Stage-1

    73 Stage-1 Dave

    A few different things could cause a noise like that. Watch all of the pulleys (and fan blades) to see if they have any wobble. Get a mechanic's stethoscope (they are inexpensive), an extra long screwdriver or even socket extension and put one end on the various components (PS, Water Pump, Alt etc) and the other to your ear. You'll be able to trace the noise and find the area it's coming from pretty quickly.
     
    Max Damage likes this.
  3. Jim Blackwood

    Jim Blackwood Well-Known Member

    I've got an electronic stethescope and was touching it to various places on and around the engine. Haven't identified it so far but I don't think I tried the water pump so that will be next.
     
  4. Matt Knutson

    Matt Knutson Well-Known Member

    I'd check the pulley bolts, the timing chain, fan clutch & water pump & fuel pump first. Its not easy to guess with out hearing it.
     
  5. GSX 554

    GSX 554 Gold Level Contributor

    Make sure the pulley bolts are tight on the balancer
     
  6. BQUICK

    BQUICK Gold Level Contributor

    Take all belts off and start motor.
     
    johnriv67, m louk, GSX 554 and 2 others like this.
  7. Stevem

    Stevem Well-Known Member

    It could be the timing chain slapping around?

    Make a easy check of the timing chain.

    Yank all the plugs out , remove the distributor caps and spin the motor back and forth 2 to 3 inches by the balancer.
    If all is well the rotor will follow the movement of the change in direction of the crank closely,
     
  8. Jim Weise

    Jim Weise EFI/DIS 482

    Put your stethoscope on the fuel pump, it is in direct contact with the camshaft, so any noises from that area should be greatly magnified at the pump housing.

    JW
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    X2, I have had V belts make a clicking/rattling noise. You can try spraying some belt dressing on the belts. That will temporarily silence the noise.
     
  10. Jim Blackwood

    Jim Blackwood Well-Known Member

    Thanks guys, I'll check that stuff in a bit. Puts me in mind of popcorn the way it's so irregular. Not a noise I can remember ever hearing before. So I'll pull the belts and make sure everything is tight. No mechanical fuel pump, no mechanical fan or clutch so that's less to check. Pulleys could be it. Or maybe the damper if it's gone really rotten, it is an original damper. Water pump seems unlikely, no leaks but who knows? Timing chain is a double roller with less than 50K miles, you wouldn't expect chain slap yet and it doesn't really sound like it but I guess it could be.

    Jim
     
  11. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    I once lost my shirt with a cracked balancer pulley. I thought for sure my 430 developed a rod knock. It was the same noise but not the consistent rod knock rhythm. I decided to punt and pull the motor. After I removed/pulled just about everything to pull the motor I removed the belts and saw the lowet pulley wiggle. I replaced it and the noise was gone.. now if I have a weirdo engine noise I pull the belts immediately. Its amazing how much different the engine sounds without the accessories turning.
     
  12. Jim Blackwood

    Jim Blackwood Well-Known Member

    OK, did all that except checking the timing chain and it's next. Pulleys are tight, damper doesn't move, noise is still there.

    I'm starting to think it could be spark knock. So I'll be checking the timing.

    Jim
     
  13. Stevem

    Stevem Well-Known Member

    You be shocked how fast some of today’s roller chains go south even when not loaded with solid roller Can spring pressure’s!
     
  14. TORQUED455

    TORQUED455 Well-Known Member

    Spark knock at idle?
     
  15. BQUICK

    BQUICK Gold Level Contributor

    Maybe but only when motor hot.....
     
  16. TORQUED455

    TORQUED455 Well-Known Member

    He says it “slacks off when the motor is hot”.
     
  17. Jim Blackwood

    Jim Blackwood Well-Known Member

    OK, well I'm measuring about 3 degrees of play in the distributor shaft rotation relative to the crank. Some of that could be gear play in the distributor gears. At any rate I don't really think a couple of degrees would cause chain slap.
     
  18. Jim Blackwood

    Jim Blackwood Well-Known Member

    I think that might be it. It has one of those MegaJolt boxes with the EDIS ignition so I've got to get into the map but the timing light shows a lot of advance at idle. Could be over 30 degrees. I didn't think to try the dial back knob on the light when I was looking so I don't know for sure. I had to find a laptop that could connect with it and the only tuning files I've found so far are 4 years old but judging from that the numbers are way high.

    This is a basically stock engine but with TA SE heads and the cam has a bit of a bump but I don't know how much. Exhaust is a little restrictive, mostly 2" duals. What would you guys say should be the total advance at idle, 1800 rpm cruise, WOT at max torque and any other point you might suggest? I don't want to steer anyone so I'll wait to hear back before saying what numbers I have here.

    I suspect the zero offset number might have been lost from the tuning file. I'll try to download from the MJ today and familiarize enough with the program to see.

    Jim
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I run my timing locked out at 34*. That would not cause a rattle or detonation, certainly not at idle. Most Buick V8 engines like 30-34* degrees at WOT for best power. The aluminum heads like a bit more in my experience. Moderate cams like a lot of initial timing. I locked it out years ago. It likes it, except at hot crank, for that, I have a 20* start retard in the MSD Digital 6 box.
     
  20. Rossco

    Rossco Greetings Earth Creatures

    I've had a leaking exhaust gasket that sounded just like a rattle and behaved just as you describe
     

Share This Page