1973 455 Olds Occasional Rap

[Low Bridge]

I'm trying to determine whats causing an occasional rap It seems to occur once she's warmed up. She's coming from the front of the motor and has & sounds also close to a detonation problem. Timing is 10 degrees back and at idle the mark tendas to jump around a lot. It's not a constant knock like that of a bearing.<br /><br />Any help appreciated

 

[Reel Poor]

Re: 1973 455 Olds Occasional Rap

Check the mechanical fuel pump, they can make a knocking or clattering noise if it is failing.<br /><br />You can also check for timing chain slack by removing accessory drive belts and turning crankshaft back and forth by hand to see how much slack is in the chain. If there is any slack the crank will be fairly easy to turn back and forth on the slack part of the chain. The more back and forth movement, the more slack in the chain.

 

[rodbolt]

Re: 1973 455 Olds Occasional Rap

the mechanical fuel pump drive on the cam gear can fail. the chain can get slack and whip. to test the chaine remove the distributor cap. rotate the engine by hand in the normal direction of rotation until the mark on the balancer is at the TDC mark. then while carefully observing the distributor rotor rotate the engine backwards until the rotor moves. if the mark on the balancer has moved more than 8* or so before the rotor moves, you have excessive slack in the chain. olds also used an air bleed/oiler on the port oil galley plug that sometimes gets removed or clogged causing rapid chain wear.

 

[Low Bridge]

Re: 1973 455 Olds Occasional Rap

Checked it-<br /><br />Yep she's right around 8* + or - Slack-!<br />As I remember Often the oil pan must be dropped (SB Chevys)<br /><br />This 455 olds has a moroso pan might they have a more forgiving design for timing chain r&r ?<br /><br />I'll take a look at the disrubtor teeth next?<br /><br />Thanks<br /><br />

olds also used an air bleed/oiler on the port oil galley plug that sometimes gets removed or clogged causing rapid chain wear.

What / WHere should I look if I end of pulling the TC Cover?

 

[Low Bridge]

Re: 1973 455 Olds Occasional Rap

Ok so the chain is out actually everything looks fine I wish I found some evidence of something banging around- <br /><br /> Are the sharp teeth are evidence enough? & the jumping mark? <br /><br />They look the same on the crank sprocket.<br /><br />Any good after market double roller? Gears & Chain?<br /><br />Where do I get a marine mechanical fuel Pump? for a 455.<br /><br />Thanks all-<br /><br /><br />

 

[Low Bridge]

Re: 1973 455 Olds Occasional Rap

Well she's got a new timing set and the the timing mark has stiffened up but the rap still haunts me

 

[rodbolt]

Re: 1973 455 Olds Occasional Rap

are you sure its not just a momentary lifter noise when first starting? its normal for hydraulic lifters to clack a bit on start up. especially if someone has installed Rhoades lifters or another brand of variable lift hydraulics.

 

[Low Bridge]

Re: 1973 455 Olds Occasional Rap

She's ok when it first starts. The occasional rap doesn't show until she's warm-

 

[Richard Petersen]

Re: 1973 455 Olds Occasional Rap

Loose valve in a worn guide or a sticky one? Rocker arm starting to size up on the shaft. Pull 1 valve cover at a time and put some side pressure on each spring or rocker arm with a stick. You may even isolate the cylinder.