scary engine noise-solved??

[Werner R.]

my new neighbor at the farm works for a salvage parts place and his job is -ta da- to listen to engines and diagnose the problem so they can determine the salvage value of the car. well, he listened to the low pitch knocking and told me to find the bad rod bearing [it turned out to be number four that was bad-easy to wiggle back and forth]. i pulled the cap and took off the bearing. the inner surface is smooth. the crank journal also seems smooth, but not mirror like. saturday, a neighbor is coming over to mike the crank to see if it has to be pulled. are we on the right track?? any other ideas on things to do or look for while the pan is off? thanks to all who took time to comment on this problem.
werner

[Don H.]

Re: scary engine noise-solved??

You do not osay the year / HP / matching #, etc. Unless you plan to sell the car, I would pull the engine and do a complete rebuild and do it right. Don H.

[Werner R.]

Re: scary engine noise-solved??

don
it's a 64 with a BB [unknown cam]. i just moved into a new house and am overwhelmed with stuff there. i would like to use the car as a 20 mile per sunday driver [may -sept] for two years until my new shop is set up. i personally cannot pull things apart now and do not want to take it somewhere. so, although i agree to do things the right way at some point, i now want only expediency. if i can just replace the bearing and obtain 1,000 miles of light use, i would like to go that route.
obviously it is not #'s matching.
werner

[John R.]

Re: scary engine noise-solved??

The knock you originally described sounded like a top end problem to me. More like a worn cam lobe, worn lifter which is not uncommon with big blocks. It doesn't sound like there is enough visible wear for it to be a bad rod bearing. I would recommend pulling the engine and going through everything but, short of this I would rule out a cam/lifter problem first.

[Werner R.]

Re: scary engine noise-solved??

john
i have no personal experience with rod bearings, so i feel like a fish out of water. when i wiggled the rods from side to side [perpendicular to the shaft], everything felt tight except the #4 rod which had noticeable play and wiggle side to side. they all had a little fore and aft play, but that must be normal. i figure this one is bad, but again, as a complete amateur, i have no direct way of knowing. the inner bearing surfaces looked smooth, and there were no metal shavings anywhere in the oil pan. i know that pulling the engine is the way to go, but i cannot get to that for at least a year because of new house projects etc. all i want to do is drive it a few miles a week until i can pull the engine. if i can do that by putting in a new bearing, i will. also, i definately will check out the cam related system while i am at it. of course if the guys that mike the crank shaft tell me it has to be ground, i will have no choice but to pull the engine. i am praying, lord, praying, on bended knees that i can just put in an undersize bearing as a dirty temporary fix.
werner

[Michael H.]

Re: scary engine noise-solved??

Werner,

It is uncommon to find only one rod bearing worn enough to cause a knock, especially if there is no sign of gauling or scuffing but it is possible. I think you have the right idea so far. Have the shaft carefully measured and inspect the rod bearing bore in the rod but if both are to factory specs, I would definitely NOT install an undersize bearing. Even a .001 undersize would be disaster if the crankshaft pin is standard size. Undersize bearings are made specifically for crankshaft pins that are worn the amount of the undersize bearing. If everything measures to near factory dimensions, you will probably be ok with just replacing that bearing.

As others have stated, big block rattles and knocks generally come from above in the valve train but anything is possible. Good luck with your project.

Michael

[Stephen W.]

Re: scary engine noise-solved??

I would use Plasti-guage To check the bearing clearance first. If you wanted to replace it you would need to know the that anyway. You need to know the specs to know what size bearer to buy.

[Werner R.]

Re: scary engine noise-solved??

mike
since i wouldn't know gauling or scuffing [aren't they an old vaudville act?] if i fell over them, i will have to rely on the good eye of the guy coming over saturday to look at the shaft and bearing etc. but to my eye, the bearing surface is smooth, and to my thumbnail, the creank surface is smooth. we'll see.
best
werner

[Werner R.]

Re: scary engine noise-solved??

so, what i think i'll do is just replace the rod bearing with a new one and start the car. if it has no effect on the noise then i will have learned somthing; ditto if it reduces the noise. i figure i can't hurt anything doing this; the new bearing cannot be too tight; if i'm lucky i can get a few miles of pleasure driving before i pull the engine for a rebuild next year. is this a dangerous thing to do?? my engine won't blow up, will it?? also, the old bearing has a very fine record groove pattern on the inner surfaces [and the outer as well]; nothing too deep, but i can feel it with my thumbnail. the crank surface also has this same feel. there is also a darker 1/2 inch wide band circumferentially on the outer surface, about in the middle of the outside surface. does this tell me anything?? as always, i can use the helpful advice.
werner