im working on a 324 olds and i seem to have a rod or wrist pin knock. is there a way to tell the difference? i cranked it up the other day and started to hear a knock so i shut it down. i cranked it up today and same thing so i let it run trying to pinpoint the source of the noise and after it warmed up it seemed to go away drove it down the road and back and still no noise. if it was a wrisrt pin would the rod be loose enough to feel move back and forth if i torn the bottom end apart? any help is appreciated thanks
Cracked piston/sloppy wristpin makes niose under acceleration...rod knock makes noise at coast...like reving up and letting off...makes noise as soon as you let off or feather the throttle.
If it does not knock next time, it could have been a chunk of carbon that broke loose and was sitting on the piston. The carbon gets stuck to the piston and driving at higher rpms makes it heat up and blow away. Carbon does get loose in an engine that's been sitting unused for a while. If it does do the same knock the next time it is started when cold, I would think it is piston slap. That will go away with heat.
Sounds to me like a bit much piston to wall clearance, and when it warms up the piston swells enough to eliminate the noise. Could just be worn, how many miles on the motor? Ever heard a cold start of an engine with forged pistons? Because of the requirement for a generously loose fit in the bore, a lot of them will piston slap/knock pretty bad until they build a little heat, then all is well.
miles unknown if it is piston slap and the piston is expanding as as it get warmer is it time for a rebuild? or is it something i can live with?
Yes. Many decades ago, shops had a bench power tool that was like a miniture drop hammer. It was for peening the piston skirts to expand them, so they would not slap on a cheap ring and valve job. Before that, they also had aftermarket "skirt expander rings" that fit inside the lower part of the piston. Those kept tension on the skirts to prevent cold slap.
so is that a yes for rebuilding or dealing with it? what would you guys do? dont drive it much lately just on weekends.
Are you sure its lower end? A simple test to run to see if its upper end or in the ba*****t is to put your timing light on it right as you start it up cold. If the sound happens every time you see your mark, its upper end, and if it makes a sound every other time the mark goes by its downstairs. Once you figure that out, grab an auto stethascope or a length of vacuum or fuel line and jam it in your ear. Put it on all spots of the motor untill you can locate the loudest knock. This will also help in saving time trying to figure out which cylinder or section of valvetrain is the offender. Im not sure what year your motor is or if it was a low oil pressure motor by design. What is your oil pressure reading when at idle and when driving? Is your oil level good? How many miles are on the motor? Had it been sitting for a long time before this happened? Are you using detergent or non-detergent oil? What weight? Does the motor have solid or hydaulic lifters? Just a few questions and tests to do to help us help you. I wouldnt tear into the motor just yet. Its easier to diagnose when its still a runner.
Also, without pin pointing the sound and detecting the cause for certian, its hard to say what it is. Could be a collapsed lifter that starts to work again once its juiced up.
oil preesure isnt great 10 at idle and rises with rpm, oil level is good, not sure on mileage, it hasnt been sitting, i think i used castrol gtx 10w30 at last oile change, and it has hyd.lifters
Just FWIW: Most (all) Subarus have piston slap when cold. There is a factory bulletin telling folk not to worry, ie: "they all do that, sir". Take it for what it is. And, don't give me **** about knowing this, it's how I make my money... Cosmo
Ok, good info. Without first doing the tests I suggested, were still not sure if its up top or below. With 10 psi at idle, Im voting for valvetrain as a first guess since its goes away when it warms up. And this is the easiest to check and rule out if thats the case, What year is the motor/car?
Ok. The reason I ask about the oil is because if it was running old school oil with no detergent, (recommended for older motors, especially ones with known low oil psi) all the gunk in the motor just stays put. Once you start using detergent oil (most modern oil) it takes all the gunk and makes it float around. Thats bad cause it can plug up oil p***age ways with all the pre-existing years of gunk and starve certain areas of the motor of oil. New cars or rebuilt fresh motors should use detergent oil from the get-go and never use the old stuff, cause then the oil floats the gunk from the begining, getting rid of a large amount of it in the filter or when draining the oil. Hope that made some sense, haha
yea that makes sense thanks for all the info from you guys ill try the timing light test tommorow evening so as to see the light better ill post back what i find
Knock on a cold start, at idle, is usually pistons or wrist pins. Rock the throttle, if it rattles as the revs just come steady, it's rods. Mains thump under acceleration at low revs. Lifters come and go at any speed, plus they rattle "half time".
checked with the timing light like monster said and it definitly coming from the top end but the lnock was not as loud today as previous days idrove a couple miles and couldnt hear anything
ok, so if its definately coming from the top end (valvetrain) then you can rule out all the things you thought it was. Its not piston slap, wrist pin wear or con rod bearings or anything connected to, or operated by, the crank. So upper end. Cam, lifters, pushrods, rockers, springs, valves. Out of all of these parts, only one comes to mind that would "knock" when cold and fade out when warm. Let the car sit for a whole day allowing any failed lifters to collapse (lose their oil). With a cold motor, I would first take off the valve covers and run through the entire top end looking for anything loose or bent or out of shape. At the same time I would perform a valve lash adjustment. (If you dont know how to do a proper valve lash adjustment on your car, look it up online, but it needs to be done properly, or your just wasting your time.) See if you find a collapsed lifter. Youll know if your rocker nut needs to be tightened down much farther compaired to the others. Your valve adjustments may be way off and in need of a thourough adjustment anyways, so do the job right. If youre motor has no rocker adjustment nuts, then see if any push rods have noticable slack. Run through the entire adjustment process, bumping the motor or turning it over by hand. Check all components to see if one or more have too much slack. Once you do your adjustments, leave the valve covers off. With the low oil pressure you described I doubt youll have to worry about it splatting and running all over the place. Start the motor and see how much oil is being pumped up and through the valvetrain. Make sure oil is coating every working part. While looking at that, listen for any sounds if you havent already found the problem with your valve lash adjustment. If you do find that you have one or more collapsed lifters and need a walk through on how to replace them, just ask! Good luck and tell us what you find! BTW, if you dont have a Chilton or Hanes or something like that for your car, try to hunt one down. some argue that info in them is debateable, but its a great start and good source for torque settings.
Gee The Monster last time I looked 324 Olds' did not have any valve adjustment . Solid pushrods and non-adjustable rockers on a shaft. Old Olds' were known for clatery valves.
Yep but I'd still pull the valve covers and look things over to see if there was anything out of order.
Hey JohnEvans Im just trying to help a guy out whos asking for some ideas. I dont claim to know it all, and have never worked on a 324 Olds, but the symptoms and troubleshooting steps are basically the same with most engines.
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