Well,
here I am... spent the last year and a half working on my first project, intake, carb, headers, custom exhaust, rims tires, the whole brake system, Lots of work for a newbie. I had the exhaust put on today, and boy was I excited! Drove her home only to hear an absolutely HIDDEOUS knock on acceleration. Im kinda stumped here (or maybe I dont want to believe that I'm going to need a new block)...Any suggestions on how to diagnose wether its just a bad bearing, or a rod ready to SMACK out the side of my engine? I am in tears, but I'm sure this has happened to most of you sometime.. Advice? sympathy? Laughter? I need some input.

 

Maybe it's not as bad as you fear. If the engine ran fine before your upgrades, chances are something has been changed uptop. Such as timing, or distributor wires shorted or crossfiring, even aged harmonic balancer. My 289 V-8, for instance, would knock on #1 at idle if the distributor vacuum line was hooked up to the OEM recommended port. (Ford then came out with a change, saying hook it at the carb base.) Presto. I mention these things because I've had them all happen to me.Good luck. We'll be watching for your update.

 

It's a little tough to troubleshoot a knock without hearing it. Is it a mechanical knock or maybe just spark knock? Spark knock is relatively cheap and easy to fix, but a mechanical knock, well, ain't! Spark knock, detonation, pinging, or whatever else you may want to call it typically is only noticeable on acceleration. Try backing your timing off some and see what happens. If it goes away or is less noticeable, then that is likely what you're hearing. Leaving the timing retarded is one way to cure it, but with all the changes you've recently made, I'd say that your best bet would be to rejet the new carb for your current combination and put an adjustable vacuum advance on the distributor. If your fuel mixture is too lean, it can cause high combustion chamber temps and hot spots leading to detonation. This not only creates an annoying noise, but it's hell on pistons, too. Rejetting the carb will get your fuel mixture dialed in which has several benefits, and the extra fuel will help cool the combustion chamber and reduce the knock. Small block Fords like to run a little fat anyway. There is a proceedure involving a stopwatch and a marked off stretch of highway with no law enforcement in the area used to get it dialed in right. The adjustable advance is dialed in the same way. Good luck and let us know what you find.

 

It doesnt knock at all while idling, or reving the engine in park. It does however knock fast and sharp when Im in the upper rpms, especially in 2nd gear. Once my automatic tranny goes into 3rd its fine. Only in the upper rpms do I hear the knock, but it isnt always there, and never at idle.... Hope this can help. The only thing I've done is corrected? my timing and suddenly I'm getting this sound. It is unnerving to hear this.

Thanks guys. I hope to figure this one out.

 

As Blue Oval stated, knocks are tough to diagnose unless you hear them yourself. Exceptions to every rule but here is my opinion. Main bearings are generally most noticeable at idle and have a very low pitch to them (rhythmic thud). Rods often smack the most violently during acceleration or decelleration and often to a random beat. If the knock occurs without driving the truck, pull the spark plug wires off one at a time while engine is running. When you remove the spark from the offending cylinder, the knock will almost always diminish VERY noticably. If the knock only occurs under load when driving the truck, well then have your wife remove the plug wires while you do a few hole shots. Sounds like perhaps your top end mods put a little more power to a tired lower end and she just wasn't up to the task. Good luck and keep us posted.

Dewayne

 

I bought a Chevy S-10 thinking that the V6 engine had a rod knock. It would make a knocking sound when I accelerated or decelerated (sp?). When I pulled the engine and transmission I discovered that the torque converter/flywheel was missing its locating dowel on the crankshaft, it was knocking on the 6 bolts that bolt the flywheel to the crank!

Other things that make a 'knock' sound;

Misfiring cylinder, especially when you cross to plug wires!

Exhaust leak. It's spooky to install a new engine, fire it up and hear what sounds like a rod knock.

Engine part banging on the frame or chassis.

If it's a rod knock, it should be evident when you jazz the motor when it's in park, either on acceleration or deceleration.

Best of luck,

Paul

 

Well, I changed my oil, and used 20/50 and some STP oil treatment. My engine seems to run alot smoother, and the knock is only evident when I really get on it. I can drive it at normal speeds, and she runs great. I have about 55psi oil pressure when hot. As soon as i hit it hard i get a fast sharp high pitched knock. I am a little relieved, and am hoping it is going to be something short of taking my engine out, and starting over. That will be nice when the day comes, but I want a little time to settle into my project. I havent even driven the old bittie to work yet. Thanks for the info, Ill keep you guys posted...

 

You didnt say what kind of engine.
But it could be a lifter that either isnt getting enough oil or is adjusted too loose. Either one could cause rapid cam wear.

Another possibility is wrist pin knock. This isnt fatal as long as you quit goosing it. Ive driven over 40K on a 396 Chebby with that knock.

 

 

Well it wasnt a bearing, a rod, or anything wrong with my bottom end. The problem was: When I put my starter back in, my transmission got backed off of my engine a bit. This was causing the weights on my fly wheel to knock on the plate keeping out rocks and debris from my tranny. I tightened up the bolts, added a few where there werent any, and PRESTO! She runs, and purrs- no knocks. There is a God! Thanks to all of you that helped me with my problem, I learned alot in the process. Now its off to bigger and better things-mainly suspension.

 

Moral to this thread is when you replace a part and then the vehicle won't run, don't start replacing everything else. 90% of any repair is the analyzing/diagnosis of the problem.

 

Great News, Ive heard of that same problem before.
Put a note on the dashboard " The job aint finished until the last bolt is torqued down"