Need everyone’s input

[bill8333]

I bought an engine from a guy who said it had a knock in it. The engine is a brand new 350-crate motor not re-built with less than 50000 miles on it.

So I thought about it and bought it for 100 dollars, complete. I tore it down thinking it was a rod knock and to my surprise I can't find anything wrong with it.

I called the guy back and asked him a few more questions about the knock. He said you could only hear it while sitting in the truck at idle and it never went away even if it was warm or cold. Plus remember he drove it like that for 50000 miles with no problems with oil consumption.

So what I need is every possible thing that y'all can think of that would cause this problem. I was starting to think the guy had a cracked flex plate but he gave me the one that was in the truck and it's perfect.

Thanks up front
Bill

[pro street 70]

piston to wall to large clearance piston rattle in bore .wrist pin binding or to loose . crank end play to large crank walking back and forth:

[bill8333]

Ill check all those today

Thanks

[bill8333]

Would a cam bearing make that noise and not show wear.

?????

[1LoC10]

maybe he dropped a socket in the frame horn

[68Stepbed]

My engine had a knock when first started then it would go away. I did still have ticking noise all the time after about 30,000 miles. I also didn't have very good performance out of the engine the last yr or so of driving it. It had about 50,000 miles on it when we took the truck apart.

While I had the truck apart for the resto, I changed the cam and lifters with a set of roller rockers. It doesn't make any strange noises now.

I kept the cam from my crate engine. When I had wiped lobes in the 305 in my 86, I swapped in the cam from my crate engine. Afterwards, the 305 had the same knock and ticking as my crate engine did before I pulled out the same cam.

I would check the cam and lifters. They may be too soft or these new oils may not have enough zinc to protect them.

[HavinSomeFun]

ask the PO if the noise stayed the same at idle or did it speed up with the rpms?

[cdowns]

bad fitting harmonic balancer/cracked or loose flexplate/worn out engine mounts //fuel pump or pump pushrod. i've seen them all cause mystery knocks

[odog]

Stupid answer, but maybe sticking lifter, or exhaust leak. One guys knock is another mans exhaust leak. I've had guys ask me "what is knocking" take it for a drive, check it out, exhaust leak. Simple as that. Just an opinion.

[bill8333]

No the noise stayed the same and could be heard mostly from inside the cab.

[Premium72]

stayed the same? hmm thats odd. doesnt sound like anything in the engine. if it was it would speed up when the rpms would go up. ahh the majic of owning a piece of history..

[mtndewmaniac66]

I probably cannot add much to this, but after I fashioned up my own custom exhaust, one of my pipes were "knocking" against the tranny cross member, the "noise" migrated from the contact point to the header.
A simple hanger adjustment is all that I needed.

[retodd7711]

Might be time for the stethoscope trick.
1. Go to drugstore and buy cheap stethoscope.
2.remove"microphone" from end of rubber tubing.
3.Insert 18-24" of steel brake tubing into rubber end. I've seen small solid stock used too.
4.Place steel tubing on various engine components until you isolate the noise.
This works much better than the screwdriver to the ear trick and keeps your head/hair away from moving parts.

[bill8333]

The engine is out of the truck and in parts all over the garage. I bought it from a guy who said it had a knock in it. So for a 100 bucks I couldn't go wrong. I figured it be an easy fix but now I'm kicking myself for getting into this mess. Well I guess I'll just replace the bearings and put in a new cam, pistons and buy those summit steel heads to replace my 76cc 882 heads that are in perfect condition. I just want more horse power.

[bill8333]

Well I took it down as far as I could today. Got the heads off and the cam out and everything looks good. I did see a little wear on the #8 rod and main bearing but didn't have any plasti gage to check it out. Tomorrow I'm planning on removing the pistons to check the wrist pins. I also saw a little wear on the rear main bearing like the crank was walking a bit but nothing that would make it knock.

Please keep the ideas coming.

Thanks Bill

[powerbench]

When my wife bought her 88, just after she had it for a month or so i developed a knock when you fired it up and would go away after it warmed up, ithough oh great i have a piston slapping the cylinder or a main going out.So i left it and it started getting really bad and started doing it at idle as well .. long story short the truck also had a bit of a shake as well , so i decided to jack it up and try and locate the noise...sounded low in the block like the crank..pulled off the inspection plate for the tranny and found the problem after i fired it up flex plate had broke at the bolt holes and was smacking the torque converter around .....best i can figure,when the oil was cold at start up crank was sling it around and causing the knock, when the oil thinned down from heat it would go away...changed flex plate knock went away.

[powerbench]

man i missed the part about you getting the old flex plate....

[powerbench]

does he have the old converter?

[bill8333]

No he used it when he changed out the engine.

[bill8333]

Well today I got off early and tore it down the rest of the way and nothing, darn I hate problems like this. Maybe I should take the block into a machine shop and have them look it over. The problem with that is there isn't even a little bit or a ridge at the top of the stroke so I can't see the block being bad. I did however have a hard time getting the cam out of the engine. Seems like it has a tight bearing but after a closer inspection they all look fine. Somebody anybody help. Anything that I maybe over looking.

Thanks all for the input

[streetstar]

find a reasonable deal on a 383 stroker kit if you can stretch the budget a little.

An all new rotating assembly should take care of it --- lol (part of my "when in doubt, just throw money at it" approach to engine building)

[bill8333]

Stroker is a good idea but then I cant buy the 64cc heads

[AH619]

was the timing chain loose and slapping the cover?

[bill8333]

Timing chain was lose but nothing in the way of being junk. But I've already bought a new one.