Nocking at high RPMs
 

Hey gang, rookie home taught floundering mechanic here again.
Had Rusty out for a drive today, noticed a Knocking sound at high RPMs, more so under load (ie. up hill or quicker acceleration). Seems to be left side, under the valve cover, but its a guess.

I was a dummy and neglected to check the oil level recently, it was lower than I care to admit but still registering on the dip stick.
Added oil and the sound improved but has not resolved.

I plan to look under the valve covers this weekend. What am I looking for?

I realize this is a vague and rudimentary description, but I made a disclaimer in the first line of this post. I have never been inside an engine before! Lol.

-thanks:helpsign:

Re: Nocking at high RPMs
 

Is it really a Knocking, or is it the normal clatter from the rocker arms? If the rockers are looser than they are already the tap tends to be much louder. Have two I need to tighten a bit on my 305.

Re: Nocking at high RPMs
 

It is hard to locate a knock at high speed and under load very accurately.
I would look first at ignition timing to make sure it is not too advanced. Fuel problems are a possibility as are spark plugs.
I sure wouldn't take too many things apart without some guidance from a friend or relative with mechanical experience.

Re: Nocking at high RPMs
 

Possibly engine timing like Jim A describes. You will need a timing light to check this. The distributor most likely has a vacuum line coming off the back side of the manifold and goes to the distributor- this provides for more vacuum advance (less throttle/gas) or less vacuum (more throttle/gas). The distributor also has springs under the cap and are "calibrated" to have a specific mechanical advance at a given RPM to advance or retard mechanical timing, or advance. If you don't have a timing light, then;
1- take off the valve cover on one side and check for anything in the valve train that may be loose, like a rocker stud or the nut that holds the rocker in place which would cause the rocker to make a lot more noise than the others. I would say that given your admitted lack of experience, you would be wise to elicit the support and knowledge of either someone you know, or a shop in your area that is capable of diagnosing a big 'ole V6 that is definitely old school.
Good luck! - hope that it is something that can be identified and resolved without emptying your wallet.

Re: Nocking at high RPMs
 

If you don't have a light you can always retard the timing a bit by ear. Retarding the timing Lowers engine idle speed and advancing Increases. Not gonna hurt anything to play with the timing a bit. But I would retard it a little and see what happens. You can always put it back.

Re: Nocking at high RPMs
 

So after some valve adjustment (a few needed small adjustment), learning how to use a timing light (it was at 10deg, turned back to 6ish) and new plugs, wires, cap, rotor and points, it starts quicker and runs smother at idle .... Buuuut no change in the nock at high RPM under load.

I'm resigned to the diagnosis that I've burned a rod bearing.

Stay tuned for panic posts about pulling a Big block V6 in the driveway!
And the subsequent need for gaskets and bearings!


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Re: Nocking at high RPMs
 

A gasket kit can be purchased from O'Riellys that works for the 305's. Rod bearings can be purchased from them as well. As for Mains you will have to get them NOS on Ebay. Good luck, and ask away. :ok:

Re: Nocking at high RPMs
 

I have one in SW WA that purrs like a kitten. My project wont need it and it could use a good home. Besides, I'd like to have the indoor storage room. Make me an offer.

Re: Nocking at high RPMs
 

Thanks Timmy, I'll keep your offer in mind.

In the mean time, I pulled the motor last week and today got around to taking the heads off, valley cover, and generally started cleaning the gunk off the top half.
I got my first look at the bottom half after I removed the oil pan....low and behold...

The number #4 piston rod was loose!

I removed the nuts that hold the rod on to the crank shaft (what's the term for that?) they sure seemed torqued down tight, and found the bearing/bushing was loose and pretty worn looking. I suspect his was the cause of the noise?!?

So, now... how do I go about replacing this worn bushing/bearing? I would like to just replace the one that is shot, am I foolish in not doing them all?
How do I go about sizing a replacement with out pulling the crank shaft and taking to to a machinist? Fwiw the crankshaft looks and feels fine in this spot.

As a reminder this is the first motor I've ever pulled and the first crankshaft I've ever laid eyes on. Lol

Re: Nocking at high RPMs
 

If the bearing is just really worn then a set of standards should be ok. I did that with mine but it didn't have a knock. The unaided eye can't see the small damage that could have been done to that crank so I would have it checked and ground if needed. I am not even sure if .010 over r Normally if you do one you may as well do all. I ended up doing rods and mains in mine! Can you post some pics so we can see?

Re: Nocking at high RPMs
 

Since you already have the pan off, it would be foolish to not pull all the rod bearings and have a look at the crank journals.
Beg, borrow, or buy a micrometer that will handle that diameter crank journal, and measure them all.
That will give you a chance to see if any others are scored or badly worn, and you will likely have to buy a whole set of bearings anyway.
The manuals show the dimensions of a standard crank. You can gauge how much the crank journal is worn, and compare it to the others.

CAUTION:
Since this is your first 'rodeo', so to speak in this, realm:
Understand that connecting rod caps ONLY go on one way.
They are bored out of a casting, but the hole is not exactly centered between the rod bolts, so if the cap is put on 'backwards' the circumference of the bored hole will not necessarily be exactly round.
Nearly all rod bearing caps have some sort of marking, grooves, numbers or notches, that will indicate the correct alignment.
If you get them installed wrong, you Will do damage to the bearing and/or the crankshaft.
If installed incorrectly, you probably will not be able to turn the engine over with a standard ratchet. If the engine does turn over, but seem to crank very slowly, I would also suspect an incorrect bearing installation, even if it is only one rod bearing.
Do not attempt to tow the truck down the road to try to get it started.

If you are already aware of this possibility, then GREAT and I have wasted a few words, but if not it might save you a whole lot of frustration nd expense.
Good luck,
Rod Johnson
Issaquah WA

401M in a RM7500 chassis

Re: Nocking at high RPMs
 

Rod,

I, too, am an amateur at all this. Your words were not wasted on me. Thanks for the detailed info.

John

Re: Nocking at high RPMs
 

WE7X--- not wasted at all! I'm always weary of Pitfalls and things an experienced guy might take for granted. I'm proceeding with caution but keep the wise words coming-thanks!


I'm trying to load pics from y iPad..... grrrr

Re: Nocking at high RPMs
 

Here's the pics I just took. The one with the screwdriver is pointing out a noticeable gap but I guess that gap was previously filled in by the shiny silvery residue in my oil pan.

Re: Nocking at high RPMs
 

I cannot be sure, from the pictures, but it looks like that bearing has spun in the connecting rod. I don't see any trace of the tabs that should have fit into the notches in the connecting rod and the rod cap. It also looks like there are scrape marks on the outer surface of the bearing shell.
I would strongly suggest pulling the others, to have something to compare. BE SURE to mark the caps, so they go back on the same connecting rod, and in the same orientation, when you finally assemble it.
Rod J
Issaquah, WA

Re: Nocking at high RPMs
 

Yea... my thinking is that it spun as well. What I have now are two semi circles that are just a piece of metal, I was thinking they would actually be a bearing?
I'll pull another so I can compare.
Assuming the that it spun: would I expect significant damage to the rod/rod cap or crank journal? To recount: this noise started abruptly after driving w low oil level


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Re: Nocking at high RPMs
 

Judging by the wear on the notch of the bearing I'd say it spun. It is pretty scarred up. Luckily you caught it quickly. Pull All of the caps off and check them over. Thing is if ran with low oil that can cause major problems. 1 quart low isn't bad, but much more and you can had issues. Just cause one was knocking doesn't many any others aren't going to or are far behind. I'd be checking the whole bottom end over. Pulling the mains and rod caps and checking all bearings. You have the motor Out and Apart so why not? Bearings are "cheap" insurance. I'd also have the crank checked over, mainly that one journal where the bearing went south. You may have to have over size bearings installed on that one. My 305 didn't have a knock but the bearings where worn down. So a standard set was fine, but slight damage needs to be ground out and may not be visible to the eye.

Re: Nocking at high RPMs
 

Looking at the pics again I noticed a groove in the bearing that runs straight along both bearings?

Re: Nocking at high RPMs
 

Great, thanks for the advice guys. I'll pull them all and take the crank in to a machine shop.

Now... how do I get the crank shaft out? Lol


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Re: Nocking at high RPMs
 

It's gonna be a pitb. But doable. I did this in August. haha Pull all the main caps off. The rear main is a large block and will take some tapping with a hammer to remove. Like wise the rest of the mains. You'll have to remove the water pump/timing cover housing off so you can remove the crank. Not as bad as it looks. Then remove all the caps. As stated, Mark EVERYTHING!!! All the main caps Must go back on as they came Off. And same with all the rod caps. I just number them and make a mark on the left side reminding me which side they way they go on.

Re: Nocking at high RPMs
 

While the crank is out you should check the connecting rod for out of round. While it was knocking it might have cause the rod to go egg shape. To check for it place the rod cap back on the rod and torque the nuts then mic the rod end, it should be round. If not corrected it can cause your rod to knock again and you will be back to square one again. If you're not able to check this the machine shop can do it for you. If it is out of round they can resize it.

Re: Nocking at high RPMs
 

I would never re-use a connecting rod that had spun bearings unless it's been resized:thumbsup:

Re: Nocking at high RPMs
 

Big Block V6 is right, I would cut the mains and rods to whatever size to make it right. Also, I would have the assembly balanced. In the long run you will end out on top and not doing the job twice and possibly ruining the rest of the motor. Most of the time a short cut leads to more expenses than what's it's worth. A good machine shop will tell you exactly what is needed and then you can hunt down the parts if he cannot.

Re: Nocking at high RPMs
 

Ok, got the crank out today. The #4 journal is darn rough. The others seem ok to my finger nail test but I'll be dropping it off at the machine shop next week.

Called Egge machine today and they have bearings in stock, sizes up to 30 thousandths. Forgot to ask about mains tho.

Thanks everyone for the input. I marked all the caps and such, pretty simple if you know to look, the caps are all stamped with a number that goes on the rod of the same stamp.

So my next source of anxiety: I tried to keep the timing chain sprockets in the same place but I ad to move the cam sprocket to get the chain off...
How the heck do I make sure I get the cam and the crank lined up again???

Re: Nocking at high RPMs
 

There are timing marks on both gears. They will be Dots. When you go to install, line them up so both marks are lined together at the closest spot.

So basically...if the motor is on the stand....TDC would be Dot on Top for the Crank and Dot on the Bottom for the cam. Lined up and closest together. Maybe someone has a picture.

Re: Nocking at high RPMs
 

TJ--- so the dots point toward each other? (I'm trying to imagine this while it's in the stand upside down when im working on the crank lol)


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Re: Nocking at high RPMs
 

Ok... since I have hijacked my own thread and it's now "help the new guy rebuild a 305"...

Rings??? I'm staring at the pistons and scratching my head if I should pull them out and re-ring them? The top of the cylinders have a slight ridge that I can feel with a fingernail. (Was not planning on having the block machined due to cost)
When running the motor used a little and leaked a little oil, only smoked for a second on start up. Had good power. The heads are already removed (cuz I'm an idiot) so I missed the opportunity for compression testing.

I kinda want to leave the rings alone.

What say the forum???


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Re: Nocking at high RPMs
 

Check out this link on Rufton;

http://67-72chevytrucks.com/vboard/s...d.php?t=575596

Re: Nocking at high RPMs
 

Yep, they don't actually Point to each other, but if you rotate the assembly you'll see they where they line up Closest together...Upside Down would be the dot on the Crank would be on the Bottom and the dot on the cam gear would be on Top.

Re: Nocking at high RPMs
 

That engine should be pulled completely down and cleaned at least. There is probably metal from the bearing failure that got pulled back into the oil pump and some usually finds it's way into the oil galleys.

Oil smoke on startup is usually valve guide seals.

Re: Nocking at high RPMs
 

OK TJ, I see the dot on the camshaft gear where the fuel pump pulley goes but I don't see another doctor, I see the groove for the spline on the shaft itself.

On the crankshaft year there's a spline and what looks to me to be 80 stamped on the gear. Is that the dot you're talking about there?

Re: Nocking at high RPMs
 

Pics

Re: Nocking at high RPMs
 

In reference to your picture of the cam sprocket the dot is opposite of the key way (in the casting area and not the machine area), look like a center punch mark.

In reference to your picture of the crank sprocket the mark is the "O" to the left of the key way.

This also match the layout shown in my service manual.

Re: Nocking at high RPMs
 

Ok..... that's what I get for posting from my phone... I'm gonna start a new thread with new pics.

Thanks to everyone