Ok, here's the story....... Aprox 20 years ago my father rebuilt this engine and it was bored .30 with new pistons, cam, lifters etc. he ran it for no more than 1 hour and parked it. When I got it the engine would not turn over. I removed the heads and found water had gotten into the engine and caused 2 valves to seize and corrosion in 3 cylinders. I replaced 2 valves and one guide. To make a long story short I replaced the pistons, rings and rod bearings, replace the all the top and bottom gaskets, and replaced the lifters and pushrods. I have it running again and it has 35 psi oil pressure at about 2000 rpm. The problem is that there is a substantial knock that sounds like it is in the middle/front of the engine (depending on where you are standing) and seems to get better when it warms up but is more pronounced under load. BTW... I have adapted a 700r4 to this engine but I know I have tightened all points to spec. My current thoughts are: -Aftermarket fuel pump -balancer not tightened to spec Does anyone have any thoughts?
Anytime I hear "substantial knock" I think rod bearing. Is it possible that the crank was ground undersize at some point and a standard size bearing was used buring assembly?
Especially if there was water involved somewhere. I'm thinking it has a spun bearing, the oil pressure and the knocking makes sense. If it's a double knock, then it could be a wrist-pin...
Thanks for the tips everyone. Here is some more info.... After I cleaned up the cylinders and repaired the heads I put it back together. It ran well and the blow by went away (stuck rings). i decided to pull the pan and found a lot of jello like substance in the bottom even though I had drained and filled it with fresh oil prior. I cleaned it all up and and made sure the pan was straight. I packed up the engine and set it aside till I was ready for it. When the frame was complete I installed the engine, 700r4 and got it running again (without the body). It ran well but had a lot of blow by and then developed a knock. I thought that maybe i spun a bearing with the Jello oil or that I broke a piston when I broke the engine loose. I ordered new pistons, bearings, gaskets, lifters and pushrods. When i tore it down the only thing I found wrong was the rings were stuck in the pistons. The rod bearings were impeccable and all looked good except rings. I replaced all the above parts and put it back together. no more blow by but I still have the same knock. It goes away when I pull #3 wire off (just like before). When it runs for quite a while and warms up real good the noise goes (almost) away. It "almost" sounds like it is pinging hard on one cylinder. The timing is set to 12 degrees. I "think" this is the cylinder that I had to do some grinding on the valve seat to clean it up..... If the valve is sitting higher, would it cause a lifter noise? BTW... the noise seems like it's coming from the top, not the bottom.
If the noise completely goes away when you pull #3 wire I'd be wiling to bet it has a bad wrist pin/piston.
If the engine was cranked with water in it, it could have bent something, like a rod. Maybe that caused a later problem with the possible wrist pin/piston noise Tom mentioned. 12 degrees of initial timing is too much if you have a standard 1x4 distributor. You'll have close to 40 degrees total mechanical advance! Exceptions would be the 2x4 or Dynaflow distributors which are setup with less mech advance and can run with a lot of initial timing. Is it more of a solid 'knock' sound, or more of a 'tink' sound?
I have a dual quad set up with an 111058 distributor so 12 degrees is correct. the Pistons and wrist pins are new a few weeks ago and mounted on the rods by a very reputable engine shop. The engine broke loose quite easily with a 1/2" ratchet on the crank pulley after the heads were removed. all good thoughts, thank you for your input
Dumb question: Did you replace the cam? if so, did you resize or replace the cam bearings? Sometimes those get missed, and I've seen a lot of guys actually leave the old ones in and then stuff in a new cam.
Good question, The cam bearings were replaced when the engine was rebuilt initially by my dad and a new 425 dual quad cam installed. BTW, oil pressure is good.
Then I'm leaning to a few little things; -1) lifters; - are they correct? One Nailhead kit I bought actually had one Chevy and one Cadillac lifter in it. If it isn't flat, it's going to knock. It'll also cause a lifter knock that's next to impossible to pin-point. 2) Cam snap ring; - was it reinstalled? I know I had to triple check on mine. Otherwise the cam could waddle. 3) did you put in aftermarket rockers? Are they possibly hitting on the valve cover? I had one that was hitting on the deflection tray for the PCV when I did mine. The joy of buying supposedly American made but in actuality sourced in China parts. 4) Timing chain and gears; - any slap? Double roller chain and gears in a stock cover? (possible rubbing or clicking issues) How about the fuel pump? Is it in good shape or is there a chance that it's hitting the eccentric wrong? Without actually hearing it, it's tough to diagnose. By the way, I've had "every one of the above" over the years on the numerous engines I've built. o No:
It would help to cut an oil filter. Instead of guess, tear into it measure everything correctly. Engines that get run near their limits get torn down periodically, by schedule or a "mystery problem".
If cancelling the #3 cylinder makes the noise go away and the noise goes away as the engine heats up you might have a collapsed piston skirt (unlikely if the pistons are new) or a piston which is fitted loose in the cylinder bore. The noise goes away because when the piston warms up it expands and stops slapping in the cylinder. My `96 Suburban developed such a noise at about 90K miles. The dealer told me there was a problem with collapsed piston skirts in the `96 Vortech engine. The engine now has 315K miles on it and is still running like a bear...no oil consumption, great oil pressure, but a slight knocking when cold which goes away within a few minutes. The knocking is much more pronounced when temps are at or below freezing but clears up when approaching operating temps. I`m tempted to stuff a piston into it because as a mechanic the noise really bothers me but I have left well enough alone for this long...if it aint broke dont fix it! I hesitate to violate the Old Bull! Tom Mooney
need a video to determine if it is top end noise or lower end noise. you can record it and post it on youtube and add a link on a post. Have you pulled all the plugs and compare to number 3. is their any damage to the plug? is it running clean or is it a dead cylinder. When you put new pistons in how did the rod bearings look. does it seem like it is half the rpm or the same as rpm? their is a lot of us here that have exsperiance with engine diag. Grab a video so we are not guessing and we can help you out. Best of Luck Paul turbo Nailhead
The weirdest thing is that before I tore i down and put in the new pistons, bearings, lifters, pushrods and gaskets it had the same knock on the same cylinder. THAT is the reason I tore it down. The old bearings (if you want to call them old because they had less than a couple hours run time on the them) were like new. I pulled the #3 plug a few days ago (haven't run it since) and it was decent. a slight toast color. Shining a light down the hole and the piston still looked new with a slight black tinge to it. because everything looked good except for stuck rings when I tore it down and the only things that haven't changed are the cam, rockers and valves, I am narrowing it down to those areas. I read in the shop manual that if you lap the valve in and the stem sticks up to high it can cause "valve train noise" so I am going to pull the valve covers and check that as well. I will get a video on Thursday (my first day off). Thanks for all the input guys, much appreciated.
