new motor has gremlin knocking

[nvrsatisfied]

a buddy of mine put together an ht 383 crate motor. Started it up, gave it a break in time for the cam and so on. took it for a couple of short test drives with open headers. he then heard a slight knock, thinking because he had no exhaust this caused the problem. he then got the exhaust put on and the noise is still there. he can't really pinpoint the knock. It's not a lifter knock and all of the rod bearings felt good. I could turn the engine over a full revoulution and didn't feel or hear anything hit. It does not knock all of the time and it definitely sounds like it's internal. the oil pressure reads great. he has taken an engine stethascope to get a better idea of where the noise is coming from and it helps but he still can not pin point it. he has dropped the pan twice and everything feels and looks fine, thought it was the flex plate and it turns out to be ok.......he has a mud event coming up and is wanting to get it going....but now is hesistant because of the noise.....ANY IDEAS!!!!!!!!

[CUSTOM/10]

Does this motor have a mechanical fuel pump ? I had a fuel pump that the spring broke inside and it made the pump push rod knok and it sounded like a faint connecting rod knok.

Gary

[nvrsatisfied]

he is running an electric fuel pump....

[Stocker]

If it's an auto trans, check for loose flex plate bolts -- or the flex plate could be cracked. That can sound a lot like a rod knocking.

[nvrsatisfied]

we have already checked the flex plate........(last line of orignal post ).

[truckdude239]

Piston slap? Did he check all of the clearances in the cylinder bore rod and crank bearin clearances I had a motor with woreout bearings the felt good but had a knocking sound

[nvrsatisfied]

he was thinking that..he is hoping it is not but sometimes you gotta bite the bullet. he is running new bearings....he said he may look more into this option........

thanks for all the help guys.....if you can think of anything else keep them coming.

[Stocker]

Originally Posted by nvrsatisfied

we have already checked the flex plate........(last line of orignal post ).

Ah shoot, sorry, I thought I read the whole thing, but obviously I did not...





[hiding in corner now]

[nvrsatisfied]

Originally Posted by Stocker

Ah shoot, sorry, I thought I read the whole thing, but obviously I did not...





[hiding in corner now]

its all good no reason to hide in the corner


for anyone== is it possible to pull a piston out from the bottom with the crank still in???

[truckdude239]

nope you wouldn't be able to put itback in

[jerry moss]

wristpin maybe ?

[72blue]

I have a 383 that was hittin the oil pan (the counterweight) and had been clearanced properly, but when I removed the windage tray, the pan sat in a slightly different position and then made a sound like that. It just barely hit, and made a noise and my heart dropped. I thought about it all night and then dropped the pan once more and sure enough.....then used a bfh on the pan AGAIN and I do not hear it anymore.

[nvrsatisfied]

he did some more tinkering this weekend....

1. pulled spark plugs off/on one at a time and when he got to cylinder 8 the noise stopped.
2. dropped the pan and did a plastic guage on the #8 bearings (again) and all was fine.
3.CHECKED WRIST PIN IN ALL DIRECTIONS AND WAS GOOD.
4. for the hell of it switched bearings with cylinder #7
WE KNOW, WE KNOW NOT TO SWITCH UP BEARINGS BUT AT THIS POINT TRYING ANYTHING.
5. put everything back together (with bearings switched) and the noise once again appeared at cylinder 8....

now getting to the process of just pulling out hair and beating the wife

so anymore ideas........why would the noise stop when spark plug is removed....

72blue=
great catch BUT when first put together he had noticed that 5&6 hit the windage tray. he removed the try and looked for other signs of hitting and to avail.

so like said above, the cylinder would still mechanically work just no fire....so why would the noise appear when it only has fire???

don't you just love gremlins....

thanks for all the help guys, he is really impressed with the answers rather than the BS...and i told him "IT'S BECAUSE ITS THE BEST SITE ON THE NET"

[liftmeup]

ok now that your done that you can go back and reclearence that rod. it must be barly touching when the motor is running. crank it around by and you will see where that rod cap and nut are paper close to the block. just trim the cap/nut ever so slightly and your done. I have fixed 2 other 383's with the exact same problem

[LONGHAIR]

Originally Posted by liftmeup

ok now that your done that you can go back and reclearence that rod. it must be barly touching when the motor is running. crank it around by and you will see where that rod cap and nut are paper close to the block. just trim the cap/nut ever so slightly and your done. I have fixed 2 other 383's with the exact same problem

If that were the case, I doubt that disconnecting the spark plug would make a difference in the noise. I would vote for piston slap or wrist pin.
Unfortunately neither can be tested for or repaired w/o taking the whole thing apart.

3.CHECKED WRIST PIN IN ALL DIRECTIONS AND WAS GOOD.

With it in the block? I call "no way" ...but I am more inclined toward piston slap anyway. Forged pistons by chance? Fitted by your machinist?

[nvrsatisfied]

Originally Posted by LONGHAIR

If that were the case, I doubt that disconnecting the spark plug would make a difference in the noise. I would vote for piston slap or wrist pin.
Unfortunately neither can be tested for or repaired w/o taking the whole thing apart.



With it in the block? I call "no way" ...but I am more inclined toward piston slap anyway. Forged pistons by chance? Fitted by your machinist?

as far testing the wrist pin goes......he dropped the piston down as far as he could, the piston "slid" left to right fine. but if you went to "twist" or move the connecting rod in a "binding" motion it was solid, it moved the way it was suppose to, so there was no slack in those movements...is that o.k. to check like that?

everything needed to know about his motor:

http://www.sallee-chevrolet.com/Chev...V8s/HT_383.cfm

thanks guys.......

[liftmeup]

LONGHAIR I take it you have not been inside to many engines or your just unaware that metal flexes including cylinder liners,rods,crank,block. Thats why you cannot put infinate power to a crank or rod. My years of building sprint car engines trump your knowledge in this area by a long shot for sure. Again I delt with this same problem before. I read the post before I just tossed a anwser out. You should do the same.
If you would like to learn start with google "cylinder block deflection"

[LONGHAIR]

Well, liftmeup, I don't have even a small clue as to where that comment comes from....
We are all just trying to help a guy, w/o being able to see or test anything ourselves....and I am not even attempting to say that you are wrong, that may indeed be the problem. It's just that block clearncing is a "known issue" and I would hope that this was checked during assembly....or at least during one of the "pan-off" inspections.

My theory:
At an idle, which is were I am assuming the "removing the plug wires" to test for the noise was done, I doubt that there is that much deflection in anything. So if the rod didn't hit the block when turned by hand, I wouldn't think that there could be enough flex to make it hit at idle. Of course, there should be more clearance than "just not touching" for obvious reasons.
If it really was a rod touching the block, I would think that he would have been able to pin-point it with the stethoscope?

A piston slap or wrist pin knock however will usually respond to disconnecting the plug wire. Since there is no combustion, the piston may not move around as much, thus less noise.


nvrsatisfied, no that is not adequate for testing the wrist pin. Sliding back and for tells you nothing, it sould do that. Your "twisting" test just tells you that the rod bearing is keeping it from moving in that direction. You really need to have the piston/rod assembly out of the block to be able to tell. Same with piston slap. It really has to be apart to be measured and inspected. Piston slap will usually show on the skirt but doesn't have to.
That's why I asked about forged pistons and wheter they were fitted by a machinist. It is possible that one is simply too loose.

I sure hope I didn't offend anyone else with my ignorance.........

[nvrsatisfied]

sorry to keep poking a stick at the situation and this could be lack of info on my part, but i wanna make sure.....cause piston slap is the the most common word being used........

when we "tested for movement" on the wrist pin we did have the rod disconnected from the crank, the piston as far down the sleeve as you can get and then started to test for unproper movements. we know what movements should occur with a proper set wrist pin, rod, piston setup. so is still o.k. or does it honestly needed to be pulled all the way to look at movement, when i am still able to see/twist the same movement while it is in the bottom of the block?

piston cleareance is the same as the others...

******************update**************************
he took it out last night and after a good run time the "knock" became very faint.....so now what




as always thanks for the info from everyone both liftmeup and longhair. i know there is always a lack of who knows what between everyone. i just don't want this to lead to far off subject (battle of the internet brains)my buddy(s) and i greatly appreciate all that has been given......

[liftmeup]

That confirms my thinking, the rod has dimpled itself or the block. now you can just sit back and pray it did not smash the bearing at all. Time will tell.. If it spins a bearing this winter please post back It will be interesting to know.

[70rs/ss]

Well I am with Longhair, the disconnecting the plug wire and the knock going away is a sign of piston slap (or rock) or the wrist pin. It doesn't confirn a rod contact with block as it would do that reguardless of the plug wire. The run time quieting it down has really only done one thing in my mind which was to heat everything up and expand the piston enough to do away with some of the piston rock/slap and or wrist pin.


BTW NO what you did isn't adequate to check for piston slap/rock or a wrist pin, nor is "looking" at a bearing, unless of course your eyes are trained to see thousands of an inch difference? You need to disassemble at least that one piston out of the motor and Mic it, don't eyeball it or move it etc none of that will tell you anything, UNLESS a part is so far out of tolerance it would be plain as day, but then it wouldn't be a light knock it would sound like a diesel!!!

I had a rod knock in an original 327 motor I had, disassembled the motor, all of the bearings looked fine, so did the crank (ie not a spun bearing) but with a Mic I found the oe GM bearings from 68 were worn pretty bad. I had the rods resized (as they egg shape over time) and polished the crank! Yeah ya gotta love forged cranks, since 68 it hadn't worn at all!

[liftmeup]

OK I will explain one more or make a comparison for you all. When you get a engine bored you use torque plates... why .. because they flex. taking the power off a cylinder does not / is not the definitive answer to the problem. If this was a 327 your theory works better than with a 383. This is a hybrid. IE NOT PRODUCED BY GM but by meir mortals who sometimes forget to clearance or double check clearance values. This topic would not even be on the table if it was. When you change rod length or crank throw you need to be triple careful on clearances.
engine parts expand when hot. water is wet. the sky is blue and so on.

just going by the two I already fixed with what seems like the same problem reading the post.

[70rs/ss]

OK but how many times did you have the pan off before you saw the tell tall mark? I'd guess once, since a rod hitting the block or the pan would be pretty obvious, right? This guy says the dude had the pan off a few times as well as the windage try, I think he even mentions looking specifically for a witness marl and not seeoing any cooled off or not a rod hits something it's going to leave a mark, right? I believe he also says it was a GMPP HT 383 so I'd guess maybe GM would do the clearancing??

[liftmeup]

Right I understand both of the ones I had problems were GMPP motors from scoggin dickey. you just can't look and see huge dent or something like that you need to take grease (red or blue ) easy to see and coat the rod cap and bolts with about 1/16th- 1/8th along with the crank counters and spin it over anywhere the grease "sticks" you need to examine further. you also need to check that its not touching the cam. they make small base circle cams for a reason. but again you can just clearance the rod cap/bolt.


oh and if I'm wrong I will buy everyone who disagrees with me in this thread a beer. Now when I'm right you can send me one.

[70rs/ss]

Not tryin to say you're wrong, but the more logical is the piston or wrist pin, but heck I may be wrong, doesn't matter to me, I just hope this guys bud can get it figured out. BTW if I had a GMPP motor new making a knocking sound, I'd send it back and get another, they warranteed, right?