THE KNOCK !! shes out now what?

-
wyoduster

wyoduster

live free or die
Joined
Nov 2, 2007
Messages
708
Reaction score
1
Location
Weare,New Hampshire
OK I just pulled her and tore the pan off ...Wasn't the windage tray ...I don't know what else I should be looking for????? I took off the intake and there is one pushrod with a scar on it (picture below) But can't see anywhere it would be hitting.But it was a loud knock!!! we talked about it in another thread of mine.

DSCN2324.jpg
 
Wyoduster, I would start by looking at the rods, both ends, to see if there is any play whatsoever. Even a little play in anything bolted down would indicate to me where the problem lies. I would suspect a rod journal bearing, either spun, worn gone or scored and burned up. I'm sure others will also have some suggestions, but I would start with the most common cause of a "knock". Hope you find it and it did no other damage, I would like to see the 340 go back in. Too bad you're not closer to Michigan, I know of a nice running 360 here that a buddy just bought for $300.00. Hope you find the source of the knock and get it all sorted out. Geof
 
I have a 360 shortblock, new never fired. It has KB190 pistons .040. Has a hughes cam and an sfi balance , a moroso 7 qt pan. Have reciepts for 2400.00. Have all the machine shop paperwork and reciepts on every part. I'll take 1200.00 for it may take less if u want to get rid of the 340. I'll also take less without the cam and lifters and without the oilpan and sfi balancer. Thanks Rick
 
I'll also sell the motor that is in my car now complete. I keep all the bolt on stuff like the carb waterpump distributor pulleys. Here is a video of it running holds 60 lbs oil pressure cold and 50 when hot. Low mileage engine runs on pump gas. Thanks Rick

http://www.youtube.com/watch?v=9pPmmV93YJg
 
Hang in there you will find the problem, no sense buying other possible problems, look everything over carefully and as suggested above rods both ends, if it is a loud knock it should be easy to find, be patient and find the problem, you will feel much better when you whip this thing and she runs hard for many years.

Bruce
 
Dartfinity, is that where you sent that goat last night??? Serves him right, now maybe he'll learn some road manners, like MoPars first, then who cares who comes next!!! Geof
 
Did you do the one plug at the time while she was running?
 
i think if u shorted the cylinders one at a time and did not here a difference then it is not the rods, but the mains. just my .02 good luck dude!
:read2:
 
You havent found it yet... No way a mark like that would make a knock.
 
Loose torque converter bolts or broken flex plate could make some bad knocking noise, but you probably would of found this problem while removing engine.
 
Yes I do 4 speed...
I've got her tore down to just rotating assy. But how do I figure out whats loose/knocking? Trying to move rods and things nothing seems ..loose... But again what am I looking for and how???
 
Pull the rod and or main caps and see what the bearings show. Any gouges, scoring, bluing or unusual shiny areas? Any hammering evident between the halves of the rod cap? Or between the main caps and the block?
You can check side clearances with a common feeler guage...and bearing cleances with inexpensive Plastiguage from any auto parts store. Somebody here have a service manual handy with the acceptable cleances?
Other things to consider...excessive fore and aft play of the cam, thrust clearance on the crankshaft, vavle/piston interference.
Piston slap (usually worse when cold) can anybody think of anything else to check on? Clogged oil passages to a main bearing?
Hope this gives you some possibilities.
Alan627b
 
Thanks Alan! I quit for the day Just poured a whiskey and relaxing. But I'll get on it first thing in the morning.
QUESTION:If the crank has end to end/fore and aft play, or there's too much slop between pistons HOW is that remedied ???
 
Crank shaft end play should be between .002"-.007" and not exceed .010". But too much end play is not what is causing the knock.
 
wyoduster said:
QUESTION:If the crank has end to end/fore and aft play, or there's too much slop between pistons HOW is that remedied ???
Click to expand...

The end thrust play is caused by one of 2 things. Either a worn thrust bearing or worn thrust surface on the crank.

I assume when you say slop between pistons you mean between the rods. Again 2 possibilites. First is the sides of the rods are worn or second the crank is worn out.

First thing I'd check is the rod and main bearing clearances. You can get a strip of plasti-gauge at the local auto supply and pull each cap one at a time and clean all the oil off every part of the bearings and caps and rods where the bearing rides and cap goes on then lay a 1/2" long piece of plasti-gauge on the crank surface and torque the cap back down to factory specs. Then remove the cap and use the guide on the plasti-gauge package to determine your clearances. For the mains use a 3.4" long piece of the plasti-gauge. Normally rods should be between .0015" and .002" and mains between .0015" and .0025". More than that and your getting pretty loose but I've seen racers run up to .0025" on the rods and .003" on the mains without any knocking but those engines get tore down every year to rebuild them. You don't want that much clearance on a sb street engine. If all the bearings check out ok you need to inspect the pistons. Maybe a cracked piston. Sometimes if it's a cracked piston it'll leave scratches on the cyl wall you can see without taking the piston out.
 
OK MYSTERY SOLVED!!!! I think.... Just plastigaged the bearings.. (lesson learned Don't trust machinist!!!!! ) The crank bearings even with the thickest blue pack pastigage .102 to .229 mill/.004-.009 in. they never even touched it theres that much play ... and the rods have .002 clearance. So I'll be making a phone call to the machine shop in the morning....
 
Maybe they turned the crank but didn't put the under sized bearings in to take up the slack.
 
Measure the diameter of the cranks rod bearing surface. Then figure out from the standard size how far the crank has been ground. If you have a .030 under bearing with that much clearance a .040 bearing may be needed.
 
I would think if the crank bearings were that loose the rod bearings would not get sufficient supply of oil. Any metal shavings in the oil?
 
Could a rod pin be doing this, I know a chebby will, they had to replace the block because the pin wore a deep ditch in the cylinder wall on one piston.
 
You must log in or register to reply here.
-

Back
Top