Ok, so i spun a bearing. Man did the thing knock loud as hell. Anyways, me and my buddy pulled the engine out, 7mge bone stock, and tore it down to the block. Ths is when i realized the headgasket was blown along with a spun crankshaft bearing. i figured why not go ahead and replace the crankshaft so i bought a 6mge crankshaft. i ordered the bearings for a 7mge crankshaft before i researched and found out i would gain 500 rpm before redline with a 6mge crankshaft. question now are there any differences between the bearings for a 6m crankshaft and a 7m crankshaft. I used them and they seem to fit. i figured if the crankshafts are interchangable then the bearings should be the same. if i am wrong someone correct me. i also replaced one piston and the rod considering it was the one where the bearing spun and also because the rod was dark black and the oil hole in the rod for the bearing was melted shut. after all new bearings, gaskets, crankshaft, piston and rod, fluids my next question is - why would i still have a knock? another piece of info is that the knock is half a quiet as before and after the car been running at idle, up to temp, the knock seems to get quieter. Does this make any sense to anyone? can someone shed some knowledge. thanks to everyone in advance
Rod Knock?
- Thread starter heister00
- Start date
did you check the bearing tolerances? did you check piston to cyl. wall gap? its kinda sounding like piston slap to me... but it could be several other things also...
-AcId-
-AcId-
I did not check piston to wall gap considering the piston, rod and crankshaft all came from the same engine. opps forgot to mention that before. sorry. anyways all 3 components came from the same engine which was in perfect running order before being torn apart to be parted out. i figured the piston would be the same as my original. Am i worng? Are 6m pistons different than 7m? I was told the crankshaft and pistons are interchangeable.
As for the bearing tolerances, I dont understand what you mean.
As for the bearing tolerances, I dont understand what you mean.
by tolerances... i mean the oil clearence between the bearing surfaces and the crankshaft.... if the clearence is too loose... it will knock
and the problem with piston to wall clearance isnt in the pistons.... its the block itself that wears... with 100k+ miles on a block (not sure how many yours has on it...) the bore size will increase a few thousandths of an inch... more so if it has more miles on it and has been driven hard... which is enough to give the piston room to rock back and forth giving you "piston slap"
-AcId-
and the problem with piston to wall clearance isnt in the pistons.... its the block itself that wears... with 100k+ miles on a block (not sure how many yours has on it...) the bore size will increase a few thousandths of an inch... more so if it has more miles on it and has been driven hard... which is enough to give the piston room to rock back and forth giving you "piston slap"
-AcId-
Sounds like either piston slap or bad clearances somewhere.. If you didn't check the other rods it's possible some of them are a little banged up as well 
Yeah, you should have at least checked the clearances with plastigauge, not the most accurate but will do. The TSRM shows you the way and clearances. Even if you were using the same crank, block, etc., clearances need to be checked. Did you change out the mains and thrust washers?
for all those saying piston slap, please stfu!
its obvious this is a stock motor with stock pistons and if it didnt have piston slap from new then it wont have it now no matter how many miles are on it!
too the op:
whos to say your crank needs replaced?? how bad is it scored? if the car is pre 89 then it forsure already has a 6m crank and you wont "gain" more rpms with a 6m as its controlled by the ecu....the 7m crank has more potential for high rpms as its fully counter balanced but its heavier. before you go and start playing motorbuild...take the block to a good machine shop and have them get whatever it needs as we can tell you really dont have much clue as to whats involved with this.
its obvious this is a stock motor with stock pistons and if it didnt have piston slap from new then it wont have it now no matter how many miles are on it!
too the op:
whos to say your crank needs replaced?? how bad is it scored? if the car is pre 89 then it forsure already has a 6m crank and you wont "gain" more rpms with a 6m as its controlled by the ecu....the 7m crank has more potential for high rpms as its fully counter balanced but its heavier. before you go and start playing motorbuild...take the block to a good machine shop and have them get whatever it needs as we can tell you really dont have much clue as to whats involved with this.
You are correct but not intetionally, I ordered the crank and piston the same day i ordered the 7mge main and crank bearings. little did i know the crank i was getting was a 6m as opposed to the actual 7m crank i pulled from my block. so if that made sense you will see it was not intentional.tbcmorris;1337412 said:
OK the clearance thing makes sense now. I will ask my buddy who basically did all the work. I mainly watched. I know he measured some stuff but not sure what. i will let you know.AcIdBuRn02ZTS;1337422 said:
I thought of that too and we are considering replacing the restnsngarage;1337483 said:Sounds like either piston slap or bad clearances somewhere.. If you didn't check the other rods it's possible some of them are a little banged up as well
As said i to Acid up above there were some measurements made. Not sure what kind though.AJ'S 88NA;1337655 said:
I decided to replace it because of the scratches put in it. The engine in it was from a 90 so NO it does not already have the 6m crank. As for gaining rpms, i read about that on supraforums. maybe they were wrong. as for me knowing whats involved with this your right i dont thats why my buddy did the work. Am i supposed to be right about everything? am i supposed to know what i am talking about? If that was the case and nobody should have questions like this why have forums? people come here for information and answers from sources that know more then them not for criticism. thanks anyways for your input.gaboonviper85;1337832 said:
Thanks to everyone for all the responses.
gaboonviper85;1337832 said:
Only takes a couple of thou wear for a motor to slap like a bitch, if he's swapped in a low size select fit piston to a high side hole there's your tolerence stackup and slap. (NOT saying this is the case just that's it's a possibility)
gaboon... he did mention that he replaced one of the rods/pistons with one from another motor.... bore size differences between the two blocks could EASILY cause piston slap if its out by a few thousandths.... and considering it quiets down as the engine heats up... it sounds like piston slap... considering piston expansion when heated closing the excess gap... a rod knock isnt going to quiet down as the engine heats up... but more likely get louder...
i would definately talk to the person who put the motor together because its obvious something isnt right whether it be an oil clearance issue or piston to wall clearence issue...
-AcId-
i would definately talk to the person who put the motor together because its obvious something isnt right whether it be an oil clearance issue or piston to wall clearence issue...
-AcId-
not always the case... ive had engines with a rod knock and oil pressure be within limits... if only one bearing is loose... and the others are in spec... oil pressure wouldnt be effected much....
really... its all up in the air untill its pulled apart again... the builder should have checked these things before hand
-AcId-
really... its all up in the air untill its pulled apart again... the builder should have checked these things before hand
-AcId-
i have a bit of piston slap with stock pistons when temps get near freezing. You can hear it slightly when its warmer out, but not for very long at all.
fully warmed up = just injectors and valve noise.
fully warmed up = just injectors and valve noise.
Thank you everyone for all the input. I love this forum. i never asked any questions or posted because i could always search and find answers. i learned quite a bit from searching. this was one question i had to ask instead of search considering the circumstances. i am taking all advice and tearin it apart again and have everything measured. thanks again, i will post new results when finished.
by the way, oil pressure is correct.
by the way, oil pressure is correct.