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View Full Version : Rod knock in #4 piston on fresh rebuild.



BARRON
06-28-2006, 10:41 PM
so I have a 2.5L commonblock I built for my van.


block bored .020" OS
.020" OS Mahle pistons
crank turned .010"
all new clevitte77 bearings
new OEM oil pump


So I leave out the balance shafts and install everything and torque to spec. I should have checked everything with plastiguage but the crank was turned .010 and I bought .010 oversize bearings.. so why bother right? whatever.

I brilliantly weight balance the connecting rods on a scale in GRAMS by grinding away at the pads on the rod caps. Some of us think this is why my engine vibrates and hums like mad. That or the absence of the balance shafts.

Anyways.. it has done this right from the start. Put the scope on all parts of the block here an there and I find that if I rev it slightly I get a VERY HEAVY knock noise in the area of the #4 piston. Its loudest right down where the oil pan bolts to the block. Its not loud at all... but its there.

Now another word about the rods. I never got the small end bushing replaced and resized. It was on the edge of spec.. I should have done em.. but I didnt.

I plan right now sending an extra set of connecting rods down to the machine shop and getting them done.. and replacing the ones in it right now.

ANYONE have any input on this? WHY ould there be a quiet,heavy knock on a freshly turned crank and new bearings?? I KNOW that the small ends of the rods are questionable.. can they KNOCK.. or do they "clack"?


NOTE: I need to install a manual oil pressure guage this weekend too.

Tony Fields
06-29-2006, 11:15 AM
Just a thought....did you drill and tap the oil passage for the balance shafts and put a pipe plug in it?

NeonShowCar
06-29-2006, 11:25 AM
I'm gonna go out on a limb here - do you have an automatic in your van?

If yes, have you checked your flex plate bolts? Loose flex plate bolts will sound exactly like rod knock. Make sure you use Loctite (blue) on those flex plate bolts.

Garry W. McKissick

BARRON
06-29-2006, 02:19 PM
Oil passage was tapped and plugged.

blue loctite was used on the flexplate bolts and torque converter bolts. All is tight.

BARRON
06-29-2006, 02:57 PM
Oh well. I guess I am sending another set of rods to the machine shop to be checked and redone.

My machine shop told me another little tidbit of information. The blocks they order in from Quebec,when they are behind on rebuilds, come with a tag saying, "BALANCE SHAFT ASSEMBLY ELIMINATED"

The major rebuild shops dont even reinstall them! lol! Tells you how usefull they are.

Lee'sdaytona
06-29-2006, 09:40 PM
just another thought. I don't know if this would cause a knock type sound, but when I dropped the oil pan on my 2.5 to start the rebuild, I bent that stupid cover plate that is on the tranny. Luckilly, while turning the crank by hand, I heard the flexplate rub against it. I now have to remember to bend it back out when re-installing the oil pan.
-Lee

BARRON
06-30-2006, 06:41 AM
Lee, that makes more of a tinny rattle noise. This is a really heavy TOCK TOCK TOCK noise that isnt really even heard till you put a scope on it.

Even after describing it to the guys at the machine shop,they are out of Ideas too. Its something going on somewhere with the #4 rod.

Well fixer! dont wory. That van hauls too good to park it! :)

deuce dodge
07-02-2006, 09:31 PM
just a thought ......pull rocker cover box and check lifters.......

deuce