I'm in the process of re-assembly. Had the crank assembly balanced to within 1gm at 50%. Installed the Mains and wanted to torque to 100ft/lbs, but Shawn? at Weberracing said that was too much and 80-85ft/lbs should do with stock main bolts. Is this correct? For now they're torqued to 85ft/lbs. The crank was able to be turned by hand evenly, but with a little effort. All Mains had clearances between 0015-002" with mic before then plasigage during install. Once I began installing the Pistons and Rods, I double checked clearances which were .0015-.002. I finished the Odd side(1,3,5) then proceeded to the passenger side. When I got to piston #4, the plastigage looked tapered with a clearance of slightly over .002 on one end and slightly over .001 on the other. I decided to clean off the plastigage, lube up and install. Once installed I turned the crank 4-5 rotations (effort now 25ft/lbs...normal?). I removed the #4 rod cap, and it now looks like the attached picture....normal?
Odd Rod bearing question with pic
- Thread starter fast400
- Start date
Rods are new K1's...I'd be really surprised if they're out of round.
I think I'm going to put it together. It's a .001 difference from one side to the other side of the bearing.
ek02
Well-Known Member
- Joined
- Jan 31, 2008
I've had the same problem with aftermarket rods when using Plastigage. I have gone back and checked the crank with a micrometer for taper, and the rod bearing with a dial bore gauge, and could not see a problem. The only cause then would be the rod bore not being square to the rod. Your bearings do not look like they are contacting unevenly, but turning it over by hand will not show much of a wear pattern. You might try Plastigage on both bearing halves to see if the clearance is uneven on opposite ends. That would prove if the rod needs to be trued.
turbodave231
Moderator
- Joined
- May 24, 2001
X2 on checking that rod! A stock rolled fillet crank (with no taper) should not have that type of contact on the bearing. That type of contact is common on cheap cranks with wide fillets. Lots of the cheap offshore stuff has considerable taper in the journal and the bearing rides the fillet. Not the case here. Your rod big end may be barrel shaped causing the bearing to pinch in on the edges. Easy and cheap to check it now, difficult and expensive to check it later.
Here is a good video of the problem that many run into with offshore cranks:
Here is a good video of the problem that many run into with offshore cranks:
I've never seen that with a stock crank and rod that was known good. For the heck of it I'd throw a stock piston/rod in there and check it after verifying the rod is is round. Good catch and kudos for not slamming it together.
dr_frankenstein
Mad Scientist
- Joined
- Mar 17, 2008
Update: I removed the rod, installed an old rod...plastigage is perfect with the old rod, so it's not the crank. Re-checked the new rod with a micrometer, and I'm getting .06mm difference between twelve o'clock, one and two o'clock positions (rod upright). I'm having a hard time believing these two rods are bad...but that's what it is.
fast400 said:
This is why people just don't understand whats really involved in properly assembling an engine. They assume new equals good. They couldn't be more wrong. Everything needs to be checked. Good job in catching this and not running it.
I'm sure it would have ran great....for about 100-200 miles
It sounds like your connecting rod big end may have more than one problem. The measurement you described in the above quote indicates the big end is out of round. The plastigage on the crank indicates the big end is may not be concentric. Aside from the plastigage, the only other way I know to check concentricity is to measure the big end with a dial bore gauge at the left, center, and right. Then compare the measurements. Perhaps someone else knows another way? Perhaps I am not understanding?
I would think a good machine shop will take care of both problems. Every once in a while my assumptions get me in trouble though.
Many people would have missed this - good work on catching it.
Paul Lohr
turbodave231
Moderator
- Joined
- May 24, 2001
Paul,
The best way to check the rod big end is on a Sunnen AG-300 Rod Gage. It is basically a very fancy precision bore gauge that has a precision parallel face to keep the rod square to the measuring points.
The best way to check the rod big end is on a Sunnen AG-300 Rod Gage. It is basically a very fancy precision bore gauge that has a precision parallel face to keep the rod square to the measuring points.
