Thread: Connecting rod help!

Tweet

Hey guys this weekend i was helping my friend put togather the low end of his engine, and when we torque the caps onto the connecting rods the engine isn't rotating smoothly. He is working on a budget, and sent out is rods and pistons to a machine shop to have them assemble, and he didn't stamp tham, and now we think the machine shop switch the caps with the different pistons. Is there any way we can figure out which cap goes with which piston? Any suggestions would really help.

Well, there's certainly a few things you can do:
Switched caps are a serious problem. Get it wrong and you might spin a bearing in the first thousand miles. Check out these things:
1) The caps and rods have camfers on the big end. These camfers have to go towards the thrust side of the crank. Check to see if the camfers on the rods AND caps show this way:
Cylinder # 1,3,5,7: camfer to the front of the engine
Cylinder # 2,4,6,8: camfer to the back of the engine
Where two rods meet (i.e. 1 and 2, 3 and 4, ...) there is never a camfer.
Switch this and the uncamfered side of the rod will drag on the radius ground onto the crank where the journal meets the thrust face.
2) Does the crank spin freely without the rods installed?
If not, then of course you'll have to check your main bearings
3) Take the pistons out again and check if the caps match the rods visibly or not. You can probably see hone-marks on the journal bore. If these line up, you've got the caps and rods correct.

Check in this order and you should be OK. If you're in doubt anywhere along this line and you're not 100% sure that everything is correct, take the rods back to the machine shop and tell them to reface and hone them.

That's what I would do, but let's see whether someone else has any ideas...

Hope I could help you a bit,
Max

Hey max thanks for all the suggestions, and yes the crank spins freely without the rods installed.

tangs to the out side of the oil pan rails this is were the bearing sets in the rod will have a machine low spot to holde the bearing half called a tang .there may be a small mark on the pistons dent or dimple this is by one side of the piston this will go to the front of the engine if the cap were move a round then sometimes you can match me up by the finsh in the rods or a bore indicator

Hey pat i was just wondering what to you mean by tangs to the outside of the oilpan rails?

looking at the rod the tang go to the out side of the pan rails the out side of the block