jkrum10238

hey everyone its been a while, im knee deep in a 306 build i had a little "miss-understanding" with the first machine shop and ended up with my rods coming back to me in a box. i can see the numbers on each rod but im unsure how to tell whats the front or the back. this is my first engine job im sure there someone who can explain it really easily. its a 86 block and rotating assembly if that helps thanks

jkrum10238

connecting rod question**** now i feel stupid haha

TrimDrip

It really shouldn't matter as long as you have the correct rod for the correct piston. If you have a gram scale, you can check them to see if they did it right.

Venomantidote95

If u are using stock rods the direction matters one side around the big end is angle cut for the rod to clear the crank correctly the other side is flat if u put them in wrong even just 1 and tq it down itll lock the engine where it wont turn over! Aftermarkets are reversable.

TrimDrip

if they are stock, do they not have to be pressed on???

take them back to the machine shop and tell them to finish the job

Venomantidote95

This is true! Make sure they do it right though!

NTGuru

usually they are referred to as Press fit or Floating. Press fit is usually done with heatint the piston end (small end) evenly and just sliding the pin in until it is centered. if you are inexperienced have your engine builder put the pistons on. also it is worth the approximately $200 to get the crank balanced to the rod/piston weight.this may seem like an un necessary expense but it will reduce vibration dramatically and increase the rpm's that you can turn safely (depending on your cam and valve train setup) also helps decreases the chance of breaking the crank from being out of dynamic balance.

Venomantidote95

Finally someone else who understands the importance of a balanced rotating assembly!

tinman

Nope...
Some of us have been balancing things for 40 years,LOL.........

NTGuru

I have seen (due to a young kid about 25 years ago going cheap), a SBF shatter the crank, he spent all his money on Manley pistons and Carrillo rods, put them on a stock crank which was ground .010 undersized and did not want to spend the $100 extra after spending about $900 at the time on the rods and pistons, bring it into my shop with the crank in pieces. And tried to blame us for the fragged motor. all we did was set the timing and idle mixture on his 84 GT. He gave me the name of the engine builder (Who was a friend of mine unknowingly to him) who told him to read the estimate and the disclaimer / waiver he signed when he did not want to balance the engine. Surprisingly enough I did put in another 5.0 that i had built with less expensive rods and pistons, Balanced properly and used hi heads (after replacing a few valves) and he was amazed. If i remember correctly it started as an 8.5:1 motor and i had bumped the one he got to 9.5:1 and used a basically stock roller cam (88 5.0L HO motor I believe) and port matched the heads, intake and exhaust to the factory parts.