SICAMG

Looking for information on swapping out stock connecting rod bolts on the M113 engine to ARP bolt's. I am told that the connecting rod big end will distort and will have to be resized when changing out bolt's.
I am not seeing this possible with a bolt that will only see 30lb's of torque. Anyone do a rebuild and run into this? Trying to avoid any work on the rod's big end and just swap to stronger bolts.

Critter

Hi, questions
Inside the car ?? or complete bottom end rebuild ?
If using brand new bolts torque as required, then re-torque numerous times as the stud must be bottomed out in the big end
If this is a rebuild then the big ends must be checked for oblong hole and possibly resized to factory spec- machine shop required
The big end after HP usage, high rpms and just normal usage will stretch the hole and new bearings will not be perfectly in a circle, the engine will run perfect for a short time then bottom end knock will occur as the bearing retains the big end oblong shape.

30 lbs of torques is very small value for the rod bolts ?? Is this factory value??
Did a small block 340 ci Dodge engine years ago and found out i had to re-torque rod bolts many times and this was with the same values, did this over numerous days, BUT the engine has sustained high usage for going on 20 years so the bottom end is very good STILL
New bolts will stretch and need to be fully seated in the big end.

hachiroku

if you torque them to factory spec they should retain the same shape generally speaking...if the "stretch" the bolts as all high performance fasteners used for rods generally require then you'll need to resize your big ends.

best to use a bore gauge and measure shape with factory bolts versus ARP bolts to be 100% sure.

Critter

But the big end must be checked for roundness and they do go oblong with usage and will not be good for new bearing inserts.
If you are just changing out rods bolts then from my perspective you are wasting your time, rod size check from machinist and new bearings are a must, do it right the first time.

SICAMG

These bolts are not nut and bolt, just a cap screw so NO bottoming out with the bolt itself.
Just found out also that the big end is also a cracked cap setup so you can not resize it.
28lb's is the spec from ARP with a 6.5 to 7 stretch.
After calling around today to Weistec and a Winston Cup engine builder I know of they both said that since it is a 4340? forged rod with such a small, light torque bolt, "28 lb", that there should be no problem. I will buy a spare rod to test on and verify as well.

Critter: yes new bearings going in for the hell of it.

Critter

Thank you, I was not thinking of just bolt setup.
But for sure measure big end for roundness.
You sound like you know what you are doing.
Happy wrenching

blackbenzz

No need to buy a rod. PM me your address

SICAMG

Dang...I new I should have checked with you. Let me see if I can cancel the order I just made and I will let you know. I would need a piston ,pin,rod and rings to weigh them for future custom pistons as well.
Aside from that what are your thoughts on my original question on swapping bolts .

blackbenzz

I should have all that. I don't think swapping the bolts should be a big deal

SICAMG

Just picked up 8 piston and rod assembly's and will put the ARP bolts in and do some measuring.
I have to say that the piston is very well made with pretty good ring lands and top ring depth.

SICAMG

Just did some testing just to see where things will be at. Installed new bolts into 8 rods and found zero change on the big end of the rods so no resize needed. Most bolts where torqued to 30lb's...depending on stretch so looks good for the install in the engine.

KorsMichael

Hello ! I know its an old thread , but if anyone knows part number of arp rod bolts is much appreciated for m113k !


Thank you

Exotic-metal55

I had them make a few hundred for us and just sent in a factory bolt for them to measure.

rmaier

Blackbenzz are you still on this forum? If so your messaging is full and I need some help please.