Connecting Rod Bolts

[Thoglan]

Yeah I’m tackling this decision now - I have an early car with the m11 bolts.

BMW says to reuse them.

Lang says they have never seen a stock bolt failure.

It’s kind of hard to move to an ARP bolt with slightly unknown results when doing it in-car and not being able to measure the bore distortion.

My OE non torque to yield bolts have held up great for the life of the motor and in a way are known quantities. Makes me want to reuse them. It seems to me that introducing ARP bolts introduces more variables, not less.

2 options:

1 - stay with stock ‘good’ bolts
2 - move to ARP bolts and have an unknown bore distortion

I kind of like my odds on number 1. That’s what BMW would do. This is what they did with all the recall cars and they have been proven to be very reliable.

actually, how can I find out if my rod bearings have been done once already? I don’t have documentation.

I went with option one, I know of a few racecars that have been running around for years after several rod bearing changes on the original bolts. They aren't TTYL bolts, they don't stretch an appreciable amount at the stock spec. The reason BMW didn't sell replacements of the old bolt is because they were specific to the rod (they even have to go in on the same side of the rod cap that you took them out of) and BMW wanted you to reuse them. In the same vain it just doesn't make sense to replace them with ARPs when they're so specific. I think unless you're on your 3rd or 4th rod bearing change and you are taking the rods out anyway, then reusing the OE bolts is a no brainer. Worst case if your rod bolts do fail, you might be the first ever with this chassis, which is cool I guess.

[eacmen]

Yeah I’m tackling this decision now - I have an early car with the m11 bolts.

BMW says to reuse them.

Lang says they have never seen a stock bolt failure.

It’s kind of hard to move to an ARP bolt with slightly unknown results when doing it in-car and not being able to measure the bore distortion.

My OE non torque to yield bolts have held up great for the life of the motor and in a way are known quantities. Makes me want to reuse them. It seems to me that introducing ARP bolts introduces more variables, not less.

2 options:

1 - stay with stock ‘good’ bolts
2 - move to ARP bolts and have an unknown bore distortion

I kind of like my odds on number 1. That’s what BMW would do. This is what they did with all the recall cars and they have been proven to be very reliable.

actually, how can I find out if my rod bearings have been done once already? I don’t have documentation.

I’ve used the stock reusable bolts twice with no issues. Really depends on the condition of the bolts. If they look perfect when you take em out then send it!

[tlow98]

Appreciate these responses all! Confirms what I suspected.

[tdott]

So I guess unless you are pulling the rods to have them resized ARP bolts should never be used in any engine....

There are 1000s of running S65/S85s and S5x that say otherwise, While arp recommmends rehoning/sizing, it is due to liabilty.

On s65, bore distortion was measured by auto talet (I believe) and it was cloest to OEM.

I think it's listed somewhere here, but it's been a while since I gone through it:

http://wiki.rcollins.org/core/index.php?title=Engine_Specs_-_S65_Rod_Bearings

[bimmerfan08]

My M3's S54 has 13k miles and ~52 hours of track time since my last rod bearing change. I reused the factory M11 bolts. No issues.