ARP bolt fitment, help!

[ajwans]

I bought these ARP conrod bolts for my 2.0S conrods and they just
don't quite fit. The shoulder of the cap won't push past the shoulder
of the conrod with hand pressure.

So, do I:

a. send them back
b. machine the conrod, it doesn't need much by the look of it
c. force them, it's pretty close and it looks like it might be possible to force it down


Arp, on Flickr

andy

[Flat6pac]

Regardless of type, they dont always seat. I always tap them with a hammer to seat them, resting the edge on the table to make the tap work to seat.
Bruce

[Henry Schmidt]

Massage the rods so the bolt goes in without any side loading.
There was a batch of improperly machined bolts sent out by ARP a few years ago and these look like one of those sets.
If you force it in the bolts actually point to the center and create a undesirable load at the cap end of the bolt.

[ajwans]

"massage"? with a file?

I am merely an amateur, hence the amateur question.

andy

[Henry Schmidt]

When we encountered that issue we used a mill but a file will work just fine.

[ajwans]

Thanks for the advice Henry. Another question if I may:

Why did you not modify the bolt cap rather than the rod?

andy

[tadd]

Rod bolts are far, far more stressed than the cap. Notches create stress points where failure can occur. It is usually not wise to modify a critical high strength fastener. The high strength, high yield point fasteners require extra care.

t

[ajwans]

Originally Posted by tadd

Rod bolts are far, far more stressed than the cap. Notches create stress points where failure can occur. It is usually not wise to modify a critical high strength fastener. The high strength, high yield point fasteners require extra care.

Agree in principle. But... the point of modification in this case is not a functional
surface once the clamping force is applied. It just stops the bolt from turning initially
until the clamping comes into effect.

I'm thinking ease of machining will be the critical decision point which will lead me
to modify the rod cap rather than the bolt cap.

andy

[tadd]

I have to disagree. A surface defect in a notch sensitive material will be a problem even if it's not in the direct load path. I've seen high strength fasteners fail just from shortening the threaded portion which is out of the load path given it's on the other side of the nut.

t

[ChrisBennet]

Why can't you send the bolts back and get new ones that fit?
It's times like this when you appreciate the value of dealing with good/great vendors.
-Chris

[Henry Schmidt]

Originally Posted by ChrisBennet

Why can't you send the bolts back and get new ones that fit?
It's times like this when you appreciate the value of dealing with good/great vendors.
-Chris

Of course ARP will replace the bolts but sometimes, convenience/ time is an issue and properly massaging the rods has absolutely no down side.

[ajwans]

ARP have offered to replace the bolts and pay shipping both ways which
is very professional of them.

I have declined the offer since I already modified the rods to accept the
larger end cap bolts.

andy