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ARP rod bolts - interference issue
http://slantsix.org/forum/viewtopic.php?f=19&t=63301
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Author:  GregCon [ Wed Feb 13, 2019 3:11 pm ]
Post subject:  ARP rod bolts - interference issue

I've read in other threads (which I can't find now) about ARP rod bolts having an interference issue with stock rods. I ordered a set of the ARP 142-6001 rod bolts for the Slant Six and sure enough...they don't fit the rods properly.

The inner side of the bolt head needs to be ground away in order to allow the head to rest squarely on the rod's surface. Without the grinding, only a small portion of the rod bolt will contact the rod...could well lead to a failure over time and heavier loads. The grinding needs to be done so that there is no shoulder (or 'lip) on the inner side of the head.

Attachments:
ARP.JPG
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Author:  slantzilla [ Wed Feb 13, 2019 3:18 pm ]
Post subject:  Re: ARP rod bolts - interference issue

You do know ARP bolts need pressed in and the rods resized after, right?

Author:  GregCon [ Wed Feb 13, 2019 3:35 pm ]
Post subject:  Re: ARP rod bolts - interference issue

You know that has nothing to do with an interference issue, right?

Author:  Greg Ondayko [ Wed Feb 13, 2019 5:03 pm ]
Post subject:  Re: ARP rod bolts - interference issue

I think Dennis is saying that those ARP's are an interference Fit.

After the Press / Interference they need to be resized for proper roundness.


I never used them that I can remember in any of my builds Just stock Rods and bolts or aftermarket rods.
Greg

{Doc can Probably Chime in here as I believe he was one of the original collaborators with ARP in getting parts like that to market}

Author:  Charrlie_S [ Wed Feb 13, 2019 6:09 pm ]
Post subject:  Re: ARP rod bolts - interference issue

There are two different rod bolts for the slant six. They are different between the rods for the cast crank and the forged crank. Don't know if that is your problem or not.

Author:  Greg Ondayko [ Wed Feb 13, 2019 6:49 pm ]
Post subject:  Re: ARP rod bolts - interference issue

Good point charrlie.


Greg

Author:  GregCon [ Thu Feb 14, 2019 8:03 am ]
Post subject:  Re: ARP rod bolts - interference issue

The 6001's are the rod bolts ARP lists for the pre-cast crank engines so it's not a part number/application issue.

By 'interference' I don't mean the light press fit that occurs around the shank of the bolt. I mean the rod and bolt do not interface properly; the bolt has too much meat on the inner side and that prevents the bolt from seating fully. I'd take a photo but the rods are at the machine shop now. The original rod bolts have no shoulder on the inner side; this allows them to fit as intended. But the ARP's have some inner side shoulder and that is the problem.

It's good that ARP offers the bolts and not big deal to relieve them - but if this is overlooked (and I bet lots of people overlook it) then it can be a definite weak point.

As for the shank press fit, the stock bolts had very little - maybe 200 lbs. The ARP's are tighter with around 750-1000lbs. which I'd consider 'better'.

Author:  Dart270 [ Thu Feb 14, 2019 8:12 am ]
Post subject:  Re: ARP rod bolts - interference issue

I remember Doug Dutra mentioning this long ago. I just got cast crank short block parts back from the machine shop with the later rod ARP bolts. Need to check them for interference, but I didn't notice anything when I eyeballed them after pick up.

Lou

Author:  slantzilla [ Thu Feb 14, 2019 8:29 am ]
Post subject:  Re: ARP rod bolts - interference issue

There was someone on here who just ground them down and whacked them in. It did not end well as I recall.

Author:  and739 [ Thu Feb 14, 2019 8:43 am ]
Post subject:  Re: ARP rod bolts - interference issue

Doc mentions interference with new con rod bolts (not ARP specific) in the engine assembly thread:

"If you have new con rod bolts, now is the time to install them. Always check to be sure the new bolt heads clear the bolt head cut-out on the rod and sit flush on the surface. (some clearance grinding may-be needed to allow the bolt head to sit flush)"

Here's a link to that post:
http://slantsix.org/forum/viewtopic.php?t=27439#p174993

I hope this helps.

Author:  Rick Covalt [ Thu Feb 14, 2019 9:34 am ]
Post subject:  Re: ARP rod bolts - interference issue

I installed mine without resizing and had a rod failure about 8 races into the season. All the rod bearings looked bad "distorted" from not being resized. Lesson learned.

Author:  drgonzo [ Thu Feb 14, 2019 10:35 am ]
Post subject:  Re: ARP rod bolts - interference issue

I got away with reusing a set of the old SPS rod bolts in a SBC race engine without resizing one time, but I agree it's not good practice.

Author:  coconuteater64 [ Thu Feb 14, 2019 12:46 pm ]
Post subject:  Re: ARP rod bolts - interference issue

Now I'm worried because my ARP rod bolts fit perfectly. :shock:

Author:  and739 [ Thu Feb 14, 2019 12:58 pm ]
Post subject:  Re: ARP rod bolts - interference issue

coconuteater64 wrote:
Now I'm worried because my ARP rod bolts fit perfectly. :shock:


In that case, I recommend the break-in procedure described here:
viewtopic.php?f=19&t=63275#p475522
:P :lol: :lol:

Author:  DadTruck [ Thu Feb 14, 2019 2:02 pm ]
Post subject:  Re: ARP rod bolts - interference issue

I used ARP rod bolts in the stock rods that went into to 83 D150,
Probably 5 years and 30k miles ago, I don’t remember grinding the bolt heads to get them to fit.
Maybe the interference is a forged crank - rod issue.

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