identifying the rod bolts in my 79 930 engine--ARP or OEM?

fredmeister · fredmeister's Garage

I am tearing down the 79 930 turbo 3.3 engine to rebuild and suspected to find normal hex head nuts on the rod bolts for my 930-64? 3.3 liter engine.

However I was surprised to see the aircraft style 12 point nuts on the ends of thr rod bolts when I removed the pistons and looked down in the case. did Porsche use these 12 point nuts on OEM turbo engines in the 78-79 cars or are these perhaps ARP bolts that were installed during a previous rebuild?

Is there any markings on the ARP rod bolts that I can see to identify them by looking at the end of the threaded bolt or perhaps at the head end?
Would like to save a few hundred $$ bucks and not order ARP rod bolts if I am lucky to have them already.

Fred

Flat6pac · 06:10 PM

There was a time when the 12 point were supplied by the jobbers. I just know they were there to be removed originally and then used to rebuild with because that was the new supply, 12 point.
Bruce

Steve@Rennsport · 02-07-2011, 11:39 AM

ARP bolts are usually marked as such "ARP 2000" right on the head.

mamut · 02-07-2011, 05:55 PM

12 point nut on ARP's, std. square nut on OEM.

Jon B · 02-07-2011, 08:06 PM

Original Turbo rod bolt nuts were hex; 10 x 1.25mm for 3.0 Turbo, 9 x 1.25mm for 3.3 Turbo.

mamut · 02-08-2011, 02:30 PM

Ups...that's what I ment by square.

ornas · ornas's Garage

hi, is this OEM or arp bolt?

930LDR · 06-03-2011, 10:16 AM

What are the concerns of re-using the ARPs? I'm in the same boat right now and trying to figure out if I need to replace the ARPs that are in mine.

CaptainCalf · 06-03-2011, 04:21 PM

Quote:

Originally Posted by 930LDR

What are the concerns of re-using the ARPs? I'm in the same boat right now and trying to figure out if I need to replace the ARPs that are in mine.

IMHO APR rod bolts can be reused, but before I'd reuse them I'd check them to make sure they haven't been over stretched.
RC

fredmeister · fredmeister's Garage

thats the beauty and one of the benefits of arp bolts is the fact they can be reused.
Besides the increase in strength with them. Like anything else you must makes sure they were not damaged or overstretched in the first place.
To answer my original question....ARP should be marked on the ends with ARP initials, I found this out after I ordered a new set.

930LDR · 06-04-2011, 07:22 AM

Quote:

Originally Posted by CaptainCalf

IMHO APR rod bolts can be reused, but before I'd reuse them I'd check them to make sure they haven't been over stretched.
RC

What's the best way to check this?

andrew15 · 06-04-2011, 07:36 AM

Well, the problem with checking to see if they are stretched or not is that you need the baseline figure from when they were installed. I'm pretty sure you measure the length of the bolt, record it, and then install the bolt to the proper stretch. At a later date when you dissassemble, you compare the current bolt length to the previous recorded length and if they are within a particular value, they are fine to reuse.

Basically, if you don't know what the base length was prior to install, get new bolts as they could have been over stretched during the initial install.

Regards,
Andrew M

930LDR · 06-04-2011, 10:28 PM

Sounds like good advice.

304065 · 06-05-2011, 04:07 AM

If you don't see a headmark, you don't know.

If you didn't install the fasteners yourself AND log the unstretched length it makes sense to replace them. Even ARP fasteners have a yield point and if stretched into the plastic deformation range will be permanently longer (and thinner). The trouble is, if you don't know the pre-installed length you don't have anything to compare to.

In the context of an engine rebuild budget of time and dollars a new set of rod bolts is a minor item. In the context of critical parts, it is a major item.

BURN-BROS · 06-05-2011, 11:39 AM

Raceware?

930LDR · 06-07-2011, 05:55 AM

New ARPs arrive today along with the stretch gauge. After everything I've read I think I would be foolish to try and cut corners on this one. Curious to see what the original ARP bolts measure out to once I get them in the stretch gauge.

CaptainCalf · 06-07-2011, 06:10 AM

Quote:

Originally Posted by 930LDR

New ARPs arrive today along with the stretch gauge. After everything I've read I think I would be foolish to try and cut corners on this one. Curious to see what the original ARP bolts measure out to once I get them in the stretch gauge.

Since you'll need to measure your rod brg clears anyways you can put the brgs in and do a little study. What I did was after measuring them unstretched and recording it I then torqued them all at 30 ft-lbs measured the stretch and recorded it. IIRC you're looking for 0.010- 0.0105" of stretch, so if more is needed you can go up to 35 ft-lbs then 40 ft-lbs for each of the 12 bolts till all are stretched correctly. Then once you measure your big holes with brgs in recheck the length after relaxed.

Then when you're ready to actually bolt them to the crank you'll know approx where to torque each bolt then measure stretch again to make sure they hit the mark and adjust accordingly...RC

Walt Fricke · 06-14-2011, 07:42 PM

Like Aaron, I wondered if these were Racewares. They use the 12 point nut. So I dug out some ones I used in the late '90s on a race motor which blew up (not due to bolt failures) I had been saving to reuse on a stock motor some day. They had RTE stamped on the head. End divots (needed for the stretch gauge) also look different, smaller on one end, larger on the other.

Maybe stock bolts with aftermarket nuts?

My experience in getting the needed stretch is that a lot more than 40 lbs/ft was needed to get the stretch. Even with well lubed threads. Well more than Pauter, for instance, suggests using the ARPs which come with their rods, when not using the stretch method.

ARPs (and Racewares) are made out of super strong steels. Though I recall that on another race motor after one use at least one of my Raceware bolts had stretched beyond what RW said was the max for reuse.

My take: factory stock stuff and procedures are fine for stock street motors. Special bolts and a stretch gauge are the ticket for a race motor.

j911brick · 06-14-2011, 07:53 PM

I have discovered that if you stretch APR bolts as recommended it ends up being about 65 ft. lbs. Far more than the alternative 40 ft lbs torque recommended. This has a major impact on bearing clearance. I have finally settled on 45 ft lbs and have the rods sized with that torque.

lucittm · lucittm's Garage

It is a shame that someone would produce such a well-finished bolt and then not mark it with their name.

I have heard that many factors can affect the torque reading: thread friction, material friction under the nut, temperature, bolt twist, phase of the moon, etc. But bolt stretch is the engineered way of determining how "tight" the fastener is. I would not have expected a 20 ft. lb. difference in the two methods. Maybe ARP is adding a safety factor for folks without a stretch gauge or the ability to use it properly by decreasing the torque value read from a torque wrench?

Mark