Swapping in ARP rod bolts without splitting the case

[kamaro]

I'm in the middle of replacing my stock 3.2 pistons and cylinders with 3.3 p&c to lower the compression and achieve a bit more boost. I decided to put in ARP connecting rod bolts while am at it. I know that its possible to RR the rod bolts without splitting the case (I'd rather keep the stock rod bolts rather than splitting the case, as this engine was fully rebuilt by the previous owner less than 1000 miles ago), but I can't find any description/videos/photos of anyone who did that job. Looking at the partially disassembled engine I can see that I can unbolt the nut and pull out the connecting rod but then I have to very carefully rotate the cap on the crank journal so I can pull it out, then pressout the old and press in the new and install the same way, is that the correct way doing it? .. Also I'm planning on measuring the bolt stretch outside the engine and figure out the needed torque and applying this torque value on all nuts when installed, what do you think of that?

[ObrHaus]

I did it once, I believe I plastigauged all the journals as well, never had an issue.

[stownsen914]

Don't forget to check for ovality due to the increased torque of the ARP bolts. I think ARP recommends resizing.

[ObrHaus]

X2 - I had the rods resized with ARP bolts installed so the clamping force was the same.

Originally Posted by stownsen914

Don't forget to check for ovality due to the increased torque of the ARP bolts. I think ARP recommends resizing.

[PeteKz]

I'll be the naysayer. There's no good reason to replace with ARP bolts. The Porsche bolts don't fail unless the engine is really abused. You are just making extra work and expense and possible headaches for yourself.

If you were building a race engine that you would disassemble regularly, THEN ARP bolts make sense, because they are reusable, whereas the Porsche bolts are supposed to be used only once.

Frankly, I don't know why the Porsche rod bolts are one-time use. They are not TTY so what is Porsche's reason? If anyone knows, please share.

[kamaro]

Originally Posted by stownsen914

Don't forget to check for ovality due to the increased torque of the ARP bolts. I think ARP recommends resizing.

I just took off one rod and compared between a stock bolts vs ARP bolts and they were exactly the same diameter/ovality (stock ones torqued to 20nm + 90* and ARP torqued to .010 of stretch as per the instructions. So lets hope the remaining 5 are the same.

[kamaro]

Originally Posted by PeteKz

I'll be the naysayer. There's no good reason to replace with ARP bolts. The Porsche bolts don't fail unless the engine is really abused. You are just making extra work and expense and possible headaches for yourself.

If you were building a race engine that you would disassemble regularly, THEN ARP bolts make sense, because they are reusable, whereas the Porsche bolts are supposed to be used only once.

Frankly, I don't know why the Porsche rod bolts are one-time use. They are not TTY so what is Porsche's reason? If anyone knows, please share.

Already got the ARP bolts and already have the pistons removed, so I thought that's the correct time for the upgrade.

[mikedsilva]

Originally Posted by PeteKz

I'll be the naysayer. There's no good reason to replace with ARP bolts. The Porsche bolts don't fail unless the engine is really abused. You are just making extra work and expense and possible headaches for yourself.

If you were building a race engine that you would disassemble regularly, THEN ARP bolts make sense, because they are reusable, whereas the Porsche bolts are supposed to be used only once.

Frankly, I don't know why the Porsche rod bolts are one-time use. They are not TTY so what is Porsche's reason? If anyone knows, please share.

There's plenty of threads on here that back up the use of ARP and similar.
Especially the 9mm bolts on 3.2, 964, etc...

[Flat6pac]

The rod bolts are 12.9 and the last spec on the 12.9 Carrera and 3.6 bolts is 15ft# then 2 90,degree swings.
The earlier bolts, Carrera, were not 12.9 and required a single 90 degree swing.
The 12.9 rod bolts are marked
Bruce

[PeteKz]

So the 9mm bolts are TTY.

['78 SC]

I did this a few years ago after an overrev (money shift) in order to check the rod bearings without splitting the case. I already had ARP hardware installed and had a spreadsheet showing the torque and stretch data from the original installation. FYI, the required torques were quite consistent (+/- 2 ft-lbs). Steve Weiner (RIP) had described using a similar procedure to measure required torque in order to re-install rods without splitting the case.

When re-installing the rods, I re-measured at the bench the torque needed to reach correct stretch for each bolt. I repeated the procedure multiple times to burnish the threads and ensure a consistent torque/stretch. Lubricate the threads per ARP instructions.

Getting the rods reassembled around the crank is a little fiddly since the cap has to be inserted first and spun around to the far side before offering up the rod. The assembly lube will help hold the cap on the journal. Keep track of where each nut/bolt goes and reinstall the rods in original locations/orientations. Double check the match numbers on the rod and cap to make sure everything is aligned.

Bruce mentioned the 90* technique for torqueing rod bolts. My ARP instructions did not include that option, but it's worth noting that rotating a bolt with 1.0mm thread pitch by 90* corresponds to a distance of 0.250mm, which is the ARP stretch spec.

Good luck with the installation.
Steve

[PeteKz]

The ARP bolts are not TTY (torque to yield). They are intended to be reused.

Despite Mike's reply above, I'm still not sure whether the 9mm bolts are or are not TTY. They did not feel that way to me. Has anyone measured the free length, then torqued them, then untorqued them and measured the free length again? Sorry if that answer is buried in the threads somewhere--I didn't find it.

[Jeff Alton]

Originally Posted by '78 SC

I did this a few years ago after an overrev (money shift) in order to check the rod bearings without splitting the case. I already had ARP hardware installed and had a spreadsheet showing the torque and stretch data from the original installation. FYI, the required torques were quite consistent (+/- 2 ft-lbs). Steve Weiner (RIP) had described using a similar procedure to measure required torque in order to re-install rods without splitting the case.

When re-installing the rods, I re-measured at the bench the torque needed to reach correct stretch for each bolt. I repeated the procedure multiple times to burnish the threads and ensure a consistent torque/stretch. Lubricate the threads per ARP instructions.

Getting the rods reassembled around the crank is a little fiddly since the cap has to be inserted first and spun around to the far side before offering up the rod. The assembly lube will help hold the cap on the journal. Keep track of where each nut/bolt goes and reinstall the rods in original locations/orientations. Double check the match numbers on the rod and cap to make sure everything is aligned.

Bruce mentioned the 90* technique for torqueing rod bolts. My ARP instructions did not include that option, but it's worth noting that rotating a bolt with 1.0mm thread pitch by 90* corresponds to a distance of 0.250mm, which is the ARP stretch spec.

Good luck with the installation.
Steve

Bruce was referencing a change in PORSCHE bolts from 10.9 to 12.9. This required a different torque spec/procedure. It is detailed in a TSB and spec book from Porsche.

Cheers

[john walker's workshop]

Originally Posted by '78 SC

Getting the rods reassembled around the crank is a little fiddly since the cap has to be inserted first and spun around to the far side before offering up the rod. The assembly lube will help hold the cap on the journal.

Good luck with the installation.
Steve

When you do this, use a long thin screwdriver through the opposite side to hold the rod cap in place as you slide the rod over the bolts. Can't see it working any other way. Takes the "fiddly" out of it.