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Old 12-27-2011, 01:20 AM   #1
TexasTerp
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Re-use Connecting Rod Bolts?

I know this sounds stupid, but how risky is it to re-use connecting rod bolts on a complete rebuild?

I'm already rebuilding the rest of the engine with new everything, so it's kind of silly not to get new ones. I'm going to be boosting it eventually. I'm just curious about everyone's thoughts since I have about 40 used con rod bolts from my 3.5 donor engines.

I'm ordering new main & con rod bearings and pistons soon. If don't need to spend the extra $100 for bolts it'd be nice, but I dont mind the expense either for peace of mind.
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Old 12-27-2011, 02:38 AM   #2
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It's a must, period. Throw away all of those used bolts.

If I were you I would drop the extra money on ARP bolts, that's what I did.
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Old 12-27-2011, 04:31 AM   #3
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If you do replace them be careful to make sure the new ones are fully seated and properly torqued to spec. My machinist said that failures are more often caused by under torqued rod bolts than slightly over torqued.

There is talk about being able to re-use rod bolts one or two times depending on how much they may have stretched but for high RPM use I definitely wouldn't chance it to save a little money. For a basic cheap rebuild you could probably get away with it though.
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Old 12-27-2011, 06:21 AM   #4
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they should be replaced. it's so not worth trying to re-use them. they are designed to be used only once - people don't understand TTY bolts, but they're perfect in a rod bolt application IMO (no worries about torque wrench error, no worries about having to retorque after heat cycles, etc).

You also get a 10-20% margin of error once you've reached the yield point of the bolt, basically the clamping force flatlines after a certain point. you could almost eyeball the torque angle and it would be fine..
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Old 12-27-2011, 06:37 AM   #5
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you could almost eyeball the torque angle and it would be fine..

Ive never used anything but my eyes on the angle part of tty bolts... Never had an issue.

On another note, I re-used mine on 1 rod. I had to pull the cap to inspect the bearings, and just re-torqued them to 40ft lbs. No problems yet, but then if I do have a problem I have a entire spare engine to fix it with.

What I did isn't what I would recommend to others... Just sharing experience.
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Old 12-27-2011, 08:04 AM   #6
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Thanks y'all. I knew it wasn't a good idea but I'm glad I got confirmation. I'm trying to decide if I want to build the bottom end myself or have the machine shop do it for me. I need to send out the block when I get back to MD in two weeks.

I'll be buying a Brownline digital torque wrench when I get back too. the only tool I won't have is for the pistons rings, but I can get one. I've never built a complete engine before.

Edit: Just an FYI here is my build list:

Maxsil Seta Pistons (.48mm overbore)
Eta 130mm rods
Eta crank
Main Bearings (post 3/88 Production Seta)
Connecting Rod Bearings (Seta)
OEM Main Bolts (M10x75 #11111735525)
OEM Con Rod Bolts
O-ringed block
Stock seals and gaskets
ARP Headstuds
Rebuilt 885 Head (<5k miles from one of my donor engines. Still has all the Sharpie markings!)
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Last edited by TexasTerp; 12-27-2011 at 08:24 AM.
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Old 12-27-2011, 08:07 AM   #7
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the M20 isn't hard at all and is a good engine to learn on. I'd go ahead and give it a shot. just make sure your piston ring tools are good. I cheaped out and ended up breaking a ring putting the pistons into the block. instead of having a $50 tool and a completed bottom end, I had a $75 overnight charge for a single new ring and still needed to buy a good tool so I could finish..
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Old 12-27-2011, 12:36 PM   #8
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That's what I figured. I mean I've already disassembled 3 full engines and a 4th bottom end. I understand the ins and outs of these engines really well by now. There are a good number of e30 guys in VA that build their own engines and are full time mechanics. I'm sure one of them can come by to help me out with the pistons.

These really are fairly simple engines, Thanks for the encouragement! I'll let you know how everything goes!
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Old 12-27-2011, 05:57 PM   #9
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Engines are very very simple. Hell it only takes 4 things to run. Oxygen, Fuel, Compression, and Spark. Air in, inject fuel, compress, boom, exhaust. Repeat.

My brother is a computer programmer, I helped him do an engine and next thing you know he does all of his own work.

BTW, if you ever need help I work for beer.
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Old 06-06-2012, 12:48 AM   #10
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Resurrecting this thread to say that I'm replacing my rod and main bearings in a 250k mile 325is beater track car I'm building and I'm going to reuse the bolts.

Nowhere in the Bentley manual does it say they stretch and need to be replaced with each use so I'm not going to.


It's the same situation with watercooled VWs which I'm very familiar with. Everyone says you need to replace the head bolts _every time_ but the VW Bentley doesn't mention it and my father who is a metallurgist also says it's not necessary especially if the manual doesn't tell you to. So I've pulled the head on my turbo Scirocco at least 8 times and I only replace the head bolts after every 3rd or 4th use. Never had a single head bolt related issue even with the turbo.

If my e30 connecting rods fail after I reuse them I promise I will post here and eat my words.


I do have a question though: I'm replacing the rod and main bearings with the motor in the car, is that a difficult job after I drop the pan? Has anyone else done it? It's easy on VW's because there's no crossmember in the way, but on this car it may have space issues
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Old 06-06-2012, 01:00 AM   #11
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Connecting rod bolts are torqued far less than head bolts so its hard to compare the two. rod bolts have far less stress on them than head bolts do. ive re used connecting rod bolts before.

op, your not going to have any issues here. make sure the fasteners are clean and the threads are quality. Use some sort of graphite thread lubricant (arp) makes some good stuff and make sure you get your torque settings right. you probably already knew that tho.
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Old 06-06-2012, 01:25 AM   #12
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ive reused them on 3 (2 I's and 1 eta)different motors and and a close friend has reused his twice. we run our cars pretty hard, no issue so far. always locktite them and torque them just a hair on the hightside of spec.
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Old 06-06-2012, 02:46 AM   #13
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If don't need to spend the extra $100 for bolts it'd be nice,
If you hate your engine, don't buy rod bolts. The connecting rod is the most stressed part of the engine. Therefore the fasteners that hold them together are critically important. If you had ARP rod bolts, I would consider it a possibility for reuse if you had documented the pre stretch length of each fastener and it's time and cycles 97% of engine builders do not do this. But even doing so I would only keep as a scary spare. But factory rod bolts go in the trash as soon as they come off the rod cap. Example, if head bolts stretch you end up pushing coolant due to a lifted head. If a rod bolt stretches beyond it's tensile strength you throw a rod {see photos below}... Or best case spin a bearing. Either way it's much cheaper to buy new bolts and have the peace of mind.

This loctite and reuse idea is wrong, unless the guy your building the engine for did something bad to your little sister and you want some payback. Rod bolt failure happens due to plastic deformation once the bolt has exceeded it's stretch threshold. Unless your using a rod bolt stretch gauge you won't know which bolt is stretching to much at your torque value. And the idea of using loctite on a rod bolt is not addressing the root of the problem. It's not that the rod bolt loosens and causes a failure. It STRETCHES and causes a failure.

Also using improper lubricant can cause fasteners to sheer torsionally {ie using loctite}. This is due to the fastener being designed for axial loading (torquing the fastener and the bolt stretching to the proper preload, ie stretch) and not for torsional loading. Proper lube for rod bolts, head studs, main studs etc are either engine oil if moly based lubes such as ARP lube isn't available. Don't install fasteners dry, but at the same time don't use loctite for crap sakes. Loctite on other components like cam fasteners, crank, flywheel hardware etc are highly recommended, but NOT for rods, main cap hardware, and head studs/ bolts unless they are head/ main studs for permanent installs or they need sealing due to the hole intruding into water jackets etc.

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Old 06-06-2012, 05:31 AM   #14
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Connecting rod bolts are torqued far less than head bolts so its hard to compare the two. rod bolts have far less stress on them than head bolts do. ive re used connecting rod bolts before.
uh.... no.

also, there are lots of things that are flat out wrong in the Bentley manual for E30s that we've known about for years. it's a reference, not an absolute holy bible of E30s. E30 Rod bolts are TTY, they stretch by design, and must be replaced. End of story.
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Old 06-06-2012, 12:03 PM   #15
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Are these pictures from E30 rod bolt failure after reuse?
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