Re-use Connecting Rod Bolts?

[aventari]

lol I'm building an M10 for my 2002 and ran across this thread again.. (going to reuse rod bolts in that too)

THREAD UPDATE #4 - 3 more years
7 years total since reusing M20 rod bolts.
==========================

3 more years, 6+ more track days including Laguna Seca and getting my NASA race license. Lots of redlining, not a lot of street miles though.

Motor is running great oil pressure is superb, but rings/pistons are going bad and it's burning a lot of oil. Gonna build a stroker M20 with S50 crank (and ARP rod bolts).

[digger]

The rod bolts are tty that's one reason why they have the necked down section. The sky won't immediately fall down if you reuse them but you probably don't get the same clamp that was intended. high tensile bolts dont have a huge amount of plasticity before they start to neck/fracture so reusing them they can snap or start to neck, you could test a bolt and see how many times you can do it before they break might be a decent margin built in. The consequences of failure are pretty severe so it's up to the individual what risks they are willing to take ...

[aventari]

THREAD UPDATE #3 - 2 more years
==========================

2 more years, 8 more track days, lots of redlining and hard street miles.

Motor holding up like a beast

[nando]

Crank bolts are not tty.

[efficient]

My motor has reused crank bolts, has a couple thousand on them already after rebuild. I beat on it and has been fine.

[aventari]

Thread Update Number 2
================================================

Two years, more hard street miles and 10+ track days later, motor is still running superbly and connecting rods are still safely inside the engine block.

aside: Whodwho's MSPNP is fucking *awesome*


edit: skifree: can you point me to those failed M20's with reused rodbolts? Genuinely interested.

[TobyB]

Huh. This thread has some value, it looks like, because I just dug through the BMW
PDFs, and it sure looks like the rod bolts are torque to yield on an M20.

Enough that I'd NEVER reuse them.

M10- sure, for a utility engine that won't go over 6k.

M20- only for something that I wanted to use to oil down the track spectacularly.

...and here I thought they weren't tty. Thanks, all.

t

[e21jps]

I've banged dirty chicks with no rubber before. Just because i've done that doesn't make it okay or safe.

haha... yea guilty on both accounts!

You have to weigh up the intended use and invested value of the engine, i wouldn't hesitate reusing them on a dayly driver or mild build for the odd track day

I have reused them on many occasions even engines that have seen a LOT of track use and never had a problem, but in an all out high rpm race engine i would only use ARP's and custom rods etc. I guess its just piece of mind but in my opinion its not an area of weakness, MOST bottom end failures in M20's come as a result of oil surge not rod bolts

i think it comes down to rpm if you want to go over 7000 then you need to start paying a lot more attention to the bottom end.

[LJ851]

I'd go buy a lottery ticket.

Indeed.

I have reused rod bolts in a pinch but always accompanied with a bolt stretch gauge. If the bolt stretches in spec at the required torque it can safely be reused.

However, i never do this if it can be avoided.The consequences are severe if it goes pear shaped.

[SkiFree]

Thread Update
================================================

One year, lots of street miles and 5 track days later, motor is still running superbly and connecting rods are still safely inside the engine block.

Over the same course of time I can point you to at least 5 M20's and more M10's who did not replace them and have had them fail. I'd go buy a lottery ticket.

[aventari]

Thread Update
================================================

One year, lots of street miles and 5 track days later, motor is still running superbly and connecting rods are still safely inside the engine block.

[ForcedFirebird]

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.

Says the guy that tells people to use an impact on the crank bolt. :p

lol. IT'S NOT A FACTORY MANUAL.

there are many errors in the Bentley. It's a nice resource but it's far from the "end all" source.

Bentley says to tighten the valve cover nuts to 11ft/lb and they will snap every time lol. BMW says 6ft/lb.

Take this with a grain of salt, but I have re-used TTY bolts in a pinch, second time only, never a third (except once on an iron head engine, re-used the head bolts a 3rd time) and never had any issues. Not doing it on customers' cars, but my Triton V10 in the haul truck has been 22k miles towing a race car and trailer all over the country after changing out the bearings and re-using the TTY rod bolts.

It's a gamble, if you don't mind tearing it apart again to save $100, go for it. For me it's different, I'll change a motor out fairly quickly with a shop at my disposal, but wouldn't even think about it working on a home garage floor, or for an engine I was going to run high RPM's on a track.

[CarsSuck]

^^ you guys got 'em good, but let's get to the real point. OP isnt building a motor for a cheap-skate, shit box, challenge race. From what I gather he wants a reliable street motor that will be driven strenuously. My rule of thumb is this: if the part is cheaper than the labor to access it, replace it when you're in there. Not that I pay for labor, but it's logical.

[Exodus_2pt0]

Oh yeah you are correct sir, I withdraw my previous comment. I wasn't thinking about the other pistons.

I'm also not terribly worried about a 250,000 mile engine in a $300 car blowing up. I'm just throwing in new bearings while I have the pan dropped to eek a little more life out of it because it's going to be hard miles on the track from now until it lets go. The car is getting built for 24 Hours of LeMons / Chumpcar.

If it blows I'll drop in an $80 junkyard motor over a weekend, no big deal.

See you guys on the track :)


edit:


Really? Following the instructions in a factory manual is the dumbest thing you've read on an message forum? I don't know which internet you're on, but I'd like access, please.

I guess you don't care then if the motor lets go in the middle of a race?

That being said, I reused rod bolts on one of my cylinders when I got my engine. Just wanted to inspect the bearings, I haven't had an issue. Then again, I rarely take my car past 4.5k

[nando]

Oh yeah you are correct sir, I withdraw my previous comment. I wasn't thinking about the other pistons.

I'm also not terribly worried about a 250,000 mile engine in a $300 car blowing up. I'm just throwing in new bearings while I have the pan dropped to eek a little more life out of it because it's going to be hard miles on the track from now until it lets go. The car is getting built for 24 Hours of LeMons / Chumpcar.

If it blows I'll drop in an $80 junkyard motor over a weekend, no big deal.

See you guys on the track :)


edit:


Really? Following the instructions in a factory manual is the dumbest thing you've read on an message forum? I don't know which internet you're on, but I'd like access, please.

lol. IT'S NOT A FACTORY MANUAL.

there are many errors in the Bentley. It's a nice resource but it's far from the "end all" source.