Rod Bolt Question

[2590402]

Do the rod bolts stretch? If they dont should the be replaced when replacing the bearings?

Thanks,

Andrew

[c.d.iesel]

Do the rod bolts stretch?= they will if over rev'd - do know if they ever were in 30 years?

If they dont should the be replaced when replacing the bearings? = the BMW Repair Manual does not say to replace them - and there is no check or spec for 'stretch'.

if your not going to rev the motor above 5,700 rpm - and the bolts and nuts 'look' unmolested - re-use them

tightening torque is 38 ...41 ft. lbs.

if yer going to zinkher above 5,900 rpm all the time - replace the bolts

and nut - they have to be the most stressed bit in the car -....next to the rocker arms. "do you feel lucky?"

........BUT then again - in the E30 S14 BMW Repair Manual - it states

when removing and installing pistons to "replace the connecting rod bolts and nuts"

[TobyB]

I'm with CD on this one-

but since they're not very expensive, I'd just replace 'em.

I've built 'quickie' motors and not, (and never broken a rod bolt)

but if I spent real money on machining and parts, I'd spend the

few extra for new rod bolts. And nuts. And I'd reuse the head bolts.

Toby

[john_a]

BMW sure does tell you to replace the M10 engine's rod bolts.

Check the attached screen print from the BMW TIS. New bolts, washed & oiled. (Need to click on the image to have it appear legible in a new window.)

In the old blue service manuals, the E21 M10 section warned never to machine connecting rods, but that was when BMW was selling reconditioned rods themselves!

Changing out the rod bolts should happen before the rod's big end is checked & machined.

FYI, while the M10 rod was considered strong enough to be used in the big six (M30) engine, they do distort the big end with higher HP & RPM.

Using a CMM machine, I've checked stock M10 rods for roundness, cylindricity, position (length), and parallelism.

After seeing the changes after one season of hard use, I'd never assume an M10 rod is in good shape without a real inspection with the right tools.

These rods tend to stretch the big end bore along the thrust axis, which results in a pinch condition across the parting line (where you would never see it with plastigauge.) When the big end is pinched across the parting line, and the rebuilder installs a new bearing shell, it can wipe out the oil film even though the clearance looked OK in the thrust axis. This is likely the reason you sometimes hear about early rod bearing failure on a "rebuilt" engines.

The shape of the rod big end is something to be concerned about, and it just makes sense to replace the bolts at the time they are reconditioned.

It's gotta be worth the $100 you'll spend to be able to rev it up.

[TobyB]

Changing out the rod bolts should happen before the rod's big end is checked & machined.

But then again after, too-

the last set I sent out to be reconditioned came back torqued to about 100 ft-lbs.

I bought another set of bolts, torqued 'em, and rechecked them myself.

t

[jgerock]

Did a few different searches but did not really find my answer.

 

When installing the crankshaft should you use Loctite on the main bearing saddle bolts?  I did not but made sure everything was clean and torqued to 44 ft-lbs. Penskeparts website shows the main bearing bolts and washers are still available. 

 

I see that new connecting rod bolts and nuts are still available. I may order some before installing the pistons.  Should I add some Loctite to the rod nuts?

 

BMW Blue Book and other publications don't mention using a thread locking fluid.

 

Jim

 

 

['76mintgrün'02]

Not sure what happens, but I just had my finger twitch over the Troll/Spam button... and clicked on it.  

Sorry.

[jgerock]

Not sure what happens, but I just had my finger twitch over the Troll/Spam button... and clicked on it.  

Sorry.

Tom   - not sure I understand why you clicked on that.  I unearthed an old thread asking a question.

['76mintgrün'02]

Total accident Jim.

Twitchy mouse finger had bad timing.

I didn't even see the Troll/Spam thinger 'til I had accidentally clicked it.

Does that click show up on your end?

 

You are not a Troll.

Old threads are great.

 

Just a slip of the mouse...

Sorry.

[Tommy]

No loctite. Just good and clean hardware. Bottom end bolts and nuts can be reused if there's no damage...but if you want to be sure, then new.

 

  Tommy

[TobyB]

Nope, no loctite- it'll mess with torque settings.  Engine oil.

 

t

[AustrianVespaGuy]

Double check your main bearing bolt length!  The factory ones are 75mm and the 'modern' ARP replacements only come in an 80mm length.  Fine on many cars but wasn't on mine; tightened down with good torque and a good cold gap, but they were all the way bottomed out and as soon as things started warming up, clearance got bigger and oil pressure started tanking! Managed to catch it and fix it on my rebuild, but now I want to spread the word: beware of main bearing bolt lengths!

[jgerock]

Thanks for the responses.  Not sure why these did NOT show up during my last two days of "show me all updates". 

 

I'll see how many livers it takes to buy new rod bolts/nuts.  

 

ps: Tom - no hard feelings about the "troll/spam" button.  

 

Jim