Re-use con rod bolts/nuts?

Simufly said:
No No definitely not. Unless you want to drop a rod at some time in the future!
Click to expand...


+1

humm con rods bolts ? i do not know what is that, are you referring to the nuts that fix the halves that support the piston rods ? never heard of those nuts not being reusable,

i recall the only bolts that you should not reuse are the head bolts

theoretically when you do those bolts (those that fix the head to the block) if you follow the specs about torque you enter the plastic area of the material, so these bolts can not be reusable
i assume that in other countries they reuse everything, think about cuba or india, well known for reusing and reciclying, sometimes those engines broke, and back to the start again, but in our case...
 
Yes that is the connecting rod Bolts.
Lots of speculation but no hard evidence that shows they cannot be re-used. Most people assume they are torque to yield bolts but the tightening sequence says otherwise.
 
Common sense says says change all bolts,but I am looking for a concrete answer.here in Norway they cost 16 dolllars per nut/bolt x12
If I was to replace every part that the book/people say,it would be 5,000 dollars for a refresh an engine.

Dave
 
16 euro's... are these bolts & nuts so exotic ?
Do you have the specs on hand: thread size, thread pitch, head type and size, strength class etc?
I can check if I can find them generic for less (Via local nuts & bolt factory, supplying for instance also the large vehicle manufacturers Belgium, France & Germany) .

Erik.
 
For M30 motors head bolts are fine to use again. Just be sure to clean the threads well and also clean the holes in the block. You could even use a thread chase.

Rod bolts are torque to yield bolts and should NOT be used again.
 
Here is a page that talks about torque to yield bolts. The key point is: "since torque-to-yield bolts become permanently deformed when installed, they should never be reused."
Below is a BMW torque spec pages showing that head bolts are TTY, at least since 1980.

I have only found this reference for rod bolts:

"My little blue book - Tightening Torque Values from model 1983 on (Ord. Nr. 01 67 9 099 587) has the same information in section 11 24.

The M10 & M30 connecting rod bolts are to be torqued to 52 - 57 Nm. or 38 - 41 ft. lbs. There is also a note at the bottom of the page which states:
Washed and lubricated with oil.
Always install new bolts.

The M20, M21, M70, S14 and S38 rod bolts do require angle torquing."

BMW torque values.jpg
 
Yes, I've heard that and everyone states the tightening procedure with the torque angle.
The reality is hardly anyone uses the torque angle procedure and just follows the sequence and stops there.
Even Paul Burke recommends this procedure with the original head bolts.
You can look at all the M30 builds on myE28.com and the consensus is replace rod bolts but use the head bolts again.
Most M30 head problems are from over heating or bad machine shop work.
I have an 88 M5 with an S38 which is the same block as an M30 and it uses the very same sequence and numbers for it's head.
I have 40K on that rebuild with 100hp more than stock.
Head bolts are $7 ea so if you're not comfortable with reusing them then it won't break the bank to buy new ones. Or is that brake the bank............lol
 
I've experimented with angle torques on big six engines at length.
Huge difference in torque required for final tightening sequence. I've seen 65 lbs and I've seen 90 lbs.
The numbers have been radically diverse.
Not interested in the least to continue with angle torques
 
Thanks for the replies, it makes for an interesting thread.
I have now ordered rod bolts,but what about main cap bolts? Grey area again.

Dave
 
m5bb said:
For M30 motors head bolts are fine to use again. Just be sure to clean the threads well and also clean the holes in the block. You could even use a thread chase.

Rod bolts are torque to yield bolts and should NOT be used again.
Click to expand...

it is the first time i read this
i have been thinking just the opposite
are you sure ? where do you find such instructions in the blue books ?
i must look again but i recall the blue books saying use new head bolts and saying nothing about rod bolts
please advise

edit, i have been reading carefully the engine chapter at the blue books, it says nothing about new bolts, neither ones nor the others,

and BTW, provided that the torque values of the rod bolts are lower than those of the head bolts how is possible that the rod bolts are TTY ? i recall they are the same diameter, and i guess the same quality probably 10.9 ?

in any case the common procedure here in the two workshops that i know is that they always change the head bolts and never change the rod bolts

on the other hand just as a comment to the different things that have been written in this thread, be careful with the torque as far as i know it is not the same to have lubricated threads or dry ones, usually the values are specified for dry conditions, if you lubricate the real torque will be higher, and there is a risk of cracking the cylinder crankcase
 
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m5bb said:
Yes, I've heard that and everyone states the tightening procedure with the torque angle.
The reality is hardly anyone uses the torque angle procedure and just follows the sequence and stops there.
Even Paul Burke recommends this procedure with the original head bolts.
You can look at all the M30 builds on myE28.com and the consensus is replace rod bolts but use the head bolts again.
Most M30 head problems are from over heating or bad machine shop work.
I have an 88 M5 with an S38 which is the same block as an M30 and it uses the very same sequence and numbers for it's head.
I have 40K on that rebuild with 100hp more than stock.
Head bolts are $7 ea so if you're not comfortable with reusing them then it won't break the bank to buy new ones. Or is that brake the bank............lol
Click to expand...

when i overhauled my engine i retorqued it according to the blue books in three stages, and after 1000 km i did retorque the bolts by losening them a quarter of a turn and giving the final torque as specified
20000 km later alles is still gut
 
Can't remember how many engines that I have done over the years and never replaced either head bolts, rod bolts or main cap bolts. Never had a failure. At least half of those engines were done at the dealerships I worked at. I remember the TB ( but not exactly when , this old age ) coming out about the the whole torque angle thing. I questioned our BMW tech rep at the time about it and his comment was it was done so the customers did not have to come back for a retorque after 500-1000 miles The torque angle was suppose to take care of that. BUT I agree with Don, don't like using it, I would rather do old shool way like deQuincey did. That way I could get the customer to come back within a reasonable time to do a quick check on my work. As far as the rod bolts being TTY, I don't think so, my understanding of TTY bolts is that they require a measurement of their length with a special gauge to see what the stretch is compared to the manufacture's specs

Race engines or high performance engines are a completely different ball game.
 
stphers said:
Can't remember how many engines that I have done over the years and never replaced either head bolts, rod bolts or main cap bolts. Never had a failure.
Click to expand...

Same with me. For street engines I always wire-brush the bolt threads, run a tap through the nut or block, clean and oil the threads, and torque to spec. Never had a failure on a hundred or so engine rebuilds. On racing engines we always replaced every fastener with new ones.
 
Sorry to ressurect an old thread, but just checking, the consensus is it's ok to re-use the connecting rod nuts and bolts or no? I get that the original head bolts are reusable.
 
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