Connecting Rod Bolt removal and installation

[320iAman]

BMW Service Manual states to replace the connecting rod bolts when the connecting rods are removed from the crankshaft and so forth. They are compression fit in the upper big end of the connecting rod.
This is an an very easy job removing and installing them. To remove screw the nut on flush to the bolt threaded end or not and then with engineers hammers 1 lb-2 1/2 lbs strike the end with the nut on or off it - medium strong-- the bolt will start to move out, take the bottom end off and then strike the bolt with the nut on-flush or off it will go down and then fall out to reinstall new ones can do like picture 3, make sure the tab is in the right position and that it is seated flush when installed. It takes less than a minute to remove a connecting rod bolt,no heat or lube required, can do with a press yet this is overkill.
Easy does it.
Yes the threads are good on the connecting rod bolts and so are the nuts using the nuts when completely removing the connecting rod bolts.


DSCI0428.JPG DSCI0429.JPGInstalling New Connecting Rod BoltsDSCI0430.JPGDSCI0431.JPG

I have 12 new ones in bound by priority mail for $40 plus change , when looking at these use the older numbers at realoem, new numbers are from a different manufacturer and quite expensive per bolt like $12 each or so, I'm paid $3 plus change each, brand new. The nuts for these have changed in design, still M10 x 1 mm-tp , new manufacturer.

Update on the 2.0 Crankshaft 80 mm stroke 77-79 -realoem shows (01/25/1999 (ENDED)) ,, No BMW Group is selling them again ~ $1400 plus tax state side around $1050 delivered out of Germany... remember BMW crankshafts are better than these off the wall cast ones,, much much much better.

Randy

[320iAman]

NOS 12.9 Grade Connecting Rod Bolts came in 12 ,paid $3.61 each incl taxes & Priority Mail Shipping, 8 is required, 4 spares. BMW number 11240618111 , cross reference numbers 11240618110, 11241719991,05406009001.
s-l1600.jpgs-l1600a.jpgs-l1600b.jpg

I just measured the new connecting rod bolts versus the old Connecting Rod Bolts, its different than what I first thought, The new connecting rod bolts are all longer than the old connecting rod bolts, thus the connecting rod bolts become compressed rather than stretched. So BMW figures to change them out on rebuilds due to compression effects not stretching effects.


old connecting rod bolts---- 65.64,65.58,65.40,65.57,65.58,65.44,65.65 and 65.58 mm length

new connecting rod bolts--- 65.79,65.76,65.86,65.87,65.88,65.80,65.85,65.79,65 .78,65.88,65.81, and 65.84

Randy

[cgifool]

That seems odd to me, can you explain how the bolts become compressed after use, rather than stretched?

Thanks for the post!

[WantingAfunE21]

Randy,
you posts are always very detailed and informative, but I believe you are incorrect with regards to the bolts compressing. When tightening the nut you are putting tension on the bolt, this compresses the rod components together.
-Roy

[ross1]

NOS 12.9 Grade Connecting Rod Bolts came in 12 ,paid $3.61 each incl taxes & Priority Mail Shipping, 8 is required, 4 spares. BMW number 11240618111 , cross reference numbers 11240618110, 11241719991,05406009001.
s-l1600.jpgs-l1600a.jpgs-l1600b.jpg

I just measured the new connecting rod bolts versus the old Connecting Rod Bolts, its different than what I first thought, The new connecting rod bolts are all longer than the old connecting rod bolts, thus the connecting rod bolts become compressed rather than stretched. So BMW figures to change them out on rebuilds due to compression effects not stretching effects.


old connecting rod bolts---- 65.64,65.58,65.40,65.57,65.58,65.44,65.65 and 65.58 mm length

new connecting rod bolts--- 65.79,65.76,65.86,65.87,65.88,65.80,65.85,65.79,65 .78,65.88,65.81, and 65.84

Randy

All you are seeing is manufacturing tolerances, unless you bent them pounding them out. No way the bolts shrink.

[320iAman]

There is nothing wrong with the measurements, they compress a small amount due to the environment they are in and how they are attached in this environment, there role in the environment of internal combustion in other words with resistance to movement.

These bolts have been in the motor a long time. 65.79-65.64 = 0.25 mm = 0.0098 in--Ninety-Eight Ten Thousandths of inch difference in length , imperceptible by the naked eye yet measurable by tools.

If you have some proof of your statements bring it on.

Proof here would be connecting rods from an M10 motor with similar mileage than was on this one and measure when taken off the crank shaft and then measure when extracted from the connecting rod. This will find the same results, Leaving me and my colleague in NY in the first know of it.

These bolts are grade 12.9 the hardest steel of bolts used on these BMW Cars they go way over torque strength and overall strength of lesser grade bolts 10.9,8.8 and so forth. It would take more than an engineers hammer to compress them..

It would take internal combustion over a long period of time to do this as it did here.. lol

metric 10.9 bolts exhibit high tensile strength and good wear resistance. Tensile Strength 900MPa = 136,335 PSI

The 12.9 is the Class head marking under ASTM F568M standard for Bolts of a high grade (1220 MPa), being Alloy steel, quenched and tempered. ASTM F568M is an ASTM International standard for metric bolts, screws and studs that are used in general engineering applications. 1220MPa = 12200 Bar = 176,946 Pound -Force per Square Inch (PSI).

The minimum tensile strength of a 12.9 bolt is 1220 MPa. Therefore, the approximate shear strength of a 12.9 bolt is 732 MPa. The minimum yield strength of a bolt is the pressures needed to stretch the metal of the bolt. A 12.9 bolt has a minimum yield strength of 1100 MPa ~160,000 PSI.

Randy

Quoteable Quotes

And His eyes were opened and his sails were unfurled.

[WantingAfunE21]

Randy,
When you torque the bolt down you are stretching it some (modern bolts are actually tightened until a certain amount of stretch has been achieved IE "Torque to Yield"). There is no load between the crank journal and rod end that generates compressive force. To generate compressive force you would have to squeeze the ends of the BOLT with more force than is generated when torquing the bolt plus that of the crank journal pulling on the rod.
You can not compare new bolts and used ones unless they were manufactured at the same time, using the same equipment (same lot).

I linked below and article discussing the world rod bolts live in and what is done to prevent them from failure.

rod bolt article

[320iAman]

Wrong, Connecting Rod Bolts are not torque to yield bolts, the flywheel bolts are torque to yield.

12.9 is 12.9 ASTM specifications and the rest is called BMW Specifications, although even new bolts can vary in length by small margins and they do.

You have missed the point entirely , There is tremendous downward pressure on these bolts and its instantaneous and repetitive and is caused by the Combustion Cycle or Power Cycle. The steel faces on the big end of the connecting rods are not smooth as glass they look like microscopic mountains and valleys if pictures were available of new and used faces you'll see the faces on the used connecting rods are flatter than new due to the Power Cycle putting tremendous pressure on them, when they flatten no more, the compression starts on the connecting rod bolt its weakest part. The nut locks the upper and lower end of the big end of the connecting rod together. Its Like Intake cycle torque pressure , Compression cycle more psi on these bolts and faces, Combustion cycle- tremendous pressure on the bolts, faces , ect, -pressure going downward- exhaust cycle back to torque pressure and this is going on a lot over the long haul.

I initially thought here they would be stretched and then measured and recalled they are not stretched from earlier work in this area as well too many years before.

Do you see now ?

You doubters need to study internal combustion and its parts and where the pressure, heat and so forth is and what it does.....



Randy

[WantingAfunE21]

Randy,
Thanks for taking the time to write out an answer. I'm going to have to really think my way through this. I don't understand how these bolts can even see compressive loading, and as a structural design engineer I'm at least familiar with load transference in dynamic systems.

[320iAman]

The bolts are compression fit to the top part of the big end of connecting rod, when pressure is applied by gas expansion thru the piston top thru the piston pin the pressure goes downward from the small end thru the connecting top half or so for which the connecting rod bolt is compression fit so the bolts get the pressure that drives the crankshaft connecting rod journals as well. The connecting rod big end top half diameter or so gets slightly smaller , this is completely reasonable since it receives the tremendous pressure and transmits it to the crankshaft connecting rod journals with the bearing shells in place and a thin layer of oil between the two.

The clincher: the diameter of the big end gets smaller than the compression on the connecting rod bolts this explains it all, including AERA work when the nuts are secured by red compound or better and when dissolved and the nuts did not untwist-the torque is 1/4 to 1/3 or less then when initially put on very old rebuilds. The transportation industry is the largest private employer in these United States.



Randy

[jsquared1013]

He's wrong. There is no compression loading on a connecting rod bolt, it's all tensile. The heat and engine loads don't change that. There is absolutely no mechanism by which a compression force could be induced on the bolts without something externally clamping them. A quarter-mm difference in length is almost assuredly due to the manufacturing batch or a different supplier. They 1000% ARE torque-to-yield bolts, that's why BMW says to toss them when the rods are removed from the crank.

[WantingAfunE21]

He's wrong. There is no compression loading on a connecting rod bolt, it's all tensile. The heat and engine loads don't change that. There is absolutely no mechanism by which a compression force could be induced on the bolts without something externally clamping them. A quarter-mm difference in length is almost assuredly due to the manufacturing batch or a different supplier. They 1000% ARE torque-to-yield bolts, that's why BMW says to toss them when the rods are removed from the crank.

That Is what I'm not understanding a bolt and nut pre-tensioned can't be compressed unless they are squeezed on both ends. Nothing in normal operations does that, and if it did happen wouldn't that allow the rod end to oval (they are machined to be perfectly round when the bolts are tightened)? this should cause excessive bearing wear.

[320iAman]

They are not to torque to yield they have been reused with no problems in rebuilds forever, if they were torque to yield you could not check the oil clearances with plastigauge , you would check them and then have to remove them and reinstall new ones and have no idea if oil clearances have changed-that they seated-too little clearance oil starvation -too much clearance and the oil pump ect could not keep up with it---- lol.

Torque-to-yield fastener. A torque to yield fastener (TTY) or stretch bolt is a fastener which is torqued beyond the state of elasticity and therefore undergoes plastic deformation, causing it to become permanently elongated.

Can you reuse torque to yield bolts?

Torque-to-yield (TTY) head bolts are designed to stretch when used. Once stretched, they are not as strong as before. Consequently, they cannot provide the same amount of clamping force and may break or shear off if reused. Same is true of all torque to yield bolts !!!!!!!!!!

@ $9 to $12 each or $100 per throw, I dont see any price gouging and making a fast buck here, Do you ?

Why do you two think center to center specification is adjusted by honing the big end diameter ? Obviously the big end diameter has changed inward and got smaller by compression forces, this is true of all connecting rods over a long period of time. The weakest part of the connecting rod is the big end as its split in two and a large hole and its compressed fit connecting rod bolts as they have material removed from them at the top and about 1/3 to 1/2 the way down each bolt compressed fit in the upper part of the big end and secured thru the lower part of the big end by a fine thread nut of 1 tpmm under torque, yet tough enough to get the job done for the long haul or 1 or more rebuilds if not compressed too much.......

Do you see now ?

Its a tough concept to grasp , good luck.

Randy