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Front sub-frame TTY bolts

11K views 25 replies 13 participants last post by  DPDISXR4Ti 
#1 · (Edited)
Hey guys,

I wanted to confirm part numbers and quantities before I ordered the TTY bolts needed when the front subframe is removed. I'm planning on doing the oil pan gasket soon.

Achbid posted a link to Boltdepot for the 8 M10x35 mm 10.9 grade bolts and washers in another thread:

https://www.boltdepot.com/Product-Details.aspx?product=17511
https://www.boltdepot.com/Product-Details.aspx?product=7743

They're $0.69 and $0.16 each.

I also found them on McMaster . com:

https://www.mcmaster.com/catalog/126/3342

https://www.mcmaster.com/catalog/126/3424

Bolt is $0.72 and washer is $0.08

These links take you to the catalog. Just scroll down to the correct line item under "M10".

Questions:

1. The outside diameter of the McMaster washer is 18mm while the boltdepot is 20 mm. Any opinion if 20 mm is ok or is 18 mm a better idea?

2. We need a total of 8 M10x35mm bolts and 8 washers?

3. Do we need 4 of these bolts as well: 31116781023 M12x100mm? These are about $9 each on FCP or ECS. I believe McMaster has them but you have to buy a box of 25 for $81.

4. Oil pan bolts can be reused?


TIA
:thumbup: :thanks:
 
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#3 ·
Oh heads up, not sure how much information is posted about this but some cars have regular hex bolts for the subframe and others use an etorx
 
#24 ·
Is it the long (140mm) bolts that are sometimes E-Torx heads or the shorter ones? Did the switch to E-torx occur on the later e46's? Do you happen to recall what size? E18 would be my guess. For that matter, just to also have it documented here, do you recall the head size on the hex-head bolts? I'm thinking that's 18mm. For reference, BMW Part# on those is 31101095617
 
#7 ·
To add to what overboost has written, TTY means the bolt is tightened to a specific torque spec, and is then tightened an additional number of degrees. The bolts for the aluminum re-enforcement panel on the 330Ci are torqued you 44ft-lbs. They are then tightened an additional 90 degrees. That’s why they have to be replaced after a single use.
 
#8 · (Edited)
You're talking about the light aluminum reinforcement plate for the 8 TTY bolts.

The large heavy engine-supporting subframe has four larger bolts.

Read what Archbid said in post #2.
 
#9 · (Edited)
It has been a huge debate over on the X5 forums about the reinforcement plate bolts being reused. Personally, I always reuse them as I have my plates off my E46 and E53 all the time to do work on replacing parts and seals on 200,000 mile cars. I know that replacing the bolts is recommended but at this point, I have not seen any downside on reusing them. I just tighten them down and move on.
 
#10 ·
I do the same. That thin flimsy aluminum reinforcement plate held on by 8 large fine-thread bolts always made me laugh. I realize it’s shaped specifically for strength in the needed directions, but still. You can throw that thing like a frisbee. Ha!
 
#11 ·
It has been a huge debate over on the X5 forums about the reinforcement plate bolts being reused. Personally, I always reuse them as I have my plates off my E46 and E53 all the time to do work on replacing parts and seals on 200,000 mile cars. I know that replacing the bolts is recommended but at this point, I have not seen any downside on reusing them. I just tighten them down and move on.

+1 We almost never replace owing to ambiguity over which flavor has been installed. Furthermore I've seen hundreds that have been over-tightened. Not one failure to date.

All of these and the subframe bolts need the threads cleaned on the chassis and the fastener. Especially if you're in rust prone areas of the world. Coat bolts with a thin film of anti-seize before installation.
 
#12 ·
I have reused the reinforcement plate bolts many times and never torqued them to spec. It's a simple plate and this didn't look like something of big importance to torque them to spec imo.
 
#13 ·
pretty sure these are not TTY but TTT (as in "Torque To Turn" or "Angle Torque"). it's been clarified recently and probably good time to start calling them what they are.

either way BMW says to replace them. but i don't. :shhh:
although if yours are showing corrosion i wouldn't want to have these snap on re-installation as some have had happen to them in the past.
 
#15 ·
pretty sure these are not TTY but TTT (as in "Torque To Turn" or "Angle Torque"). it's been clarified recently and probably good time to start calling them what they are.



either way BMW says to replace them. but i don't. :shhh:

although if yours are showing corrosion i wouldn't want to have these snap on re-installation as some have had happen to them in the past.


The Bentley manual sez to torque them to 44ft-lbs and then tighten an additional 90 degrees. The bolts are expensive when you buy them from the dealer or an online vendor. You can buy the same grade of bolt from McMaster Carr (www.mcmaster.com). I always replaced the bolts whenever I had the panel off.
 
#17 ·
I have to believe that there's an assumption that's all to easily drawn here with respect to these bolts.
While the manual states to replace the bolts, they're not a "one time" TTY fastener.

The assumption is easily made because just about all of the critical TTY (one time use) fasteners also have the same torquing specification of torque, then angle torque. Also with "Replace with new bolts" in this particular case.

I have an entire box of aluminum TTY bolts that are truly a one time use fastener, from electric water pumps, oil pan bolts, motor mount arms etc. Albeit there are two distinct differences between the lower pan bolts we're discussing here and what's in the aluminum scrap pile:

The later are truly "one time" use that attach mainly to the aluminum alloy engine blocks of the newer "N" generation engines.
Furthermore they are aluminum and have threads running the entire length.
Hold up a regular bolt and a one time side by side and you'll quickly see the difference. Both in weight and the one time are aluminum. (non magnetic)

They are meant to stretch one time and then be disposed of.

The headbolts that are used for the S14 (E30 M3) and the S38 (all variations of M5 engine 6 cyl.) are the best headbolts that BMW ever made. They're so good in fact that the Gruppe A & Gruppe N repair manuals clearly state that when rebuilding the engine the OLD bolts are to be reused and NOT replaced. Reasoning is that they're seasoned and will not stretch.
These are also torqued and then angle torqued.
They DO NOT get tossed and replaced.
 
#22 ·
I have to believe that there's an assumption that's all to easily drawn here with respect to these bolts.
While the manual states to replace the bolts, they're not a "one time" TTY fastener.
The assumption is easily made because just about all of the critical TTY (one time use) fasteners also have the same torquing specification of torque, then angle torque. Also with "Replace with new bolts" in this particular case.

Furthermore they are aluminum and have threads running the entire length.
Hold up a regular bolt and a one time side by side and you'll quickly see the difference. Both in weight and the one time are aluminum.
Now this gentleman understands what I was stating :thumbup:
 
#18 ·
An addendum to my last post.
(Don't you just hate it when you remember something later after hitting send?)

The important distinction here is the difference between TTY: Torque to yield VS: that of angle torque.

Fasteners often use angle torque much anymore. However the "yield" part is applied to a bolt that is usually made of aluminum and is supposed to stretch. Making it a "one time" use.
 
#19 ·
TTY can also be steel-

8v Volkswagen head bolts make me throw up a little,
as you stretch them about 2 turns....
and every rotation feels like the bolt's going to break,
as your internal torque wrench associates the 'yield' with

'oh, hell, get out the drill'

t
Doesn't usually feel BMW head bolts yield.
 
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