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Discussion Starter · #1 ·
I'm rebuilding a 2010/2011 Mazda 3 2.0 engine.

I'm at the point of torquing the crankshaft main bearing cage. I verified that I have the correct numbers and procedure based on getting it from a couple different sources. (For what ever reason this information isn't included in the 3000+ page service manual that I have.)

The problem I'm having is with lubrication of the bolts prior to torquing them. One source says to install them dry. Another source say to oil them with engine oil prior to installation.

I have the 104 mm bolts (yes, they're new), and the instruction says to oil them. So I did. Upon completion I used the torque wrench to check the level of torque required to remove them. It was relatively low; somewhere less than 35 - 40 ft lbs.

My question is: does this seem right? Is it low because the block is aluminum? I think the head bolt removal torque is going to be higher.

any insight to this would be greatly appreciated.
thank you..
 

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I'm not sure if you are supposed to put oil on the bolts in this motor. Old iron block V8s yeah a bit of 30wt on the threads but aluminum, ? There is no mention of wet torque numbers, but I suppose its possible. Its the bearings and journals you are supposed to put oil on....

Did you use this torque sequence?

Main Bearing bolts: 2.0 and 2.3L engines in sequence



104mm length bolts:
step 1: 62in-lbs, 7Nm
step 2: 19ft-lbs, 26Nm
step 3: 30ft-lbs, 40Nm
step 4: Loosen all bolts 2 turns
step 5: 62in-lbs, 7Nm
step 6: 16ft-lbs, 20Nm
step 7: Tighten an additional 90°​


Yes the numbers are low because of the aluminum block. It always requires a bit more force to loosen a bolt than to tighten it also.
I see that the bolts are apparently single use torque to yield . So, if you torqued them properly and then removed them, you'll need new bolts again.
 

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Discussion Starter · #3 ·
I'm not sure if you are supposed to put oil on the bolts in this motor. Old iron block V8s yeah a bit of 30wt on the threads but aluminum, ? There is no mention of wet torque numbers, but I suppose its possible. Its the bearings and journals you are supposed to put oil on....

Yes the numbers are low because of the aluminum block. It always requires a bit more force to loosen a bolt than to tighten it also.
I see that the bolts are apparently single use torque to yield . So, if you torqued them properly and then removed them, you'll need new bolts again.
I tried checking the breaking torque again last night and this time I got from 55 to 76 ft lbs. that’s a little better, but I’m still not comfortable with it. I think after setting for a few days, the threads had a chance to settle. I'm no expert in this area, so if you think that sounds nuts I won't argue.

It would be nice to know what the additional 90 degrees adds to the 16 ft lbs from step 6. I’m sure there’s a way to calculate it. If I had to guess I’d say it’s more than 50 ft lbs and definitely more than the 25 or so that I got from the first check.

I did make a mistake in my original post: they are not new bolts. The head requires new bolts but not the bearing cage. I think it was really late when I wrote the original post on another forum. I got no response there so I copy/pasted it into a new thread here and didn’t notice the mistake.

I’m going to torque them dry tomorrow night and see how much it adds to the breaking torque. Plus, I’m hoping to get a tighter range of numbers. That just seems odd. I would expect it to be different across one cap, but each cap should be a bit closer relative to the others. I think that’s the whole reason for the multi step procedure.

I know it’s not a racing engine; I just don’t want to screw it up. It’s my first aluminum rebuild.
 

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I tried checking the breaking torque again last night and this time I got from 55 to 76 ft lbs. that’s a little better, but I’m still not comfortable with it. I think after setting for a few days, the threads had a chance to settle. I'm no expert in this area, so if you think that sounds nuts I won't argue.
Breaking force is totally irrelevant. It has no bearing on how much torque is needed to secure the fastener. What is important is that the proper torque is applied on installation.


It would be nice to know what the additional 90 degrees adds to the 16 ft lbs from step 6. I’m sure there’s a way to calculate it. If I had to guess I’d say it’s more than 50 ft lbs and definitely more than the 25 or so that I got from the first check.
This isn't something you want to guess on. The bolts are torque-to-yield, the 90° part is to make sure you don't go past that point.

I did make a mistake in my original post: they are not new bolts. The head requires new bolts but not the bearing cage. I think it was really late when I wrote the original post on another forum. I got no response there so I copy/pasted it into a new thread here and didn’t notice the mistake.
From a factory instruction manual on LF engines -

Keep experimenting with torque and the bolts will be out of spec, probably already are.

I’m going to torque them dry tomorrow night and see how much it adds to the breaking torque. Plus, I’m hoping to get a tighter range of numbers. That just seems odd. I would expect it to be different across one cap, but each cap should be a bit closer relative to the others. I think that’s the whole reason for the multi step procedure.

I know it’s not a racing engine; I just don’t want to screw it up. It’s my first aluminum rebuild.
Again, how much it takes to free the bolts is not relevant. Stop doing it unless you have another aluminum block to replace this one when you strip out the threads or bend or break the bearing support frame while experimenting with torque values. Just follow the instructions and assemble it. FYI, wet torque numbers are lower than dry torque numbers. A couple drops of oil on the threads, torque it, move on.
 

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Discussion Starter · #5 ·
Breaking force is totally irrelevant. It has no bearing on how much torque is needed to secure the fastener. What is important is that the proper torque is applied on installation.

Just follow the instructions and assemble it. FYI, wet torque numbers are lower than dry torque numbers. A couple drops of oil on the threads, torque it, move on.
I can’t agree with you more. The important thing is the proper torque in the end. The only reason I’ve been doing this is because I don’t trust my results. It just seemed way too easy to get to the final position after the 90 degrees. And I was only trying to see how tight they were because they seemed (to me) too loose. I understand the final torque and the breaking torque are different.

In my opinion, there’s a considerable difference between wet and dry torques. Yes, the wet numbers would be less based on the lubricated threads. Unfortunately, the torque procedure and values are the same for both instructions that I found.

And for me, the worst part is judging how much oil.

Thanks again for your insight. I’ll leave it alone. A few drops, torque it and move on.
 

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And for me, the worst part is judging how much oil.
Just enough to wet the threads. If the bolt is going in a blind hole, you don't want any oil pooling in the end of the hole under the bolt. This can cause a hydraulic block and make the bolt appear to be torqued properly even though it might still be a quarter turn or whatever from being actually tight.
 

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Discussion Starter · #7 ·
Just enough to wet the threads. If the bolt is going in a blind hole, you don't want any oil pooling in the end of the hole under the bolt. This can cause a hydraulic block and make the bolt appear to be torqued properly even though it might still be a quarter turn or whatever from being actually tight.
Thanks again.
 
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