Main Bearings -- need advice

RoyLuke

Well-known member
Apr 18, 2007
200
5
Just got my second set of bearings in the mail.
The Centre bearing STILL will not allow the crankshaft to seat. I tried the spare crankshaft. Doesn't work either.
With the last set of bearing the centre one broke when I tried to pull the crankshaft back out.
What am I doing wrong?
This engine is fighting me every inch of the way !!!!!
 

4Runner

Well-known member
May 24, 2007
494
42
Boise Idaho
There are two different main bearing sizes. One for 4.0 / 4.6 and one for 3.9 / 4.2. Are you sure you are getting the correct ones? I don’t know which one you are rebuilding. Does the crank not fit due to the journal size or because thrust bearing interference? You can leave that bearing out and see if the crank fits in the rest of them. I will say that you are not alone. Between getting the right parts, making them fit is harder than it should be. I will build one and at the end say that I will never do another. I just finished a 4.6 a few weeks ago and it might be my last one of that vintage. Good luck and let us know how it goes.
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
Is that centre bearing supposed to come apart? If not, I have broken ANOTHER one. See pix below.
It simply will not fit !!!! It binds on the way in. It seems to fit to the crankshaft outside of the engine but not when fitted into it.
I am sooooo frustrated with this.

broken bearing.jpg
 

4Runner

Well-known member
May 24, 2007
494
42
Boise Idaho
Wow. I am sorry to see that. Here is a picture of a 4.6. The thrust bearing is on the 3rd journal from the front. Sorry for the dumb question but are you placing it in the right journal. I would not place use a new bearing until you get the issue worked out with the broken one. You do need to adjust the clearance for thrust but when all is good your crank should fit in there without having to force it at all. I have never seen one , let alone two break like that.
 

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simondewing

Well-known member
Feb 10, 2020
54
11
Texas
Have you had the crank re-ground?
If so did they grind the thrust faces as well as the crank journals?
Need to check the specs on both, chances are a +10 bearing is expecting 10 thou off both journals and thrust faces.
maybe just the journals were machined.

Need to accurately measure everything (with a micrometer or good quality digital caliper) before assembly and not force anything in or out it either fits correctly or not at all!

Simon
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
Have you had the crank re-ground?
If so did they grind the thrust faces as well as the crank journals?
Need to check the specs on both, chances are a +10 bearing is expecting 10 thou off both journals and thrust faces.
maybe just the journals were machined.

Need to accurately measure everything (with a micrometer or good quality digital caliper) before assembly and not force anything in or out it either fits correctly or not at all!

Simon
I had a machine shop polish the journals. Nothing was ground so Standard bearings should work.
The centre bearing is the problem. It came apart whe I was trying to seat it. It snaps back together but I can't tell if it was ever permanently attached.
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
it’s the thrust surface your having a problem with. It looks like it’s too thick for the crank your using.
Yes, that could be it but this is the original crankshaft that was in this engine.
The thrust bearings keep coming apart. I can snap them back together but is that acceptable or do I need yet another set of bearings?
I am seriously considering taking it to the machine shop. $$$$$$$$$ !!!!!!!!!!
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
I really hate to admit defeat but this has TOTALLY ceased to be a simple problem. The thrust bearing is NOT going to allow the crankshaft to go in.
I think the only option is taking it to a machine shop. $$$$$$$
Exactly which bearings are these which are not fitting? Part #, brand, and vendor please.
It is the centre thrust bearing. The fist set of bearings was made in Israel and the second was called BritParts. Neither fit correctly. I have two crankshafts and neither would seat correctly
 

ERover82

Well-known member
Nov 26, 2011
3,623
277
Darien Gap
It is the centre thrust bearing. The fist set of bearings was made in Israel and the second was called BritParts. Neither fit correctly. I have two crankshafts and neither would seat correctly

That is better, but I would encourage you to go back in your email records, or find the packaging to tell us the exact part #, brand, and vendor. There may be an issue with the bearing you got, but without exact info it's hard to offer suggestions.
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
Hi All;
I am about to order the third set of bearings. The last two were different brands from different venders so I suspect the bearings are not really the problem.
I have two options: take it to machine shop or try to shave the bearings just enough to make them seat correctly.
Is it an orthodox procedure to try to sand the bearing (it is made of aluminium) to make it fit?
This engine block is fighting me every inch of the way.
 

ERover82

Well-known member
Nov 26, 2011
3,623
277
Darien Gap
Bearings are built to precise tolerances and should not be shaved in any way. If the bearing doesn't fit perfectly, it was manufactured wrong, it's the wrong bearing, or there's something else wrong with how the parts are being installed.

Which part # do you currently have, and which are you considering purchasing?
 

RoyLuke

Well-known member
Apr 18, 2007
200
5
Today I got the third set of main bearings in the mail. Same brand as before, I was all set to take them and the block to the machine shop.
I planned on gently trying to see if the crankshaft would fit before I took it.
You guessed it, it fit like a glove.
There is NO explanation as to why it worked this time.
Maybe the engine block is haunted,


1630806786407.png
 
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