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engine builders.. Need some crank shaft bearing advise

2K views 35 replies 8 participants last post by  Gausswave 
#1 ·
So my barn find came back to haunt me finally. The engine is a surefire rebuild. It was rebuilt in 2012 and I got it off craigsist a month ago it's crate, in the shipping bag covered in oil. It had been sitting for 4 years. It was never installed. The engine has ~ 400 miles on it. The rear main started leaking ( shocker I know.) so I went to replace it last night and was greeted with this.....



The crankshaft still looks and feels ok. I can't find a burr or score of any kind on the shaft.



I'm assuming this is a Mclevite bearing the is .010" over sized(?). date of mfg. being 01/12 and (+?) .010". I'm not totally sure of the marking.
The part # is MB226p.





So to fix this I need to order a +.010" crank bearing set? Or should I pull it and actually measure it?
 
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#2 ·
I don't build engines. But don't you have to consider what the rest of your bearings look like, both rod and mains?

But either way, at least you're bumped a little for the morning crew.
 
#3 ·
I don't build engines. But don't you have to consider what the rest of your bearings look like, both rod and mains?

But either way, at least you're bumped a little for the morning crew.
Hey Opihi,

As far as I'm concerned Yes. That's why I'm pulling the engine. That and I can't for the life of me get the top half of the rear main seal out which is just one more reason to pull the main crank. I did pull the rest of the main bearing caps and they were all fine. Given the evidence I'm reasonable sure it was a localized problem but the only way I can imagine it got messed up was either some thing in the oil inlet or some ting that was a result of the build. Since I have to tear the rest apart I'm going to put my 4.0 carb hack in while I go through this one and well since I have it apart I might just have a bit of fun. I'm seriously looking at doing a cam but I'm still not sure which one.

Another question to the engine builders that know......

What would happen if I put a 4.2 cam in a 4.0 with a carb? Would I get more low end torque or is the stroke too short to gain that back?
 
#7 ·
And of course, best to use a brass punch to knock on the end of the seal. This won't damage the surface. I found a long enough piece of brass dowel rod and ground the end to the right size for the job.
 
#8 ·
I got tired of not having enough room to work while doing this. I have a brass rod I turned down on my lathe to .185" for this application. It put the end far enough down I don't have to worry about the bell housing getting in the way. It's probably 10" long. If I tried to hit the part that has the wire in it nothing happens. When it slipped towards the inside of the seal where it's all rubber I sank the punch easily a 1/2" and still nothing moved. The crank is probably 1/8" off the seal. All the main caps are loose. I suspect the guys did a poor job of sealing the seal halves and some got in the upper par of the seal. I should have the engine out tonight and on the stand so I can get a better view of what's happening.
 
#9 ·
If the engine only has 400 miles and the bearings look fine then reuse them. If you're in the copper on any of them then have the crank polishes and get new bearings. I'd advise you to purchase a cam designed for what you want. I drove a jeep with the Jacobs 6=8 cam and it was nice.
 
#12 ·
The local Car Qwest actually has a real semi retired machinist behind the counter. I finally got down to go see him at lunch today. His take was on the 258 the rear main bearing is the first thing that gets oil. What probably happened was the oil galley wasn't cleaned properly and some thing got through. So far all the rest of the mains and thrust bearings look good. I'll feel better when I find the schmutz that caused it. I'm close to getting it pulled out so I can tear it down. Just need to pull the manifolds and mounts. It should be out tonight so I can get a look at the top bearing, dump the oil filter and check the oil pump.
 
#16 ·
With the exception of break-in oil especially for non-roller lifters I am a believer you drive it at day one like your going to always drive it. That's a position I have from building racing engines but every build I have ever been associated with took on that approach. We chamfer all the bearings and prime the oil pump but once we're satisfied the lifters are broke in we let it roll. You're in the copper on that bearing so you need to clean polish and replace. Good luck
 
#17 ·
I was changing out the Zinc heavy oil at the time. It had just started to settle in and was making better torque. I got the engine out and on the stand last night and I'm itching to go through it. For the moment I need to concentrate on getting the temp engine back in since I plan on taking my time with this. My junkyard engine does leak around the head so I may replace the head gasket while it's out. It has the 7120 head. Is there any special precaution I should take when taking this head out so it doesn't crack? Seems most stories I read about the 7120 say the heads crack near the middle.
 
#18 ·
No advice on the head removal but if you're going to build some power do you have a plan? I suggest some head porting so you can appreciate a cam swap. If the bore is good then maybe shave the head for some more compression. Match port the intake and make sure the exhaust is free flowing. I'd love to see a stroker build but that is a new crank, rods and pistons. It's in my future but not until my drivetrain is finished. Good luck.
 
#20 ·
Most of the engine builders I talked to locally have said don't bother with the port and polish because low revving engines won't benefit from it.
My power goals I think are pretty modest. I want low end torque for moving @ idle and enough power to make 70 comfortably over the pass. Want to run well on regular gas and have no computer to worry about. I like simple. It makes sense on a trial rig. I want " enough" power not every thing I can get out of it.

So far I have a Weber carb, Clifford intake, Borla headers and more or less a fresh build to work with. I also have a 4.0 and worn out 4.2 That IIRC is supposedly 0 decked. So I could do a stroker but that seems like a lot of work for an extra .5L. So I'm thinking the best bang for the buck in my case is refreshing the head on my 4.0 ( 7120 casting) and either a Clifford cam or a Compcams high energy 252H and sticking that in the jeep. CC recommended the 4X254H which seemed to be more than I wanted.
 
#23 ·
The machine shop can clear the casting flash in the valve pocket when grinding the valves. That should set the stage for porting. Be sure and post pics. I like how you roll.
 
#29 ·
Yup it's out! I'm reinstalling my "4.0, carb hack, junkyard get me by for now engine" for the time being. It misses at idle a bit but it runs well. Wheeling season is closing up as far as the nice weather is concerned in my neck of the woods. Lots of places I wanted to get to this season will close in November. Left to my own devices I have ~ $1000 work I'd like to do. I gotta save up some toy money for a bit. I'm also thinking I'll get a better deal from the machine shops during the slow season. Once I get things running again I'll tear in to it later this week most likely. I'll post up what I find.
 
#31 ·
Not sure if you are already past this, but....

...yes, those who said that was due to sloppy assembly are correct.

If desired, you can check all your bearing clearances with Plastigauge.

It is not textbook correct, but there is plenty of meat left in the scored bearing and that groove just holds more oil. It can be reused. If after 75000 miles it gets noisy, you can drop the pan and replace it with the motor and crank in place.
 
#34 ·
Not sure if you are already past this, but....

...yes, those who said that was due to sloppy assembly are correct.

If desired, you can check all your bearing clearances with Plastigauge.

It is not textbook correct, but there is plenty of meat left in the scored bearing and that groove just holds more oil. It can be reused. If after 75000 miles it gets noisy, you can drop the pan and replace it with the motor and crank in place.
Yup I'm past it. That's not to say the thought of just replacing the one bearing and getting on down the road didn't occur. However the bearing is just a symptom. The real problem is the oil system isn't clean so it really needs to be a tear down clean and reassemble. You can see in my last post the streaks happen right at the oil port.
 
#32 ·
He has the motor out so I'm guessing at least a partial rebuild is in order. Not sure I'd reuse that bearing but in desperate times it would probably be ok. Believe the OP is going for a mild performance build.
 
#33 ·
OK well the old engine is back in the rig and I finally got a chance to tear into things a bit. Found some interesting things.

First bearing has some un usual wear as well.



but again nothing showing on the bearing.

Here's the top half of the rear that was worn through to the copper.




The rest of the bearings looked like normal wear.


I did find some small chunks. Black spots in the middle were what I found. Size of a grain of sand.


Other things of interest.... Looks like they shimmed the Cam.

A little piece that I tore out.

Chunks in the oil pan....
Bah.....

I decided If I keep trading engines out more often than I get shoes I should have a pre lube tool that fits my drill and won't loose tips in the sump. Magnetic tips suck in this application. Don't ask me how I know. Any way the tool turned out really well.


`

At least the rear main came out easily once I got all the caps off. Sigh....
 
#35 ·
Believe I would have the crank measured and polished and let them supply the proper bearings. I would also pull those cam bearings and have new ones installed. That may well be where your trash came from. Looks like your hard parts are all good.
 
#36 ·
And it's back in! But it's not totally happy. My 4.0L junk yard engine started pushing oil out of places it shouldn't so it was time. The 4.2 has been torn down, cleaned, hot tanked checked out by a machine shop and re assembled with all new bearings. FWIW The cam bearings were so tight on the sure fire build that the Babbitt material had melted over the oil holes. When we put the new cam bearings in the cam shaft barely fit so I had the shop scrape them to size. The Babbitt material was what that stuff was that looked like shim material around the cam bearings. Just the Babbitt material melting off the bearing core. Since the install I've also had to replace the oil pump. What ever got in the old motor ate the walls of the pump and it wouldn't make pressure when hot at idle. I'm also taking a step back or side ways depending on your POV. Found a deal on a new in the box HEI dist. So I'm evicting the MSD for now. It kept eating the contacts in the cap so much so the idle was typically rough.
My current issue is one of the lifters is making noise. The are all new and were primed when installed. Does this happen on a new engine or do I need to pull the head to replace a lifter and how would I figure out which one it is?
 
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