main bearing placement.

[TurboDave]

OK, laugh if you must. I should know the answer to this but I don't, and for the life of me, can't find the answer in any of my reference materials.

Anyway, after sitting bare for 15 years, I'm going to slowly start putting my numbers matching engine back together.

I'm going to try and re-use all the original parts as much as I can (except the cam and lifters of course).

Anyway, here's my question. I dug out the old main bearings (don't worry, I'm not re-using any bearings) to see how they came fitted and mounted from the factory. A couple of the uppers were labeled .001 so it's important for me to figure out what position they were in. One of them is the one with the "partial" groove not covering the entire length of that piece.
I'm thinking it must be the #4 position, because it's REALLY obvious which one came out of the #1 pos. It has a LARGE black imprint on the back caused by the larger oil hole in the number one web.

And of course it's obvious which is the thrust bearing.

And why would the only one's marked .001 u.s. be the uppers???

TIA

 

[LOT]

bearings

The partial groove is # 4. I can't answer why some are .001 under and some are not. I have disassembled many untouched block and I have seen this also (mix and match). I can only assume they were done this way to get the necessary clearance or keep the bore "in line". Someone like Richard Clark might know for sure. I was once told that the bearings had letters on the denoting .0001 measurements. Maybe they had some way of getting the clearance tight and bore straight (IMO would be time consuming) as to why they run so long when not beat to death. Best of luck in your assemble.

 

[TurboDave]

Thanks! I kinda suspected it might be the #4 bearing. I'll have to determing which one's were .001 u.s. and try and figure out why they did it so strangely and look for some other numbers/letters.

I knew about the letter designator thing, but I thought that was just for rod bearings. I'll look closer at the mains.

 

[LOT]

letters on rod bearings

You may be right--years ago I heard that.

 

[TurboDave]

I'll start a new thread with the markings I've discovered, and hopefully somebody can disect them for me.

 

[turbofabricator]

Dave,
The bearing shells go into the bearing saddles at the bottom of the block, but would actually be at the top of the block with the engine rolled over on an engine stand. They snap in place. One half in the block (that big cast iron thingy with (6) 3.80" holes in it for pistons and stuff) the other half in the bearing cap. (though it really doesn't look at all like a cap. They really look more like a little bridge) Then you have to put two bolts in the bridge lookin' things and with a little oil on the threads and under the heads, you have to tighten them down REAL tight. (hundred foot pounds, but that doesn't mean you kick it 100 times with your foot, you have to have a long wrench thingy that clicks when you get to the right tightness.):biggrin::biggrin:

Just messin' with ya Dave.

I, too, have seen alot of wierd combos from the factory, but haven't in a long time. Most of those engines have been rebuilt a time or three by now. I even bought a set of .002" oversized pistons years ago. It was the only set of factory pistons I could find. They really were cool. I could hone the block to fit them nice. Man that was a LONG time ago, though.

Place the .001US bearing halves in the block side, though. (if needed to tighten clearances up) This helps tightening the chain a bit.

Good luck with the build.

 

[dr_frankenstein]

Place the .001US bearing halves in the block side, though. (if needed to tighten clearances up) This helps tightening the chain a bit.

genius.

A.j.

 

[TurboDave]

Dave,
The bearing shells go into the bearing saddles at the bottom of the block, but would actually be at the top of the block with the engine rolled over on an engine stand. They snap in place. One half in the block (that big cast iron thingy with (6) 3.80" holes in it for pistons and stuff) the other half in the bearing cap. (though it really doesn't look at all like a cap. They really look more like a little bridge) Then you have to put two bolts in the bridge lookin' things and with a little oil on the threads and under the heads, you have to tighten them down REAL tight. (hundred foot pounds, but that doesn't mean you kick it 100 times with your foot, you have to have a long wrench thingy that clicks when you get to the right tightness.):biggrin::biggrin:

Just messin' with ya Dave.

I, too, have seen alot of wierd combos from the factory, but haven't in a long time. Most of those engines have been rebuilt a time or three by now. I even bought a set of .002" oversized pistons years ago. It was the only set of factory pistons I could find. They really were cool. I could hone the block to fit them nice. Man that was a LONG time ago, though.

Place the .001US bearing halves in the block side, though. (if needed to tighten clearances up) This helps tightening the chain a bit.

Good luck with the build.

Loved your explanation above!! :biggrin:


I mounted a set of standard main bearings (King) and torqued the crank in place and checked the clearances with plasti-gage.

Here's what I found:

#1 .0017 to .00175 (tending a little toward .00175)
#2 .0015
#3 .0010
#4 .0012 to .00125 (tending a littel toward .00125)

Now, with the factory clearences listed at .0003 to .0018;
What would everybody's recommendation be??? leave them as is or try and tighten them up with some mixing and matching with a .001us set

IOW, what crank clearences work best for what will be a street engine with minor external mods??

 

[turbofabricator]

I shoot for .0018" on rod and main bearing clearnces. If it ends up .002", I'm not concerned. .0016" or less, I hand clearance the bearing, or polish the journal. A few wipes with scotchbrite on the upper shell, and that'll probably loosen things up enough. If it's still too tight, scrape CAREFULLY with a razor blade. Use a caliper to measure the shell at about 5-6 points to verify consistancy of your handiwork. I have been doing this for 30 years with out an issue. Take your time, and think about what you are doing. Might be easier to have the journal(s) polished to the desired clearance, though.

 

[TurboDave]

I shoot for .0018" on rod and main bearing clearnces. If it ends up .002", I'm not concerned. .0016" or less, I hand clearance the bearing, or polish the journal. A few wipes with scotchbrite on the upper shell, and that'll probably loosen things up enough. If it's still too tight, scrape CAREFULLY with a razor blade. Use a caliper to measure the shell at about 5-6 points to verify consistancy of your handiwork. I have been doing this for 30 years with out an issue. Take your time, and think about what you are doing. Might be easier to have the journal(s) polished to the desired clearance, though.

scotchbrite won't hurt them?? I never would have thought about that, even though I used it on the old bearings I took out to clean them off, and look for debri that might be imbedded.

 

[TurboDave]

Speaking of the old mains, here they are.

The #1 and #3 uppers (grooved halves) were the ones that were .001 u.s.

Looks to me like #3 might have been a little tighter than needed.

These are 100,000 mile units.

Dispite the color in the photos, there is no copper.

 

[Just a Six??]

100K on those bearings shows the factory did a decent job.
They look pretty good after 100K compared to what some shops put out now as good work & after 20K look way worse than those.

 

[turbofabricator]

Just slide the old bearings in and run it. They will work fine, if the crank is good. It lasted 100K, it'll last another 50K+ They fit the block well. GM did a decent job assembling the GN engines. I had had GM short blocks with ALL kinds of problems, though. Spun bearings, crooked head bolt holes (3 different blocks), etc. I think that many of the factory 109 short blocks were rejected turbo engines from the assembly line, or so it seemed. Pretty bad to have a factory short block spin a bearing on start up. THe replacement short block they warrentied, I checked it out prior to installing it...........SPUN bearing in the journal. The locator tabs were SMASHED flat and the parting line was about .25" off of the cap parting line.
Three factory short blocks had head bolt holes crooked'r tha a dogs hind leg. I also had a factory GN engine with one head bolt hole off by 15* and when It popped a gasket, upon replacement, I torqued the bolt, and it would back off as I watched. I had to slot the hole in the head and use self aligning washers under the bolt head.

 

[TurboDave]

Just slide the old bearings in and run it. They will work fine, if the crank is good. It lasted 100K, it'll last another 50K+ They fit the block well. GM did a decent job assembling the GN engines. I had had GM short blocks with ALL kinds of problems, though. Spun bearings, crooked head bolt holes (3 different blocks), etc. I think that many of the factory 109 short blocks were rejected turbo engines from the assembly line, or so it seemed. Pretty bad to have a factory short block spin a bearing on start up. THe replacement short block they warrentied, I checked it out prior to installing it...........SPUN bearing in the journal. The locator tabs were SMASHED flat and the parting line was about .25" off of the cap parting line.
Three factory short blocks had head bolt holes crooked'r tha a dogs hind leg. I also had a factory GN engine with one head bolt hole off by 15* and when It popped a gasket, upon replacement, I torqued the bolt, and it would back off as I watched. I had to slot the hole in the head and use self aligning washers under the bolt head.

It really has crossed my mind several times the last couple days to do just that. They look SO good, especially after I lightly dusted them with scotch brite.

I'm going to mount them up in the block and measure the clearances!!