L28 Main Caos

[Zed Head]

Here's another place to call.  They might have some advice.

http://www.rebelloracing.com/index.htm

[Racer X]

5 hours ago, Zed Head said:

I'm sure that you realize that any good machinist who heard you say that would take that as a challenge.  Machines are just metal formed to do what we want it to do.  There are pros and cons to everything.

https://www.practicalmachinist.com/vb/general/knurled-bearing-fit-how-engineer-324497/

If the machinist has to work on it then does it really "do"?  A good machinist could just copy one of the existing caps to steel and get a perfect fit from the start.  Remix doesn't even need a used part.

 

The thread you linked to discusses a bearing in a bored hole, but doesn’t say it is a crankshaft journal.

Reading further in the discussion, knurling valve guides to avoid replacement is commented on. 
 

There is also discussion about the lack of suitability of knurling a bore to correct for bearing retention. Indeed, knurling would only be able to “correct” for a couple of thousandths of an hour inch, and even then there wouldn’t be enough contact to keep the bearing from spinning inside the bore.

So knurling might be adequate for tightening up worn valve guides, but it would be a fool’s errand to expect it to correct for an incorrectly machined crankshaft journal.

 

 

 

[S30Driver]

Ok, I'll be third in line as a source for caps, behind I think CaptO and Terrapin Z if you decide to replace the one cap and go the line bore route.   I have 2 blocks which are not likely to see a engine bay, one is missing one cap.  Genuine Nissan bolts included....

The caps are numbered from front to back with a directional arrow, which number is missing.  Might as well go for numbers matching.  lol

[Zed Head]

Open your mind, just a bit.  Imagine.  Where's that racer's edge?  It's a thing.

https://www.google.com/search?rlz=1C1SQJL_enUS862US862&sxsrf=ALeKk01ZNoDPG6LyF_XQ9GV88CT2vdY9Ig:1619128301557&source=univ&tbm=isch&q=knurling+engine+block+main+bearings&sa=X&ved=2ahUKEwiw54n66pLwAhVQjp4KHdTGCOQQjJkEegQIChAB

https://mysql1.racingjunk.com/Engine-Machining/184133622/Main-Bearing-Cap-Knurling-Tool.html

 

How about shims?

https://www.speed-talk.com/forum/viewtopic.php?t=28780

[grannyknot]

7 hours ago, Racer X said:

Journals cannot be knurled like valve guides to correct clearances.

This.  The only reason knurling works on a valve guide is because there is very little side to side pressure on that knurled surface so you can get tens of thousands of miles on knurled valve guide, on a crank or conrod journal the bearing shell needs to be fully supported. The bearing shell on a modern engine isn't thick enough to support itself on a knurled surface. 

Now if you want to knurl your Model T poured babbit bearings that is whole other discussion.

 

[Zed Head]

Valve guides and pistons experience friction and wear from movement.  Main bearing saddle journal knurling just raises a static surface so that the actual bearing can be placed on top of it.  It's a different application.  

I'm not saying anyone should do it, I'm saying that it should be possible and has decent odds of working.  As shown by the apparent fact that people do it.  There's a difference between following instructions and understanding enough to write them.  No offense.  Kind of surprised at the resistance.

 

Here's some ingenuity.  Seems outside the "accepted practice", but apparently it is okay in their world, but they know what they're trying to achieve.  And they had a deadline.

https://www.enginelabs.com/engine-tech/blueprint-series-measuring-and-setting-bearing-clearances/#:~:text=Never mix bearings of different,the proper housing bore diameter.

"Some performance bearing companies like Federal-Mogul offer optional bearing sizes such as 0.001 undersize or oversize inserts that make it much easier to set an ideal clearance. In our case, we needed 0.011-inch undersized on some of the journals and 0.009-inch-undersized bearings for the front two. Federal-Mogul offers these and saved our bacon. This allowed us to increase or decrease the clearances to get closer to our ideal. While mixing half-shells is acceptable practice, never mix shells with more than 0.001-inch spread and always stay within the same manufacturer. In other words, never mix a 0.009 bearing shell with an 0.011-inch version.

One down side to performing all these customized clearances is that we were faced with purchasing two (and in our case, three) sets of main bearings for one engine. So do all measuring before you buy the bearings. The same is true with rod bearings...

The best way to fix this would have been to have the engine align honed to establish the proper housing bore diameter. In our case, the engine had to go back together due to deadlines beyond our control so we did the best we could. The final 0.0035-inch clearance is well within factory tolerances, but it is also 0.0005 inch wider than we would prefer..."

 

Edited April 23, 2021 by Zed Head

[Zed Head]

Fun topic.  p.s. I think I've been using "journal" incorrectly.  Replace all of my "journals" with "saddle".

https://www.mahle-aftermarket.com/media/local-media-north-america/pdfs-&-thumbnails/cl77-1-205r.pdf

Edited April 23, 2021 by Zed Head

[Zed Head]

This moved "Edit" button is really screwing me up.

Edited April 23, 2021 by Zed Head

[Zed Head]

I'll stop after this.  Here's a cap surface that looks kind of knurled.  But it's just a factory machining flaw.  The engine ran.  Good info in the article though.

https://www.enginelabs.com/engine-tech/enginelabs-blueprint-series-the-keys-to-proper-block-align-honing/

 (Right) JGM’s owner, Ryan Peart, showed us this big-block Chevy main cap out of a running truck engine...

Edited April 23, 2021 by Zed Head

[Racer X]

3 hours ago, Zed Head said:

 

https://mysql1.racingjunk.com/Engine-Machining/184133622/Main-Bearing-Cap-Knurling-Tool.html

That tool is for knurling the sides of bearing caps, and raises the metal up to 0.01" (.25mm). It is for fixing caps that have become loose (common in race engines that see frequent assembly/disassembly cycles). The outsides of the caps where they slip into the machined recess in the engine block are worked over to raise the surface (remember, the knurling process displaces metal, the resulting surface having much less surface area than previously as it is now peaks and valleys), then sized to fit.

 

Quote

How about shims?

https://www.speed-talk.com/forum/viewtopic.php?t=28780

Shims are used after worn caps are resurfaced where they mate with the cylinder block, to help maintain the crankshaft centerline position in the block.

 

Replacing the missing cap will require a line bore because the cap isn't matched to the block, and wasn't machined the same time as the block and all the original bearing caps. Since it is impossible to machine just the one bore, and have it be aligned with the other six journals, they must all be machined together. It is a routine process in a machine shop that does engine machine work.

The OP would be well served to find a cap that was from the same journal on the donor engine as the one that is missing on his, as they are all marked for location and direction, to avoid confusion during subsequent engine teardowns.

Edited April 23, 2021 by Racer X

[Racer X]

7 minutes ago, Zed Head said:

I'll stop after this.  Here's a cap surface that looks kind of knurled.  But it's just a factory machining flaw.  The engine ran.  Good info in the article though.

https://www.enginelabs.com/engine-tech/enginelabs-blueprint-series-the-keys-to-proper-block-align-honing/

 (Right) JGM’s owner, Ryan Peart, showed us this big-block Chevy main cap out of a running truck engine...

 

I've seen stuff like his before. Amazing that poorly manufactured parts like this get past inspection at the factory.

[Zed Head]

We're just starting at different ends of the spectrum Racer.  You're at "this is how it's normally done".  The "right way".

I'm at "what is possible" to be done.  

Look at that big block main bearing cap and you'll see that there are possibilities outside of normal manufacturing specs.