Fitting connecting rod shells

[BobH]

  Hello,

  I'm fitting a new set of rod shells where crush is good (not great) but bearings are too tight. (verified by measurement)

  After studying all the options, I'm seriously considering simply lapping them to fit. I would start with paint polish.

  I only need a couple/few thou. Surely the babbit, if there is any, is thicker than that. Clean up with lacquer thinner

  Any input would be greatly appreciated.

  Thanks!

[luv2weld]

After studying all the options,

Are you sure you looked at ALL the options???


Instead of cutting off the babbitt on your bearings (which wastes half the life of them),
Spend $20 for an assortment of shim stock and make your own shims.
This should be enough shim stock to last a lifetime with that engine.

http://www.use-enco.com/CGI/INSRIT?PMAKA=TE406-0288

Ralph

[Crofter]

No you cannot shim them out for clearance because they interfere at the edges and you have to put in huge shim pack and then have excess clearance top and bottom. You need to scrape the sides. Got to run to a wedding so I am out of here for now. You cannot lap babbit worth a sh t without embedding grit in it.

[BobH]

  Thanks for the replies.  Heres what I think I know.

  The "stock"  shims are designed to NOT shim the bearing, just the cap, which kills the crush.
  Shims kinda suck as a solution to the problem anyway.
  I could make custom shims that would also engage the insert, but seems like the compression stresses between the cap/rod and insert/insert would be totally different causing uneven squishing of shims, cracking, breaking,  

  I can turn a shaft of the appropriate dimensions for a die(s) to lap with.
  There must be something that will cut the babbit but is soluble in lacquer thinner (or ) to remove the grit.

  If the babbit is too thin, I'm back to shims. Is there a definitive answer anywhere as to how thick the babbit is? Do you make shims that engage the bearing insert? OR use the dipper in the cap to pin the inserts and not worry so much about crush, OR Red Loctite, OR
  Again, what I THINK I know - -

  I'm hoping my bearing supplier chimes in soon. Surely he's dealt with this before.

  Thanks!!

[vdubnut62]

Pardon the question, but just how much clearance DO you have? Measured at the top? Sides? Is the rod big end egg shaped?
Ron

[BobH]

  Crank pin - 2.4985 - 2.499

  Big end  -  2.4965 - 2.497

  Crush: - .004 - almost .005 (measured by the loosen one side and feeler guage method)

  Locks up tight when torqued. One "stock" shim (.005) on one side fixes (well , it turns anyway)  pin/big end clearance but negates the crush (doesn't it?) as the shim material  is only between the cap and rod.

Thanks

[vdubnut62]

Try some plastigage on the top, bottom and sides just above and below the bearing split. Not all these places at once!
If this is a dumb question just slap me, but you did torque the rod cap before you measured?
It's possible that you just have a set of screwed up inserts, do you have another set you can try? What about the old ones?
How do they measure out?
Sorry about playing 60 questions.
If everything is that round, I'm baffled by the stock shims. I think Ade may be your man here.
Ron

[Crofter]

  Crank pin - 2.4985 - 2.499

  Big end  -  2.4965 - 2.497

  Crush: - .004 - almost .005 (measured by the loosen one side and feeler guage method)

  Locks up tight when torqued. One "stock" shim (.005) on one side fixes (well , it turns anyway)  pin/big end clearance but negates the crush (doesn't it?) as the shim material  is only between the cap and rod.

Thanks

BobH, I think you are correct about what a shim will do to the crush if it does not extend under the shell ends. I dont like to depend (I would not) on the dipper projection to locate the insert if there were no crush. I think you will find that very little scraping needs doing except near the sides and since 90% of the wear is in the center of the upper insert scraping is not going to remove much "useable" bearing material. I have not tested to see how thick the babbit really is and I am not sure it is the same on both indian and genuine lister items anyway. There have been a few times this issue has come up and I have not seen it chased down yet.

I am in the process of fitting a new rod and plain inserts and hollow dipper but it is on hold at the present. I have machined and polished a length of shaft which will have a single flute cutter effect to do the initial scraping. I also have hand scrapers. Some of the original hand scraping on the listeroids is wild and random. I have seen 7 thou clearance top to bottom but dragging at the sides. Totally the worst contact pattern. I will have to use about three thou shim and have cut them to extend under the ends of the shells. Placement is critical because as Mobile Bob has mentioned any shim projection in towards the crank could restrict the formation of the rotating oil wedge. Placing the shims has to be done a bit blind inside the engine. I am not real impressed with the design as it commits too much to faith. With the machining finish on the listeroid rod and cap I dont think the method of loosing one bolt and measuring the resulting gap is very indicative of how much crush you really have.

[Geno]

About a 1000 hours ago when I put my new shells in they were tight. I put an .003" shim on each side and it turned nicely. I had the rod out yesterday and the bearing looked the same as when it had 100 hours. They were a set from JohnF and a hollow dipper. My crush can be felt with a fingernail but was never measured.

I didn't think it could be done but yesterday I was able to remove the piston through the top of the cylinder and the rod through the bottom. Saved a bunch of time and made the inspection/cleaning much easier.

There is a local guy around here who pours bearings. He measures the crank, mounts the rough shells in the rod and bores the shells to fit. He made a set of .010 under for my original, which is still not put together.

Thanks, Geno

[NoSpark]

A thousand or two isn't much, you could probably get that with a scotchbrite pad. Its been mentioned before about using a soda can for making shims, I suppose different brands of soda have different thicknesses.

[BobH]

  Heres a pic of the shims I have.



  Some are steel, some are copper.  They all measure .005.  You can loosen the cap,
  slip them in and retorque. Real easy.  They do not engage the insert.

   Geno, is this what your shim looks like? Did you do anything to your
   dipper (cap end) to index the threads for the best engagement of the insert?

   Crofter, hand scraping bearings is one of those mystical processes that
   I always wanted to learn but never had the occasion to. I know
   this is a ridiculous subjective question but - Is it hard? Or would
   I plan on ruining a LOT of inserts first. The thought of scraping
   my brand new, hard to get, somewhat expensive bearings with
   a chisel, scares the hell out me.  Even after a bunch of pratice
   runs on junk. If you can do it, I am envious. Ever done a video?

  Heres what I think I know now:

  If Geno's shim looks like mine, I can safely install a 5 thou COPPER shim on one side.
  Anything more might turn a lack of crush into slop.

I may need to fit the dipper for best engagement by:

   turning the shoulder at the insert end
   removing material from the end to prevent the dipper from protruding into the insert too far

  I want it to be all BUT touching the hole in the insert.

  If its still a whisker tight (turns, but feels draggy) , scotch brite (thanks NoSpark) on
   a shaft built up with duct tape to taste.

I can't thank you all enough for helping me with this. I will definitely report on how it all works out.

Thanks!!

[Crofter]

Simply going by whether or not you have lockup, or barely feel drag when the cap is torqued does not tell you where that clearance is, or the contact pattern. If everything bolts up perfect circle but zero clearance and you add shim at the part line you increase top and bottom clearance but still have contact at the sides exactly where you should have a bit of relief to bring oil between the journal and bearing. I am sure they almost always run themselves in to a workable arrangement but it is far from an ideal fitup right at the get go and maybe not conducive to those 100,000 hour engines of Lister yore.

below is a pic. of bearing shell as fitted from a listeroid. It took a fair bit of work to get uniform clearance and contact but do no have a pic of that. Shimming is tricky because how they are placed affects whether or not the bore remains round or oblong and certainly plays all kinds of potential havoc with the crush. There have been more than a few engines pulled down to find the end of the dipper had slotted the lower shell half an inch

[NoSpark]

Another good argument for plastigage. If you get enough clearance top and bottom and it still binds then adding more shims would not be good. My roid connecting rod was cut so crooked that I wouldn't even think about using the Nip measuring method.

[Crofter]

I would not use scotchbrite as the abrasive comes loose. I would rather use stainless steel potscraper. Really a bearing scraper is not at all like a chisel and it removes very, very thin scrapings. Take nothing from the low spots is the idea!  Using a dye like Dikem shows the contact (so will candle smoke) As long as you are patient and prepared to assemble and disassemble dozens of times you wont go wrong providing the rod bore is true to start with. Probably if you did a search on "scraping babbit bearings you would get lots of hints. It really is no black art.

Re. getting cap bolt nuts to index with the cotter pin. I dont like the idea of going to the next slot or having to back off; I lapped the face of the nuts on one of those 2x6 inch diamond impregnated whetstones to take the nuts on a bit without hedging the torque.

Not too fussy about those horseshoe shims with limited contact area. Their only redeeming quality is they can be slipped in without dis assembling; quick and dirty. Will they compress later and shed the torque preload?

The fit of connecting rod bearing is heart of the engine!

[BobH]

  Well, you're right. Still tight along the parting line with a shim. Crappy photo,
but I think you can see it in the upper left.
 


The scotch brites I was thinking of are the gray ones for scuffing a car before painting.
I think there are white ones that are even finer.  Are those bad too? I would feel a lot more
comfortable with a scotch brite wrapped around a small piece of  2 and 7/16 ish 
ground/polished shaft. It might take me forever, but I don't think I would eff it up.

Thanks!