Stovebolt.com Forums The Shop Area The Engine Shop 55.1-235 crank cap gap

We have turned the crank. #1 journal measures 2.6737. #2 is 2.7046. #3 is 2.7360 and #4 is 2.7665. The shims will be installed soon. The book calls for the clearance with the bearings in place and sequentially torqued to 85 lbs, to have a oil clearance of .0005 to .0031. My question is, does this engine enjoy that clearance? We are using a bearing gauge to set the journal opening.

You're over-thinking things. Put a small piece of .001" shim stock between the bearing and the crankshaft, torque the bolts, and see if the crank will turn with a moderate amount of pull on the flywheel. Add shims between the cap and the block until the crank will move with a little drag with the shim in there, then don't forget to remove the shim. Do the same thing for all the bearings. It's OK to use .0005" less shim on one side than the other to tweak the clearance a bit if necessary. You're dealing with a glorified tractor engine, not a Ferrari!

Edit: You've also got too many zeros behind the decimal point on that upper clearance spec. It's supposed to be .0031" That's WAAAAYYY too much, BTW- - - -if the rear main bearing in particular has that much clearance, the rear seal will leak like crazy, even if you use a "Best Gasket" rope seal. Main bearing clearances in the .001"-.0015" range have worked for me since the 1960's.
Jerry

Thank you Jerry, I do have the Best Gasket rope seal. The main clearance was a nice bit of information.

I use that same trick when fitting Babbit rods. The shim stock method is much more accurate than Plastigauge, and it's usually quicker, too. The first operation when working with Babbit rods is to scrape-fit the bearing to exactly match the crankshaft using Prussian Blue, and then shim for the correct oil clearance.

"You've got clearance, Clarence!"

"Roger, Roger!"

Jerry

Thank you Jerry.Today we installed the third and fourth cap, without the bearing. This process was also done on the first and second caps. The caps are checked for horizonal fitment because there are no registers to set the cap in.The third cap was not centered. A 9/16 adjustable hone was introduced to both holes in the cap. One of the holes was worst then the other, more honing was done.The third and fourth set of bearings were installed and the clearance was checked. All is good tonight.

Good luck- - - - -you might have just ruined any chance of the bearings fitting correctly. The people who designed the engine took that possibility into consideration when they chose not to put an alignment step into the block. The cap is supposed to self-center when the bearing shells are in place so the only alignment that is required is the vertical oil clearance. The design of the bearing shells makes it virtually impossible to get a sideways misalignment if the caps are installed the way they were intended to be.
Jerry

fitment of the 3rd cap was improved after honing. Bearings 1,2 caps were offset by no more 1/2 thousand. Now the 3rd cap is also. The main was perfect in always.

After re-reading your post, I understand what you were doing. It appeared at first reading that you were honing the inside diameter of the bearing saddle, which has all sorts of possibilities for error. I have fitted non-original bearing caps to engine blocks at times, but I always line bore all the bearing caps afterwards. Most machinists refuse to do that on stovebolt blocks, since there are four different diameters to bore. My line bore tool can be set up with four separate cutters, so I can bore all the holes with one pass.
Jerry

Not for an engine with staggered main bearing bores but for the omnipresent SBC we had a heaping wheel barrow full of main bearing caps for the "lost", "misplaced", "never had" or broken. On each missing one we would try one after another from the wheel barrow till we had one that passed the fingernail test. With the cap torqued ONLY the one that matched the bore in the block would give a seamless mating surface and not hang a nail passed across the seam. Still bored or honed. On our race engines EVERYTHING was machined off of a mandrel through the main bearing bores; decks, pan rails, cylinders, even the bell housing surface. This along with balancing to 1/10 of one gram gave a longer lasting and cooler running engine.

Several years ago I retro-fitted a 305 Chevy engine for 4-bolt main bearing caps that were designed for that conversion. It was necessary to file-fit the caps for side to side concentricity, and then line bore the assembly afterwards. The step in the caps was slightly too wide so they could be fitted to the recess in the block. Then the main bearing webs were drilled and tapped for the extra bolts. That engine, with a 3.100" stroke crankshaft for a 262 V8 outran a bunch of engines 100 cubic inches bigger because all of us were limited to a 350 CFM carburetor and I could wind my engine 1,000 RPM tighter than they could! Check your private messages, please, Evan!
Jerry