Rod Bearing Question... Please Help

Hi Guys,

I'm new to the forum and new to Pontiacs.  I recently purchased a running 1968 GTO with a 400 and automatic transmission.  The guy told me the engine had just been rebuilt, but they did not take the time to clean it up and get it looking nice.  So the first thing I did was pull the engine and tear it apart, clean, bead blast, and paint all of the parts.  I pulled the crankshaft out to replace the rear main (it was leaking) I noticed every one of the rod bearing "locking tabs" were sheared off or shaved off.  All of the bearings were 1/4 to 1/2 turn from where they should be.  It seamed to run fine before, no knocking.  Is this some kind of high performance trick?  Ive rebuilt alot Ford engines and I've never seen or heard of anything like this.  I'd love to hear what you guys have to say about this.  By the way, the crank has been turned before, it's stamped .010/.010.

Thanks,
Jason  

i would come to a complete stop at that instant

do you have a micrometer and a standard to verify the calibration...

do you have some kind of dial bore gauge.. or snap gauge.. to use with your  micrometer..   rig a rod vice up.. so you can torque the rods to specs before you measure them...

could have been a DRY start.. where the assembly lube dripped out over time and there was no priming the oil pump done before first start up...

i will post some crank sizes and rod bore sizes probably tomorrow morning..  if i don't get to it later tonight..


the rod bearings are larger on the outside than the bore of the big end of the rod.. this is called bearing crush.. it holds the bearings in place.. prevents them from spinning in the big end..

with the rod bearing installed and the rod torqued to spec...  now you can measure the bearing bore size to see if you have the proper clearance...

its really easy for clearances to get off in a shop .. one guy machines the part for the high end of tolerance .. the other part is machined for the low end of tolerance... the parts just don't have the proper clearance...   even though they seem to fit..  

WOW, well first it would help to have a little more info. In addition to the good questions Waynepp has I also have just a couple. At his point all I can do is assume the following. Since you have rebuilt motors before you should know what a scored bearing or crank is etc. Is this the case? What shape are they in?

If the bearings are not scored which seems unlikely and the crank is not scored you have a mystery to me, here’s why.

If the bearings had the tabs on them originally and they are now gone it would only be because they lost oil, got dry seized onto the crank hard enough to spin in the journal. Your motor could not run once the bearings seized and you would have to chisel them off the crank, therefore with the limited info you have provided I can only guess that your clearances are fine and someone intentionally ground the tabs off for now worldly reason.

The bearing size will also be stamped on the back side. What are all the numbers and letters there?

The bearings are "clocked incorrectly" because they simply "floated" out of place, they could not easily be installed that way so it's likely unintentional.

The fact that they made no effort to claen the parts combined with your bearing problem strongly suggests to me anyway, that it was done by a pair of rocket scientists because engineering like this couldn't have possibly been thought up by just one person.

At this point I would check everything for proper size and wear like pistons, CYLINDER BORE, valve guides, etc.

Do at least check the measurements Waynepp suggested though.

Do you plan to replace the piston rings?

Post what you find if you like.  

numbers you will need.. print this.. paste it to the wall of your work area..

this is from a Clevite engine bearing catalog..    feel free to ask questions.. there are a LOT of serious engine machinists on this forum..  i am going to leave you in their hands...




this is JUST FOR THE 326, 350, 400 motors...

there are tiny differences for the 389 motors...

and serious differences for the 421, 428, 455 pontiac motors..


note the right hand column on the top row..

the ROD big end bore size is....   2.3745 to 2.3750..     thats half of a thousands variation..

the rod throw is at standard... 2.2487 to 2.2497

but you said the crank is -010"  ten under..

so that would put the crank at 2.2387 to 2.2397        thats a whole 0.001 of possible variation..

but the rod vertical oil clearance shows.. 0.0015 to  0.0040   so thats .0025 possible variation.. but this is determined by how the crank is ground then polished..  do you want tight rod clearances..  to you want loose. depends on usage..   smarter heads than i will give you an answer..

i should also state that one engine rebuilding shop i worked in.. the boss and i were boring and honing late into the evening as he had fired the last few machinists do to poor clearance issues on the bores...  he picked up the sunnen dial bore gauge and dropped it into the master setting gauge.. and i noticed that  the needle bounced as he inserted it.. what the heck.. i grabbed the setting standards and looked at the BIG DEEP dents in the ends where the carbide balls on the dial bore gauge rubbed against the standards..  that brought everything to a stop and explained why the sleeves the previous guy had bored allowed the sleeves to freefall into the block...  the next morning the sunnen rep came out and looked.. grabbed our entire kit.. carried it to his car and left his almost new one..  he had never seen such a worn set of standards..

oh.. and for the machine shop guys.. a tip... chevy vega timing belts will fix a stripped drive belt on a sunnen CK10... as they are only one tooth longer but slightly thicker because of the micro V grooving on the back side to drive the water pump.. .. if there are any CK10 models left after 40 years of service..


lastly.. see the device between the anvils of the 2 calipers on the right.. those should be exactly 1.000 and 2.000" long.. so you can close the micrometer down on them at the proper tension and prove the caliper is accurate...

 

this is the cheep way to measure the ID of a bore



i have personally been thinking of one of these for a while.. they are only 20 bucks..  i don't know how sharp the tip is.. but unlike a micrometer you cannot judge if its just a little over or a little under unless you have one that reads.. 0.0001 instead of these at 0.001 resolution



more money spent on precision measuring tools.. is a good thing as if you take care of them and DON'T drop them..  they can last a lifetime if you don't wear them out with massive amounts of use.. .  

Jason

That was the smartest move you could ever have done. Pull the engine. All you had to do was drive that engine hard a few times and it would have been junk.
 I agree with Wayne. the more you spend on precision tools the longer they will last. (+1 Just don't drop them). I have a set of micrometers that are 1960. I have them checked every year. The same with the rest of my engine tools.
  If you use your mics once in a while keep a little machine oil on the shafts. By Machine oil I use Singer Sewing machine oil, I have had since I can't remember. Well enough of that. You saved your engine.  


Bob Aka-pepsi1  

Jason.

I purchased a beautifull Big Block 427/435 1968 Camaro from a guy. The car and engine were as clean as you would want them to be. All the numbers were correct ETC. He told me the engine had about 15 passes on it. He only started it for me as it was 20* out. I did see the car run on video....But there was something that it just bothered me?...A gut thing if you will!
  I got the car home. I said to my son drain the coolant and oil, I'm going to pull the engine out. My son said the guy told you it was just done. Blah,Blah,Blah. I said I don't care what he said just do that for me Okay!
  I took the pan off the engine, same as you the engine bearings were getting ready to puke. The reason: They installed a short (OR STOCK) oil pump pick-up on a deep 9quart oil pan. I saw the videos this Hot-Rod was almost on the back bumper...So you could understand when the front end was in the air the engine had no oil pressure....
  I went back to the guy I bought the car from. I just wanted him to see what I found. He had the engine built by a Pro. But it still came down to apples and oranges. Who did what. Did someone order the wrong pan and oil pump combination? It was done correctly anyway.
  You did the correct thing if your gut tells you something go with it. Your engine being dirty was a tell-tale sign. I'll tell you what they did. They through bearings in the engine, with the engine in the car. They shaved the tabs enough to slide the shells in the rod part. They would have hammered out and you would have been up the creek. Nice catch....You should give yourself an ATTA-BOY!

Bob Aka-pepsi1  

What I didn't mention is this. The oil pan measured 10.1/4" deep. The oil pump with the pickup that was on it measured 6.3/4" deep. 3.5" difference. He told me they only put 6 quarts of oil in the crank case. (No dip stick). I don't know how that engine lived.
  It also shows how the driver was never concerned about oil pressure, I'm sure he didn't notice water temp. either. I watched the films and as I said that Hot Rod was in the air. Big Blocks aren't like small blocks. That engine should have blown up????

Bob Aka-pepsi1  

Make sure you install the rods bearings to clear the crank fillet.  I made up a few pics..

http://firstgenfirebird.org/forums/ubbthreads.php?ubb=showflat&Number=258166#Post258166

A write up from Kelly who had issues with this..


http://www3.telus.net/public/68bird/engine_mistake.htm