The Stovebolt Site Forums The Shop Area Engine Shop Chevy 283 main bearing clearace question

I just got my 283 block back from the machine shop.They bored the block 0.30 and turned the crank 0.10 on the main and rod journals.I just checked my main bearing clearance with plastic gauge and this is what I am getting.on the front main cap
#1 .004
#2 .0015
#3 .001
#4 .001
#5 .0015
The #1 is what I dont like .This is out of the .003 spec .Would you guys be concerned about this or run it like it is.I check it twice to make sure and I got the same reading.
Thank you for your help .
Jim

plastic gage is ok but it really should be check with a dial bore gage, and torqued to 65 lbs. .004 will bleed oil from that main,and starve that rod bearing because of the loss of oil at the main(the rod get feed from the #1main), take it back and have them check it, you may get away with just cutting the cap to tighten up the clearance,baldybenny

Okay ,just to see what would happen I switched cap 1 and 4 and torqued and checked them again and I got .002 on both 1 and 4 ?
What do make of that?
Thanks Jim

I would think that you need to measure the journals.

It's not a good idea to be swapping main caps to different positions.

As Don said, its not advisable to just randomly swap main caps unless you have a dial bore gage to confirm they actually fit that main saddle. You should take it back to the machine shop so they can verify that the caps are not in the wrong position and number them for you. Unless you numbered the connecting rods and caps, they should check them and number them for you as well. Plastigage is only good for checking the clearance at the exact spot you place it on the crank journal, it cant tell you what is happening at other places around the housing bore.

Yes, don't be swapping main caps around. Unless of course you got them mixed up in the first place. You need to check for dimension, and out of round of the bearing bores in the block with the caps installed and torqued to the proper spec. check the crank journals. Install the bearings in the bores without the crank and once again, torqued to the proper spec. Set up the dial bore gauge with a micrometer. You should see some eccentricity with the area 90 degrees from the separation line of the bearing cap being the number you want to see, while if you turn the gage right or left it should get incrementally larger somewhere in the range of .002" (I can't remember for sure, but just look it up). If it comes down to it you could just turn the one journal down to the next size smaller and get a single bearing. (remember in the inlines, EVERY journal is different size) If you cut the cap, without line boring, you would essentially be making the hole oval, assuming of course it was round to begin with, not to mention off center. To summarize, there are a few issues that could be at play here. the bore is too big, the bearing is out of spec, or the crank got turned too small. Each situation requires something diferent, if the bore is too big, you will need to have the cap(s) cut and line bored, the bearing would need to be replaced ( I would assume at someone else's expense), and if they ground the crank to the wrong size, I would assume they would be responsible for that as well, I do know if it was mine, they would find me another crankshaft and make it the way I was paying them to make it. I got very cynical during the rebuild of my last engine, I made so many trips to the machine shop, I had to take the head in 4 times before it got right. The cam grinders lost my brand new cam, that had never been in an engine, never did find it. If I had the money, I would buy all the equipment and do it myself.

The 283 I just put together had the number cast onto the cap. Wasn't any question about which cap went where and didn't have to number them. Also make sure you install the cap with the cast arrow pointing toward the front of the engine.

If the block is out of spec then it will need to be line bored to correct it.

And they bored it way out of tolerance at .3, I think you mean .03 ??

It is either likely they goofed up on the grinding of the journal or the bearing shell is not correct. You need to find someone that can measure everything. The plasigage is fine to find a problem but its not going to tell whats causing the problem.

Did they line bore the block, or just bore the cylinders and turn the crank?