Chevy 350 Engine Bearing Problem

Reply

  #1  
Old 09-19-06, 11:09 AM
Member
Thread Starter
Join Date: Aug 2006
Posts: 9
Chevy 350 Engine Bearing Problem

Hopefully someone might be able to help me here. I am rebuilding a sbc 350 motor. I got the crank ground .010 on the rod and mains. The bearings are all .010 as well. I had the walls .040 over, new rings and pistons also.

When I put the crank in, I went 75 ft lbs on all main caps. Crank was fine and turned smoothly, and all bearings had 2-3 thousanths clearance which the machine shop told me was just right. When I put the rods and pistons in, again all clearance was good but at 35 ft lbs on cap bolts the crank would not turn at all. The cap nuts are 9/16 don't know what size the stud is, but i noticed that the torque spec is different for all stud sizes. So I even went down to 15 ft lbs on the nuts, and the crank will turn but it turns at 60-70 ft lbs on the harmonic balancer bolt. When the heads are on, it won't turn at all!! So i took it all apart and the bearings are all marked up and in some places the dull silver color is gone, its a really shinny chrome color, all the coating is wore off on the edges and sometimes the middle of the bearing, even the main bearings which i thought were turning smooth are scuffed up. so i asume the bearing clearance is wrong, but why would the plastiguage show that its OK, and why would both sets of bearings be so far off. Am i maybe messing up the measuring? I'm using the red plastiguage.

What should i check for? any help would be greatly appreciated

thanx
 
Sponsored Links
  #2  
Old 09-19-06, 07:39 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,673
350 chevy engine

Corvette:

Your tolerances of three thousandths on a rod and main are ok. Did you lube the bearings before you put them in? Use a white lithium based grease if you didn't. Also lube the cylinder wall with oil and wipe off the excess.

Are your bearings scuffed or is the surface just shiney instead of the dull babbot color. If your plasti-guage is reading the clearance you've said and you have taken it at the prescribed torque specs, you should be ok. Adding the heads isn't changing anything where the crank is concerned, so don't worry about it. If you want them on there leave out the plugs until you have the crank working.

First make sure you have the correct torque specs for the rod caps and mains. It won't mean anything to check a tolerance without the proper torque.

35 ft lbs sounds a little low for a 3/8 stud. Just make sure of what you're using, those specs are critical. Clean and lube the bearings/crank and assemble the caps. Then tighten the nut/bolts to about 5lbs over the spec. Then loosen each to about ten below the spec and retighten to the spec.

If your bearings weren't lubed prior to assembly the first time and they have been gouged they would have to be replaced. If they're just polished a little, I would use them.

I suspect what has happened is the drag of the pistons on the newly bored cylinder walls has made turning the crank difficult. This added to just rotating the extra parts required a lot of extra effort.

You probably don't have a major problem yet, just make sure you have the torque specs correct and lube everything.

Let us know how you come out,

Hope this helps,

Bob
 
  #3  
Old 09-20-06, 12:24 PM
Member
Thread Starter
Join Date: Aug 2006
Posts: 9
hey bob, thanx for the info

what i have run into is...........
some of the bearings are just shooth and shinny, but others are very very badly scuffed. the crank was so hard to turn i was stripping the threads on the harmonic balancer bolt.

Some other people have told me maybe the rod caps are mixed up, unfortunatley they are not stamped.

The other funny thing is that the crank was smooth until i put in the pistons and rods, but the main bearings were scuffed too. so i don't know if they got scuffed only because i had to put so much effort into turning the crank with the rods on.
 
  #4  
Old 09-20-06, 12:39 PM
Member
Join Date: May 2006
Location: Iowa!!!!!
Posts: 3,673
Did you have the bearing locater tab in the notch in the rod and cap respectively? Also make sure you haven't rotated the cap 180 degrees on the rod.

The mains should be marked front to rear with a cast in arrow pointing to the front.

If you're having damage like that, you'll have to work through the rods and bearing caps one at a time, assembling them to the journals, then checking them for movement. I wouldn't put a damaged rod bearing back into an assembly.

If you can't get it worked out, I would take them all to the machine shop and get them matched up for you.

Bob
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'