Hard to turn crank while rebuilding GM 350

[salvageyard saviour]

I started working on this motor more than a few years ago and am just getting back to it.
Boat Background: 1972 24ft Starfire. Someone Frankensteined it badly. The 307 was replaced with a 78 350 and the Electric shift was geared for 120 -155 HP

Motor Background: casting #3970010 F48 date code - had a seized piston from water in cylinder #1. Cracked outer block water jacket. Planned to replace motor with 82 truck 350.

After disassembling decided to rebuild the 78 and save the 82 for a spare. As I also had extra parts from putting the truck engine back together.
I was able to knock the piston out without hurting the cylinder wall. Installed new piston and rings after honing wall. Honed rest of cylinders and cleaned rings and pistons. Reassembled with new bearings same size (crank and cam journals looked smooth and unscratched) ground and welded crack in jacket.

Here's the problem: when I tighten the mains the crank gets very hard to turn, especially after rear and middle caps. I did a plasti gauge for all the mains and seemed okay. The pistons seemed to move okay before installing crank.

What did I do wrong? Somehow got wrong bearings? Warped block or out of round crank? Installed crank wrong?

Getting frustrated, everything looks so good any suggestions of where to start?

 

[Scott Danforth]

Go back and measure journals and sadles

 

[alldodge]

Plastic gauge looked good, so might need to be line bored and the crank checked for straightness

 

[Bt Doctur]

mic the journals, install the bearings in the caps and torque to spec, mic the ID of the bearings

 

[Bondo]

Motor Background: casting #3970010 F48 date code - had a seized piston from water in cylinder #1. Cracked outer block water jacket. Planned to replace motor with 82 truck 350.

After disassembling decided to rebuild the 78 and save the 82 for a spare.

Ayuh,..... So yer rebuildin' a Cracked Block,..??..??

 

[salvageyard saviour]

Ayuh,..... So yer rebuildin' a Cracked Block,..??..??

I know, more time on my hands than brains.
Had the weld work on a 120 that I've been running for years since. Hopefully will work here also.
The cylinder and heads looked good, no cracks, just some discoloration from seized piston.

 

[salvageyard saviour]

I never did mic anything since I thought I was putting the same sizes back in.
It's been a year or two since I did it, but if I remember, the top mains were the .005 under from the factory. (Replaced with all new Clevite)
When I take the caps off and inspect the bearings, I see a shine on the sides where the bearings meet. I've only been turning it by hand.
I'll take it apart again and mic and do the math. Maybe I put the unders on the wrong half.

 

[alldodge]

I did a plasti gauge for all the mains

What did the plasti gauge show?

 

[Scott Danforth]

Motor Background: casting #3970010 F48 date code - had a seized piston from water in cylinder #1. Cracked outer block water jacket.
I was able to knock the piston out without hurting the cylinder wall. Installed new piston and rings after honing wall. Honed rest of cylinders and cleaned rings and pistons. Reassembled with new bearings same size (crank and cam journals looked smooth and unscratched) ground and welded crack in jacket.

I know, more time on my hands than brains.
Had the weld work on a 120 that I've been running for years since. Hopefully will work here also.
The cylinder and heads looked good, no cracks, just some discoloration from seized piston.

so how did you fix the bores on the overheated motor that had seized?

you stated you honed. did you use a sunnen ridgid hone system after boring, or did you use a useless dingleberry or spring-loaded 3-jaw deglazer?

because the block was overheated, the bore is no longer round. it is also tapered

the discoloration was when the motor bore and piston got to meet each other as the piston expanded well beyond its stock OD and the bore became egg shaped.

I bet if you run a bore gauge down it, you will find about .020" of taper and about the same amount of out-of-round

 

[salvageyard saviour]

Guess I should have mentioned this engine didn't die from oil starvation or overheating. Here in Michigan most cracked blocks are from freezing. The water in the cylinder came from a cracked exaust manifold and leaked past the open valve then sat in there for 15+ years. Thus seized piston. The rust in the cylinder was able to remove with the 3 stones or I wouldn't even be trying this with that much damage. Again more time than brains.

I did the Plastigage under the middle of each main cap, was between .0015 and .0020

I'm replacing bearings because I'm there and the old ones were starting to show pitting and fatigue.
Had a grandkid b-day to go to today, I'll start taking apart tomorrow to mic crank and journals

 

[kenny nunez]

Just a wild guess, is there a chance that the crankshaft is bent?

 

[salvageyard saviour]

I'm thinking more of a warped block from not being winterized. Have not measured anything yet, the only place that had micrometer and calipers in stock was HF.
Going to go get better today.
After starting to disassemble, dug old bearings out of scrap pile to double check sizes. Gave wrong info, the .0005 OS are the piston connector. All the mains were Std. Replaced everything with Std.
Just for giggles put the .0005 OS back in and it seems to turn a little easier.
Going to measure everything tonight.

 

[Scott Danforth]

a brand new production SBC block is only $800. a used block machined is about $350, a core block is $50

dont waste time on a junk block

 

[salvageyard saviour]

Think I got it.
Mains mic just as Plastigage shows
1-4 = .0015 and 5 = .0018
The connecting rods had problems
With STD bearings measured .001 and less a little
With old oversized measured .002 plus a little.
Going to get some .001 X of same brand and see if I can mix half and half with the new STD to keep at .002

Just want to mention for the average sane person.
DON'T try any of what I'm doing with an abused block.
It's a hobby of mine trying to save old metal from being turned into refrigerators.

 

[salvageyard saviour]

Update,
Ran on makeshift test stand.
Sounded really good for junk metal. Satisfactory compression. 135 to 145
The real story will be when I get oil pressure gauge to it

Thanks for the help and getting me back to bearing basics