Thumping noise when turning motor over by hand

[jimmyebay]

Rebuilding a 1987 johnson 175. Got all together but the intake. Waiting on reeds. All went smooth. Noticed when turning over by hand I get a thumping noise at certain points from the top 2 cylinders. Noticed if I put some upward pressure on the rod by crank, noise gone. Got rods aligned very well. All new bearings. Didn't see anything wrong with rods. Measured out good and not pitting/flaking. Any ideas?! Thanks.

 

[jimmyebay]

This noise is there when verticle/operational position. Lift the top two rods and gone. If lay motor down onto heads it's fine also. Gravity is doing something to cause binding. All ideas will help. Tempted to run it but don't want catastrophic failure. Be back at square one.

 

[Faztbullet]

Seal ring damaged,main/s not lined up on pins when front half installed,

 

[jimmyebay]

When installed the front half, went smooth as can be. Half fell right together. Made sure mains were in the pins. If I rotate motor so top cylinders piston is about 3/4 way up, clunks. If stop and back it up, clunks at same point. Take screw driver and slightly lift up on rod near crank pin, noise gone. Like rod binding on journal?!

 

[racerone]

How did you line up the connecting rod caps ?

 

[jimmyebay]

Lots of time with a sharp lead pencil. They seemed damn good! Just weird it's the top cylinders only

 

[Faztbullet]

did you have it bored ????

 

[jimmyebay]

Yes I did. .040

 

[Faztbullet]

Machine shop may not have bored cylinder all the way down into the aluminum below sleeve and this will leave a small step at bottom which piston will hit on ..

 

[jimmyebay]

It's all the way down. Investigated that before. Do notice the rods have slight amount of metal rolled up around the outer edge of big ends. Not sure been ran low on oil before. Vro bypassed but before project started, someone had slid 2 new pistons in it so maybe starved for oil before I got it. Or is the metal rolled up normal? Doubt it...