964 build with crankshaft turnover binding issue(s)

Old ITW · 12-12-2023, 02:08 PM

This is the start of a complete rebuild with the crank/rods assembled and the case back together. The rods are suspended from the head studs with rubber bands and the engine turned over by hand via the crank pulley. The chains are hanging with the cam side chain sprockets in place. At multiple positions in a clockwise turnover the assembly binds up with a hard stop. Flicking the rod ends, which have always been free moving, and lifting the chains can, but does not always ease the binding. A slight, few degree, counterclockwise rotation will release the binding only to have the same hard stop repeat with sometimes less than a 90 degree clockwise turnover. I would like to have some idea of where the binding is occurring before I tear the case down. My sense is that the intermediate shaft chain sprockets and/or the chains are the issue. I would appreciate any ideas on how to diagnose the binding issue(s).

Are the connecting rods symmetrical, meaning can they be installed with the stamped numbers up or down?

The chains can be installed in two orientations is there a correct orientation that I have missed? If I am not able to determine a cause or causes of the binding I will tear it down and dry assemble the case without the chains to test for binding.

Any comments or suggestions are appreciated.

Old H2S · 12-12-2023, 02:32 PM

Chains are omnidirectional.
Get stronger rubber bands.
The rods will hit the case if they are not centered all the time.
Get a friend to help hold the rods while you turn.
The chains must be hanging down tight to keep from knotting up inside the case.
Then get back to use if you still have actual crankshaft to main bearing binding..

Old ITW · 12-12-2023, 03:38 PM

It is good to know that the chains are omnidirectional. The rubber bands I’m using are strong keeping the rods centered. Then you wrote having the chains “hang down tight”. I was skeptical, … what is “tight”? So I put some weight on the sprockets and engine turned better, but still would bind. While turning the crank over I looked to where the chains enter and exit the case and noticed that ONLY on the 456 side of the engine the section of the chain coming out of the case would move smoothly and then hang up for a few links and then would bind. So, I pulled on the 46 side sprocket out perpendicular to the case keeping enough tension on the chain to prevent the links from catching and that allowed the engine to turn over smooth! I’m all smiles … problem solved. I’ll sleep better Many Thanks Old H2S

Old ITW · 12-12-2023, 03:59 PM

It is good to know that the chains are omnidirectional. The rubber bands I’m using are strong keeping the rods centered. Then you wrote having the chains “hang down tight”. I was skeptical, … what is “tight”? So I put some weight on the sprockets and engine turned better, but still would bind. While turning the crank over I looked to where the chains enter and exit the case and noticed that ONLY on the 456 side of the engine the section of the chain coming out of the case would move smoothly and then hang up for a few links and then would bind. So, I pulled on the 46 side sprocket out perpendicular to the case keeping enough tension on the chain to prevent the links from catching and that allowed the engine to turn over smooth! I’m all smiles … problem solved. I’ll sleep better Many Thanks Old H2S

stownsen914 · 12-12-2023, 05:14 PM

The chains can "bunch up" inside the case and stop things from turning, something to check.

JoeMag · 12-13-2023, 08:55 AM

If the chains are hanging out of the motor with no chain box attached, put some tape over the studs (that are used to attach the chain box) that the chain is riding over to give them a smooth surface to ride over. Building my next race motor and just had same issue.

Remember on the left side the "lower" part of the chain is pulling into the case over the studs and on the right side the lower part of the chain is pulled out of the case over the studs by the weight of the gear you have in the chain.

mikedsilva · 12-13-2023, 12:51 PM

Post a pic so we can see exactly how you are centering the rods with the rubber bands. Are you using 2 bands per rod, or only 1?

Rotate engine 90degrees on your stand.
Bottom chain will hang out.

Rubber bands should keep rods centred.

hold "top chain" vertical and suspend with a finger.

Rotate crank with ratchet handle.

If you still have resistance somewhere, check that your chains are correctly mounted on the sprockets.

If they are, pull it all apart and start again. Something is very wrong.
Maybe you fit one or more rod caps back to front.