30 replies to this topic

[Spider]

 

 

Center cap the right way around?

 

^ This was my first thought, my next is what condition are the hollow dowels in ?

 

There are a couple of nicks on them where they were gripped to pull them out, prior to machining the block.

 

 

They need to be perfectly clean.they are there to locate the cap absolute. the nicks can easily push it off. Even as much as 1/20th of one thousandth of an inch is enough to give issues. Assemble and Torque the caps to the block, the right way around, without the crank of bearing shells. While not the ultimate way of testing, feel with your finger or even the edge of a 0.001" feeler gauge across all the cap to block mating points to see if there any step there. Check from the cap to the block and the block to the cap. They must align firm on the dowels and have no step.

[poohbah]

 

 

Center cap the right way around?

I believe so.  The lettering on the top is in the same orientation as the lettering on the other caps.

 

 

I wouldn't rely on that.  The cap should be placed such that the tangs on the bearing shells go together on the same side of the crank

 

Thanks.  That happens to be the same too.

[poohbah]

 

 

 

Center cap the right way around?

 

^ This was my first thought, my next is what condition are the hollow dowels in ?

 

There are a couple of nicks on them where they were gripped to pull them out, prior to machining the block.

 

 

They need to be perfectly clean.they are there to locate the cap absolute. the nicks can easily push it off. Even as much as 1/20th of one thousandth of an inch is enough to give issues. Assemble and Torque the caps to the block, the right way around, without the crank of bearing shells. While not the ultimate way of testing, feel with your finger or even the edge of a 0.001" feeler gauge across all the cap to block mating points to see if there any step there. Check from the cap to the block and the block to the cap. They must align firm on the dowels and have no step.

 

 

Many thanks for this.  I will try this and let you know how it goes.  Looking at their condition it could well be this.

Edited by poohbah, 10 February 2022 - 06:22 PM.

[poohbah]

If you have a DTI it might be worth checking how much run out there is on the centre journal

All of the journals are spot on, but I think it may be the dowels as noted elsewhere on this post.

[poohbah]

New dowels from Swiftune ordered, so I shall see how they get on.

[Gaz66]

Did you check to make sure the new shells are the same size as the old ones?

[poohbah]

Hopefully!

[Cooperman]

The last time I experienced this it was because the centre main crankshaft journal was not concentric with the mains at each end. It was only a couple of thou, but that was enough.
The solution was to re-grind the mains to the next size - another 10 thou.

[poohbah]

I have fitted the new dowels (top quality items, by the way, from Swiftune).  There is still binding when just the centre main cap is fitted.  Next step, I think, is to get the crankshaft mains checked for concentricity.   

[GraemeC]

Although you have checked the centre cap is on the correct way round, just try it the other way.  It may always have been wrong.  You've nothing to lose!

[Gaz66]

And put the old shells back in if you have them

[Earwax]

Swap out mains bearing, just to make sure no dirt has been embedded first?

[poohbah]

Thanks chaps.  Removing everything, cleaning meticulously and refitting solved the issue.  I guess the tolerances are so fine that even the slightest misalignment somewhere causes a big problem.  

Thanks again for all your help.

[mini13]

sounds like it could have been the dowels causing a slight misalignment, it dosent take a lot.

 

I always run a stone over the back of the bearings to check theres no burrs on the stamping where the letters are, also, clean clean clean!

[poohbah]

The last time I experienced this it was because the centre main crankshaft journal was not concentric with the mains at each end. It was only a couple of thou, but that was enough.
The solution was to re-grind the mains to the next size - another 10 thou.

Thanks for this, and sorry to revive this thread, but I am still not happy as there is binding.  I have measured the runout at the centre main, with the two end mains torqued down.  I am getting 0.01 mm deviation on the centre main journal.  I think this equates to only 0.4 thou.  Is this enough to cause the crank to bind?  It runs beautifully smooth and free when just torqued down on the two end bearings.