Big 4 Big End

Some accurate measurements need to be made here to ascertain what is wrong using the original outer race and pin as a reference. I would not be comfortable if the outer race 'fell in'to the rod eye, without knowing the interference fit. I have found a new Alfa assembly to be a few thou out of spec from the original part, it doesn't take much.

I'd like to think Alpha have addressed their oversized assembly by now. I had the same issue this Spring.

Hi Ian, doesn't look like it and not what was agreed.

The boss asked for me to send the assembly back, along with the rod. When it returned it was a perfect fit. It was the assembly that was wrong.

Hi Ian. From what you say above, when the con-rod is heated the outer track is a pretty loose fit in it, so in this state there would be no compression on the outer track and will not have been compressed to a smaller diameter and it will be bigger anyway due to expansion....So surely to get the bearing back together you simply have to dunk the end of the con-rod with sleeve already in place again in boiling water to expand it. Then it MUST fit over the rollers as the whole assembly would have been sold originaly together as one piece proving the whole thing does fit together.

HOWEVER I am not saying there isn't a chance that once it is together and has cooled, the bearing will be so tight as not to turn, but then again I reckon that it could be OK and will revolve freely enough.

So try telling your mechanic to try heating the con-rod with the fitted outer track in a boiling pan of water first before attempting to fit it together over the rollers....Les

Never had to heat a con rod to get it over a roller bearing big end, it should be a sliding fit with it all at room temp. If you have to heat or wind the con rod on its too tight, difference between right clearance and too tight can be microns.

Have to agree John, this should be a slide fit, not even a push fit and certainly not a drive fit, facilitated by expanding the ring.

The proven fact is that Alpha retailed some oversized big end assemblies. I hope they have got to grips with that now as they are good bearings but as much use as a chocolate fireguard when not manufactured to spec.

Previously ian_burgess wrote:

Previously Neil Wyatt wrote:

I'd like to think Alpha have addressed their oversized assembly by now. I had the same issue this Spring.

Hi Neil thanks for your in put please tell me how you fixed it, did you have the ring honed

I have fitted a number of big end bearings over the last thirty years, not just Norton. I have always pressed them in and out cold. Sometimes the pin and rollers fit straight away but often they are tight or feel tight. Alpha may have had a problem but I think that it may depend on the condition and shape of the rod. when I did both my Velo and ES2, one was slightly tight and you could feel the rollers skidding and the Norton was too tight.

The answer and I believe the accepted way is to have the bearing ring honed in situ by an engineering company using a Delapena hone. As someone already commented, some careful measurement is required.

Colin