1963 88.
The drive side big end eye, without shells, measures perfectly round, but the timing side is 0.005" bigger across a certain diagonal, corresponding to shiny areas, compared to the evenly lined surface elsewhere.
I can't see how wear could occur under a big end shell, but I imagine it would suggest the shells would be less well supported in the shiny areas.
As far as I know it's always been like this without causing any problems that I'm aware of. So does it matter?
I'll try to attach some images, but this often gives me difficulties. Last time I tried, the whole post disappeared.
Attachments 20140703193119-jpg 20140703193534.jpgOld rods have been found t…
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It could be that the rod i…
It could be that the rod is beginning to stretch at the big end. If that is the case I would be wary of reusing the rod. That said, when con rods do fail, it is usually at the top of the rod where the small end eye opens out rather than at the big end. If you dodecide to reuse it,I would suggest you keep to a sensible rev limit.
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I would be putting my mone…
I would be putting my money on the bolts stretching as being part of the cause of this issue. This in turn has allowed a slight movement of the shells and the fretting away of the big end eye. I would suggest that all the chunks are replaced. 88/99 conrods are readily available through the likes of eBay and A/Js. There is no real need to fork out £200 for new conrods when good second hand items can be obtained for far less. Try the NOC Spares Scheme.
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Some useful replies there,…
Some useful replies there, thanks.
As it happens, I bought an old conrod from NOC Spares a while back, just in case it came in useful one day. Maybe that day has arrived. There aren't any shiny areas so I'm hopeful it's OK. I'll get my friend with the professional bore measuring equipment to check it for ovality. He can also do crack testing using a dye method, which might be a sensible precaution given that I don't know its history.
He did mention the possibility of getting the stretched rod re-sized, but after my recent experiences with so-called expert engineers I'm not hopeful of finding anyone competent to do it, not to mention the expense.
Now I just need to decide whether my re-ground crank is safe to use. (That's a plug for my other recent post "Big end journal radius", by the way!)
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Old rods have been found to be oval , polished areas with a tighter measurement seem to suggest movement of the shells.A good engineer could re-size these ,The cost of doing this compared to new rods from Thunder needs to be considered ,what with the fatigue that old rods must have. As a poor shade tree mechanic,i would polish up the meeting faces of the rod and cap and refit with some plastiguage to check clearance on the crank.If ok and rod free on crank I would use in a classic thats going to have light use.But then I'm a bit of a chancer!!.