Jig to Hold Head in Lathe

[oexing]

Yes, Flo, that is why I posted the matter of reamers which do not necessarily produce perfectly round bores - and hones neither. There is the thing called body of constant width - German "Gleichdick" - which every Brit will know - the 50 Pence coin. You cannot measure these shapes with internal mics in case of defective bores - unless it is a triangular type for a three point mic. But these shapes may have 5 or 7 or 9 etc. "corners" so no way to get real sizes with 3 point mics. You can only get some idea that something is somehow wrong by looking at inconsistent mic readings.
Maybe the link below could give an idea about my effort of explanation.

Vic

Wundersames, Mathematisches, Gleichdicke

www.wundersamessammelsurium.info

 

[Cyborg]

Ouch, that looks too rough for me, just circular ground. Look at any needle or roller bearing inner race for suitable finish, that is my orientation about surface quality - no surface test equipment at home. In your place I´d do a lapping job on this conrod, but then it will be oversize for the rest of the bigend set you got. A used conrod will show polished surface where the rollers go, so I don´t think this to be a factor for skidding rollers. As to skidding there, it will be in no load areas, so no problem at all. There is some oil film for this reason. There is heavy skidding in another place with high load in an engine: The cam-and-follower assembly sees high skidding at high loads , is allright with decent oil supply, even though there is no rolling element between components. No, skidding is not a headache for me in needle or roller bearings, but I would not accept that Manx rod finish, reason for returning it.

Vic

I had a major brain fart when I posted that. I forgot about the fact that the race must be honed or lapped after installation.

 

[oexing]

Ah, allright, this is a conrod made of high tensile, no case hardened like my own. So you got the outer race for pressing in that has to be lapped for size and roundness. You do that yourself plus lapping ? You can certainly, no rocket science, get some 5 micron diamond paste and do a slotted cast iron lap ring not too wide as it has to wear parallel in operation for avoiding bellmouthed bores.

Vic

cast iron slotted lap ring on alu tapered mandrel:

 

[Cyborg]

Vic, the reason I said “major” brain fart is because I have actually lapped rod bearings to size in the past….. I was sober when I posted that photo so it has me a little concerned.

 

[Peter Holmes]

Post? Sublet work out? Get a grip on yourself man….

But whenever I have tried to correct a slightly out FF3 using my trusty Record No1 bench vice and a half round file the results have never been that good, hence the use of the postal services, and of course Maughan and Sons engineers, I think it is a wise decision.