Big End Advise Please

[Stuart Giles]

As AIS says, lots of motors came from the factory with shimmed white metal big ends. US car makers were still doing this in the '50s, the shims were there to be removed as wear occurred during the motor's life.

But on an A7 motor where this has been done, I'd be keen to check the fit of the cap to the rod, just in case someone has filed the cap and been a bit over enthusiastic, and then tried to fix it with shims. Several motors I've come across where the caps have been filed they don't seat properly on the rod when the cap is pushed down onto the rod with light finger pressure. Pulling down the cap with the big end bolts will "fix" this but the resultant bending load on the BE bolts is just asking for an expensive failure when the motor is run. A bit of gentle fitting with a file and scraper on the cap face has sorted this before boring the big end to size. If the whizzy little boring tool used by white metallers isn't available, a micrometer boring head in a mill will do the same job once the rod is set up parallel to the mill table. A bearing scraper will do the same job if the bearing is close to size.