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+--- Thread: Big End Advise Please (/showthread.php?tid=174)
Big End Advise Please - Mark McKibbin - 31-08-2017
The special I am restoring is one of those purchases that in hind sight should have been avoided at all costs, but the up side is that as everything was knackered, it's has been educational. I have just removed the head and the sump assuming it would be like the rest of the car and was surprised to find the it looks like the engine had been reconditioned as the pistons are 60 thou. OS and there is very little carbon build up in the head and no lip in the bores.
I have attached a photo of one of the big ends (with dodgy split pin work) and it looks like there is some brass shim between the caps so I assume when it was assembled there was not enough clearance?
Also the big end bolts seem to be a mixed lot although the small end bolts look new and have tab washers.
When I bought the car the engine ran and sounded OK in the couple of hundred yards that I drove it.
As the head and sump is off what would you do?
RE: Big End Advise Please - Ruairidh Dunford - 31-08-2017
Mark,
I have dismantled a number of engines that have had this type of shim placed in them - personally I always remove them and re-white metal the rod or line bore to suit having had the crank re-ground. I presume that they are used when caps have been filed or the rod is being fitted to a larger journal.
I always replace the big end bolts with new and use nylocks instead of split pins.
I always replace the little end bolts with new and use a spring washer and Loctite in preference of the tab washer.
If any of these bits let go it can get expensive very quickly.
RE: Big End Advise Please - "Slack Alice" Simon - 31-08-2017
I shimmed a big end, in a hotel car park, at night, in the snow, on the way up to the 1982 JOGLE run.
The crank had been re-ground, and the rods re-metalled, but something wasn't right and the shim was the only way to loosen off the engine.
In preparation for the 2012 run, I found the crank to be cracked, and changed it. The shims were still in place and the metal fine.
We hadn't done a lot of miles in the meantime, less than 10,000 I guess, but the bodge worked.
I would put the rod on without the shim - of course, it may not tighten up, but if it does, blue it and see where the problem lies. Maybe a bit of scraping will sort it.
If not, I would put it back and run it - but that is the way I usually work. My engines are un-modified, and not worked hard. I don't count JOGLE in under 24 hours as "working hard" in a lightweight special.
Simon
RE: Big End Advise Please - Robert Leigh - 31-08-2017
(31-08-2017, 09:33 AM)Ruairidh Dunford Wrote: Mark,I agree with Ruairidh. Assuming the crank proves to be in good condition with cylindrical crankpins line boring the rods to suit (without the shims) will enable you to throw away that botch. I have hand scraped big ends to fit the crank with good results, not having a line boring facility, and being unable to find anyone who would do it without re-metalling first. It's not a task for the inexperienced, but my fitting lasted 25,000 miles of hard driving at up to 6500 rpm, before other things led to an engine rebuild. Most old big end bolts have been stretched by overtightening to get the split pin in the next hole. Use new with nyloks every time.
I have dismantled a number of engines that have had this type of shim placed in them - personally I always remove them and re-white metal the rod or line bore to suit having had the crank re-ground. I presume that they are used when caps have been filed or the rod is being fitted to a larger journal.
I always replace the big end bolts with new and use nylocks instead of split pins.
I always replace the little end bolts with new and use a spring washer and Loctite in preference of the tab washer.
If any of these bits let go it can get expensive very quickly.
RE: Big End Advise Please - Austin in the Shed - 31-08-2017
I didn't think the brass shims were a bodge,more of "The old way" of whitemetalling allowing a means of taking up the wear.I'm sure this method was used in marine and other industrial applications.
RE: Big End Advise Please - Ruairidh Dunford - 31-08-2017
I have certainly seen enough of them to suggest that they were used as you suggest AiS, some look to have been professionally made.
Robert - I line bore almost the rods I use in my workshop. Hugh has seen the set up and, if you need some done in the future, get in touch.
RE: Big End Advise Please - Mark McKibbin - 31-08-2017
Thanks everyone for your help. I will definitely use new BE bolts and nyloks and new Small End bolts
Can I check the clearance with Flexigauge to see if the clearance is actually OK, I have never used it before and am not sure if it's appropriate in this case
RE: Big End Advise Please - Ruairidh Dunford - 31-08-2017
I have never used the stuff.
I use feel and engineers blue.
RE: Big End Advise Please - Stuart Giles - 31-08-2017
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.
RE: Big End Advise Please - Bob Culver - 31-08-2017
A fitted bearing may have almost no clearance so is not well suited to Flexiiguage type product. Care also necessary with old stock whcih becomes too hard.
Effective economica and completely reliable solutions are regularly dismissed as bodges on this forum. A neatly fitted shim to correct poorly fitted halves or to simplify the refitting to a larger shaft is not a bodge.
Shims can be shaped so that when flush with the exterior surface, not rubbing on the shaft.