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Big end bearing Shells question

U

unk-tantor

Just got it firing!
Joined
Jan 8, 2011
Messages
4
I am in the process of restoring my 77 T3 , I've replaced the barrels and pistons but there seems to be some wear of the small ends obviously the removal of the con-rods is necessary to enable this and so the replacement of the con-rod bolts and the bearing shells, what I'm trying to figure out is
A: Are my bearing shells showing excessive wear?
B: the best way to confirm what size shell bearing I have.

I intend to replace the shells anyway but just want to establish if they show signs of excessive wear and ensure I get the correct sized shells ( I am the thirteenth registered owner for this bike!!!). On the back of the shells is the marking 'BT-20'

P6250148.jpg


P6250149.jpg

Any advice would be appreciated.
 
Measure the crankpin, measure and if needed get the rods re-sized choose shells accordingly.

Yes, I'd say those shells have done their work.

Don't forget to clean out the sludge trap.

Pete
 
Only one standard size these days + O/sizes. The various standard sizes in the manuals (So the legends tell) was to accomodate machining tolorances/variations etc.
Look for out of roundness in the big end journals and any signs of scoring and skuffing (my own have chewed a set of big ends +300k KM ago and not been resized) just plonked in a set of standard shells. She's also had a small end set in a full resto a little while back but still runs the original rear main in spec with 400,000km under her belt.
 
Thanks, This project is suffering from serious mission creep.
This was meant to be just a new clutch and new Barrel and Piston kit plopped onto the bike but I needed a inlet stud removed from the heads and when it went to the shop I got the valves guides checked and found wear so had K-liners inserted and while I had the frame off I thought I might as well get the frame and other bits powder coated. The rods as I previously said need to have new small ends. I wasn't planning to pull out the crank and clear out the sludge but at this stage its hard to justify any reason not to.Apart from laziness and cheap-skating.
I'm fairly certain that the crank is the original size but my digital vernier is a cheap one that only measures down to hundredths of a mm. Can't really get an accurate enough reading on the pin or from the bore gauges to be useful.
Guess I need to get a micrometer or take it to a shop.
 
You can measure your big end clearance with these http://www.plastigaugeusa.com/ I'm sure there is an equivalent in the UK. Once you measure the crank journal, you can decide if you need to do a grind, or just use standard or over size big end shells. Desired clearance is 0.000433 - 0.0024 inch or 0.011 - 0.061mm. Also side clearance should be 0.0118 - 0.0196 inch, or 0.3 - 0.5mm.
 
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