Big end tolerance

[KerryAJS]

Just trying to find a tolerances for up and down movement of the Conrod on the Crankpin.. mine is just over one thou, measured as in the photo. In the Army reference book, it states 0.001" clearance between Crankpin and bearing as acceptable. I have to replace the timing side axle as it's damaged, so I guess replace the Crankpin and bearing while I'm at it.. what's the opinion?

[Les Howard]

With that small amount of wear it is perfectly acceptable to replace the rollers rather than the entire big end assembly...

[SPRIDDLER]

As Les, I wouldn't be concerned to use it provided that the crankpin and conrod liner were O.K., although it must be tempting to replace it whilst stripped down and merely as a precaution if you were planning a 10,00 mile foreign tour, but at £300 for a new assembly.......nah, it'll probably see you out.
As an aside, Russell Motors have stocked 1 thou oversize rollers in the past.
http://www.russellmotors.co.uk/

The big end on my '54 G3LS got a bit noisy but the crankpin wear was a tad over 1 thou.

Knackered crank pin..jpg

[g80csp11]

a bit noisy , was that with out your hearing aid turned on

[Les Howard]

Wow that is some wear Spriddler. I would be interested to know if the most worn side was at the top when the crank was at TDC or was it at the bottom?...I reckon slogging it hard at low revs would have caused the former and high revving would have caused the latter for the distinct wear you are showing....PS: If only we had the "React to Post" function switched on...I would have given a big laughing smiley to GS 80csp's post Maybe several others would have done...but we will never know...Oh well

[John Jarrett]

On the topic of big end failures... please see two examples.
No 1 (top) seized solid when the big end cage melted due to an oil circulation problem and would you believe No 2 (bottom) was running fine but just sounded a bit tappety!

IMG_20221229_122546.jpg

[Joker_Bones]

If you have 1 thou clearance/play, would 1 thou oversize rollers fit?

[KerryAJS]

Thanks Gentlemen, some interesting pictures there!! Yes, when I strip it, I'll have a look at the condition. @ Joke-Bones, I guess you'd have to purchase to see if the oversize rollers would fit?
As an aside, as I'm changing the timing side axle, should I get a new pinion/gear, old one looks ok, with a little bit of wear as per the cam gears, where do you stop!!

[Joker_Bones]

I don't how much oversize rollers for the crank pin cost, the 1 thou oversize rollers for the clutch are many times the cost of standard size.
I assume looking at your photo you have measured the clearance with the existing rollers in place and pulled/pushed from one extreme to the other. If oversize rollers were 1 thou bigger in diameter than what you have you would need at least 2 thou clearance to accommodate oversize rollers all around the pin, is that right?

[SPRIDDLER]

......should I get a new pinion/gear, old one looks ok, with a little bit of wear........

No. It'll be fine.
I don't know of anyone who has needed to fit a new one on account of just a bit of wear.

As 'ITMA', one of the wise old sages on the Forums and an ex AMC factory employee and latterly an AMC dealer in South London used to say:

'A half-worn original part will last longer than a new pattern part'.


Bearing in mind your commendable attention to detail are you sure you need to replace your t/s axle?

Wow that is some wear Spriddler. I would be interested to know if the most worn side was at the top when the crank was at TDC or was it at the bottom?...

I don't remember now, Les, and I doubt that I noticed at the time.

a bit noisy , was that with out your hearing aid turned on

It wasn't working, Thrifty.
You've forgotten that I had lent the battery to you for your digital caliper as you said you were too hard up to buy a new one.