Bottom engine rebuilt-splitting crankcase

[David1977]

I mamaged to splitt the crankcase today so thank you for help so far. Next step will be remove the conrods and check the crankshaft for wear .

[David1977]

Hello guys, today I had chance to remove conrods from crankshaft and made rough measurement . I used work shop instruction manual to compare the radius but I want to share with you what I found . I found out that he crank was already grinded once I think so I suppose to do second grindig ? Please have a look for my photos. Center journal has 1,643 - 1,616 inch .

[Groily]

Hmmmm . . .
Not sure about those readings David. Clearly there is some ovality but I would get your measurements confirmed to a higher degree of accuracy before making any decisions. Some of the ones you show in the pix are, to be honest, suspicious when compared to the standard and regrind sizes in the workshop manual you have consulted. Also, what do the journals look like? Are there ridges, or scoring, on them - or on the bearing shells?

As a next step, I would therefore see if there is a local engineering workshop that can measure the journals in multiple places with a high quality micrometer, not a digital vernier gauge. (I don't really trust them that much. I also quite often don't trust myself on these things even WITH decent micrometers, and therefore I like confirmation from people who do these things every day!)

I know that where you are this isn't necessarily going to be easy to deal with . . . but short cuts are risky and could be expensive. The radius questions could also be answered at the same time I think (if you provided the people with the data for the big ends and the centre main.)

[SPRIDDLER]

Groily has mentioned this elsewhere and I don't know which manual you're using but as I'm logged in and browsing and you decide on a regrind I'll mention the important guide to grinding crankshafts in this link below:

http://archives.jampot.dk/technical/Spe ... _twins.pdf

[Groily]

I think David's using the same data Spriddler, hence my suspicion of a misprint (or dodgy caliper) in his report on the centre main, where 1.64-anything-at-all isn't a possible number as that's bigger than standard.
Seems clear there is a fair bit of ovality on all three journals though, regardless of the accuracy of the measuring stick, hence suggestion to get a second opinion using better sticks, to be sure not to go further than necessary with another regrind. (And to get the state of those radii confirmed before proceeding, as their absence or damage can be fatal as many owners of twins including me can attest.)

It is quite difficult for people in some countries to get to grips with these engines, as there weren't any / many AMC agencies in Europe back in the day. Compared with the ubiquity of much-loved A7s, A10s and Triumphs various, plus more-than-a-few Nortons, our twins are actually quite rare and are an acquired taste. Even here in France, there aren't that many around, and the experience of folk like T&L Engineering isn't easily accessible.
Luckily, the Club and this forum are the lifelines . . . and relaxation of shipping policies from AMOC Spares, and the ever-present AMC Classic Spares, all make the machines practical propositions as regular rides. Plus - of course - their legendary reliability (says he!)

[David1977]

Hello Billy. Please what is the standart diametr for big end and centre . Tomorow I am going to local specialist who specializes for crankshaft grinding and he has all tools .

[Groily]

Hi David,

Standard sizes of the journals are these:

1.
BIG ENDS 1.62575" (maximum) 1.62525 (minimum)

2.
CENTRE BEARING 1.62675 (max) 1.62625 (min)

This data is listed on Page 4 of the workshop manual in the link you have.

The local engineers will need all the information on PAGE 24 of the workshop manual which gives all the regrind information down to '3rd Regrind' or "-30 thou" on the crankshaft.

In fact it is possible to grind further than that, and BIG END shells are available from the Club from Standard to 60 thousandths of an inch oversize (-60 of the crankshaft).
CENTRE BEARING shells are also available in the same sizes BUT there are no 10 thou oversize shells available at the moment as far as I can see.
See the Engine section, Twins, at https://www.amoc-parts.com//store/comer ... ategory=53 and the following page for the Big End parts, if you can access the AMOC Parts site.

Good luck with the engineers!
Bill

PS - VERY important to have or make the correct size grinding tool for the narrow centre bearing, which is the hard one to do I believe as it is so 'deep'.