Main Bearing, Line Boring

[AlanBartlett]

I was wondering if anyone could tell me the process of this, how an engineer does? Whats the purpose, how it differs from cylinder boring. I know this may sound a dim thing to ask but am just curious as to what is involved.

[Keith Clements]

With cylinder boring it is not so critical to align all the holes as on main bearings where each one has to be within .0005" so that the cranshaft can turn without binding. Thus all three holes are bored in one operation with the block halves together.
cylinders do need to be at 90deg to the axis of the crankshaft but I do not know what the tolerance should be.

[george garside]

I have a vague recollection of someone in the club having a hand opperated boring bar for the twin mainn bearings or was it a part of the clubs tool library? Perhaps Ian priestley will know the whereabouts of one.

george

[Tony Fearn]

I have a vague recollection of someone in the club having a hand-operated boring bar for the twin main bearings.

So have I George, and I think it was George Nicholson (from Kendal) some years ago. I also have a feeling that it was advertised in a Jowetteer, but don't know where it went.

Alan. I didn't reply to your original post because this is outside of my knowledge.

Tony.

[george garside]

Tony, so it looks as if somebody somewhere may have it! Again a dim memory but I have a feeling that it was one originally suppied by the factory to main agents for use when renewing main bearings etc.. All the twins needed line boring including most of the CC models exept the very late ones which I assume had a crancase/bearing modification intended to eliminate the need for line boring on the CD's ?

george

[AlanBartlett]

Thanks for all the comments, well after long chat with the engineer whos doing some of my work, he explained what they do and how its done, so I've now got a little idea of what goes on. Another question has cropped up, I know that a while ago JCS have made up new mains and sell them, but are they finished or unfinished sizes, has anybody had any encounters with mains from jcs?

[Keith Clements]

Probably worth sending a Request via jowett.org to Spares.

[AlanBartlett]

I didn't realize JCS was connected too Jowett Talk? Can you connect with them? Via online method?

[Keith Clements]

Look at the top of this page and follow the link. A request sends an email. It is not a chat session or other type of communication.

[AlanBartlett]

Email is fine, I just didn't realize were able to contact people like that online via email.