Square Four main bearings-line boring.....

[bob cottam]

Hi All, the ongoing rebuild of my `58 Square Four continues at positively glacial speed. I have fitted new Drags. white metal lined main bushes and now need to have the line boring done...... Anyone had this done lately?-any recommendations for a suitable engineering shop who can carry out the work for me??? Cheers, Bob.

[Paul_Linden]

Bob, where abouts are you? I can recommend a good place in Somerset that did mine.

[bob cottam]

Hi Paul,Thanks,I`m Up in Preston(well someone has to..) looks like its headed to T&L engineering at Bedford.From searching this forum, they have done this job recently for other members and got good feedback. Good Website,looks like they have the knowledge and skills needed!Bob.

[Alec.Elliot]

Hello Bob

Coventry Boring and Metalling did mine. (A bit closer than Bedford) Seems like a good job although I will really be able to let you know once I get everything back together and running!

[john.whiting]

The simplest way to check the job is to blue the journal,insert the crank and turn one turn,remove and see if the bearing is even.I would always check lineboring,unless I watched it being done.The temptation is great to put the half case on the table and bore to size.Regards John.

[bob cottam]

Hi John, wise words indeed!. I`ve been in touch with the engineering company that i had intended to do the job, but from conversation with them, it seems they intend to do just that- pick up on the bush bores and bore to size, they say they only need the crankcase half......Hmmmm.....
I think that is taking a risk, especially on sixty year old cases......

That said, the Ariel specs for running clearence in the main bushes is one and a half to two thou. That necessary clearence would produce a
lot of "Waggle" at the other end of the crank, allowing easy assembly of the cases with cranks in place, any inaccuracy would cause the crank to "lean" slightly in its bush- not ideal, but unless the cases were a long way out, it would be a minimal amount surely?.

It does puzzle me though, surely the bare cases would have originally been bolted together and bearing housings line bored at the factory -(and stamped as a matching pair as mine are), cases then parted, bushes fitted, and finally sized in a seperate boring/reaming op? (assuming the bushes themselves were accurately made). Any Production Machinists out there to enlighten me?

I wonder how many motors really are line bored during re-build, or just bored to size, with your average machine shop considering that accurate enough?

[nevhunter]

If you machine the faces (with step) and bearing locating surfaces at the same time, for each case, they must line up, when new.. The deck for the cylinder(s) is machined with cases clamped together as well as fettling around outside edges of the mating faces (for looks mainly). Some used cases will not be in alignment due distortion with use and where both sides have hardened bushes to run rollers in they should be honed as a pair to keep in good alignment, if possible. There is not a lot of material removed in this instance, but the fit is close so accuracy essential. '002" clearance for a whitemetal lined bearing will shorten it's life due more hammering, but a copper lead or alutin bearing needs clearances like those to provide extra oil flow for cooling as they have a higher frictional coefficient. They should also run on a hard shaft for best results. Nev

[john.whiting]

If you dont line bore,or line hone the assy,you will certainly have "spot contact" of the bearings.This will result in local seizure spots when the motor is first run,before the bearing wears to a running contact.If line boring/honing is not possible,then you will have to fit the bearing by scraping in.To expect a fifty year old split case to maintain its factory alignment is not realistic,and new from the factory the cases had manufacturing tolerances.Which is why the bearings were line bored/honed when the motor was assembled at the factory.More importantly,dont take a lot of B/S from machinists who cant be bothered doing the job right,but who charge top dollar.The most notorious example is the BSA A65,where the t/s main is often .015 out,and BSA relied on line reaming with a fixture that piloted on the timing gear bores to get things right.Regards John.

[Knud.Degnbol]

Old truck workshops had lots of guided adjustable reamers, which were formerly used to line ream kingpin bushes. Nowadays trucks don't have king pins, so those reamers are redundant. Look out for one. It can be used to line ream your bush.

[bob cottam]

Hi Knud, truth is, I`ve got one! with pilot, ready to go..... I got it intending to do the job myself, when i was going to fit plain lead bronze bushes, but after some thought I was unsure if this would be accurate enough, as the other end of the reamer is not supported and could "wander" a little. I have also opted for the white metal lined bushes now, and I wonder if the reamer would give a good enough finish on white metal? Bob.