Originally Posted by gunner
Have a look at this YouTube video - Here which shows one way to line bore the timing side bush.

Note that careful measurements are made with the cases assembled to check the drive side housing is Concentric, then the drive side is removed and the timing side is also checked for concentricity.

By using a mill with the cases bolted down the result should be that the timing side bush is perfectly Concentric with the drive side once bored.

There are other ways to do this but using a solid mill seems best.

Yes that is the right way as long as you are completely confident that the split face and the outer face are dead parallel ....by the look of the gear the guy in the vid has i would say he didnt miss that point.

However the question i ask is "is it necessary and why is it necessary? "

back in the day all you did was get an undersize bush and grind the crank to specified sizes and shove the new bush in and guess what it worked.

The internet has turned this whole thing into some kind of back art!

People go on incessantly about "line boring or align reaming" which by the way are totally different operations, and few seem to be able to explain what they involve, For those who think u can support a reamer from the ball/roller bearing and it will magically make the reamer line up the bush , you cant! ...if you don't believe me just put the crank into the bearing and see how much lateral movement there is over that distance, A reamer will follow the hole , the only way to make a hole "shift over a bit" is with a single point cutter ..

it is only necessary to do the milling thing as per vid if the bush hole has become oval or hammered out of round or if the cases have slightly warped by 50 years of hot cold cycles , but generally they haven't perceivably "shifted" ....other that that , well ya know.... racing guys shouldnt bother cause they are going to blow the things up any how ,


I dropped a rod on my A10 on the timing side it blew that side of the case to bits, i didnt lose my case numbers a VERY GOOD THING!

MAN did the experts in the club have a fielded telling me what i had to do if (as i did) i got a half case ( obviously from another motor) and fitted that . you MUST GET IT LINE BORED ETC .........i told them i would if it was necessary . IT wasnt! ....i made a new bushing to match the crank (which unbelievably was still ok) and with a bit of careful hand fitting reassembled it ........the bottom end is perfect. 5k miles and counting

I did not spend thousands and wait 6 month for some prema donna to do it.

man that ecercise shut a few mouths, fact is BSA did a very good job on making therir cases uniform and doweling insures alignment

but having said all that i would advise someone who isnt an engineer to just go with the latest trend and get it done , finding someone will be the hard part as will paying for it , doing that sort of work takes skill and a lot of gear and i dont grudge what they charge for a second ...its the lengly wait i object to.and if you get a comedian they will stuff it up big time

Just saying ....but ive only been a fitter turner for 40 years so what would i know?

now i will sit back and wait to be howled down hahhaha ive got sore figures after that lengthily post with probably no one will read anyhow ROFLMFAO

"There's the way it ought to be and there's the way it is" (Sgt Barnes)