There has to be a reason for line boring the bushing for the crank on a bsa. Please what is it? If you do this should you start with a smaller bushing if you have a matching set of cases?I am wondering why.What differance will it make. Help I am confused
A day with out learning something new is a bad day indeed.
I'm not an expert in this area but I can repeat what I've been told.
Sometimes the left and right side bearings are not perfectly in line.
I was told by an engine builder from New Zealand that sometimes there is some fore-aft play between the two halves of the crankcase, sometimes as much as .010", and that he had on occasion precision-doweled the cases to eliminate this fore-aft play (and then line-reamed the main bush).
On the other hand, I asked the guy who rebuilt my '67 L if he had done any of this stuff and he said "no". I rode that bike regularly for twelve years after that rebuild, and retired it with some upper end noise (small end bushings I believe). As far as I know, the lower is still ok.
You line bore to get all the bearings in line with each other. When you press in a bearing with interference there are slight reduction in inner diameter. If it is not pressed exactly square it can be misaligned along the rotating axis. To get the clearance equal all around and along the length of the bearing it is line bored using the drive side bearing as a guide. You should use a slightly undersize bearing to start with. If it is exact size any misalignment installing the bearing might put the bore outside the final tolerance. Matching cases does not guarantee a pressed bearing is aligned. Given how many people beat cases apart, the cases may not still be "factory aligned".
Does anyone have some pictures of this line boring operation? I am curious to see just how the "reamer" is supported and guided. The parts of the castings that are in alignment are the bores of the ball bearing and solid crank bearing, then the cam shaft bores and also the dowels that align the two halves of the engine cases.
It is very important that a bushing be pressed in squarely! If it goes in crooked some metal will be shaved off.... making the bore out of round at that point also. So just installing the bushing is an important step.
To actually inspect the bores of both halves of the cases would involve specialized equipment and the skill to use them. I wonder just what the factory allowable tolerance was between the bores. (including the tolerance after line boring)
I would love to see some pictures if anyone has them.
What were the factory's instructions for replacing the bushing for the typical BSA repair shop?
Richard, the so-called align-boring process can be performed in a couple of different ways. I've done it two ways with good success and am going to do the next one yet another way.
First method (milling machine or jig borer): After installing the undersize timing side bearing, attach the timing side case to the machine's table and indicate the the spindle on the TS bearing. Check that the case mating surface is perpendicular to the spindle axis, shim if necessary. Then install the upper case half and indicate on the DS bearing race. If it is out of line with the DS bearing, small adjustments to within the excess material thickness (usually .005") can be made. Any more than that and the case needs to again be shimmed to bring them into line. Once aligned, remove the DS case half, install an adjustable boring bar and machine the bearing to diameter, repeatedly checking with a bore gauge. This process is extremely tedious and last time I did it still took me about five hours to get right. Also, even with a CBN tool, the surface finish is not the best due to the long boring bar chattering at times and spindle error in the milling machine.
Second method: (Piloted reamer) Get an adjustable reamer and a pilot that fits into the drive side bearing. Install the reamer adjusted smaller than the starting side and expand until it starts cutting. Remove reamer and measure bore. Noting the position of the adjusters on the reamer, now slowly repeat the above procedure until the desired diameter is achieved. This process is also quite tedious and requires many iterations of removing and installing the reamer. It sitll doesn't produce a great finish.
Third method: (Dedicated boring machine) Sunnen makes dedicated boring machines with multiple adjustable spindles and a wide variety of adjustable honing heads. With this, all you do is install a solid aluminum dummy bearing in the drive side bearing as a "pilot" and then hone the diameter to the correct value. The hones are indexable to a particular diameter and produce a very nice surface finish. As another bonus, the cam bushings can be done at the same time.
So, you see, there's more than one way to skin a cat and how much money, time, and access you have determines the way to go. Hope that helps.
A smattering: '53 Gold Flash '67 Royal Star '71 Rickman Metisse '40 Silver Star '37 Rudge Special sixtyseventy Lightboltrocket road racer...and many more.
I have seen pics of it here before. Myself, I took mine and had a machinist do it, since I had to grind the crank any way.All totaled, I paid the fella 250 dollars to grind all the journals, grind in the right bush to the right size and balance the crank. I thought that was a fair price.
The factory tool is a long bar with a spiral tapered reamer on one end. The opposite end is slip fit in the drive side bearing. The cases are loosely bolted together with the barrels in place. All are tightened to get the two faces mated square. The bar is inserted through the bush and passes through the drive bearing. The reamer is pushed and twisted through the bush.
Thanks for the info.... I have access to milling machines and have an understanding of those procedures. I have not seen the Sunnen machine you describe! I am a tool maker by trade. (sounds like you are too Alex)
I was wondering about the adjustable reamer and just how that is guided. I have never seen a picture of one and wondered how it was done. I am thinking it was a "hand" operation and not done in a machine.... Was this a job that all BSA dealers could perform without machinery? Or did they have to send it out to a machine shop or a specialist with a dedicated fixture to hold the case square while machining. Or was this done by hand in the bench with the two halves bolted together?
Just my opinion (but based on many years in engineering trade) Alex's method 1 and 3 are the way to go. Adjustable reamers (if he is meaning adjustable hand reamers, with the long HSS or Carbide flutes, not "david brown" style floating reamers(which are totaly unsuitable) OR adjustable machine reamers) should be a banned tool only avaiable those who have done an apprenticeship in fitting or toolmaking.
IMO this process can only be done (unless NASA will help) with a single point cutter. Good luck getting tool geometry, speeds and feed and correct coolant/cutting oil (if any) for bearing material right first time!
As he said its a surface finish issue.
Im glad AKA Homer asked this question as I have heard so much tripe about line boring. Often the ones who go on about it the most are unable to explain the process. (PS I am meaning in the real world not on this board)
The need to line bore or not is dictated by 3 things 1 the condition of the cases 2 how well the bearing housing diameters were aligned at the factory, Some were and are (if your lucky) still spot on. Others made on a Friday afternoon after a union meeting are scrap metal. 3 the material the bush is made of. Try line boring a factory "babit metal" or what ever the right name is bush with an adjustable reamer and you will scrap it for sure. Unless its in realy good contition (sharp) which few are.
In the factory workshop manual no mention is made of line boring. It specifys the bearing to get and the dimensions to grind the crank to. Ok I know we cant just pop down to the BSA dealer and get the Vandervelle bearing. The bearings were made to factor in things like crush ect.
The way I have done them is to make sure everything is square and grind the crank to suit. Admitttedly Ive been lucky and had good true cases.
I would love someone to expalin to me how you can use the DS bearing as a pilot when is its a CN bearing its internal clearances mutiplied by the crank lenght is going to give around 1-2 mm free play at the TS end of the crank. If you have clocked and are guiding from the DS bearing you will still have an "eliptical" cut situation with a piloted multi flute reanmer.
You can not expect a multi flute reamner to skim a few thou out of a bearing it will only follow the hole thats there.
IMO the only way to go about line boring (which isnt realy line boring at all) would be to bolt down DS case clock for true agains bearing outer race (if roller) or remove bearing if ball and clock housing, drop machine table and fit TS case half with TS bearing in machine out with micro boring head to minimum clean up and gring crank to suit (the bore of the bush may need a polish/hone to get a decent surface finish first)
Bet I get quoted a bit for this post ..... we need another good debate on the issue!
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
I did mine very similar to Alex's description #3. Only minor changes. I think the best way is on a vertical jig boring machine but not every shop has one. I did it on a small laboratory grade vertical jig boring machine. It is highly presision and will put a mirror finish on the bush. You put together the cases and mount them on the table using precision parallels with TS down. The cases must be parallel to the table. The primary side bearing is not installed but could be. The bush is pressed in place beforehand and is over size (or smaller than the final finished diameter). You dial up the spindle on the primARY SIDE BORE or bearing if installed. Once it is perfectly centered (within a few tenths), you remove the top half of the case without disturbing the setup and procede to bore the bush to the .015 clearance over the finished crank.
BSA reamed these bushes and many assemblers grind the crank to fit the bush. This will work if you are absolutely sure that the bores are aligned, but sometimes they are not. Ask Lannis, his bores were misalligned by .020". If you grind the crank or hand ream a bush on a misaligned bore, you will wear out the bush very quickly, lose oil pressure and wear the motor out. If you are sure that the bores are aligned because for example the motor ran fine with good oil pressure for many, many miles, then you can probably get away without an align bore, but you take a chance assuming the bores are aligned. Crankshafts need to run near perfectly true to have any longevity.
I wonder how close the bores are for the bearings in Triumphs? I wonder if anyone ever checked them out or went thru this trouble?
It's hard to believe cases were out .020 but somehow I am not surprised.(just when you think something is impossible.... someone comes along and proves you wrong)
At the factory...... there had to be tolerances on the bores in the casting. not only size but location. I would love to see the original blueprints with those dimensions. There has to be tolerances! Nothing is absolutely perfect!!!! It would have been interesting to actually see how it was done at the factory.
I have talked about this with Mr Mike before..... proper procedures are important in machining if you want the desired results! I think Mr Mike meant ,0015 clearance on that bore..... I'd love to have a jig bore to use.... That probably would be the best machine to use for this.(for a boring operation) What ever machine is used.... a good solid "set up" is most important. As "rigid" as possible..... including tooling!!!!!! (a long reach boring bar will chatter easier that a shorter more rigid one)
I think the other aspect is to find a machinist/ machine shop you can trust to do the work. Some people's "good enough" are just not good enough! Precision costs!!!!!
Origional blueprints Unless you have a time machine Rich forget about!! the engineering rooms and offices were set on fire and most of the dies and tooling were smashed and sold for beer money, very little was rescued.
In regards to build specs. for those of us who believe their was any degree of accuracy or consistancy at least by today's standards, NOT LIKELY. Remember that one of the reason,s they went under was their refusall to stop using 1930,s technology and corporate ideaology.
Ignoramus is abselutaly correct in regards to the machining method the only thing I would do different though is install the new race for the drive side and index off of the machined surface.
And yes trying to find not only a machinest but a shop that is capabil of performing small diameter jig boring is harder than the job itself or at least here in N.H.
This is in the cases with guide screwed on the ream, the cone centres in the case and the guide spins in it. Creep the adjustment up and cut a little at a time checking after every little cut when it gets close because suddenly the crank will fit:
This actually does a good job the bearing ends up very square and if you can stop at the right point the fit can be very precise. The finish isn't too bad but there is metal all through it to be cleaned out.
By far my preferred device:
I might do a post sometime on doing this type of conversion, because its not that expensive considering the sort of milage it gives. My experience has the D/side wearing out first (after a long time).
It's just an adjustable ream and handle/guide, there is a box of them at work, you can buy them, GM but I wouldn't, I'd always do a roller conversion on anything I own. How the reamer corrects slight misalignment is that it is straight and when the cases are bolted up and the cone jammed into the D/side case it reams square to that, you think that where the roller bearing mounts might put the bearing at a slight angle from where the cone sits but the two motors I've done with a reamer had minimum bush clearance (though I don't have accurate tools to measure) yet spun very free, so they were not badly misaligned in the first place I guess, the cases are spigoted to each other and should be good, even mismatched cases should align at the crank though the top and bottom faces and cam alignment need checking and perhaps fixing. A ball bearing will lock the crank from endfloat which is good but the size that can be fitted to the BSA case is too small and not of sufficient load capacity even in a double row type. Usually a heavy needle roller with a small ball race combined in the same bearing is used and end float is controlled in that. I had trouble with that pulling loose in the case (using a 30mm Norton crank the bearing was likely smaller than what could be used)so replaced it with a straight heavy series roller(much cheaper) experiencing no side load and put a bearing in a plate outboard of the alternator which while controlling end float also supports the crank from primary drive pull.
My brother has an adjustable reamer set but no tool, as Mark describes, to insure alignment with DS bore. The adjustable reamer by itself is designed to slightly enlarge a bore on it's own center. It's good for sizing small ends, truing oval rods rods etc. The reamer as a tool for sizing a timing bush was probably recommended for BSA dealerships as very few would have the in-house ability to machine, so they specified a certain undersize and the crank was ground to match or the bush was resized. I dunno for sure, I am just trying to guess what a motorcycle manufacturer with big labor problems and declining marketshare would do to save itself particularly with a twin that had a reputation for very high waranty repairs.
I would be suspect of mismatched cases as the two cases were not originally bored from the same accurate set up where bores were piloted from one case and transferred to the other case in a single operation. There could be problems with parallelness, cam bore alignement etc. For all the good engineers England had in those days, it is kind of surprising to me that the cases were not doweled. I have no idea why it was not done. It certainly would not have been expensive and was done on primary covers.
If you go to the complexity of converting the timing side to a roller/ball conversion, you are esentially starting from scratch with the crankshaft bores and they will be trued in the process of machining the bore. As long as the cam shaft is checked to make sure it is parallel and true to the crank bore, you will be OK. The ideal setup, and BSA knew about it, was twin rollers and a ball bearing to keep the crank from moving back and forth. BSA incorporated that design in the 71 B50 which is arguably bulletproof and that is the same idea Mark is embracing with his roller conversion. I think that if BSA had any idea where the motorcyle industry was going and competition they would see from Japan, they would have made these kinds of changes change back when they went to unit construction in the early 60ties. Of course hindsight is 20/20.
Mike: Dont know for sure about earlier but my 70 has a doweled C/case. You are dead right about the inteneded purpose of an expanding hand reamer when you say "The adjustable reamer by itself is designed to slightly enlarge a bore on it's own center".
Sorry but I dont accept that it is a suitable tool to correct missaliighnments no matter how well it is supported. Unless of course it is supported at BOTH ends which is what "line boring" actualy is.
MarkP kind of bore this out (no pun intended) when he said "I've done with a reamer had minimum bush clearance (though I don't have accurate tools to measure) yet spun very free, so they were not badly misaligned in the first place I guess"
That is exactly the point Im trying to make.
MarkP is obviuosly a very skilled and knowlegable guy (going by his previous posts) regarding bikes and just becasue HE had sucess with a hand reamer doesnt mean that everyone who reads this on the internet and goes down to "JOES HIRE BARN" and pays $30 to rent a smashed up blunt old adjustble reamer for half a day will do anything other than wreck their bearing when they continue to grow the ID of the TS bush to try to get a missaligned crank to spin freely.
"There's the way it ought to be and there's the way it is" (Sgt Barnes)
IG, I agree with you. I would not use the reamer on crankshaft bore either, but I do understand why some do. It can be made to work if the bore is true to start with, but unfortunately you don't know that unless it is properly set up in a machine. If it is not true to start with the reamer will not get it right.
Gees over the years when I didn't have any money, I've used 400 grit paper wrapped around a wooden dowel to fit a small end bushing to the pin. I have honed cylinders with an electric drill and a brake hone. I've used suction cups to do valves. I've replaced rings when a bore job and new piston was really necessary. That got me going again, but they are certainly not the best methods or even good methods.
When I did my A65, I read everything I could find from this site and I learned some good stuff about A65's. I also disregarded lots of ideas. But in the end I took the best ideas, found a good automotive machine shop that can do everything, and I was very careful about assembly. For all their bad reputations, my A65 has been trouble free for about 4 years now. Always starts easily, has excellent power, it doesn't smoke, burn oil or even leak much. It has been real reliable and a good ride for me and I've enjoyed it a lot.
I'm just taking a guess at this but I think the main bearing holes might have been machined as part of the operation of machining the male and female mating surfaces of the casings, (not line bored at all) then bolted together (where if the machining was accurate they would have alignment) and then cam bearing surfaces machined and top and bottom decks and maybe G/box shafts and door behind clutch, and alternator housing. I don't think the machining for the crank gets out of line even in the miss matched cases I've put together just when opening the bush a little to fit, I've done that with sand paper etc in the past too, sometimes cranks were tight to turn all bolted up, the ream at least aims the opening up of the bush at the other bearing hole, but It's dodgey to use because the hole can be suddenly too big!