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Originally Posted by Magnetoman
To digress, but not really, for some years the thought that I "should" have CNC capabilities has been festering in the reptilian complex of my brain. Then, two weeks ago, Tormach's largest CNC mill showed up on the local Craigslist, described as in excellent condition and at just over half list price.

I added 3 axis DRO to my 1942 Adcock & Shipley mill with a Bridgeport M head of same vintage. As soon as you can accurately position the tool and then get back to exactly the same position every time, then you realise CNC is not worth it for one off's and I also stopped looking for CNC controls. I then added axis locks to all axis so the backlash issue was defeated.

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Originally Posted by kommando
I added 3 axis DRO...then you realise CNC is not worth it for one off's
That's the point, at least for the types of work I do on a mill. Although at least some CNC controllers allow the operator to "drive" the axes as if it were a manual mill, I don't know how well that function is implemented since it isn't the reason CNC machines exist.

Another non-trivial advantage a manual mill has for me is that I can go back to it after not using it for a month and know exactly how to operate it, whereas that's enough time for some of the nuances of G-code to have been lost from memory (and I don't mean the mill's memory). Anyway, essentially everything I do with my lathe and mill are one-offs so manual machines, with a DRO on the mill, are the best choices for me.

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You can't beat manual-operated machine tools for "one-off" jobs.

Unfortunately, it's getting increasingly difficult to find machinists willing to do these jobs.

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Originally Posted by kommando
I added 3 axis DRO to my 1942 Adcock & Shipley mill with a Bridgeport M head of same vintage.
There must be a lot of Adcock and Shipley mills still kicking around. I have a similar vintage #3 in the workshop I share with Trevor, which I still don't have in operation. It's currently fitted with a vertical head, and has all the parts for horizontal milling as well.
It looks like it could take a 1" deep cut in armour plate, and needs its own power station.

The much smaller Optimum column mill I'm currently using has a 3-axis DRO, which made me realise I needed a 2-axis DRO on the lathe when I bought that.

The limiting factor with both is the novice machinist.

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Originally Posted by kommando
I added 3 axis DRO to my 1942 Adcock & Shipley mill with a Bridgeport M head of same vintage. As soon as you can accurately position the tool and then get back to exactly the same position every time, then you realise CNC is not worth it for one off's and I also stopped looking for CNC controls. I then added axis locks to all axis so the backlash issue was defeated.


The Bridgeport and similar tool room mills are a wonderful pieces of kit for motor cycle work, the flexibility for one offs means its a first choice for the professional and "advanced “home workshop alike. Vintage models are very affordable, and will last forever with little to go wrong. A DRO of course makes the whole thing so much easier with the backlash thing, which otherwise keeps you on your toes.

Having the luxury of both CNC and traditional for my day job, I tend more and more to CNC for one off work. These days controls have canned cycles or even conversational modes so you can say call up a pocket routine to make a valve seat counter bore, say where you want it, see what tool is handy is in the carousel, press the button and you are cutting metal.

With a Renishaw Probe you can even see how the size is shaping up as you progress, and let the control work out the final cut. The machine can even generate a report as to the deviation in location and size from programmed to achieved, and if you have several to do such as a multi cylinder head, you quickly start saving time.

The point being progress in CNC controllers over the last 20 years or so blurs the traditional view that CNC is a production only machine.

Roland.

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My Adcock is a No1, came to me with the Bridgeport but I have recommissioned the horizontal mill including the power feed table using the old motor sitting in the bottom casting. I added a new support shaft 6 inch higher for the M head and the old shaft the M head was on is free to be as originally intended the arbour support for the horizontal mill shaft. With the M head 6 inch higher I can now fit crankcases on the table and machine the top.

That allowed me to finally fix my Commando 72 cases to add a mesh filter to protect the return side of the oil pump from large pieces of debris.

[Linked Image from i.postimg.cc]

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Originally Posted by Shane in Oz
The much smaller Optimum column mill I'm currently using has a 3-axis DRO, which made me realise I needed a 2-axis DRO on the lathe when I bought that.
I have a "4-axis" DRO on my mill, with separate scales on the quill and knee that allow them to be used separately or, as I almost always use them, combined so the controller displays the sum of the movements.

While I consider the DRO on my mill to be indispensable, not so with a lathe. Instead, I have a "direct reading" dial on the cross slide that directly displays the reduction in diameter, rather than the movement of the slide (which results in reducing the diameter by 2×). However, since moving the dial by, say, exactly 0.020" does not necessarily result in the diameter being reduced by exactly 0.020", whenever I'm aiming for a precise diameter I sneak up on it using a micrometer to check as well as waiting for the part to cool when necessary. A DRO on the slide that read to 0.0001" would not be an advantage for me.

For lengths on my lathe I have an analog Trav-a-Dial that reads to 0.0005". The carbide cut-off tool I use has a width 0.086" so I bring it up to touch the end of the part, back off the cross slide, move the carriage toward the headstock by 0.086" and zero the dial. However, just because the tool is 0.086" wide doesn't mean it will cut a slice of precisely that thickness, so the less-common times I truly care about making a specific length I cut it 0.01" or so too long, mic it, and reduce the length by the necessary amount. It would be different if I needed to cut very long pieces to high precision on the lathe but, like the x-axis, a DRO on the y-axis that read to 0.0001" would not be an advantage for me.

Originally Posted by RolandM
The point being progress in CNC controllers over the last 20 years or so blurs the traditional view that CNC is a production only machine.
That's a good point, and Instagram posts showing what 5-axis (or 6-axis) CNC machines can do are amazing. Machining a new Gold Star head from billet would be a piece of cake (once the moves had been programmed...) I'd love to be able to do those things even if I have no need to do those things. Still, for the type of work I do when rebuilding motorcycles, I would have to pay a lot for CNC capabilities, 99% of which I would never have a use for.

While a CNC machine might be able to do away with tooling like rotary and tilting tables, it only could do so if the operator is adept at programming it. At least for me, programming skills that aren't frequently used soon fade, requiring time to get back up to speed. It would be different if I spent at least part of each day machining, but the nature of my motorcycle work means that I often go a few weeks between sessions on the mill.

For nearly everything I do on the mill, fixturing takes by far the most time, with the actually cutting of metal taking relatively little time. Is this the same for someone adept at CNC? For example, to mill a valve seat pocket I had to mount the head in a tilting vise and spend a fair amount of time to get the axis of the guide aligned with that of the mill. Presumably, with CNC the axis wouldn't matter since it could be determined by means of a probe and then the cutter programmed to advance along that angle. Since you have both manual and CNC mills, how much difference in time would you estimate it might take, from start to finish, to do the same one-off job on both types of mills?

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Originally Posted by Magnetoman
For nearly everything I do on the mill, fixturing takes by far the most time, with the actually cutting of metal taking relatively little time. Is this the same for someone adept at CNC? For example, to mill a valve seat pocket I had to mount the head in a tilting vise and spend a fair amount of time to get the axis of the guide aligned with that of the mill. Presumably, with CNC the axis wouldn't matter since it could be determined by means of a probe and then the cutter programmed to advance along that angle. Since you have both manual and CNC mills, how much difference in time would you estimate it might take, from start to finish, to do the same one-off job on both types of mills?

This is a good question. Maybe this helps, two jobs come to mind. Bear in mind I am not suggesting everyone should have CNC at home! But if you are trying to earn a crust as I am, this is my reason why CNC is good for us, and perhaps is of interest.

Firstly your valve seat pocket. On a 3 axis machines like we run, you would have to get your valve guide bore parallel with the spindle. Fixturing is always a time component no one enjoys having to pay for, and this element is the same for a manual operation or 3 axis setup (Though you may make the fixture in situ if possible). I suppose with a 5 axis, have the machine probe the guide at two depths if it’s something like near parallel with the spindle to start with and with a bit of trig let it work out and move to the correction, or if you felt less inclined to write the code to do this, just jog each of the sub axis and get square to the spindle manually.

However, from there, rather than bore with a manual head on your mill, with tool push off, risk of going over, and I recall you had a devil of a job on your project with hard spots, a simple stock diameter rigid carbide end mill say 16MM – 20MM dia will generate a sharp square pocket without taper, push off and of course the probe will find the diameter as you progress and adjust the last cut etc, all whist kettle can be on for a nice cup of tea.

I would argue this would be a winner for me on this job, as it would be a certain outcome. Programming time to make a counter bore is seconds using a canned cycle.

I have a job on right now making a set of custom designed flywheels for a short stroke single project. I would class this job tolerance as jig boring work if assigned to manual machinery. To make one set by hand would be tedious. To make 2 sets and a spare, the will to live would be lost. The time to machine - what is quite a complex balance cutout profile, crankpin detail, main shaft location detail, then turn the job over and rinse and repeat. With a CNC you can do this, turn the job over for second op, eye it up something like near, probe the main shaft hole, probe the crankpin hole and let the machine skew the second op program square, rather than fiddling around on a rotary table. I am sure the time saving here would extend to days rather than hours, and far, far less risk of mistakes.

Roland.

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Originally Posted by RolandM
rather than bore with a manual head on your mill, with tool push off, risk of going over, and I recall you had a devil of a job on your project with hard spots, a simple stock diameter rigid carbide end mill say 16MM – 20MM dia will generate a sharp square pocket without taper,
While the cutting portion of the job would be faster with CNC, my upgraded tooling (which would have helped had I bought it before, rather than after, I cut the pocket...) would have eliminated the issues I had to deal with. However, it still would have taken me longer than CNC because I would have had to stop several times to reset the cutter to ever-larger diameters, and I also would have taken the time to measure progress each time I stopped rather than having the confidence of a carbide end mill and CNC program.

I can imagine the cutting process for that pocket with CNC might take a minute, but with my new tooling, plus my abundance of caution, it easily could take me an hour. While an extra hour for such a one-off job would make no difference to me, it would be money down the drain for you. Of course, once the time for fixturing has been written off by doing the first job, CNC puts you several hours ahead if you have to do even just one more.

Now that you've mentioned this, it will be agony not having CNC if I have to put 4 new seats in my Spitfire's head. Damn you...

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Originally Posted by Magnetoman
Now that you've mentioned this, it will be agony not having CNC if I have to put 4 new seats in my Spitfire's head. Damn you...
I could see that coming.

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Originally Posted by Magnetoman
While I consider the DRO on my mill to be indispensable, not so with a lathe. Instead, I have a "direct reading" dial on the cross slide that directly displays the reduction in diameter, rather than the movement of the slide (which results in reducing the diameter by 2×). However, since moving the dial by, say, exactly 0.020" does not necessarily result in the diameter being reduced by exactly 0.020", whenever I'm aiming for a precise diameter I sneak up on it using a micrometer to check as well as waiting for the part to cool when necessary. A DRO on the slide that read to 0.0001" would not be an advantage for me.

I use TouchDRO on a tablet, its an Android app and one of the parameters you set is machine type, set it to Lathe and you can select radius or diameter as the reading on the X cross slide. The glass readout slide on the Y axis reads to 5 microns and the display resolution can be set to this if needed. However DRO or not the issue of checking after each cuts does not go away, tool deflection differs with cut depth and also you have tool tip wear as well. Internal boring is the worst with large tool overhangs, just take a second cut with no tool movement and you will see metal being cut showing the tool deflection of the first cut.

[Linked Image from i.postimg.cc]

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Not sure where I fit in on the original question as I have years of precision toolmaking experience and have been running my own business for 25+years with our work sent to different parts of the world. Having said that and despite having a fantastically equipped workshop at my disposal, I only make bike parts for myself, I've no commercial aspect with engineering and my old bikes. Despite all of this experience & equipment, I'm just as much at the mercy of "experts" as anyone else is here, for example, I had a B25 crank ruined by a bad machinist when it was re-ground with more than a thou taper along the width of the big end! I buy plenty of parts that I could make, if I really wanted to, but I don't see the point unless it's either unavailable or the quality is not as good as I think it should be. Why go to all of the bother making con-rods, for example, when there are some very well made ones readily available?
The main area I'm focused on these days is cylinder heads and in particular seats and guides, below is a picture of an experimental 74 T120V cylinder head that is nearly finished. The 74 T120V 9 stud heads are unusual in that they use the T140 10 stud casting (71-2863) that are machined with a 650 style chamber that is smaller volume (higher comp) because the 1.355" radius of the hemisphere was lower and there are two smaller hemispheres Concentric to each valve seat. The T140 chamber was a single 1.355 radius that intersects at the same point of both valves, making it much easier to work on. The valve guide support is longer version with shrunk in valve seats, just the same as the T140 and to my mind they're probably the best 650 head because of this...if you can find one!
My T120V head below.
[Linked Image]
As far as removing the valve seat goes the problem on Triumph B series heads is the 45 degree guide angle means the heads tilted so much that access becomes an issue, although I've CNC machinery it's not a lot of use unless it's full 5-axis. I made a fixture very similar to the one John Healy has shown previously and even then it's tight. Serdi make seat removal cutters but as far as I know they are fixed to suit a particular size, anyway I've some Swiss made adjustable twin insert cutters and they will fit the tight gap and remove the seat in no time at all. The alternative is to use a single point 90 degree cutter although I only use them as a blank to make my own seat profiles.
The picture below shows two cutter types for seat removal tool and the lack of room available.
[Linked Image]

Last edited by John Harvey; 10/28/21 2:37 pm.

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Originally Posted by kommando
just take a second cut with no tool movement and you will see metal being cut showing the tool deflection of the first cut.
AKA, the "spring cut." It's why, when you're aiming for a precise dimension, if you plan for your last cut to be a spring cut at a slow feed, you also need to make your penultimate cut the same depth as you will use for the ultimate cut, followed by a spring cut at the same slow feed.

Originally Posted by John Harvey
The picture below shows two cutter types for seat removal tool
This illustrates the point that tooling (including fixturing) for a mill or lathe can easily add up to more than the cost of the machine. This was certainly the case with both my mill and lathe. Although, with professional-class CNC machines costing north of $100k, it's probably not true for them.

Originally Posted by John Harvey
I buy plenty of parts that I could make, if I really wanted to
As an aside, I wonder to what extent a machine-shop owner looks at this issue somewhat differently because their wallet tells them the cost of every minute they spend machining a replacement part when instead they could have bought it.

For what it's worth, although I can't be sure, offhand I can't think of a time I machined a part I could have bought, with the possible exception of valve guides. The head on my BB Alloy Clipper needed oversize OD guides for the holes, which might or might not have been commercially available, although I didn't bother checking before I made them myself. Nearly all the time I spend machining it's to make jigs, fixtures and special tools for rebuilding motorcycles, or to repair difficult-to-obtain parts.

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John: I like it! The other thing about these heads is you are removing an actual intereference fit valve seat. They are Concentric to the guide. The earlier cast in trapezodial seats were never centered on the guide hole. This made removal tricky and often required welding the head to accept a new seat. It can be a lot more work to replace seats in earleir heads

I have seen so many seat (heads) ruined by "the local" automotive machine shop that I no longer cringe when I see one. It has become the norm along with machining a bent head to flatten it. They should know better as it is routine now to straighten heads with overhead camshafts.

I see the good Dr likes this. I bet he is dreaming of a way he could squeeze a CNC into the shop. Or more up his alley: Connect his lap top to the DRO to control stepper motors and turn his Bridgeport into a 3 axis CNC. I have had the same dream, but at 82, by the time I got the wife to go along with it, I would be well past my due date.

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Originally Posted by John Healy
I bet he is dreaming of a way he could squeeze a CNC into the shop.
No, I've not been "dreaming," I've been obsessing ever since I visited Ian Barry at Falcon Motorcycles ten or so years ago and saw a Triumph Bonneville cylinder muff being machined from a huge chunk of Al.

Unfortunately, even at $35k the specs of the largest Tormach show it's just not strong or versatile enough to substitute for my old-fashioned manual mill for the types of work I do. The next step up, to a professional machine, requires well over $100k. Even if I could convince my wife, which I would be afraid to even try, I couldn't convince myself I "need" it that badly. This means as far as milling is concerned, I'll remain forever trapped in the 20th Century along with my British bikes.

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Originally Posted by Magnetoman
As an aside, I wonder to what extent a machine-shop owner looks at this issue somewhat differently because their wallet tells them the cost of every minute they spend machining a replacement part when instead they could have bought it.
I often get asked "this part costs x amount, would you be able to make it for less than that" The answer is always no I can't, once you factor in everything that's involved, including buying the material etc, it's nearly always cheaper to buy a new replacement rather than to make it as a one off. Repairing something that's damaged... well that is another mater entirely, quite often that can worth doing.

Originally Posted by John Healy
The earlier cast in trapezodial seats were never centered on the guide hole. This made removal tricky and often required welding the head to accept a new seat. It can be a lot more work to replace seats in earleir heads.
It can get pretty ugly in there once you dig out the cast in seats, doable but like you say, way more work and difficult to do as good a job as the later inserted seat style of head.

John, thank you for the kind words, I genuinely feel honoured because you have inspired myself and many others with your knowledge and experience of these great old bikes.

On the subject of Triumph Cylinder Heads, I will post up a link to a YouTube video showing the complete manufacturing process of a T140 cylinder head. My early background was in castings ,so I'll try and explain the processes involved as best I can, keep your eyes out over at the Rod and Tappet pub over a beer or two.
Cheers, John


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When Dan Macias was machining heads for valves seats he had cutters for each seat with replaceable inserts that were ground to size.
[Linked Image from live.staticflickr.com]
Almost any seat size is available but he often made custom seats for old Ferraris from Ampco45 for better heat dissipation.
All that is old hat now with CNC. Extended nose tool holders get into a Triumph head no problem. Set up time is the same on a 3 Axis but the tools are set up before rather than during machining.
Spring pass - just click on the box, tell it how many times. Setting interference? Just put in the offset on the machine or program, run it, check the dimension, change the offset and push the start button again. Far simpler than manual.
Some things are impossible on a manual and simple on a CNC. I had to rechamber my 911 heads for RSR pistons (RSR heads are unobtainium) to bring the compression down for pump fuel. Put the new chamber shape into the program, tell it to cut the surface, put the head in the CNC, push the button.
[Linked Image from live.staticflickr.com]
Or putting threaded inserts into an A65 to have SpinRing pipe retainers, use a thread mill cutter, tell it the diameter and pitch.
[Linked Image from live.staticflickr.com]
New CNCs are expensive but if you are willing to put up with used they are far less and ones that need work less than that.There is a cost for all the tooling and three phase rotary. How much time and money do you spend just looking for a shop to do the work?
On custom parts such as valves and guides, I find it far more cost effective to find an auto part that is close and rework it. 7mm stem valves and guides for and A65? BMW M20 guides - 13.25mm O.D. cost $5, intake valve -1.651" head, 4.035" long, $8 from Bummer sources.
Of course, then mistakes are on you but at least you know it is done right (or wrong).

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Someone reading these posts who is thinking about whether or not to get into machining for their motorcycle work could be confused about the possible "need" of CNC. For context in what follows, for a number of years I was on the shop advisory committee of a university whose annual research expenditures were over $700M. The shop had a half-dozen machinists and a number of CNC machines, and whose principle job was turning out pieces for bespoke research instruments that were too cutting-edge to be commercially available. Because of this experience, I have a pretty good understanding of what CNC machines are capable of.

Originally Posted by DMadigan
Some things are impossible on a manual and simple on a CNC. ... Put the new chamber shape into the program, tell it to cut the surface, put the head in the CNC, push the button.
Of course, for this you have to know what new non-hemispherical chamber shape to program (hemispherical can be done on a manual mill). If I were restoring bikes as a business, preparing bikes for Bonneville, making custom bikes, or machining parts for sale, CNC could be essential. However, while for certain of my motorcycle rebuilding jobs a CNC mill could have been somewhat faster, for the types of work I do I've yet to run into a task my manual mill couldn't handle where a CNC mill could have. That said, had I owned a CNC machining center I might have been tempted to make an Al head for my Ariel. But, even then, it's unlikely I would have succumbed to that temptation given the amount of time it would have taken to program the complex shape.

As for accuracy, I calibrated the X, Y, and Z scales of my mill's DRO to an absolute accuracy of 0.001"/18" at 20 ℃. This means, for example, when I made a torque plate for my Gold Stars the holes were located to better than 0.0003" with respect to each other, which is way better than needed. And, it's not that I couldn't calibrate the scales better than this with additional effort. However, there's nothing on a British motorcycle that requires absolute accuracy over large distances at this level so even if a CNC were calibrated to an absolute accuracy of 0.0001"/18", it would make no difference. And already at my current level of calibration temperature would have to be controlled if I wanted to achieve that accuracy in the final machined part.

Originally Posted by DMadigan
Of course, then mistakes are on you but at least you know it is done right (or wrong).
For me, at least, that's a huge factor for the machining work I do. Unlike a shop with an hourly rate, I have zero incentive to pass work off to the customer, i.e. me, that I know is inferior. If I make a mistake I know it, and I redo it, even if the work might have been OK-ish with the mistake.

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Originally Posted by John Harvey
The 74 T120V 9 stud heads are unusual in that they use the T140 10 stud casting (71-2863) that are machined with a 650 style chamber that is smaller volume (higher comp) because the 1.355" radius of the hemisphere was lower and there are two smaller hemispheres Concentric to each valve seat. The T140 chamber was a single 1.355 radius that intersects at the same point of both valves, making it much easier to work on. The valve guide support is longer version with shrunk in valve seats, just the same as the T140 and to my mind they're probably the best 650 head because of this...if you can find one!
My T120V head below. . . .

As far as removing the valve seat goes the problem on Triumph B series heads is the 45 degree guide angle means the heads tilted so much that access becomes an issue, although I've CNC machinery it's not a lot of use unless it's full 5-axis. I made a fixture very similar to the one John Healy has shown previously and even then it's tight. Serdi make seat removal cutters but as far as I know they are fixed to suit a particular size, anyway I've some Swiss made adjustable twin insert cutters and they will fit the tight gap and remove the seat in no time at all. The alternative is to use a single point 90 degree cutter although I only use them as a blank to make my own seat profiles.
The picture below shows two cutter types for seat removal tool and the lack of room available.


hi john

i race a 1965 T120 fitted with this head-- in the states its called the "9-1/2-bolt head . . ." i also have two more as spares that will need some repair, possibly including valve seat renewal.

am i correct in reading your above post that these T120 heads made with the T140 casting have interference-fit valve seats, rather than the cast-in versions? i am not a machinist and may have mis-read your post.

thanks

kevin


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Hi Kevin

9 & 1/2 bolt head, that's a funny description, I've not heard that one before, I have heard them called "T130 heads" over here smile

To answer your question, as far as I'm aware all T120 9 (+1/2) stud heads, using the T140 10 stud casting, have interference-fit valve seats. I've seen about 6 of them so far and they all appear to be the same. If you look closely at each of the valve seat faces, they should appear to be Concentric with their seat insert, unlike with the cast in seats.

From what I can tell, it's important to use the lower T140 valve spring cups as they are lower by 0.100" to allow for the extra guide support, having said that, I bought one recently that has the bigger T120 style spring cup, so it's a bit confusing as there's no parts book for the 74 T120.


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Originally Posted by Magnetoman
An aftermarket bush pressed into place might work OK as-is, but the only way to know if the resulting clearance meets the original published specs and it won't fail prematurely is with a precision measurement instrument. And the only way to deal with it if it doesn't is with a hone.

Since I don’t own a Sunnen hone… other than the portable rigid variety driven by a bone snapping 3/4” drill….

Me thinks the bushing could be sized using a lap…. provided one uses the likes of Time Saver compound and a lap that is harder than the bushing material.

…. if installing Oilite bushings, you can use a driver machined so it is “approximately” .0003” larger than the desired running clearance and you can end up with decent results.


now running for the exit….

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Originally Posted by Cyborg
Me thinks the bushing could be sized using a lap…
I should have said it could be sized with a reamer as well, which is what BSA intended for the timing-side bush on A10s. They offered a "special tool" in the form of a plate that bolted to the case to align the reamer. Although, a reamer leaves a relatively rough surface that doesn't meet modern specs for surface roughness.

One of the many special tools I have (and one of the few that I know what it's for...) is that plate, although I'll never use it.

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I can’t say I’m very fond of using reamers on bronze bushings. New reamers would help. I haven’t tried lapping bronze bushings with Time Saver yet, but don’t see any reason why it wouldn’t work.
I only recently discovered the info on installing Oilite bushings…gave it a try and was pleased with the results. Seems like it’s not well known. Not sure how well it will work with other bushing material, but I think it would/ should. If ball sizing can be used then an appropriately sized driver should work?
Sans a Sunnen hone, I think it would be a good method for installing cam bushings in the likes of the BS. Press on the pinion before installing the outboard bushing, then install the bushing with the driver. That way the bushing ID ( if installed first) doesn’t shrink when the pinion gets pressed on. Might take a test or two just to make sure .0003 over the running clearance is where you want the driver to be.

Anyway…. I’m still supposed to be making drywall dust and wood shavings for the foreseeable future.

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Even with modern machinery the majority of motorcyclists skill levels are very low. It's easy going fast on any bike in a straight line, but statistics show more riders crash in sole vehicle crashes on bends. Ask any motorcyclist if they can do a feet up U-turn quickly within 6 yards and they probably cant. Ask them to do a figure of 8 within in a block of 4 car park spaces and they probably cant. Check out this channel for some very worth while relatively slow speed exercises;
and these guys are great;
If you are wondering they are using standard road tyres.

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That was interesting, but somewhat of a digression.
Now try the same thing on dirt or wet grass smile

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