270 Offy
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John,
I decided to bead blast the head (and other) mounting surfaces to give some 'bite' to the teflon gaskets that I'll be using. I once tig-repaired a (full-size) aluminum head for a pretty knowledgeable hotrod friend and when finished, I faced its mounting surface to a beautiful mirror finish. When he came by to pick it up, he told me my finish was too good and would never seal to the gasket. He had me re-setup the head and re-skim it at a higher ipm To leave very light machining scratches. I don't know if the first one really would have leaked, but I do know the second one didn't, and I always remembered how adamant he was about that imperfect finish.
The troughs create a flat reference surface for installing the valve cages. The Offy doesn't use lash adjusters, and it's going to become important later that the valves are all installed at uniform heights. I'm curious about how well that's going to work out. - Terry
Terry so glad to see you back at! You set the benchmark for all hobby machinist!
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Terry:
What grade / grit / etc are you using for your bead blasting?
Looks amazing as usual.
What grade / grit / etc are you using for your bead blasting?
Looks amazing as usual.
Dave,
I believe it's 80 grit glass bead material bought from my local Harbor Freight many years ago. I use a cabinet bought from Eastwood in 1995 and run 90 psi air pressure. The material has never been changed out and so it's probably finer that when it started out. - Terry
I believe it's 80 grit glass bead material bought from my local Harbor Freight many years ago. I use a cabinet bought from Eastwood in 1995 and run 90 psi air pressure. The material has never been changed out and so it's probably finer that when it started out. - Terry
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Looks like a nice finish. I use something rated as MIL10 from Blast-O-Lite. It's really fine. Feels like water if you fill your hand and let it run out between your fingers. It gives sort of a satin finish with 90lbs or so pressure. It's perhaps a bit too fine.
Which is why I asked. I was trying to figure out how coarse it has to be to give a finish like you're getting without ending up with a bag I might never use.
Thanks
Which is why I asked. I was trying to figure out how coarse it has to be to give a finish like you're getting without ending up with a bag I might never use.
Thanks
After completing the head, it was trial assembled with the block and gear tower and measurements taken to reconcile the dimensions in my Solidworks model. In particular, before starting work on the cam boxes I wanted to make sure the camshafts are going to wind up properly aligned with their driving gears inside the gear tower. A fixture block bolted to the top of the head was used to help verify this alignment. The block was bored for a test shaft to support the already machined camshaft gears so their meshes with the drive gears inside each arm of the gear tower could be checked. Once verified, the locations of the camshafts inside the cam boxes and the related gasket thicknesses were finalized.
The bolt-on cam box covers that will enclose the camshafts were the first parts of the top-end assemblies to be fabricated. The documentation suggests cold forming these 16 gage sheet aluminum covers over a mandrel using a mallet and vise. With the metal forming completed, the bottom edges of the long sides are to be machined to fit inside a pair of 1/32" wide grooves milled into the top surfaces of the cam boxes. These covers will contain the top-end waste oil until it can returned to the sump through passages in the block.
I tried Ron's suggestion, but found dealing with the small covers' tight bends difficult. Sixteen gage aluminum feels like it should be easy to form until you try to bend a six inch wide piece around a half inch mandrel. My first few tries would have required a lot of work to clean up the surfaces marred by the forming process. And then there would still be the issue of achieving a pair of straight sides to be uniformly machined down to a thickness of .032".
Instead, I decided to make a set of dies to form the covers using my shop press. The covers came off the press nearly perfect and, other than height trimming, needed only to be closed up another .010" in a vise to reach their target width of .705". The heights if the parts were rough trimmed and then fit-checked using a gage having a pair of 1/16" wide parallel slots milled into its surface. A fixture was then used to support the parts for their final trimming and facing operations. The final fits were verified in a gage block containing a pair of 1/32" wide grooves identical to those to be machined into the cam boxes. The photos show the various steps involved. The covers will be later trimmed to length, and their front ends' machined for close fits inside the gear tower. After completing the top-ends, they'll likely be polished. - Terry
The bolt-on cam box covers that will enclose the camshafts were the first parts of the top-end assemblies to be fabricated. The documentation suggests cold forming these 16 gage sheet aluminum covers over a mandrel using a mallet and vise. With the metal forming completed, the bottom edges of the long sides are to be machined to fit inside a pair of 1/32" wide grooves milled into the top surfaces of the cam boxes. These covers will contain the top-end waste oil until it can returned to the sump through passages in the block.
I tried Ron's suggestion, but found dealing with the small covers' tight bends difficult. Sixteen gage aluminum feels like it should be easy to form until you try to bend a six inch wide piece around a half inch mandrel. My first few tries would have required a lot of work to clean up the surfaces marred by the forming process. And then there would still be the issue of achieving a pair of straight sides to be uniformly machined down to a thickness of .032".
Instead, I decided to make a set of dies to form the covers using my shop press. The covers came off the press nearly perfect and, other than height trimming, needed only to be closed up another .010" in a vise to reach their target width of .705". The heights if the parts were rough trimmed and then fit-checked using a gage having a pair of 1/16" wide parallel slots milled into its surface. A fixture was then used to support the parts for their final trimming and facing operations. The final fits were verified in a gage block containing a pair of 1/32" wide grooves identical to those to be machined into the cam boxes. The photos show the various steps involved. The covers will be later trimmed to length, and their front ends' machined for close fits inside the gear tower. After completing the top-ends, they'll likely be polished. - Terry
The cam boxes are surprisingly complicated parts with densely packed features and little free real estate. The fasteners that will secure them to the head will also retain the bearing caps making the cam boxes extensions of the head rather than standalone subassemblies. This means that if the valve train components are not to affect the fit or subsequent alignment of the camshafts, the bearing caps must fit tightly between their guide rails.
Before starting construction, I made a few simplifications to the design. Rather than use sleeve bearings, the camshafts will be bedded directly into the 6061 bearing blocks. The cam bearings will be lubricated by pressurized oil pumped through the center of the camshaft, and so wear shouldn't be an issue. A second change involves the cup followers used to prevent side loading the valve guides. The camshaft supplied in the documentation uses straight-flanked lobes and followers with 2-d contoured surfaces that require keying to prevent them from rotating. In order to eliminate the keying, I plan to radius the camshafts' flanks and use flat top followers that can rotate. The bearing caps will also be machined with integral rather than bolt-on brackets for the cam box covers.
A sacrificial 'mule' was invaluable during the head machining, and so I started out making three cam boxes. The first step was to square up a workpiece for three nested parts to be machined in 'cookie cutter' fashion. Their nearly twenty hour machining time was spread over several days. A number of those hours were use to machine the 1/32" wide grooves for the covers. With even a 5k rpm spindle, I'd never have the patience to manually perform those multi-pass 0.7 ipm grooving operations.
The cam bearings' lower halves were machined directly into the cam boxes after developing an interpolation routine on scrap material that would produce an accurate profile. This routine was consistently repeated for all five bearings on each cam box in order to wind up with a reasonable facsimile of a line bore operation. The same routine will be also be used to machine the bearing caps.
When I originally laid out the array of parts, I spaced them for a 3/16" cutter to finish machine their outer perimeters before they would be band-sawed free of the workpiece. When it came time for this final operation, without thinking I compiled it for a 1/4" cutter which was a better choice for what was going to be three deep grooving operations. I watched in horror as the cutter traveled between parts with no apparent safety gap between them. After stopping the machine, I reviewed the CAM software to see if I had just ruined two of the three parts. Unbelievably, I had originally spaced the parts .250" apart, and since I had inputted .249" for the new cutter's diameter, the parts were unharmed. Sometimes the ball drops on the right side of the net.
After band sawing the boxes free of the workpiece, they were faced to their final heights using measurements obtained earlier from the test block used to verify the cam gear mesh inside the gear tower. Fortunately, all three parts came out to be identical. Their heights were machined so that with a .005" Teflon gasket between the boxes and head, the center distance between between the cam driving gear inside the gear tower and the camshaft driven gear is .004" greater than the theoretical on my SolidWorks model. This distance resulted in just a bit of detectable backlash. This backlash was difficult to measure because the mesh between the two gears of interest is down inside the upper arm of the gear tower. To see it, the driving gear must be held stationary with a needle probe.
A couple test caps were machined to work out their fixturing and to verify their fits. The workpieces used were short bars machined for snug fits between the caps' guide rails. The cam boxes had to be temporarily threaded for these trial fits, but they will be reamed out later. The next step will be to machine the front caps which must be installed for the end-turning operations still needed on the cam boxes. - Terry
Before starting construction, I made a few simplifications to the design. Rather than use sleeve bearings, the camshafts will be bedded directly into the 6061 bearing blocks. The cam bearings will be lubricated by pressurized oil pumped through the center of the camshaft, and so wear shouldn't be an issue. A second change involves the cup followers used to prevent side loading the valve guides. The camshaft supplied in the documentation uses straight-flanked lobes and followers with 2-d contoured surfaces that require keying to prevent them from rotating. In order to eliminate the keying, I plan to radius the camshafts' flanks and use flat top followers that can rotate. The bearing caps will also be machined with integral rather than bolt-on brackets for the cam box covers.
A sacrificial 'mule' was invaluable during the head machining, and so I started out making three cam boxes. The first step was to square up a workpiece for three nested parts to be machined in 'cookie cutter' fashion. Their nearly twenty hour machining time was spread over several days. A number of those hours were use to machine the 1/32" wide grooves for the covers. With even a 5k rpm spindle, I'd never have the patience to manually perform those multi-pass 0.7 ipm grooving operations.
The cam bearings' lower halves were machined directly into the cam boxes after developing an interpolation routine on scrap material that would produce an accurate profile. This routine was consistently repeated for all five bearings on each cam box in order to wind up with a reasonable facsimile of a line bore operation. The same routine will be also be used to machine the bearing caps.
When I originally laid out the array of parts, I spaced them for a 3/16" cutter to finish machine their outer perimeters before they would be band-sawed free of the workpiece. When it came time for this final operation, without thinking I compiled it for a 1/4" cutter which was a better choice for what was going to be three deep grooving operations. I watched in horror as the cutter traveled between parts with no apparent safety gap between them. After stopping the machine, I reviewed the CAM software to see if I had just ruined two of the three parts. Unbelievably, I had originally spaced the parts .250" apart, and since I had inputted .249" for the new cutter's diameter, the parts were unharmed. Sometimes the ball drops on the right side of the net.
After band sawing the boxes free of the workpiece, they were faced to their final heights using measurements obtained earlier from the test block used to verify the cam gear mesh inside the gear tower. Fortunately, all three parts came out to be identical. Their heights were machined so that with a .005" Teflon gasket between the boxes and head, the center distance between between the cam driving gear inside the gear tower and the camshaft driven gear is .004" greater than the theoretical on my SolidWorks model. This distance resulted in just a bit of detectable backlash. This backlash was difficult to measure because the mesh between the two gears of interest is down inside the upper arm of the gear tower. To see it, the driving gear must be held stationary with a needle probe.
A couple test caps were machined to work out their fixturing and to verify their fits. The workpieces used were short bars machined for snug fits between the caps' guide rails. The cam boxes had to be temporarily threaded for these trial fits, but they will be reamed out later. The next step will be to machine the front caps which must be installed for the end-turning operations still needed on the cam boxes. - Terry
Absolutely incredible work!
The front camshaft bearing caps are a little different from the rest and are to be installed and finish machined along with the boxes' front ends. Their stepped circular ends are natural candidates for a lathe operation. Their already machined top surfaces are pretty delicate, and so I made up a two-piece cradle to protect them from the lathe's 4-jaw chuck. Just after finishing it though, I discovered my chuck's through-hole was too small to handle the long parts with their offset centers. After boring out the chuck to the ends of its worm gears there still wasn't enough clearance, and so I gave up and moved the parts to the mill.
Supporting tall skinny parts in a mill vise can be sketchy because the leveraged cutting forces always seem to be greater than expected. In the past, I've had similar parts slip out of position during cutting even when centered and securely tightened in a vise. For this setup, I added side supports as well as some additional end mass to reduce cutter induced vibration. This setup was used to machine both ends of each box.
After completing the ends, the long sloping sides of the boxes could finally be machined. Fixturing for these 9 degree facing operations grew into a 'thing' because I added a .040" high vertical strip along the top edges of the boxes to provide a nice transition between the box's sloping sides and its covers. Inaccuracies in the setup for these operations would create a variation in this strip that I wouldn't be able to live with.
A pair of custom angle blocks was machined to support the parts at the angles needed to machine both faces. The blocks were designed so the parts would be locked in place against internal reference surfaces with shims used as wedges. There isn't enough surface area on the boxes' finished circular ends for a trustworthy grip in the vise, and so a pair of sacrificial rings were made to be inserted over them. After some experimenting, it wasn't difficult to align each cam box to the mill's y-axis to within a thousandth.
With the cam box machining essentially completed, the covers were trimmed to their final lengths. A recessed clearance ring was manually filed around the front of each cover to allow it to slip under the gear tower's bolt-on cover cap. A wrap of tape around the front of the cover provided a guide line for a safe-edge file. A .003" vinyl gasket will be used during final assembly to seal the covers to the gear tower.
Finally, the boxes's follower bores were plugged with rubber stoppers and their top surfaces bolted face down to a piece of protective wood so the boxes could be bead blasted to match the rest of the engine. The covers were brightly polished.
The next step will be to machine, fit, and install the remaining bearing caps. - Terry
Supporting tall skinny parts in a mill vise can be sketchy because the leveraged cutting forces always seem to be greater than expected. In the past, I've had similar parts slip out of position during cutting even when centered and securely tightened in a vise. For this setup, I added side supports as well as some additional end mass to reduce cutter induced vibration. This setup was used to machine both ends of each box.
After completing the ends, the long sloping sides of the boxes could finally be machined. Fixturing for these 9 degree facing operations grew into a 'thing' because I added a .040" high vertical strip along the top edges of the boxes to provide a nice transition between the box's sloping sides and its covers. Inaccuracies in the setup for these operations would create a variation in this strip that I wouldn't be able to live with.
A pair of custom angle blocks was machined to support the parts at the angles needed to machine both faces. The blocks were designed so the parts would be locked in place against internal reference surfaces with shims used as wedges. There isn't enough surface area on the boxes' finished circular ends for a trustworthy grip in the vise, and so a pair of sacrificial rings were made to be inserted over them. After some experimenting, it wasn't difficult to align each cam box to the mill's y-axis to within a thousandth.
With the cam box machining essentially completed, the covers were trimmed to their final lengths. A recessed clearance ring was manually filed around the front of each cover to allow it to slip under the gear tower's bolt-on cover cap. A wrap of tape around the front of the cover provided a guide line for a safe-edge file. A .003" vinyl gasket will be used during final assembly to seal the covers to the gear tower.
Finally, the boxes's follower bores were plugged with rubber stoppers and their top surfaces bolted face down to a piece of protective wood so the boxes could be bead blasted to match the rest of the engine. The covers were brightly polished.
The next step will be to machine, fit, and install the remaining bearing caps. - Terry
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Do not mean to teach a cat how to climb trees but as reference for similar situations...
When the part is to tall and stick out the shallow vise too much I found that I can turn my vise 90 degree. (long side of jaws vertical)
I use a machinist grinding vise which is easy to flip but even a Kurt vise can be set up on angle plates.
When the part is to tall and stick out the shallow vise too much I found that I can turn my vise 90 degree. (long side of jaws vertical)
I use a machinist grinding vise which is easy to flip but even a Kurt vise can be set up on angle plates.
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Terry, I think it would been easier and faster to have built a full scale Offy.
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Wow !!
Some tedious and tricky work completed there. And as usual done to perfection.
Fabulous.
Some tedious and tricky work completed there. And as usual done to perfection.
Fabulous.
The bearing caps were machined one at a time in multiple setups from blanks made up earlier to fit snugly between the cam box guide rails. This wasn't an efficient way to make a dozen identical parts, but after fine tuning the steps and getting usable pieces I continued on with what seemed to be working. A small advantage to making them one at a time was that a tiny setup error didn't wind up spoiling a large batch of parts. Since the cam box 'mule' was still alive and well, I made a set of caps for it as well.
Originally, when compiling the routine used to machine the bores in the cam boxes and bearing caps, I used a target diameter of .217". Although I could expect the diameters to be identical, I couldn't rely on the cap bores winding up precisely centered between the guide rails. Inevitable differences in the setups of the parts created small differences among them giving the caps a 'handedness'. After best-fit installing them, a finishing reamer was used to clean up the bores.
The .217" diameter was selected to precede the .2185" chucking reamer that I planned to use for final cleanup. With its spiral flutes and tapered nose, it was usable as a hand reamer. The flutes were long enough to bridge pairs of adjacent caps, and so I let the reamer find its own way through each bore while holding the cam boxes in my hand.
When finished, a .218" polished test rod fit snugly in all three cam boxes while a .217" diameter rod rotated freely. To avoid mixing them up, the caps' locations were engraved on their back sides. Finally, an end cap was machined to close up the rear of each box.
With all five bores in each cam box verified in line and with consistent diameters, the next step will be to machine blanks for the camshafts. - Terry
Originally, when compiling the routine used to machine the bores in the cam boxes and bearing caps, I used a target diameter of .217". Although I could expect the diameters to be identical, I couldn't rely on the cap bores winding up precisely centered between the guide rails. Inevitable differences in the setups of the parts created small differences among them giving the caps a 'handedness'. After best-fit installing them, a finishing reamer was used to clean up the bores.
The .217" diameter was selected to precede the .2185" chucking reamer that I planned to use for final cleanup. With its spiral flutes and tapered nose, it was usable as a hand reamer. The flutes were long enough to bridge pairs of adjacent caps, and so I let the reamer find its own way through each bore while holding the cam boxes in my hand.
When finished, a .218" polished test rod fit snugly in all three cam boxes while a .217" diameter rod rotated freely. To avoid mixing them up, the caps' locations were engraved on their back sides. Finally, an end cap was machined to close up the rear of each box.
With all five bores in each cam box verified in line and with consistent diameters, the next step will be to machine blanks for the camshafts. - Terry
Art K
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Terry,
I have been lurking during this build. I have Ron's book as well and have much of the engine drawn up in Alibre. This process has taken me about 2 years. Before starting on this journey I had never done an assembly. There is so much about CAD I don't understand or forget by the time I use it again, but the more I work on it the easier it becomes. I really like some of the things you've done with this build and will continue to follow along. Great work by the way!
Art
I have been lurking during this build. I have Ron's book as well and have much of the engine drawn up in Alibre. This process has taken me about 2 years. Before starting on this journey I had never done an assembly. There is so much about CAD I don't understand or forget by the time I use it again, but the more I work on it the easier it becomes. I really like some of the things you've done with this build and will continue to follow along. Great work by the way!
Art
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I started four camshaft blanks from a length of half inch diameter Stressproof (1144) that I had on hand. It wasn't originally advertised as ground and polished, but it looked and measured remarkably consistent.
The first operation was to drill a 3/32" diameter hole through each work piece for an oil passage that will eventually distribute top end oil. The Guhring drill that I used was long enough, but the 6-3/4" blanks had to be drilled from both ends. Before continuing, I set them up in the mill and machined a shallow groove along their full lengths. I used the grooves as reference marks to consistently return the parts to the lathe so I could machine their features in small groups across all four blanks. Using this method with simple crib sheets didn't require a lot of thinking during machining and helped me avoid part-spoiling mistakes.
Machining started at the gear end of each blank where I immediately ran into a requirement for a 7/32-40 thread. Although taps and dies are available for this rather uncommon UNS thread, I couldn't find information on its major and minor diameters. Using the UNF thread equations, I machined a few nuts that I later used to verify the threads on the shafts. My parts fit together nicely, but they may not play nicely with someone else's.
A flange on the front end of each camshaft will seat inside an already machined recess in its cam gear, and each pair will be bolted together using one of these nuts. Each gear and flange was drilled with circular hole patterns having identical bolt circle diameters but unequal numbers of holes. These hole patterns create a vernier for setting the engine's timing. During final assembly, a locating pin between the two will be able to establish the timing with a two degree resolution.
Beyond the threading operation, the rest of the machining was done using a carbide grooving insert in an indexable lathe toolholder. I spent a full day trying to automate the machining on my Wabeco D6000, but in the end it lacked the rigidity to handle the 1/16" wide insert that I wanted to use. I eventually moved the parts over to my 12X36 Enco lathe where I manually machined them.
The diameters of the five bearings on each shaft were initially turned to .2170" since that was the diameter of the test rod that turned freely in all three cam boxes. The bearings had to be polished down to .2155", however, in order to duplicate the results with the test rod. The .0015" difference is the effective increase in the shaft's diameter created by the TIR's of the five bearings. The run out of my 5C collet and chuck combination happens to be .0015". With no attempt to limit the TIR of each bearing during its machining, I could have reasonably expected an increase in each shaft's effective diameter equal to the rms sum of five .0015" TIR's which works out to be .0034". Although I hoped using the reference grooves would have prevented any run out, they did seem to help out by a factor of two or so. - Terry
The first operation was to drill a 3/32" diameter hole through each work piece for an oil passage that will eventually distribute top end oil. The Guhring drill that I used was long enough, but the 6-3/4" blanks had to be drilled from both ends. Before continuing, I set them up in the mill and machined a shallow groove along their full lengths. I used the grooves as reference marks to consistently return the parts to the lathe so I could machine their features in small groups across all four blanks. Using this method with simple crib sheets didn't require a lot of thinking during machining and helped me avoid part-spoiling mistakes.
Machining started at the gear end of each blank where I immediately ran into a requirement for a 7/32-40 thread. Although taps and dies are available for this rather uncommon UNS thread, I couldn't find information on its major and minor diameters. Using the UNF thread equations, I machined a few nuts that I later used to verify the threads on the shafts. My parts fit together nicely, but they may not play nicely with someone else's.
A flange on the front end of each camshaft will seat inside an already machined recess in its cam gear, and each pair will be bolted together using one of these nuts. Each gear and flange was drilled with circular hole patterns having identical bolt circle diameters but unequal numbers of holes. These hole patterns create a vernier for setting the engine's timing. During final assembly, a locating pin between the two will be able to establish the timing with a two degree resolution.
Beyond the threading operation, the rest of the machining was done using a carbide grooving insert in an indexable lathe toolholder. I spent a full day trying to automate the machining on my Wabeco D6000, but in the end it lacked the rigidity to handle the 1/16" wide insert that I wanted to use. I eventually moved the parts over to my 12X36 Enco lathe where I manually machined them.
The diameters of the five bearings on each shaft were initially turned to .2170" since that was the diameter of the test rod that turned freely in all three cam boxes. The bearings had to be polished down to .2155", however, in order to duplicate the results with the test rod. The .0015" difference is the effective increase in the shaft's diameter created by the TIR's of the five bearings. The run out of my 5C collet and chuck combination happens to be .0015". With no attempt to limit the TIR of each bearing during its machining, I could have reasonably expected an increase in each shaft's effective diameter equal to the rms sum of five .0015" TIR's which works out to be .0034". Although I hoped using the reference grooves would have prevented any run out, they did seem to help out by a factor of two or so. - Terry
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4 hole in the flange 8 holes in the gear Why? 45* adjustment?
I bet drilling 3/32 hole through a total of 28" of material was a teeth clenching business
I bet drilling 3/32 hole through a total of 28" of material was a teeth clenching business
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I'm surprised you didn't thread mill those threads. Is there a reason you couldn't modify the plan to use a more common thread?
Kvom,
I think the reason the 7/32-40 was specified was that its major diameter happens to correspond to the already being used .218" diameter of the camshaft. I'm not sure about your question about thread milling. Since the parts were being turned in the lathe, I just threaded them in the lathe as well.
Mauro,
The text explains the vernier created by the two different hole patterns.
I think the reason the 7/32-40 was specified was that its major diameter happens to correspond to the already being used .218" diameter of the camshaft. I'm not sure about your question about thread milling. Since the parts were being turned in the lathe, I just threaded them in the lathe as well.
Mauro,
The text explains the vernier created by the two different hole patterns.
Here's an online calculator for pretty much any parallel UN thread UN imperial screw thread calculator Should help next time.
LaVerne
