Cylinder head resurfacing

My take on cylinder head resurfacing in the mill is to use a single point tool - a flycutter. Multitooth cutters can speed things up, but if one cutter edge gets chipped you´re in trouble. Flycutters take longer time to use since only one cutting edge is doing all the work, but if you have a mishap you only waste one insert. And swapping from cast iron inserts to aluminium inserts is quick, you change the one insert and go to town.

Now, I seldom do heads more than a few times a month. If all I did was cylinder heads you can be sure I had a big multitooth cutter or even a cylinder head resurfacer, but since I don´t I haven´t. Thats why I use what I already have - a vertical mill and a flycutter.

If the head is warped, which it probably is if you intend to resurface it, you have (at least) three options; pull it flat against the table, shim the blocks to fit the twisted head or straighten it before resurfacing. The easiest of course is to just tighten it down and start cutting. If there is only slight twist this may be the best approach. Shimming might be necessary if the head is too warped to pull flat. But if the head is so bowed or twisted that the cam bearings are out of line, maybe even causing the cam(s) to bind, it really should be straightened first. Or junked.

Straightening typically involves twisting or bowing the head the opposite way it's already warped, and then baking it in heat to let it "take a set" and end up straight. The bearing bores, that is.
While this sounds easy in theory it may be tricky in reality. After the head is straight 'nuff, the gasket surface can be resurfaced.

If the cam bearings are out of line, perhaps you could also resurface the head as is and then grind some off the bearing caps making the bore smaller and then hone them out again. Obviously this only works if there are removeable bearing caps. The end goal is to have the cam(s) sit straight and parallel to the gasket surface.

For a typical 4-6 cylinder head, I usually place the head on ground blocks, tighten it down just a little and feel if any blocks are loose - you want the head bearing on all corners. Watch out for burrs, dents, grit and gasket remains. After any needed shimming I continue to gradually tighten the hold downs until its firm and secure. I then touch off, snug the table locks (don´t lock the feed axis) and take a skim cut of 0,001" or so. This lets me see if any corner or side sits high or low. Add shims as necessary to average out the differences. Newsprint works well for small adjustments. When you are satisfied, dial in and take a cut. I typically run 269 rpm, 0,004" depth or so and 6-7 ipm while roughing. Adjust the cutting depth according to how unflat the head is. When it's almost flat I take another 0,0015" or so at 2 ipm to finish it off, hopefully cleaning up all areas.

Rover head starting to clean up - iPhone 4s

Note in the above picture how the o-ring grooves are starting to disappear at the ends, but are still there in the middle - this was a banana for sure, and the grooves seem to be cut crooked aswell.


Now, the above procedure assumes the previous gasket surface is factory original or at least resurfaced parallel with the valve cover surface. This is important as you are averaging the cut over all four corners. If the head is banana shaped you want to hit the ends equally. If it is twisted you want to hit diagonal corners equally. If it is both banana and corkscrew, well.... you get the idea. But if the head has been cut wedge shaped by the guy before you, and you also cut more on one end than the other, you´ll have a head that sits tilted when its done. Perhaps not by much, but still.

Of course you could touch off the skim cut, find the lowest point, dial in one roughing cut to remove all warp and then take one finishing cut. But fiddling around finding the low point may take just as long as just cutting away until things start to look flat. I tend to engage a cut and then do something else while the mill hums along.


How do you measure the removed amount? I like to touch off, set zero, cut until its clean and then see how much was removed from touch-off. You could also mark a spot that you measure with a micrometer before and after cutting and see how much you removed. If you measure the middle of a concave head you could end up with 0,001" although you removed say 0,01" at the ends. I feel this is misleading and thats why I prefer to measure from touch-off. That gets you the max that was removed.
If you don´t have readouts you could set up a dial indicator on a magnetic base as a poor man´s readout.

How close is close enough? / Digital calipers.

Just how tight tolerances do you really need? In a home shop environment making one-offs, with time spent not being a concern, you can fiddle as much as you want. When you are making parts for profit - not so. And in a jobber type shop where you are making repairs or replacement parts, you have to decide just how close you need to be.


Is the part for a tractor? Harvester? High end motorbike? Porsche 911? Granddads old something?


I have the feeling that people sometimes get carried away since its so easy to throw numbers around. The guy that asks for spot on probably doesn't know just how much, or little, a thousand of an inch is.

The hairs on my head typically measure just over two thousands.


Now that the price of digital calipers is so low, the same guy probably has them and thinks he is measuring to 0,0005". Oh yeah and the inside measurement must be what the calipers say, right?
Tell me, who pressed the "zero"-button the last time? Is zero really zero?


You can probably see how easy it is to misunderstand or miscommunicate. Your calipers and mine probably wont agree, and your way of measuring will probably differ from mine. Thats why we calibrate measuring equipment:

Checking micrometer calibration - Nikon D200, AF-s VR 18-200, on-camera flash, +something 

A quick check of the digital calipers is to measure some calibrating rods for outside micrometers. You might be surprised, not necessarily in a bad way. My Limit digitals are within +- 0,0005" with some care. Would I use them where +- 0,0005" matters? No way!


There are times when you really may want to be within a few tenths. Bearing seats can be such a time. The tolerance on high precision bearings can be just a few tenths of a thousand inch. But be aware that when we get down to these levels surface finish and temperature really matters. Shrink fits are an other example where thousands matters - miss with a few and your fit is gone. Thats why we have Loctite products heh heh.


There is no sense in trying to hit a diameter to a few tenths if you have a surface that's rough. You also have to know what you are measuring. Are you measuring just one peak, the average or the lows on the surface finish? Perhaps you have to grind the surface if the tolerance is going to be meaningful.
Roundness also comes into play, it it silly to try to hit a tenth if you aren´t truly round.


So how close is close enough? Most of the time the customer can provide you tolerances. If they seem fair, go for them. If he doesn't seem to have a clue, ask if "close as a hair is enough". Or look up a tolerance chart, and use the appropriate tolerance for the parts intended use.

Thats a hair, 0.05mm. Lines are 0.50mm apart - iPhone 5s, pocket loupe (10x) 

Chanses are you'll save some time and frustration, and spend a more reasonable amount of your customers hard earned cash, by working close only where it's needed. And you'll probably see more of him when he understands you're not trying to rip him off but instead provide quality work.

Atentech Perfectly Clear - iPhone 4s

So I bought the "Perfectly Clear"-app for iPhone and have found it really nice. You've seen this already in iPhone 4s camera:

Thistle - iPhone 4s, some cropping

And this is what it looks like after automatic correction in Perfectly Clear, on the iPhone:
(Yeah, its not the same size. Might fix that sometime.)

Thistle - iPhone 4s, not the same cropping, Perfectly Clear

So, which one is better? Im not sure, the "corrected" one is perhaps too much corrected. But the original sure does look grey in comparison.

Another example:

Huseby Bruk - iPhone 4s, HDR to keep detail in clouds

After some Atentech Perfectly Clear automatic correction:

Huseby Bruk - iPhone 4s, HDR to keep detail, Perfectly Clear

This time I´m sure I like the corrected one better. It simply has more oomph. Perhaps the grass is too bright green? This was the automatic correction, I suspect some fiddling around with the settings could improve the result... but then again, if you are after serious image processing perhaps you should use a better camera to take the picture, and your computer to edit and adjust it. 

You have to experiment, sometimes this app does make things worse, but often it enhances photos - right there on your iPhone. Let it do its thing automatically or control the settings yourself, and when you like it simply save the photo to the camera roll. Its that easy.

iPhone 4s camera

I am surprised how good the back camera is on the iPhone 4s. When you have enough light available you can take some really good pictures. This was snapped while out walking:

Thistle - iPhone 4s, some cropping.

Now, it wasn´t exactly windstill, the thistle something like three inches away from the iPhone. Shooting a moving target is what it is, I´m still surprised how sharp the image is. I had to crop a little to balance the image.

If I took the same picture with my Nikon D200 and some macro lens there would be very shallow depth of field, and that rig wouldn´t fit in my pocket. And I could not hold the dog in one hand either while taking pictures.  In this case, iPhone wins!

Telescoping gauges

Telescoping gauges, sometimes called telescopic gages, are really useful for "measuring" holes in the 0,313 - 6" range. They don't actually measure anything on their own, but they transfer measurements to something that can measure - a regular micrometer for example.


How do you accurately measure a critical bore? An internal bearing seat? How do you get that last "thou" just right? Forget vernier or dial/digital calipers, unless you really know the relation between what the hole actually is and what they say it is. And you better find the true maximum diameter!

Spring calipers work well, they use the same principle as the t-gauges but with more "feel" and skill required. Go/no-go gauges also work, but have to be purchased or made. Internal (stick) micrometers work on bigger bores, but they are slower and you really cant use one in say a 25mm / 1" bore. Oh, the three-legged affairs do work, comes in a wide range of sizes but are really expensive. Really. As far as fast, fuzz-free measuring goes, telescoping gauges are the way to go in my opinion. They transformed precise boring work from frustrating to actually quite enjoyable, and the same set works for all measurements within the range, provided you also have the outside micrometers.

Mitutoyo telescoping gauge - Nikon D200, AF-S DX VR 18-200 @ 200, +1,7, built in flash

But the gauges must be used properly. You first set the telescoping ends a bit bigger than the bore, either by letting them snap open on an angle in the bore and lock them there (fastest way) or some other way outside the bore. The next step is to hold them, with the lock snugged tight enough, in the bore at an angle so the ends clear the bore, then swing or move the tips through the bore by levering the handle so the bore forces the ends to the true diameter. They will in effect get stuck, and as you force them through the bore they will find the centreline and biggest diameter "automagically", and as soon as you pass the centreline of the bore they will "pop" free.

It sounds complicated, but in practice its really simple. Snap open a little bigger than the bore, tighten lock, swing handle to force the ends through the bore, remove from bore when they pop free. Then comes the next part, measuring them to find out what the bore is:

Measuring over ends - Nikon D200, AF-S DX VR 18-200 @ 200, +1,7, built in flash

You simply rest one end on the fixed anvil of the micrometer, and rock or swing the other end while slowly closing the mic. As soon as it drags against the closing anvil thats your measurement. Its easier if you have something white or light behind the mic, then you can see the gap close and next comes the drag. DON'T look at the thimble while closing the mic. Keep looking at the anvil and swinging end, and when you feel a light drag - stop and see what your measurement is.

Be sure not to force the tips through the micrometer, because you could in effect mash the gage smaller. What you want is to recreate the drag felt in the bore when you set the gage in the first place.

Repeat the measurement at least once to make sure you didn´t bump or somehow affect the gages - you don´t want that bearing to rattle around when you (think) you are done! :-)

Advice: don´t buy cheap gages. I started cheap thinking I´d avoid spending a lot, but had to sell the cheap ones since they didn´t work properly. The plunger ends on those had a turned finish. Then I bought more expensive ones, still off-brand. They also went back, the plunger ends were smoother but the lock and action had a terrible feel. So I bit the bullet and ordered real Mitutoyo gages - and the light came on! Smooth action and feel, really well made, smooth, hardened plungers. Save yourself the frustration and get the good ones right away.

Ignore the quality of the next picture. Having said that, this job went smooth thanks to the gauges:

Repaired stud - iPhone 4s, shaky hands

This was a cast iron sheave with six equally spaced studs around the perimeter used as spring seats, all very worn. I turned the worn studs in the mill with a boring head until they cleaned up somewhat and then measured them. Bored the sleeves next, aimed for half a thou larger as measured with the t-gauge and the same micrometer, coated them with green loctite and tapped them home with a small hammer. Six different studs, six different measurements as the customer wanted minimum metal removal. They all fitted nicely. I aimed for a little clearance, toolmarks tend to smooth out as you tap things home and the loctite takes care of the rest. The harvester this sheave came from won't get that hot in service, so I felt confident using loctite. Had temperature been an issue, thermal shrink-fit would have been the solution.

So, telescopic gauges are really handy to have in the toolbox. You can easily measure work still in the lathe or mill, and using the correct technique and good quality gauges should enable you to work to really close tolerances. If you are like me you will measure bearing fits with ease. There are machinists who can hit less than a quarter thou, but that does take some skill, care and experience.

To be fair, you don't even have to use a calibrated micrometer to do bearing fits or fits in general. As long as you have the actual part that is to be fitted, what you care about is the difference in size between the parts, not their actual size. As long as you use the same mic for both internal and external measurements you'll be fine. 

Once set you can use them as a go/no-go gauge to check if you heated that shrink-fit part enough, or you can use them to...  well, thats for you to find out!

This is the start of it all!

Ok, so this is the first post. What can You expect to read here?

Anything and all things technical. Simple, right?

Wether it be about depth of field, taking pictures with your DSLR or iPhone, telescoping gauges, boring on the lathe  -  you will find it here! And if you ask for it, it just might end up here as well! Go ahead and try me! Who knows just how much you can stretch "technical".....


In this picture, note how using the longest setting (200mm) gives that shallow depth of field:

Greece - Nikon D200, AF-S DX VR 18-200 @ 200. Some cropping.