My son and I run a small automotive machineshop doing engine rebuilding and custom machine work in ruralMissouri. We try to do the very best work possible all the time.Whether we are rebuilding a Ford 8N or a 427 Corvette engine,we use the same amount of care doing the job. When our customerspick up their parts, they are confident that the job has beendone correctly.
Who should read this article?
This article was written for the small shopmachinist who may not have every piece of high tech equipmentin the world at his or her disposal. This small shop is tryingto turn out quality work and at the same time make a profit. Also,if any of the following "warning signs" exist in yourshop you should read this article on honing:
- The engines you bore and hone seem to useoil after only a few thousand miles.
- You feel the piston rings that come inengine kits cause engines to use oil and have excess blow-by.
- You hate honing engines because you alwaysend up with tapered cylinders.
- The last time you tried to hone an engine,the hone locked up, and the drill twisted your arms and hit youin places I can’t mention in this article.
Source of information
I have tried to take 35 years of automotivemachine shop experience, plus what I have seen others doing bothright and wrong, and cram it all into these few short pages onhoning. If what we talk about here helps you do a better job honingengines and making more money, we will have done our job.
My son and I enjoy doing machine shop work,but we have found that we must make a profit in order to stayin business. We need to turn out good work in order to keep customerscoming back, and we need to charge a fair price for doing it.My equipment sales representative who calls on our shop in Cuba,MO, reminds me of this very important point almost every timehe visits. He often tells me that as an industry we work too cheap.He says, "You have to charge for what you do."
How to read this honing article
I think most of us in the automotive businesslike to page through technical magazines and look at the pictures.We often read the captions under the pictures and think we havetruly absorbed what the writer was trying to tell us. I have includeda number of pictures to capture your attention so go ahead andtake a look, but come back and read the rest of the story. I thinkyou will need to read the story at least once, perhaps twice,to understand thoroughly what we are doing and why.
As machinists we are called upon to bore andhone engine cylinders as part of our job. It is a fact, enginesdo wear out – mostly from what people do or fail to do to them.If engines did not wear out, we would all be looking for differentwork.
Sometimes we fail to mention honing when wetell a customer that we are going to bore his or her engine torenew the worn cylinders. Honing is perhaps the most time consuming,least understood, yet most important part of the entire rebuildingprocess. Honing also requires a good deal of skill on the partof the machinist doing the work.
Sure it would be nice to have a new power honeto recondition our cylinders, but as I said before, this articleis written for the shop owner that does not have every piece ofequipment he’d love to own.
In our shop we use a Van Norman boring barthat has been my friend for more than 30 years. I think my 777Sis trying to out live me. I can depend on my boring bar to borestraight, round and right on size every time. I keep the toolbits sharp and the cylinders look great when the bar gets finished.
However, I know if I were to look very closelyat the cylinder bores, I would find that the surface finish isstill much too rough for new pistons or rings. We must hone thecylinders to obtain a surface finish smooth enough for the newpistons and rings.
Getting set up for honing
When I rebore a cylinder I leave three thousands(.003") for honing. For example, if I am boring a 4.0"cylinder +.030", I set the tool bit at 4.027". Thisleaves .003" for honing .
It’s a really good idea to have the pistonsyou are planning to use in your hands, before you start to borethe engine. This allows you to measure the pistons and make certainthat you will have the correct clearance between the piston andcylinder wall when you get finished boring and honing. When Iam finished boring all the cylinders, I remove the engine frommy boring stand and move it to an area of our shop where I domy honing.
Here is an important shop tip to keep in mindwhen boring an engine cylinder. Let the boring bar go down farenough so that when you hone the cylinder, the hone will not catchthe ledge above the main webs in the crankcase. On a Chevy 350,for example, I let the bar go down until it almost starts to touchthe main web.
After you finish boring an engine, do not wipeor even touch the freshly bored cylinders. In other words, keepyour oily mitts off the cylinder walls. Also, do not spray anythingon them. Do not put the block back in the hot tank or spraywasher.You should be ready to go directly to the honing operation whenyou finish boring. Shop towels and hands have oil on them; evenclean shop towels have oil on them. Freshly bored metal will pickoil up like a magnet.
We are now ready to start honing our blockdry, and we want to keep it that way until we have removed .002"of the .003" we allowed for honing. Take time to secure theengine block so the deck surface is facing up. We have two setsof simple stands made of angle iron to hold most V6 and V8 blocksso that the deck surfaces face up when I sit the block on thefloor.
The stands we use bolt to the pan rails ofthe engine block. If you are trying to hone your engines on aworkbench or engine stand forget it! Blocks of wood don’t workeither. The engine you are going to hone must be mounted solid!
Before we get started, let’s talk about someof the equipment you will need to hone engine cylinders. You willneed a good micrometer set and the standards to check them. Adial bore gauge is almost a must, but you can get along withoutone if you have to. We use a Sunnen dial bore gauge in our shop.
Here is a tip that may save you some money.When you have finished using the dial bore gauge lay it down ona flat surface, not on the top of the engine deck. The dial boregauge will roll if you place it on the narrow engine deck surface.Just like dropping a piece of jelly bread, the dial gauge willhit the floor face down every time.
You should have a telescopic gauge to use withthe micrometer to double check the cylinder bore size before andafter honing. Of course, you must also have a hone. We use a SunnenAN series hone body and stones. We made our own drive shaft tofit the hone body. Our design allows the shaft to slip if thehone happens to lock. The Sunnen drive shaft is fine, but it isdesigned to twist off if a lock-up occurs.
Here is another tip. If you are using the Sunnenhone and drive shaft, and it gets broken, replace it. Do not tryto beef it up by welding extra reinforcing material to it. Sunnendesigned it to break if the hone locks up.
Now you need something to drive the hone. Usea good electric drill that has an "on" and "off"trigger switch. We use a Black & Decker Professional modelhalf-inch drill with reverse. The drill must be a medium-speedunit.
The rpm the drill turns at, and the speed withwhich you stroke the hone up and down the cylinder, will determinethe angle of the cross hatch marks left by the hone. The crosshatch marks help hold oil on the cylinder wall during break-in.You don’t want the cross hatch too flat or too steep.
After you start honing your first cylinder,take a few minutes to look at the cross hatch lines. You willquickly get a feel for how fast you must stroke the hone. Do notspend a whole lot of time measuring the angle of the cross hatch.I don’t think it makes a lot of difference anyway. Shoot for anangle of about 35° to 45° on the lines. A little moreor a little less won’t make any big difference.
Cylinder wall finish, however, will make abig difference, so pay more attention to it. Stay away from thoseold gear drive drills with powerful motors and low gearing. Theyhave so much torque, and they take far too long to stop turningwhen you let go of the trigger. You may be sorry! You could endup hanging onto the drill for dear life while you and the drillgo round-and-round until the plug pulls out of the wall!
Now we must attach the drill and hone to somethingthat will help counterbalance their weight and that will providea positive down-stop for the hone. I use a device made by Sunnenthat has a spring and a rod with a positive stop adjustment onit. The spring helps support the drill and allows us to move thehone up and down with very little effort. If you do not have thisdevice, buy one or make one.
I attach the drill to the counterbalance devicewith a short length of chain to the threaded hole in the end ofthe drill motor. I have a chain hoist directly above the areawhere I hone my engines. I hook the spring assembly with the honeand drill right on the chain hoist. The chain hoist allows meto raise or lower the hone and drill assembly quickly and veryprecisely.
I have seen many people trying to hone a blockby hand, by just holding the drill without some type of support.You are asking for problems if you try it. That pretty much coversthe major equipment you will need. You should have most of italready.
One more comment about the hone. You must usea rigid type hone to hone a block after boring. Do not even tryto hone a block using a springloaded hone or a brush hone. Theyhave a purpose in life, but they are not designed to remove .003"metal after boring!
Having just finished boring our engine block,we now move it over to the area of the shop where we are goingto hone it. We have mounted the engine block so it wont move aroundfrom the torque of the hone. If you are going to use a torqueplate during the honing process, torque it in place now.
Make sure the hone body is clean and free fromoil and install your set of AN-100 stones (or equivalent). Westart with the coarse grit stones first. These stones are to beused dry. They go into the holes on the hone body marked withthe "X". Do not touch the stone surface if you can helpit.
By the way, keep all your stone sets in theirown boxes when they are not being used. Stones become a matchedset as soon as they are used and must be kept together. If onestone gets damaged, the whole set is junk. Normally a set of stoneswill hone quite a few cylinders before they become worn out andneed to be replaced.
Set the block under the hone and push the honedown until it is stopped by the positive stop on the spring fixture.Now, using the chain hoist, lower the hone down into the firstcylinder until the stones just protrude through the bottom ofthe cylinder. Adjust the stones out until they lightly contactthe cylinder wall.
Lightly pulse the drill motor and move thestones down farther through the cylinder with the chain hoistuntil they come out the bottom of the cylinder about one inch.When you feel them just begin to bump the crankcase webs, raisethe chain hoist slightly. Note, I said lightly pulse the drill,and move slowly, as you go down into the crankcase. You do notwant to bang your new stones into something down in the block.
The positive stop on the hone counterbalanceallows you to go as far down into the cylinder as possible onevery stroke without the stones hitting the crankcase webs. Itis very important to have the stones come out the bottom of thecylinder while you are honing to keep the cylinder straight.
Now let’s get started actually honing. Crankup the pressure on the stones, and begin to stroke the hone upand down the cylinder. Go all the way down and contact the positivestop on every stroke. The hone should also come out the top ofthe cylinder about one inch on each stroke.
If you hone too much on the top of the cylinder,you will taper the bore. You must get a feel for how much tensionto place on the stones and how fast to move the hone in the cylinder.When the stones are cutting right, there will be a considerabledragon the drill motor. If you put too much pressure on the stonesthey will make lots of noise and not cut any faster. Too muchpressure will also cause excess heat and stone wear.
If you happen to get oil on the dry stonesthey will stop cutting and become loaded with metal and stonematerial. Stop and try to scrape the junk off the stone surfacewith an old file. I have used lacquer thinner in extreme casesto clean the AN 100 series stones. However, it’s best not to getoil on the stones in the first place.
Since you are working these stones dry, dustwill be produced. Use a dust collector or shop vac to collectthe dust while you are working. I usually wear a dust mask whileboring and honing. You will need to hone a little and stop andmeasure until you get a feel for how fast the metal is comingout. Use your micrometer to set the dial bore gauge to the finishbore size you want, and start checking the cylinders.
As you hone, the cylinder will become warm.This may give you a false reading. You may think you have removedmore metal than you really have. Let the block cool a few minutesand go back and check again. You want to use the AN 100 stonesuntil you have removed the first .002" of metal. Do all thecylinders in the block with the dry stones before you change tothe finer stone sets.
Here is a tip that you won’t find in the books.This is something I found out on my own some years ago. If forsome reason the stone set you are using or the cylinder you arehoning becomes tapered, you may be able to save the day and thestones. Stones do not come from the manufacturer tapered. Theyget that way because you are not stroking far enough out the bottom,or you’re too far out the top of the cylinder.
Try this before you junk the stone set. Takethe stones out of the hone body holes with the "X" mark.Now put them back into the holes without the "X" mark.You will have to turn the stones upside down to do this. Put theadjuster back in and put the hone back in the tapered cylinder.Expand the stones out by turning the adjuster the opposite direction.
Now run the drill in reverse and stroke thehone up and down the tapered cylinder. You must run the drillin reverse to do this or it will lock up. You will be surprisedhow quickly the stones will straighten out. This will also removethe taper from the cylinder (At least one supplier of stones doesnot recommend stones be turned upside down and taper correctedas described in the above procedure. The company says if stonesshow taper they should be either filed, put into a truing sleeve,or replaced with new stones. When possible, proper overstrokewill prevent stone taper. – Editor’s note).
When you stop honing to check the cylinderfor size, be sure to keep moving the hone up and down until thedrill stops turning. The hone will usually make about one or twoturns after the drill trigger is released. It takes about 100strokes to remove about .002" of metal from a 4.0" cylinder.I usually count the strokes so I have some idea when to stop andcheck the cylinder for size.
Out of the dry and into the wet
Your cylinders are now honed to within .001"of the desired finish size. They should be straight and round,and the cylinder walls should look bright and clean if you wipethem with a clean dry cloth, not a shop towel!
You should have checked the cylinders withthe dial bore gauge after the block cooled, and now you are readyto go to a finer stone set. Install the AN-200 set and using thesame procedure as with the AN-100 stone set, stroke the cylindersand at the same time add honing oil with a pump oiler. Use plentyof oil as you hone with the AN-200 stones.
After about 30 strokes check the cylinder forsize. You can turn off the dust collector now. You will be ableto feel the hone begin to pick up speed as the cylinder surfacegets smoother. You should now be down to less than .0005"of the finish size.
After you have honed all the cylinders withthe AN-200 stones, switch to the AN-300 set and again hone withoil for about 30 strokes. The oil will keep the stones clean andform a slurry in the cylinder as you hone. You should now be atthe final size. Allow the block to cool and recheck with the dialbore gauge.
Honing a block by hand does take time. I spendabout one hour honing a V-8 block. It takes time to do the jobright. You will quickly get a feel for what is happening in thecylinder when you hone by hand. For example, when a torque plateis bolted to the deck, you will feel the out-of-roundness causedby the bolt torque as you begin to hone the cylinder. As the honingprogresses you will feel the torque on the drill become steadyand smooth.
Following the above process will provide youwith a surface finish between 15 and 20 micro inches. If you wanta finer surface finish use the AN-500 stones with oil and honeanother 10 to 15 strokes.
You’re not done yet
The engine block is now finish honed and youhave checked all the cylinders for taper and size. Double checkyour work with your telescopic gauge and micrometer.
You should always clean the block before itleaves your shop. We charge one hour labor to clean a customer’sblock after boring and honing. You can tell the customer thathe needs to clean the block because there is lots of honing gritin the cylinders, but most customers will not clean the blockthemselves correctly. If you want them to have success with yourrebore jobs you better do the job yourself.
My son, David, is an expert at cleaning blocksafter honing. He uses hot water, Tide, and good bore brushes.He cleans all the cylinders and all the oil passages by hand.
The crankcase webs need special attention,too. Grit loves to hide in the crankcase webs. After all the handwork we pressure wash the block with very hot water and then transferit to a mineral spirits bath in a clean solvent tank. Here wehand scrub all the cylinders with clean solvent to remove anywater from the pores of the metal.
You must act quickly after washing with hotwater because rust forms almost immediately on the cylinder walls.After flushing the block with clean solvent put a light insidethe engine case and look at the cylinder walls. They will be brightand very shinny with a good cross hatch pattern. The engine isnow ready to be covered with plastic until it is assembled.
Checking your work
If you want to be sure you have done a goodjob of getting the surface finish right, purchase a profilometerfrom your shop supply source, or contact your local equipmentrep and ask him to stop by and test some of your cylinders forthe Ra finish. You can’t tell how smooth the surface is by justlooking or even feeling with your finger. The profilometer willgive you an accurate measurement of the surface finish. Our ownrepresentative has tested our rebore jobs and found the finishto be right in there at 17-20 Ra.
I realize what I have described is a long procedurewith many steps. But I have found that this procedure also producesvery good results. Many of our engines have gone well over 200,000miles and are still performing with very little oil consumptionand low blow-by.
We also use moly rings on almost every jobexcept where excess dust will be encountered. In those engineswe use chrome rings. I did not say it would be easy or quick,but I did say you could do very good work if you are willing totake the time to do it right.