Mar 20, 2017 update to the BMW M3 project car

Honing Cylinders

Expensive machines? The possibility of ruining an engine? Yep.
We started by assembling the correct combination of shims and honing stones to fit our engine's bore.
Next, we set the stroke of the machine, dialing in the top and bottom points of the hone's path.
Do we look bored? We were. Most of honing is starting at a gauge that shows the amount of power required to run the hone, which gives you an idea of how fast it's cutting.
We stopped frequently to check the our progress with a bore gauge.
Success! It was time to start assembling the engine.

In our last update, we prepared the engine block from our LS1-swapped BMW M3 for honing. Now, it was time to put it into the honing machine and actually enlarge our cylinders.

We were doing everything ourselves–yes, even running the honing machine–thanks to Daytona State College‘s performance engine rebuilding and machining class. For just a few hundred bucks, we were spending two nights each week working on our engine under the supervision of a few performance engine rebuilding experts.

After clamping our block into the machine, we assembled the proper combination of shims and honing stones on the head of the hone. Then, we took a few more measurements to set the stroke of the machine, lowered it into the first cylinder, and let it work its magic. Because honing creates heat, which changes the size and shape of engine blocks, we honed to within 0.002” of our goal bore size during the first pass. Then, after allowing the engine to cool overnight, we went back and honed those last few thousands.

The result? Perfectly round, straight cylinders that measured 3.905.” It was time to start assembling our M3’s new heart.

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Comments

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spitfirebill
spitfirebill UltimaDork
3/20/17 9:22 a.m.

This is the only time use of the dingleberry is legitimate and proper.

iceracer
iceracer UltimaDork
3/20/17 10:57 a.m.

dingeleberry is a deglazing hone. It oes not enlarge cyliners.

I have a hand operated hone similar to what Tom is talking about. I used it once to remove .030" from a Jeep block.

84FSP
84FSP Dork
3/20/17 11:20 a.m.
spitfirebill wrote: This is the only time use of the dingleberry is legitimate and proper.

Best quote ever. That is all.

bentwrench
bentwrench Dork
3/20/17 11:59 a.m.

To hone more than .005" is a waste of time. To remove that much material it is best to bore the cylinder first to within .003" then finish with a hone.

Jerry From LA
Jerry From LA SuperDork
3/20/17 12:09 p.m.

If I recall, the cylinders are in good shape and he's just changing clearances between the old cast pistons and the new forged ones.

iceracer
iceracer UltimaDork
3/20/17 6:10 p.m.

He said he wants to enlarge the cylinders.

einy
einy Reader
3/20/17 6:54 p.m.
bentwrench wrote: To hone more than .005" is a waste of time. To remove that much material it is best to bore the cylinder first to within .003" then finish with a hone.

What he said, mostly. Bore to get to size minus 0.025 - 0.050mm on diameter. Benefit of boring first is that it will fix whatever geometry issue exist in your cylinder bores if done correctly (i.e. Get past the corner radius on the insert being used so you generate primarily axial vs. radial cutting forces while minimizing tool wear and therefore diameter variability). Use rough hone to get to finish diameter, followed by a minimal number of strokes with finish hone to get desired oil retention characteistics (aka cross hatch), and end machining with a finish brush to remove torn and folded material from the resulting valleys. Flush profusely during all operations. Measure with dial bore gauge calibrated to appropriate gage ring.

Typically, cutting oil is used during honing to flush chips and abrasive from honing stones out of the cut area and control temp, so no need to wait for workpiece to "cool". If the bores got hot during boring and/or honing, there is a big problem with the process you are using.

Honing as much as was done is not only a waste of time and honing stones, and can easily result in funky tapers from bore top to bottom, even possibly bell-mouthing of the bore.

Robbie
Robbie UberDork
3/20/17 8:12 p.m.

I think they only honed .005...

TiggerWelder
TiggerWelder Reader
3/21/17 10:20 a.m.

Not sure if you have access to these tools yet, but I am putting together a 6.0 for my Suburban tow vehicle. There are special tools to align the front and rear covers and install the seals. About $70 if I remember correctly. If you want to borrow them, I should be done with them in the next few days. Shipping and some GRM swag would make it happen.

Tom Suddard
Tom Suddard Associate Editor
3/21/17 10:58 a.m.
Robbie wrote: I think they only honed .005...

.007", but yeah, we didn't take much out.

Why not bore first? Our instructor said that because we were starting with round, straight cylinders, it wouldn't be worth the extra time and effort. That's why we took a few extra thousands off with the hone instead of boring, then honing.

HapDL
HapDL New Reader
3/21/17 11:23 a.m.

This thread just proves that apparently machinists and lawyers are cut from the same cloth. Ask 3 lawyers the same question, get 3 totally different answers.

TimM
TimM New Reader
5/28/17 6:30 a.m.

So glad you are doing this project. I've wanted to try it for many years. Matter of fact, I just bought a 1997 M3 4D so hope the updates come a bit quicker. I'm targeting an L33 pullout and T56. Thanks.

TimM
TimM New Reader
8/5/17 8:11 p.m.

I was hoping this project would be a help to my build, but likely I will have it done before this one.

And I'm targeting December for the swap...

Robbie
Robbie UberDork
8/5/17 8:19 p.m.
TimM wrote: I was hoping this project would be a help to my build, but likely I will have it done before this one. And I'm targeting December for the swap...

I'll just as happily follow your build from across the internet though!

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