|How to find a
HOW TO FIND A GOOD MACHINE SHOP AND A FINE BOWL OF CHILI
One way is to go to the GS Nationals in Columbus Ohio, attend the GS big block tech session then stop at
Skyline Chili on the way back to the motel. The next best way is to pop a bowl full in the microwave and to
read the GSXtra.
I had the opportunity to address those that attended the big block tech session on Friday night of the Nat’s
on the subject of how to find a good machine shop and for those that could not be at the Nat’s I will repeat
Bernie Rekus had instructed us to be as unbiased as we could in our presentations, so I decided to
concentrate on just what quality means when machine work is performed.
The following are the guidelines that I set for certain machine shop procedures and questions that might be
asked of the shop before leaving your prized pieces to be fondled by those that might not be as interested in
the quality that you might be.
Cylinder preparation: Cylinders must be bored with a boring bar whether deck mounted or positioned by the
crank, in either case the deck is used to center the bore unless a BHJ bore-tru is used, which corrects bore
centers and bores perpendicular to the crank housing bore. At least .003 must be left to hone to remove the
fracture left by the cutter (all ring manufactures recommend this). A power hone such as the Sunnen CV-
616, the older CK-10 or the new Rottler is the only way to hone a cylinder round and without taper unless
the operator has the patience of Job. With a torque plate and a power hone as described .003 to .005 can
be removed in less than an hour with accuracy of within .0002, that’s two tenths roundness and less than .
0005, that’s one half a thousandth taper. The exception to the taper is that the Buick blocks V-6 and V-8, as
with several other factory production models have unsupported sections of the cylinder at the bottom and
this unsupported section may measure a couple of tenth’s smaller. A shop with a lesser machine may only
bore to size and hone only about .0005 (one half thousandth) because it would take several hours to do the
job described with the power hone. The finish should be that as prescribed by the ring manufacturer. The
finished size should be at least the minimum clearance as described by the piston manufacturer.
Crankshaft housing bore preparation: All of the align honing machines that I have seen will do a good job of
straightening and correcting the inside diameter. Don’t use an align boring machine to try to straighten or
size the housing bore, it’s function is not for this purpose, it is used to correct drastically damaged housing
bores and when different caps are used, then must be honed for size and straightness. The finished size
must be within the factory tolerances
Cylinder deck preparation: Most machines capable of re-machining the deck of a block are pretty much the
same as far as the end result, but those that set up off the crankshaft housing bore will produce what is
generally called a square deck and will leave the same deck height end to end. Again as with the Bore-Tru,
BHJ has a fixture for most engines that corrects the deck end to end and also side to side.
Rod re-conditioning: Most machines made for this operation do a good job as long as the operator is
qualified and wants to do a good job. The finished size should be within the factory size.
Crankshaft preparation: Any good high performance crank should be ground to nearly perfect tolerances
and it takes very little extra time by a qualified machinist and a good machine to do a crank for a stock
application the same way. Rod journals should not have more than .0002 (two tenth’s of a thousandth’s )
difference measured four ways on a journal and also journal to journal. Three tenth’s (.0003) is the limit. The
same applies to the mains except the thrust might be .0005 smaller. Actual sizes of the crank depends on the
application and the clearances desired by the engine builder. The clearances should be ground into the
crank after the rod and crank housing bores have been re-machined and bearings installed and inside
diameters checked with a precise gauge for the rods and a dial-bore gauge for the mains.
Cylinder head preparation: Valves should be ground with a machine capable of less than .0005 (one half
thousandth) run-out. Seats should be ground the same way, less than .0005 run-out. The more modern way
of doing seats is with a seat and guide machine that uses three angle and radiused carbide cutters. These
machines do each seat precisely the same and also the same depth which is also important in trying to
maintain proper stem length on non-adjustable valvetrains such as stock Buick’s. An easy way to check
seats is to have the heads clean and positioned so that you can drop the valves in. If the valves pop back up
easily the seat is pretty close. Another way is to rest the valve in the seat and wiggle the valve in four
directions if they move the same, turn the valve 180 degrees and do it again, if again they move the same
the seat and the valve are concentric. With new valves and guides the movement will be very little.
If the valves seem to stick when dropped in or won’t move in one of the directions when seated and wiggled,
the job is not done properly.
It would be imposible to put everything necessary in just one column but the idea is the same in any
procedure, a better machine and a qualified machinist does a better job. How good does you job need to be
If your shop had been satisfactory to you, by no means change because of any mention I have made to
certain procedures. A good machinist is better than a better machine and a lesser machinist. If you are
dissatisfied with your current shop and want a change, ask questions of your next one before you try it. If he
can offer the services and quality previously described you have a better than average chance of getting the
job done right.
A few tools are necessary to check the work done by the machine shop and yes I said check the machine
shops work. Erasers are put on pencils for one reason, everyone makes mistakes.
A set of micrometers that measure in tenth’s of thousands are necessary to check the crank and a dial bore
gauge is necessary to check the housing bores of the rods and the mains in the block, also to check the
If you are spending thousands of dollars to build an engine, spend a few hundred to make sure it is right
when you put it together.
I hope everyone that attended the GS Nationals in Columbus Ohio had as good a time as I did. The weather
was great, the racing was great, the car show was great and so was the Skyline Chili, well I had to go to town
to get that. I just hope the following years will be just as enjoyable.
To send a question to Mike
E-mail to AMPMIKE@aol.com
Send a self-addressed stamped envelope to
6235 Hwy 54 Philpot KY 42366
machine shop, machine work, valve job, block work, honing, boring, porting, flow testing, dyno, dyno tune, balancing, rod work, engine building, blue printing,