Since the 1980's, engine remanufacturers have known of the significant cost savings that can
be achieved by reaming the valve guides and installing remanufactured engine valves that are
sized slightly larger (typically 0.008 in. O.D.) than new engine valves. By standardizing the
intake and exhaust valve O.D.'s to the same oversized diameter, both heads of a typical V8
engine can be reamed in approximately 2 minutes.
The majority of the engine remanufacturing industry agrees that benefits are to be had from
wet reaming, but little information exists showing, systematically, the specific benefits
of using coolant to aid in valve guide reaming. To achieve highly accurate and consistent
diameters with a reamer, one must consider process variables that can influence the
overall quality of the reamed engine valve guide. Variables such as reamer material or design, valve
guide material, temperature at the reamed surface, drill speed, operator movement, etc.
must be addressed.
The following study seeks to show that by controlling these variables to the best
extent possible, the reaming process can easily produce highly accurate, and consistently
sized guides. To this end, 486 engine valve guides were reamed under three different conditions.
A group of valve guides were reamed with coolant continuously delivered to the reamer,
(WR). The second group of valve guides was reamed with a reamer that was dipped into
coolant prior to performing the reaming function, (SWR). The final group of guides was
reamed completely dry, (DR).
MATERIALS AND METHODS
Engine cylinder heads with integral cast iron guides manufactured for Ford Motor Company (302
cu. in. V8) and General Motors Corporation (350 cu. in. V8 and 4.3 L V6) were the subjects
within this study. The CalValves R-3516 (11/32" + 0.008" oversized) valve
guide reamer performed the cutting operation which left the engine valve guides oversized from
original equipment specifications. An Ingersol Rand heavy-duty drill (Model 7811, rated at
2750 free RPM at 90 psi air) was used to rotate the reamer during the cutting operation.
The seat cone utilized was from the K-Line Boring Bushing Kit (K-Line part number KL8550)
and the conjoining boring bushing was a Cal Valves oolant through bushing (Cal Valves
part number CBD (0.2270 in or 6 mm)).
The reamer setup involves sliding the boring bushing over the reamer, chucking the
reamer up to the drill, and sliding the appropriate seat cone over the boring bushing.
This operation was the same for all reaming processes, WR, SWR, DR. For WR, the boring
bushing was then connected to a coolant feed pump.
For the reaming operation, each cylinder head was positioned in a
reaming station with the combustion face facing upward. For WR and DR, the pilot end of
the reamer was placed into the engine valve guide to an approximate depth of 1" and the seat
cone was pressed firmly against the valve seat. For SWR, the reamer was submerged in the
coolant as to fully coat the cutting edges of the reamer just prior to placement in the
The drill was then activated and the reamer was smoothly pushed down the guide with
little pressure. (It should be noted that for the case of WR, coolant would begin to flow
as the drill was activated and flow would discontinue only after the drill trigger was
released.) Once the cutting edge had completely passed through the engine valve guide, the reamer was
withdrawn from the guide.
With the reaming process complete, the valve guide inside diameter (ID) was measured
with a Sunnen P-310 Valve Guide Gauge. The ID was measured in three places as to achieve
an indication of the internal macroscopic geometry of the valve guide. Measurements were
taken and recorded from each end (rocker and combustion face sides) and in the middle of
the reamed valve guide.
RESULTS AND DISCUSSION
The results of the reamed valve guide inside diameter measurements are presented in
Figure 1. A summary of the average valve guide diameter is shown in Table 1.
The distribution of the WR measurements is narrow with a sharp taper around the mean
value indicating little deviation in hole diameter. The SWR distribution is less dense
with a distinguishable tail, which indicates a wider deviation in size and significantly
less repeatable sizing. The population distribution for DR is widely dispersed with only a
very minor display of central tendency that demonstrates a wide deviation in hole size and
Post-reamed valve guide ID results
Table 1. Average valve guide ID , in.
The results show that wet reaming yields more predictable and consistent results
while dry reaming gives the greatest variation of results. The data was further processed
using the Mann-Whitney U-test to determine if differences in any combination of the three
distributions were statistically significant. All combinations showed the distributions to
be statistically significantly different.
Since each of the three groups were reamed under the same conditions, using the same
equipment, with the only difference being the amount of coolant used, the results
statistically support the conclusion that wet reaming has a positive influence on valve
guide finished characteristics by allowing guides to be reamed repeatedly to a consistent
Cal Grinding, Inc. thanks Gopher Motors for providing the test specimens for this
FOR MORE INFORMATION
Cal Grinding, Inc. 1401 North 26th Street Escanaba, MI 49829-2500
P: 906-786-8749 F: 906-786-1398 E: Sales@CalValves.com