Most automotive machine shops use a substantial quantity of valve guide reamers which constitute a significant amount of shop expense over a period of time. Therefore, we have compiled this information for the machinist to use in obtaining maximum life and efficiency from valve guide reamers.
There are two types of valve guides found in a majority of cylinder heads today: cast iron and various bronze alloys. The two types of guides have entirely different reaming characteristics by virtue of their metallurgical composition. While greatly improving guide life and durability, bronze is a very difficult material to ream as it has a tendency to stretch and tear rather than cut cleanly.
Cast iron guides are relatively easy to ream as compared to bronze. It is wise to use bronze reamers for bronze only when both types of guides are encountered on a day-to-day basis by a machine shop.
Cast iron guides should be reamed dry for best results in both size and finish. Reaming dry helps keep the chips from accumulation and clogging the reamer flutes, which leads to reamer chatter and breakage. When properly used, the valve guide reamer should ream cast iron to the size designated on the reamer.
Cast iron guides will cut cleanly and are highly machinable. Normal care in maintaining reamer alignment and proper speed and feed will result in long reamer life and excellent size and finish control in the guide i.d.
Bronze valve guides should be reamed wet with an appropriate cutting oil. We find Bronze Reaming Oil to be an excellent cutting compound. We have found that a very slow steady reamer speed works best in reaming bronze. There is also a tendency for the reamer and guide to heat up and cause undersized reaming. To alleviate this, use two reamers alternately, allowing the reamer not being used to cool in a container of cutting lubricant. The finished hole will ream approximately .001 under the reamer size due to the cutting characteristics of the phosphor bronze. The coolant should be kept clean to prevent foreign material or chips from damaging the reamer and/or the hole.
FEED RATE
The best feed for reamers is usually higher than the recommended for drilling the material in question. The best feed will be best determined by experimentation and experience, but a starting point would be as suggested below.
| MATERIALS |
FEED RATE |
| Aluminum | 60" per min. |
| Bronze | 12" per min. |
| Cast Iron (soft) | 14" per min. |
| Cast Iron (hard) | 10" per min. |
| Cast Iron (chilled) | 4" per min. |
REAMER SPEED
Basically, we are trying to use the highest speed which results in the required finish and size.
The best speed for reaming is determined by the material being reamed and the final finish desired. Normally the best speed is around 2/3 of the recommended drilling speed for the material. These are examples of recommended reaming speeds in common automotive materials.
| MATERIALS |
REAMER RPM |
| Aluminum | 2000 |
| Bronze | 650 |
| Cast Iron (soft) | 800 |
| Cast Iron (hard) | 550 |
| Cast Iron (chilled) | 250 |
The closer the tolerance needed, or the finer the finish, the slower the reaming speed must be. Reamer speed should always be slow enough so as not to induce chatter. Chatter not only leaves an undesirable hole finish, but is a great destroyer of reamers.
Common causes of excessive reamer wear and/or breakage are:
1. Too fast or too slow reamer speeds
2. Too fast or too slow feed speeds
3. Reversing reamer rotation and backing out of hole
4. Stopping reamer before going through hole
5. Poor alignment - reamer to hole
6. Careless handling of reamer
7. Lack of lubricant - depending upon material
8. Excessive chip build-up
9. Reamer chatter
10. Failure to keep reamer cutting (maintain steady feed)
11. Being bumped by other reamers or tools
Remember, reamers are PRECISION tools. They should be thoroughly cleaned, oiled and stored individually after each use