Need Someone With Machinist Knowledge Too Look At This Thread

[Diesel911]

Problem = 17mmH8 Hand Reamer (17mm = 0.6693”) is cutting a larger than 17mm hole Reamed ID = 0.6716” (one end of item was mounted in a Lathe Chuck and the other end of the Hand Reamer was supported by the Lathe Tail Stock Center on the Reamers center drilled hole).

Question what size Hole would a 17mmH7 Reamer make; would it make a smaller hole? And, what would that smaller Hole ID be? Or is there another Reamer that would actually make a real 17mm Hole 17mm = 0.6693”)?

Details:
Reaming the Bushings on a Bosch VE Fuel Injection Pump
Apparently there is very little information on the Subject. There is a Post that has that the Clearance between the Shaft and the Bushing is 0.001” and there is Vanagon Blog that said that Person used a 17mm Reamer when He reamed the Bushings.

I have 2 Fuel Injection Pumps so I am only going to speak about one of them.

Pump 1 Shaft measured over the un-worn area = 0.6682”

17mm = 0.66929 (ENCO Reamer size 17mm Reamer Size 0.6693)

In theory if I use a Reamer I should get a 17mm = 0.6693” Hole.

17mm = 0.6693” Hole
Minus 0.6682” Shaft OD
0.0011 Clearance
Mathematically that sounds great.

I bought a 17mmH8 Hand Reamer. I measured the diameter of the Reamer Blades which is difficult to do accurately and it seemed like more than 17mm?

So I figured that before I do any reaming of bearings I needed to try it out on something else and see exactly what the Reamer really reams to.

I have a small Aluminum Cylinder about 1” thick and 1-¾” in diameter and I mounted that in a Lathe Chuck and drilled a 5/8 Hole through it.

The 5/8” hole is enough to get the Reamers tapered end to start in. One end of the Reamer was in the Aluminum Hole and the other end of the Reamer was supported on the Center of the Tail Stock.

As I reamed the Tail Stock was advanced so that the Reamer did not wonder.

After Removing the Aluminum Cylinder and letting it cool I measured the ID and got; Reamed Aluminum Cylinder ID = 0.6716”. That clearly is not a 17mm = 0.66929 hole.

Reamed Aluminum Cylinder ID = 0.6716”
Minus 17mm = 0.6693”
The reamed Hole is 0.0023” larger than 17mm and the Shaft is actually smaller than 17mm at 0.6682”

Reamed Aluminum Cylinder ID = 0.6716”
Minus 0.6682” Shaft OD
That means a Shaft to Bushing Clarence 0.0034” not the target 0.001”.

And that was reaming the Hole on My Lathe where the Reamer was Well Guided. Without a good guide reaming the Hole by hand is going to result in an even larger Hole.

So that raised a question as to why the 17mmH8 (this is the commonly sold Hand Reamer Size) does not ream closer to a 17mm Hole?

What I found out is that the H8 represents a code as to what level of precision and as near as I can understand it an H7 Reamer would be a more precise Reamer. I guess meaning that it would ream closer to an actual 17mm Hole but I don't know how much smaller the ID would be.