MTFCA Forum

A well known and respected T engine builder told me that if I was going to install Chevy small block 1.50 head valves in a T block, that I would need both a .015 os and a .030 os valve guide reamer. I didn't ask him why, so why would I need both? Is taking a .030 cut in the guide, TOO much, so you have to go in steps, .015 and then .030? Also, I wasn't planning to ream the tappet guides over size unless their wear forces me to do so. Is there anything wrong with my plans?

Told correct, you need to do the 2 cuts, from a worn STD guide a .030" will not start.

Thanks, Frank. I figured that was the reason.

Terry, lots to understand in this beside using those two reamers.

To begin with, I will first point out that I have not machined that many T engines (i.e.: over 100) however almost every one of them I did had enough wear to warrant resizing. So this discussion I think comes down to the issue that most people (-including some machine shops or rebuilders) lack the metrology to accurately measure the bore of the guide area. Here (https://goodson.com/products/mvg-34-spl ... bore-gauge) is what it takes to measure all 8 bores accurately. Because of this, some folks just bypass the measurement stage and begin with the reaming process. Maybe the bores could have been cleaned-up with an 0.015 oversized reaming. Maybe it needed 0.030 -or more??

So now with Reamers in hand, the next issue with using a non-piloted reamer like most vendors sell is the ability to ream the hole and have it exactly perpendicular to the deck of the Cylinder Block. One of the better ways of doing this procedure is to mount the Cylinder Block onto a vertical milling machine using the pan rails as the datum, and then locating the centerline of the guide area with a tapered carbide pilot. Afterwards, check that location using a concentricity gauge. At that point, use the mill and a collet to accurately ream the hole. When the block has been reamed to the appropriate size, the location of the valve seat and face of the block can be machined within tolerances piloting the cutter on the reamed hole. Doing this with a hand drill turning the reamer is a recipe for disaster. FWIW, I have seen fixtures used by others that pilots the reamer shank however I am suspect on their ability to accurately machine the proper angle and/or location.

I might also add that most Tappet (valve lifter) bores are worn also due to the side-thrust loading caused by the camshaft lobe rotation. This is another area where owning/using a Surfacer (-I own a Kwik-Way 858 converted to a CBN cutter) is a huge advantage because it will use the pan rails as the datum and machine the Cylinder Block deck surface to be coplanar with the centerline of the crankshaft. Then with the block inverted and clamped against the mill table, the Tappet bores can be reamed and honed while knowing they are exactly 90° in relationship to the camshaft.

I purposely did not bring up the topic on machining the block for bronze valve guides as I suspect it has been discussed elsewhere here but I can post some pix of my counterbore cutter and reamers I use, ...but just know you better have a sacrificial block, and at minimum a larger Milling machine to practice on first before you try that on a block you plan to use.

Brent, Thanks for all your information. Instead of reaming the valve and tappet bores, myself with hand operated reamers, I probably will just let the machine shop that I use to bore the cylinders and other work, do it all. Yes, I might could get buy using a .015 oversize stem T valve, but i was going for the slightly larger head diameter.

What is your hope/goal with using the Chevy valves instead of going to the next size up stock valves?

If I understand correctly, the chevy valve stems are the maximum diameter the guides can/should be bored to and if you are using a 26/27 block might more subject to cracking than the earlier blocks, through the valve seats and guides as well into the cylinder bores which may or may not cause an issued down the road. My block has cracks in it but since it has hardened seats and the crack is under one of them and another crack at a cylinder stopped in very the upper part of bore where the rings do not ride, and was advised to proceed with installing .030 over stock stems and re-cut the seat so why not use a standard .015 or .030 over, which would leave some meat on the block for Chevy stem size should it be needed in the distant future?
If it is because the goal is more performance & flow, are you going also port the block to help increase the in & out flow as well as the larger intake manifold?

Just inquiring, no critique, just want to learn more.

A wise choice, let the machine shop do it, unless you have the right tooling it is near impossible to ream a guide square to the seat by hand.