Trying to size id for valves. Using an expandable reamer. With a small bore gage the id seems to be larger where the guide is in cast iron but smaller where it is out of the cast iron, i.e. valve spring area and port area. ; is the hour glass bore typical of bronze guides? I can feel a difference in dia, bore feels smooth using the reamer, a pass or two with a ball hone and call them good?
Reaming bronze guides is tough without a reamer made for bronze. The areas you describe are likely expanding on the OD as you ream and less material is being removed there. You may be able to get by with focusing the honing at top and bottom...not ideal but I may have done such a thing a time or two. Don't want any tight spots!
That is common. Not hour glass but barrel shaped. A carbide reamer (for bronze) can be used to get to your final size but, I prefer to hone the last (say .0005) to final size using a Sunnen Honeall and honing oil. You want a straight smooth bore with some cross hatch to retain some oil. This is the right way to do it but the tools are expensive. Cheaper having it done by a competent machine shop. There is some newer tech using single pass diamond reamers but that's for shops that can recoup their investment. The ball hone is no good as it will just follow the contour of the shape it rides in. P.S. If this is just a quick and dirty deal and you don't care how long it lasts then well... it is what it is
I think I was more confused/surprised by the barrel shape bore [thanks Tomcatll/chicken] and I assumed it was the bronze [Looks like Brass to me!] flexing but wanted to hear from experience. With a small hole gage and a mic I get just about .0005 from ends [.3145] to middle [.315] . Valves stem dias are Int .314 and Exh .313 so a .316 bore in all would give me the .002/.003 int and exhaust clearance needed. I got my dial bore gage to work and it got .0004 diff from ends to middle so I was close with the mic/ small hole gage. If the guides are CI with the bronze insert [Frenchtown] in hind sight I could have lined the stock guides. I will check around for someone/shop that can do that last .001 with out making me wait 6 months. I do have some adjustable laps but I would have to use some lapping compound.
Sounds like you have a good plan Seb. I was a little worried you were not going like what I said in my reply. I bought the Sunnen hone and a split ball bore gauge just because I'm particular about these things and don't want to wait either, but boy they are not cheap!
Bronze valve guides in aluminum heads are one thing, since bronze and aluminum expand at similar rates. Bronze valve guides in cast iron heads are another thing entirely. Bronze expands at roughly twice the rate of iron. Since the OD of the bronze guide is constrained by the iron head, the expansion is forced inward and ID will contract and can pinch the valve. When setting your valve-stem-to-guide clearances, talk to someone who's successfully run those same heads with those bronze guides with those valves in that application. jack vines
Yes, he said to run .0025/.0035. I selected a lap and adjusted to have some drag in the tight spots. Applied some lapping compound and gently rotated and feed it in and out of guide by hand. I could feel it working, better or worse. Cleaned guide with nylon brush and brake clean. Checked with dial bore gage [I fixed gage with a dab of wd40] and got almost to size by .0002 and -.0002 taper. Maybe I lucked out, if I can get 7 more that would be great. Going to have to do some polish work on arbor, .315 not quite big enough and .317 hair too big.
Good deal. When you're finished, you might consider brushing the guides with soapy water. The detergent floats the tiny particles loose and out - brake clean can't do that nearly as well. Grit in guides ruins your day.
Go slow, use good quality lube, and use good quality reamers. Years back I bought a pair of high end aluminum heads. I removed the valves...to check the sizing of the guides. They were ALL "barrel" shaped ! I had a long talk with "someone" there at the shop. He gave me a hard time telling me the excellent work that they do, etc., etc. I told him to call me when they received my heads. He did. He removed a couple of valves while on the phone. His silence told me everything I needed to know. He finally admitted, that they "could have been done better". And yes, I marked the heads to make sure that I didn't receive a "fixed" set of heads. While the second set weren't perfect, they were usable. So yeah, even the "experts" can screw up. Mike
I have seven guides lapped in to nominal size, .316 with -0002 taper, #8 [exh] gave me a hard time and ended up at .3165, right at max but .000 taper. So I call that good. I have a .317 cutter pilot that I have to polish down some to work, couldn't find a .316. and an 8mm doesn't get tight enough. Thanks to all.
The Jalopy Journal
