Reamers

[Eugen]

So I got a 5/16 fixed size reamer, intending to do valve guides finishing. I thought 5/16 is 0.3125 and expected it to be very close to that. When I measured it with the micrometer it shows 0.3130 which would make the hole a full 5 thousands bigger. Do any of you have any experience with this sort of thing? Did I just get a low quality reamer?

[propane1]

No experience in that. Never used anything like that. What clearance is required between valve guide and valve stem ?

Noel

[propane1]

My mathematical genius mind tells me it's 0.0005 bigger or 1/2 a thousand. I could be very wrong. My mind been wrong before.

Noel.

[Eugen]

According to the service manual, the maximum clearance between valve stem and guide, due to wear, is 0.0065". Also the service manual lists the size of the guide between 0.0312 and 0.0313.

My measurements of that engine were

Position	Guide ID	Valve OD	Wear (ID-OD)	Wear limit spec
Intake	0.313	0.3105	0.0025	0.006
Exhaust	0.3145	0.3085	0.006	0.008

I suppose if I reused these valves and used this reamer the fit tolerance would be within the allowed maximum clearance.

And it looks like I MUST reuse these valves, because there are no k361 new valves to find (except very expensive).

[Eugen]

yes Noel, 1/2 a thousand bigger. So was wondering if this is a normal tolerance for a tool like this. I've been reading on reamers, and apparently a normal class of tolerance for reamers is the ISO H7, which is 15 micrometers. which is 0.00059 inches. ok fine, this cheap Chinese reamer seems to be within the H7 tolerance. I will not send it back then.

[thebuildist]

My only input is that I'd ream a couple holes with it and carefully measure those holes. (In the same material you intend to ream)

Measuring across the lands can be tricky. But the real question is, "What size hole does it leave behind?"

I'm not suggesting that you're measuring poorly, only that I wouldn't give up on it until I had tried this too.

Bob

[Eugen]

Actually Bob, I can't say I trust the measurement 100%,I didn't want to press the micrometer into the sharp flutes. It's pretty clear the reamer''s good enough for cleaning up some valve guides. Having read in the mean time some more on the use of reamers, experienced machinists talk about even slightly different size holes made with the same reamer but using lubrication or not.

I'll try measuring holes made new and cleaned up with the reamer, just as you suggested.