Micrometer Selection

I need a micrometer to measure camshaft lobe height, journal diameter, and the thickness of valve clearance discs.

Would this set give accurate enough measurements?


Harbor freight products will give you a “close” measurement but I don’t know how accurate that will be. You could always take the cam to a machine shop if you have one nearby and have them check it for you. That’s what I do if the need arises. I sold all of my precision tools several years ago because they were just collecting dust.

I don’t know who or what CENT-TECH is, but Harbor Freight specializes in low end cheap stuff. There are certain kinds of tools that I will buy from them. But precision measurement instruments are not among them. They’re great for low stakes, utility stuff that you don’t necessarily use all of the time. Once you’re at the need for a micrometer, you don’t really want to be relying on low end cheap stuff. The same goes for anything you need to use a lot and rely on all of the time.

How much would I need to spend to get one that would be at least 98% accurate?

What brands or models do you guys recommend?

For automotive tools, if you want the “real thing” then you’d flag down a Snap-On truck someplace (or maybe they sell online, I don’t know) - but you’d save up for 6mos first. I’m just a shade-tree guy so when I need reasonable quality I often just go to Sears. I sort of have a “Craftsman or better” rule of thumb for tools. But there’s also an auto parts store near me that sells Lisle auto tools & those are good. Normal big-box chain auto parts stores tend to sell bottom rack junk like Harbor Freight - so ok for some things, but not everything.

I haven’t priced precision tools in a while but Lufkin is the brand that I bought most. Craftsman has some good ones as well but they buy from several different makers. You could try a pawn shop and save a little money. Look for name brands like Snap-On, Brown & Sharpe, Craftsman or Lufkin.

For automotive use, a tool like this is more versatile and easier to use…

Like anything else, you get what you pay for…A professional machinist is going to spend far more on his tools than an automotive hobbyist needs to…

The outside micrometers I have are made by Starrett along with Brown and Sharp. The inside micrometer set is from Central Tool. These things are accurate and a bit pricy but worth it if you plan to use them on occasion.
I don’t remember what I paid for my stuff as it was purchased a long, long time ago.

I bought a cheap CEN-TECH vernier caliper from HF and compared it to measurements from some of my micrometers. It was off a couple of thousandths of an inch. I use the caliper at times on my lathe work or a few other things when utter precision is not really necessary. (spacers, bushings, etc)

If you want a higher end measuring tool you might check eBay or Craigslist but I think the HF set could be accurate enough to get by. If you go the HF route you should test them for accuracy by using a Standard. A Standard is a short length of precision stock used to verify accuracy, to make adjustments of the mike, etc.

If you have access to a good machine shop, they should have a set of Jo blocks or other standards that they use to check their measuring tools. Another possibility is an instrument calibration or metrology service in your area who should have the capability to check measuring equipment. Even very expensive equipment should and for some, must be periodically checked for accuracy. If you have standards that you can use to know the error, if any, of the Harbor Freight tools, you should be ok with them for light use.

A machine shop with a surface grinder could make 1", 2" and 3" standards for you. I have not seen the Harbor Freight micrometers but in all likelyhood they, like any, are adjustable to get an accurate zero reading.

The micrometers you show have measurements down to 0.001", and I’m sure the accuracy is plus/minus a few thousandths. If that won’t cut it, look elsewhere. No tool will have an accuracy equal to the lower limit of it’s measurement capability. I’d guess +/- 3 to 5 thousandths, but it could be as little as +/- 2.

This one has great reviews… If anyone sees a reason why I shouldn’t buy it, please let me know.

As long as accuracy of +/- 0.001" and resolution of 0.0005" are all you need, it should work.

A jig would be required to measure cam lobe height. And for the DIYer the Harbor Freight 3 piece gauge set might be accurate enough. When setting valve clearance using shims it’s usually a matter of assembling the valve train without shims and measuring the clearance with a feeler gauge and installing whatever shims are necessary, reassembling and re-measuring. Does a shop manual indicate measuring cam height? What make and model car is it?

That $25 caliper should do just fine…

“A jig would be required to measure cam lobe height.”

Really? Could a jig be attached to the caliper posted above?

"Does a shop manual indicate measuring cam height?’’

Yes, Haynes. I’ll be removing the camshafts to replace stem seals and figured it would be a good time to check the camshafts

''What make and model car is it?"

98 Mazda Protege

Dear mystic,

It is useless to ask people here if the measuring instruments that you suggest are accurate. Even if someone owned one identical to what you post, yours may be different; it is not the same tool. Nobody can sit in a chair at a keyboard and predict that a low cost measuring instrument is accurate to a degree acceptable for your use. You need to buy one and have it checked. Another way to check accuracy that is good enough for your stated purpose is to compare measurements done with a tool that is known to be accurate. That should be a tool that has been checked against a standard, not a tool that someone bought for a lot of money 5 years ago.

Can you or anyone tell me if my 15 dollar tire gauge is accurate? What if the identical tire gauge is for sale on Amazon; does that make a difference? No, I didn’t think so.

PS, a good way to check cam lobe lift is with a dial indicator with the cam mounted in a metal cutting lathe. Harbor Freight also sells inexpensive dial indicators. Don’t ask me if they are accurate. I own one and don’t know.

Wha Who? I understand what you’re saying and I do plan on checking whatever tool I end up with to make sure it’s measuring properly before using it.

Wha Who? is wrong, it’s easy to buy an accurate gauge from a reputable maker. Mystic, what do you plan to do with it? Are you machining things, or are you wanting to check dimensions?

Check dimensions

Camshaft wear is usually quite obvious. I’m curious as to what results the OP desires beyond setting the valve train clearance.