Bore Measurements

[lefty2cox]

I'm looking to get the tools necessary to measure cylinders. As usual, there are so many options and reviews. I'm looking for some advice on both methods and tools. Is anyone particularly happy with their tools for this process? Would you be willing to share a recommendation? From my experience, price point is usually a good indicator as to the quality of a tool. So I'll be fine with that if you don't want to recommend a particular brand. It's just that I have no idea the price point where I should be for this particular set up.

Thanks

 

[Scrubcadet10]

I always have the local machine shop do it as they mic the bores and other specs for free. Might check if anyone around you does it for free.

 

[cpurvis]

Yes, PRICE is usually a good indicator of tool quality unless you run into someone selling knock-off tools for nearly-full retail. Then you've paid quality price for junk.

If you're going to buy quality tools, buy them from a vendor. Brown & Sharpe, Starrett, and Mitutoyo are good brands. Beware of anything made in China. Some of those brands may not be around any longer, I'm quoting from memory.

 

[cpurvis]

I always have the local machine shop do it as they mic the bores and other specs for free. Might check if anyone around you does it for free.

^^^^^ This is good advice.

If you're not going to be the one boring these cylinders, you really don't need any of this stuff. If you will be the person boring cylinders, you should already have a good grasp of what machinist tools are needed and how much they cost.

 

[bertsmobile1]

Depends upon the accuracy needed and the diameter of the bore
For mowers , a good deep jawed vernier gauge will usually suffice if the block is apart.
People get hung up on numbers what is important is the difference end to end , called taper & top to bottom ( on a vert shaft ) which is ovality .
So if you use the same tool for all of them then your results should be good enough as mower specs are quite coarse.

I have telescoping bore gauges that you lock then take out & measure with a micrometer, these are the most difficult to use and subject to the most system & operators error .
Then there is the internal micrometer, again a little tricky as you must keep it dead perpendicular to the bore
For really accurate measurements I have a 3 jaw internal bore gauge which will self align but again you need to be careful to avoid oval wear sections
The finally there are the go-no go gauges in 0.0001"
After that you are well & truely into the domain of the metrologists .

Having said all of this, mostly I just use a piston ring , the old piston & feeler gauges to measure the end gap because it is quick & easy , but it does require maths to convert the circumference variation to diameter variations .
OTOH it takes about 3 minutes
Then hold the barrel to the light and look for gaps between the ring and the bore in 1/2 dozen places .

The latter two is how the auto industry & largely the aero industry worked right up till WW II and for many old timers well beyond.
In 1950 very few workshops would have owned a vernier gauge let alone a micrometer and mowers have not gotten much more sofisticated since then.

 

[Hammermechanicman]

I guess the question is why do you want to measure cylinders? Are you looking to see if a cylinder needs rebored for being out of spec? In my experience unless a piece of equipment has a very specific engine. The cost of tearing it down, cleaning, measuring, buy piston(s) and rings, having a machine shop fit them and reassemble and reinstall engine is not worth it. If you have an engine you think has a bad cyli der consider a simple leakdown test. Cheaper than a bore guage or set of snap guages

 

[lefty2cox]

Thanks to all for the info. Very helpful. Yes, I do have a vernier, so that's good news. And as far as what I'm up to, yes, I'm just looking to see if something is out of spec.

If I can get by with a vernier, I'm cool with that. I'm not currently working on anything that I would get into boring. Just not valuable enough. It's mostly diagnosing consumer-grade equipment and my own stuff. Nothing anyone would spend a boatload on fixing.

I'd just like to be able to take a look at something and decide whether or not a piston, set of rings, and honing is a good bet.

Every once in a while someone will give me a machine. And I'm looking for experience diagnosing, servicing, and fixing stuff.

Thanks again.

 

[tom3]

I like that idea of using a ring, squared up with a piston, and comparing the end gap at it goes down the cylinder. Genius, or at least ingenious

 

[lefty2cox]

If I understand correctly, I'm guessing that process would be performed with a new ring?

 

[Hammermechanicman]

I am guessing that that looking at ring end gap differences would be a relative measurement to each other rather than an absolute measurement. I guess you could take a bore measurement and a measured end gap and extrapolate that to other gap measurements but i don't have the math skills for that.
I have seen cylinders worn slightly out of round that a deglaze with a ball hone and new rings didn't make it new but definately good enough to mow grass for a few more years.
My Frankensteined HH120 on my '72 SEARS ST12 i use to blow snow has a worn cylinder to the point at idle you hear very audible piston slap. Burns a little oil but other than that runs fine.