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I gathered some junk lawnmower parts to build a go-kart for my kids.  The engine needed new rings, but was the cylinder worn in an egg-shaped pattern, or did it simply need slightly over-sized rings?  I did not have a micrometer for measuring inside the cylinder walls.  I improvised.

(I do not have an engine to show in this Instructable, and have decided to use a holesaw to represent an engine cylinder.  The bottom of the holesaw represents the top of the piston.)

Step 1: Measure the Cyclinder's Diameter

My substitute micrometer uses a wood block 3/4 x 3/4 inch cut in length to the diameter of the cylinder.

Step 2: Round the Ends for Better Fit

I rounded the ends of the block so it fits inside the engine cylinder with only a little looseness.  It is loose enough to insert and remove easily, but tight enough that it almost centers itself.  (Ignore the black crayon mark from the lumber yard.)

Step 3: Drill-end-to-end

A steel rod in two sections will run the length of the block.  It is necessary to drill a hole-end-to-end.  Choose any scrap small diameter steel rod.  A piece of wire from a coat hanger will do.  Drill a hole just a little larger than the diameter of the wire so it can move in the hole easily, but without being sloppy.

I made guide lines in pencil and drilled by hand.  Because bits this size are short I had to drill from each end to make a hole that runs the full length of the block.  Happily, my holes met in the center.  Even if they do not meet, this device will still work, but the holes should at least be close to meeting.

Step 4: Make a Notch

Make a notch in the center of the block that extends below where the hole passes through the block.  I have inserted my piece of steel rod for illustration purposes.

Step 5: Cut the Rod in Two and Finish the Ends

The steel rod needs to be cut into two pieces so the opening between the two pieces is in the notch you made in the block.  Lightly grind a point on the outer ends of the pieces of rod.  Gently round the inside ends.  The gap between the two inside ends should not be more than 0.020 to 0.040 inch when the outer ends are pressed against the inside of the engine's cylinder wall, but that is not critical.

Step 6: In Use

This device is actually easier to use if you drill a hole straight down from above one of the steel rods and insert a locking screw to keep that rod from moving. 

Raise and lower the piston to the area of the engine cylinder you want to check for wear.  Let the block rest firmly on top of the piston.  Position the wooden block so the steel rods are at the widest part of cylinder.  Insert blades from a feeler gauge until you find the maximum thickness you can place between the inner ends of the steel rods.  Record the sum of all blades by reading the numbers on each and adding them.  Turn the block one quarter of a turn and take another measurement.  Do this at the top, center, and bottom of the cylinder.  Subtract the smallest reading in any position from the largest reading in that position to determine how many thousandths of an inch your cylinder is out of round.  If it is within the specified tolerance, you need buy only slightly over-sized rings, not to have the cylinder ground. 

This method of checking relative amounts of wear in an engine cylinder is simple, but effective.
If you need to check a different size of cylinder, you will need to make new steel rods and maybe a new wooden block, too.
What a brilliant idea, I wish I had thought of it <br>I have cylinder bore gauge but this would be great for people who only ever rebuild 1 or 2 engines
Thank you.
If there's a Harbor Freight where you live can get dial indicator w/clamp stand for $29.99.Got one to check brake rotor run out.Can't beat it!
There is indeed a Harbor Freight store nearby now. Someone else made the same suggestion. However, I believe I mentioned I came up with this about 30 years ago long before I had ever seen a Harbor Freight store.
I for one think the idea is great! I have been looking for just such an item, also if for any reason the guage is off just a little bit It wont matter if you use the same device&nbsp;and method&nbsp;to measure any parts that your going to replace! How ever on engine cylinders where you have preset specs to go by it is nice to have an device that will give the precise measurments like which can be converted or are the same as store bought guages, again thanks this is a great idea!
Thank you.&nbsp; It has been a long time since I put new rings into the engine for a go-kart, but I think the cylinder was to be out of round no more than .080 of an inch.&nbsp; Although this device does not give an absolute measurement (e.g. diameter = 3.8 inches), it did tell me how many thousandths of an inch difference there were between the highest and lowest measurements.&nbsp; I hope this idea serves you well.<br />
thanks for posting this. im going to rebuild my engine soon so this should be helpful<br />
Thank you.&nbsp; Naturally, it will not tell you the diameter of the cylinder, but it will tell you how much variance in diameter there is.&nbsp; I used this about 1980.&nbsp; I had a Chilton manual with a step-by-step section on rebuilding engines.&nbsp; This device allowed me to know how much out of round the cylinder on my old lawnmower engine was.&nbsp; It worked quite well.<br />
.&nbsp; Great idea. Great job.<br /> .&nbsp; I don't think using the hole saw is a problem. If one has need of your gadget, one should be able to get the idea with ease.<br />
Thank you.&nbsp; You seem to be correct.&nbsp; Folks are understanding the concept just fine.<br />
i love this ible, and im an aircraft mechanic, and i have used profesionaly made gauges like this ont that a shop i worked for a few years back had bought, (you dont want to know the price of them) but these look very similar, and will do the job just fine, so dont worry about people like <a class="entryListTitle" href="/member/sypher12616/" rel="nofollow" style="line-height: 16.0px;padding-left: 0.0px;padding-right: 4.0px;"><strong><font color="#ff5200">sypher12616</font></strong></a>says, they will probably never undersyand the need of a habdmade item like this., but it is a grat ible and i need to go look at your others now ;-)
Thank you for your support.&nbsp; This little substitute micrometer should be quite accurate.&nbsp; The user needs to move it side to side just a little to make certain a measurement is being made at exactly the widest part of the cylinder.&nbsp; As long as care is taken to find the maximum thickness of feeler gauge blades that will pass between the inside ends of the steel rods, there is very little possibility of operator error.&nbsp; Feeler gauges are either &quot;go&quot; or &quot;no go&quot; and are accurate to within a couple of thousandths of an inch, probably even closer tolerances yet. &nbsp;&nbsp; <br />
I needed this many years before I ever saw my first Harbor Freight store.&nbsp; I know of nothing precision I would care to purchase from them now or in the future.&nbsp; I hope you will publish your first Instructable soon so we can comment on your ideas and efforts.<br />
Excellent reply, Phil! That made my day. Some people--especially snot-nosed kids who haven't had enough real-world experience to criticize anything--need to check their egos and pretentiousness at the door before dissing (I hate that word) the work of others.<br /> <br /> BTW, I've been meaning to let you know how awesome I think your submissions are. I may not have a use for many of them, or I might have done things differently, but I learn something from every one of them.<br />
Thank you for your post.&nbsp; I am glad you have enjoyed some of the things I have posted.&nbsp; Many might never need to do the job I illustrated, but maybe there is some little idea they can adapt later.&nbsp; That has been true for me regarding many things I have seen all sorts of places.&nbsp; I might not need them until many years later, but those ideas from others helped me find a way through a problem.<br />
&quot;<em>Many might never need to do the job I illustrated, but maybe there is some little idea they can adapt later.&nbsp; That has been true for me regarding many things I have seen all sorts of places.&nbsp; I might not need them until many years later, but those ideas from others helped me find a way through a problem.</em>&quot;<br /> <br /> Exactly! I could go on but you summed it up perfectly.<br />
I went back and read what l8nite posted.&nbsp; What I wrote sounds very much like what he wrote.&nbsp; I did not intentionally plagiarize him.<br /> <br /> Thank you.<br />
<a class="entryListTitle" href="https://www.instructables.com/member/sypher12616/" rel="nofollow" style="padding-right: 4.0px;padding-left: 0.0px;line-height: 16.0px;"><strong><font size="3">sypher12616</font></strong></a> says: <div class="txt" style="padding-right: 4.0px;padding-left: 0.0px;padding-bottom: 3.0px;margin-left: 0.0px;overflow: hidden;">Telescoping gauges at harbor freight cheap and accurate enough. I mean REALLY? Don't mean to sound judgmental but *exhausted sigh* c'mon man? I'm a machinist who has had to improvise alot but this...........ugh......<br /> <a class="entryListTitle" href="https://www.instructables.com/member/Phil+B/" rel="nofollow" style="padding-right: 4.0px;padding-left: 0.0px;line-height: 16.0px;"><strong><font size="3">Phil B</font></strong></a>(author) says: <div class="txt" style="padding-right: 4.0px;padding-left: 0.0px;padding-bottom: 3.0px;margin-left: 0.0px;overflow: hidden;">I needed this many years before I ever saw my first Harbor Freight store.&nbsp; I know of nothing precision I would care to purchase from them now or in the future.&nbsp; I hope you will publish your first Instructable soon so we can comment on your ideas and efforts.<br /> <br /> <br /> lol... good answer ! This site isn't about...&quot; i needed to measure cylinder wear so I ran to (store of choice) and bought a tool&quot; I mean come on.. there are &quot;ibles&quot; about &quot;how to walk up stairs&quot; and &quot;chopping an onion&quot;(mine) to how to build a computer submerged in oil and building your own led taillights to a computer mouse that runs away when you reach for it.<br /> <br /> &nbsp;This &quot;ible&quot; filled a need of the poster and may come in handy for another shade tree mechanic with out access to a toolbox/shop full of machinest tools and while it may not be up to the tolerances needed for a racing engine its more than adequate for the application it was desined for</div> </div>
Great job l8nite you just gave me the perfect definition of why i look at this site so when people ask &quot;why do you look at that stuff&quot; thanks shiftrk<br />
Hey Phil, don't listen to that guy! There are times when you're caught in a pinch and you have to improvise. My nearest Harbor Freight store is an hour and a half away,&nbsp;so I don't get there much. I've been wrenching on cars and tinkering since I was 10 years old and I'm 45 now. When I was growing up, our family didn't have much money and there was no Harbor Freight, so If I wanted or needed something, I made it. Now I have money but I still make tools. I'm an automotive restoration technician by trade and have MANY tools, but I still make new ones on a weekly basis because &quot;I need it in a pinch&quot;. This instructable, I wouldn't use it on an 8 second drag car, but for a lawn mower or go-cart engine, it's perfectly fine. I would use a hardwood like oak or maple though.Nice instructable and I'm going to check out your other ones!
Thank you.&nbsp; This is pretty much a one use tool, unless you will rebuild several engines with the same cylinder dimensions.&nbsp; For that reason, cheap wood rather than good hardwood does fine.&nbsp; <br />
this is a really great idea !
Thank you.&nbsp; It worked well for me.&nbsp; I would not care to do measurements on a V-8 by this method, but it was fine for a one lung engine.&nbsp; I wish I had an actual engine to use in the photos, but the hole saw made a decent substitute.<br />
well, a dial indicator would be nice but if you didn't have access to one this could tell you if you needed to go find one
As it happened, this fix told me the wear on the engine (old cast iron block) was within tolerances and all I needed to do was install oversize rings.&nbsp; A dial indicator was out of my price range in those days, and I did not know anyone who had a dial indicator.&nbsp; <br />
<span class="short_text" id="result_box"><span style="background-color: rgb(255,255,255);">I see a clever instructable, and it had to be from Phil B!<br /> <br /> Almost all yours works are very interesting, Phil.<br /> </span></span>
Thank you, Osvaldo.<br />

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Bio: I miss the days when magazines like Popular Mechanics had all sorts of DIY projects for making and repairing just about everything. I am enjoying ... More »
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