Plastigauge To The Test

The Butcher puts micrometers and Plastigauge to the test. On a side note, the young lad found that plastigauge makes for a good piece of chewing gum in a pinch.

It was an exciting week as I got to finally torque on some bolts. I am minutes away from "shortblock". Here are the week's stories on micrometers, plastigauge, and more. Last week I started to modify my block for an oil restrictor kit. I was a little nervous about the kit and actually ordered two of them from different suppliers in order get a better idea when the kits should or should not be used. The Ford Racing kit arrived on Monday and at the very top of the instructions in BIG letters it stated "This kit is to be used only with flat tappet camshafts". I have a roller camshaft, and you will be glad to know I have now abandoned this idea. =)

I wheeled the block outside and decided it was time to give it a coat of high heat Krylon engine paint. I gave the engine a good soapy scrub followed by paper towels and air blasting dry. This engine cleaning, painting and avoiding rust, is almost a catch22. You want to plaint your block, but this requires cleaning all the oil off it. Engines rust instantly. I was almost watching rust form before my eyes! It was really amazing. I taped up the block as fast as I could and began to spray. The paint went on smooth and dried fast. I even had a little left over and decided to touch up the crusty old Black and Decker workmate. An hour later I got the engine inside and hosed it down with WD40 (see the rousing wd40 debate on cobraforum).

The oil restrictor kit was out, but I decided to use the oil drain screens as suggested in my Ford Racing engine book. I'll admit that the screens and goop are not that pretty, but they serve a purpose. =) Their job is to catch anything that falls off the top of the engine and snag it before it drops into the crank and cam area. Here are my 7 screen circles to cover the drain areas. Most engine screen kits come with an epoxy pack. My pack was dried up and useless. Here is a pic from the short track engine book where they use JB weld. I picked up a red and black tube of JB weld at PepBoys and mixed it up. I decided that the JB was too soupy to stick to the 3 side screens. With the temperature of the day, the watery mixture would never hold the slope. I couldn't think of a good solution to hold things temporarily in place. I decided to search the Butcher's big box of adhesives and gasketing goop. Deep hidden in the back, I located a product I once used to repair a manifold on my Troy Built chipper shredder (who incidentally went under last year). This epoxy product held for some time, but then did eventually succumb to the vibration and split after a year. This unusual goop was known to a few as GAPOXI. The Butcher gives epoxy his highest rating when the substance is known by the state of california to cause cancer in the lab. Can it be used on engine stuff? Let's read further. Widely used to modify race engines. Hee hee hee, I bet Jeff Gordon and the boys use this every day! OK, well I am not so sure how widely used it is, but I think the Butcher has found a new sponsor. This crud comes as too bricks of plasterscene You cut a chunk of each, and kneed them together into a snake, This was perfect since it was solid and easy to place. Not pretty, but efficient. The next day, Corvette-Ansel and I tried to pick it off to test the strength. It was stuck good. I could bounce a 3/8 bolt on the screen and it acted like a trampoline. It feels nicely adhered.

When you buy that set of AFR 185s, they tell you right on the box, combustion chamber available in 58cc or 61cc size. This number is important since you will use it to get your compression ratio. Now if you have your heads ported, altered, or valve size changed, this changes your chamber size. The chamber usually gets a little bigger with porting. I decided I wanted to find out both my combustion chamber size, and how it varied cylinder to cylinder. I went over to mcmaster and ordered up a circular piece of plexi, a thick square piece, and a plastic lad graduated cylinder. They have just about everything at that darn store. I had a couple 3cc syringes that also came into play. The first night I tried the round thin plexi. First I drizzled thick oil around the outside of the pocket to get like an airtight bond. I then filled the beaker to 60ml. I found on the web that ml = cc. I then filled the plexiglass through a hole I drilled in the center. I then used the syringes and squirted in the remaining amount needed to fill the pocket to the glass. I started with 61cc chambers and my first test was a 68.5! I had a fit. This was way more than I expected. It was off to the sauna to sit, drink an ale, and blow the stink off me. I needed to reflect. The next day I took a new approach. I swapped out the round thin glass and used the 1/2" thick square plexi. I drilled extra holes to allow air out more easily. I started with the beaker at 65cc so there was less syringe filling. Same test. This time the results were 65.5cc. Whew! This was what I was hoping for and what I expected. I did all 8 chambers and hear are my results.

chamber cc 1 65.5
chamber cc 2 66.0
chamber cc 3 65.5
chamber cc 4 66.5
chamber cc 5 66.0
chamber cc 6 65.5
chamber cc 7 67.0
chamber cc 8 66.0

If you ever want to try this at home, here are some tips that can make the experience simpler.

1. Use thick plexiglass. Thin bends.
2. You can use water like I did. Some people suggest alcohol or kerosene. I tried alcohol and it is so thin that it creeps everywhere and I find you get a higher number do to the weeping under the sides of the glass.
3. Use a drizzle of oil or something around the edge of the chamber to help seal things before you begin.
4. Start with as much liquid as possible in the graduated cylinder since I find it more accurate. Then fill 1-3ccs with syringes.
5. It helps to use a big syringe to remove and recycle the water back into the cylinder. Otherwise you lift the plexi and make a great big mess each time. It is better to suck all the water back out the same way it went in.
6. Drill extra holes in the plexi to allow air out or else it becomes a song and dance of wiggling the head around in a feeble attempt to move the air.
7. Rather then have the head perfectly flat...you might have it tilted a little to force the air into a known area.
8. I believe the measurements are probably 0.25 - 0.50 cc on the high side , do to weeping.

I finally figured out how to read these damn things. The one bad habit I picked up right off the bat was spinning the adjuster knob far too firmly. I did it so firm that I made some scratches in my crank! Jody the machinist luckily showed me how to fix these light scratches. Here I am with the micrometer in the vise. The unit needs to be checked before you use it against a known size. This insures accuracy. I have the known 4" thing-a-majig, and I move the 0 line so it is dead on. It took me a week to finally feel confident using this tool. My first measurements were way wrong. There was a learning curve and a touch and feel that comes with using them. You can use a micrometer to measure you piston diameter, your crankshaft diameter, or the width or your piston rod at the big end.

Now the dial bore gauge gave me a conniption fit. These tools arrive and they have no instructions. They assume you just know what the heck is going on. The dial bore really doesn't measure an absolute value like a mike. Instead, it measures the difference or relative size. Say for a moment you have an engine block and it is 030 over or has a 4.03" bore. You zero out the bore gauge to this number. How do you zero it out? The way I did it was to lock a micrometer in the vise, and set it to 4.03. You then put the dial bore into the mic, and set it to to read 0. It is a weird tool because it works by moving it around. You work it back and forth and watch he needle. You are trying to find the low spot that the needle travels to. You now take you zero'd dial bore, over to your block, and start working it back and forth. The needle will read 0 through 5 + or -. So let's say your cylinder is a +1. This means that it is a 4.031. You can use this tool to check your cylinder bores and rod ends for size and shape.

One last measuring tool I played with this week was the magnetic base dial indicator. This is a dial indicator on a magnet =) You can use it to check things like crank end play....how much the crank wiggles forward and back in the block. Camshaft endplay, and crank straightness.

There is a magical tool, loved by some, and hated by others. This tool is known as "plastgauge". Plastgauge comes in three colors and is thinner than spaghetti, but thicker than hair. I'd say it might be like 20lb fishing line. This is an inexpensive device that takes the place of the micrometer and dial bore gauge, and can be used to check bearing clearances when building an engine. I was very curious to the accuracy of this substance, and put it to the butcher test.

If you have not yet attempted to build an engine, there exist a few critical measurement checks that should be done. The big check is the crankshaft to main bearings. In an engine, stuff spins, and these parts ride on thin layer of oil. If this layer of oil is too thin, friction grows and grows, until the point that the spinning part grabs the helpless little bearing, and spins it, mashing it into a molten pile of lava. The engine is toast. The peculiar thing is that the exact same thing can occur, for different reasons, if that layer of oil gets too thick. Oil pressure drops, or the crush layer is too weak, and then, thermonuclear meltdown. That engine is toast. As you build an engine, it is a good idea to check these bearing clearances with measuring tools or plastigauge.

OK, here is where the crankshaft lives. This is an engine flipped upside down. Now that black thing on top is an option called a stud girdle. This helps stabilize all those bolts when you want to rev the snot out of an engine, or just beef it up. More on this later. Now do you see those 5 silver things. Those are called Main Caps and they get bearings. These caps hold in your crankshaft. We want to bolt the engine together without the crank, take some readings, and then measure the crank, and determine the air space or clearance. That air space will be filled with oil. Just for fun, the same procedure is repeated with the spaghetti known as plastgauge Here you can see the bearings now in place and I have torqued things down with my favorite hella nuts, "the flange nut". I do love locknuts, but they are horrible to use with studs since they yanks studs out. Yes you can red or blue loctite studs, but you are supposed to torque before they setup and since I am doing the procedure 53 times, that would not work. Studs, ARP lube, and a good torquing. Here is the crank sitting in the block with the main caps removed. You can then run over with your micrometer, and gently take measurements. Don't scratch that crank like the Butcher did...go softly. Light with the finger tips. =) Back to main caps for a minute. See how these caps have 2 bolts. I am not exactly sure, but many racing blocks, some Boss or HiPo, and some mexican blocks I believe have 4 bolt mains. 4 bolts are considered superior and stronger. They are also more rare and more pricey. With 4 bolt mains, there is less of a need for a stud girdle. Here is a buick with 4 bolt mains. One new Ford block that really looks outstanding is the new Dart. It is well thought out and has all the cool features, but you pay for them at $1995.

Where were we? Oh ya, here is the green stuff, ready for test number two. You squish plastigauge, and then hold the wrapping paper up to the squished piece, after you unbolt everything. It looks squished! My O My. And here is where the trouble begins. I call it .002. This gets me in a panic since I wanted closer to 30 thousandths on my mains. My first attempt with green plasti has me seeing a lot of 020.

Here is an example of the same measurement with the micrometer and dial bore. On main cap #1, the diameter with bearing was 2.9817. The crank measured 2.9790. The difference was 0.0027 (this was also when I was squeezing too hard so it is probably higher). 27 is very close to 30 but the green string says 20.

I decided to repeat the test with one model up, the red gauge. Each color is for a different thickness range. Red is 002 - 006 I believe. Goodness sakes alive. This time, 4 of the mains came in at .003 and one at .004. The red was much closer. That 004 had would of had me spooked if I had not measured as well.

To sum it up, I give Plastigauge a 6 out of 10. I would use it in a pinch. To be extra safe with it, I would most likely repeat the test 2-3 times and maybe with 2 colors. I trust the red more than the green at this point. I did try the test on my rod bearings as well, but it made a complete mess and the stuff disintegrated. I think it is best used for the the check on main bearings.

Warning: do not try this at home...danger. Now here is one little known use for plastigauge Don't blame me if you die of some rare poisoning. I decide to taste PG. It tasted like a candle. I decided to chomp on a string. Made for a great piece of wax gum.

Have you ever seen that post on the chat boards and wondered? Well here is that little orange devil known as the 2 piece rear main seal. This is a rubber with metal core sort of gasket. Some blocks have a one piece unit which is the full circle. This sits in main cap #5 and stops oil from coming out the back of the block and into the flywheel area. Notice how it sticks out of the block a bit. You offset it so the break point is not where the cap meets the block. This helps prevent leaks. You can also add a little dap of silicone, not on this pic, under the cap edge which also prevents leaks. To remove this, you would have to remove your transmission to get your flywheel off. You would then also need to remove your oil pan, stud girdle and cap 5. What a pain in the butt.

Rods are not symmetrical. One side of the rod big ends has a very gentle and long slope. This is the side that will go toward the crankshaft. The other side has a sharper edge and this goes up against the other rod.

The old retaining ring pliers with removable tip, was crud. The new pliers worked great. I am installing the C clips and thinking to myself "I will have to write about this, but I will tell people to wear goggles....I do not need goggles, I am the butcher with superior technique and skills....sproinnnngggg! Did you ever see that movie "A Christmas Story", when he almost shoots his eye out with the BB gun? That C clips was headed directly for my eye and luckily I caught it on the tip of my big nose and it stung =) I ran for the goggles. C clips are not symmetrical. I think I said once previously, Smokey likes the flat sides out and the rounded sides touching as they are doubled up in the piston.

Here is an example. I had the feeler gauges out and I was measuring the distance between rods. Its a good idea to always add and remove rods in pairs. I believe I read that it is good to tighten them with feeler gauges inserted to keep them square. You can barely see the gap in this picture. On a stock engine you might want .010. On a performance engine you might want 15-20 thousandth. Smokey will tell you that over 25 and too much oil gets slung around.

I have been in a battle with pistons rings and they are winning. I had been in the garage too long one day, perhaps high on Gapoxi and chewin plastgauge, and I decided to file a bunch of top ring with clearances for second rings, thereby rendering them useless. Here is a box of rings. The top ring in my set is shiny. The only other way I could tell them apart was that the top ring had bevel on the inside and the bottom had the bevel on the bottom side. Only the top and middle rings get gapped. The lower ring oil sandwich just goes in. For the speedpro rings that I'm using, I am attempting for a top gap of .018 - .020, and a middle gap of .022 - .024. Speedpro explains that it may sound odd for the second ring to have a large gap, but in recent testing, it has proven beneficial. You can read about it on their page about 3/4 down. It takes like 40-60 cranks to get to the range. I start with 30 cranks, then insert the ring into the bore, pressing it down evenly with an old piston. Its then checked with the feeler gauge. I then go 5-10 cranks at a time, depending how far out it is.

In the Ford Short Track Power book, they give their secret tips on ring alignment. I don't like their choice of numbers so here is my version of their story. I call the top ring 1, second ring 2, oil ring 3 and the skinny rings that sandwich the oil ring 4. On pistons 1 thru 4, here is the pattern you want. On 5 thru 8, you want the same pattern, facing forward. I took a pic, but my numbers are wrong here. This is 5 thru 8 if you flip the 2s and 4s. =) And here we have one completed piston.

A couple months ago I sent John Brooks my engine "to do" list. He got a good kick out of it and suggested I put a link to it. Here are the Butcher's old 100 steps to building an engine. Some of the list has been altered or changed at this point. Now I worry that such a list might scare a would-be first time engine builder. There are many ways to build an engine. I like to take the long road since I have a fun time learning the aspects of how things go together. This might make engine building seem more complex than it has to be. Let me give you an example of a simpler engine build. Let's say you decide to buy a Scat 408 stroker kit. Scat has a great reputation and their parts are well regarded. You have your block, and you found the machinist. You know old "Cooter" from Hazard County, best engine man for miles around. Cooter has a very good reputation and has been building engines for your friends and family for years. All you really have to do is go over to Cooter's shop and say "Here is my block, crank, rods, and pistons. Please work your magic on my block and clearance all the bearings correctly to factory spec". If you've read a few books, you might ask Cooter for a deviation or two from spec. In a few weeks Cooter will have your parts ready. You can take things home and start bolting them together. No measuring. No gauges. No micrometers. I am not advocating this method, but many an engine has been built that way. If you choose this short route, please note that everything rides on the skill and workmanship of Cooter. You will sleep better at night, and perhaps prevent a blown engine, if you take a few clearance checks. The more checks you do, the better. Plastigauge is a good start and thousands of engines have been successfully completed with it. If you are going to try for big HP or big revs, then you should probably invest in some good measuring tools and make additional clearance checks. In the back of Building Ford Short Track Power, they have 6 pages of professional engine build sheets. I found these to be very helpful and I wanted to follow them. I made spreadsheet versions of those pages. Here is page one of two for the Butcher's Build =) That page holds the meat of the measurements. Engines are all about checking clearances and measurements.Here is the page two of my build sheet. There is less critical data on this page. It makes a good reference for future repairs and replacements.

Here are the excel docs (sheet 1 and 2) if you ever want to build an engine using these charts. Here is a cool CarCraft A-Z tutorial on how to build your first engine. Letters O and P are at the heart of engine building. These are the engine clearance checks. Q thru S are some secondary checks that I also feel are key, especially when going for big HP or high revs. It costs $16 a year, but I feel its worth the price. Here is the Ford Muscle 331 stroker detailed engine build with tons of good pics and tips.