Better Engine Building: Does Plastigauge Work? (Testing Against "Real" Engine Builder's Tools) 

At 66, I've built engines all my life. Every rod bearing is checked by Plastigauge when it's assembled. The best thing about plastigauge is you're checking all the parts involved. You're checking the crankshaft journal, the rod bearing, and most importantly, the rod too. Cranks are easy to measure with a micrometer, rods can be measured with a dial-bore gauge or inside mike. But in a production shop, Plastigauge makes this quite simple and easy. Plastiguage indicated several problems with engines over the years that the precision tool confirmed.

Uncle Tony says "A loose engine is a happy engine."

damn son.. we lived and died by that stuff in the old shade tree days of the 60's and 70's.. I didn't know they still made that stuff! It has been.. oh.. to many years to think about since I rebuilt and ole hot rod engine.. But I have been watching some of the build videos lately and feel that old bug risen again.. one more time before it's over is what I am thinking.. But what to do with it after I am done.. Not to many cars take the old school mills anymore.. and I am to slow on the uptake these days to learn all of this new fangled electronic stuff.. Well.. I will cross that bridge if I can get to it.. thanks my brother.. this was appreciated.. carry on!

I was taught to put the plastigage at the center between the bolts, wonder if you could check on another engine your doing and see if there is a difference between the center and offset towards a bolt.

I’ve built several Small block Chevy’s using plastigauge over the years. Never encountered an6 issues with bearing failures.

Great video for the beginner and it gives me faith that this is almost dead on.

This is the best explanation i have found. Thank you

Love these vids... Being in the industry as a mechanic for 19 years, this is right up my alley. Had to laugh about the metric system confusion. Being Australian and growing up in the 80's/90's I was well and truely in the metric era. I personally find the imperial system unnecessarily complicated. The metric system is far easier to use as everything works in groups of 10... Anyway, keep the vids coming

Liked the vid, fun and informative. That said, I'm surprised people still talk about the metric system as if 95% of the world didn't use it. Oh, built my first engine in school over 40 years ago almost always use plasti-gage. Never had a related failure or problem. My theory is that folks who need absolute numbers insist on tools and those of us who are ok with numbers that are well in range are cool with the plastic.

whoever invented plasti gauge was a genius. i wouldn't ever consider not using it.

Never had a problem with plastigage. From the time helping my dad do a 57 Chevy motor to LS motors...

many year,s ago building 390ford had issue with brg clearence one nite checked plasti gage twice then pulled out precision stuff they all showed wrong took crank back to machine shop monday who checked said ok then he thought because he knew me he asked if i was working in unheated building yes i was below zero he explained difference was he ground crank to specs in he building he was rite when i warmed up overnite everthing came together

Great video. Thanks for posting and sharing. Hope you enjoyed your lunch :-)

Forty years ago I worked in a production automotive engine rebuiding shop. Setting up the main bearings we would put in the crank, torque all the journal bolts than see if the crank will rotate. So now you know it has clearance, don't know how much. Remove one bearing cap at a time and put a small shim cut from .003" feeler gauge stock. Put the bearing cap back on retorque the bearing cap. Now the crank should not be able to turn. Do that for each of the bearings. You now know the clearance is less than .003" . Do you really care ,on a street motor what the clearance is as long as it is with in the specifications.

Thought about using plastic gauge to check cam endplay

Plastigauge is ok for static clearance just doesn't check journal ovality but is plenty good enough for a backyard rebuild good video

Just came across your channel and subscribed. I just started a job learning to rebuild spindles and related parts(some honestly I’m not even sure the name of yet. I’m starting out from the very beginning. Spent 9 years in hvac but a week ago started a new career. I have always been interested in engines so hoping one day maybe I can machine engines.

I’ve used plastic gauge for years and you are right it gets close but not dead on. It’s a fast way to check if you have a problem and need to go further with mics . Also bearing manufactures have books on their bearing thicknesses so you look up the bearing for your particular engine and they will have all the specs for rod diameter bearing thickness and Journal diameter this will save a lot of time and guesswork

great content man thankyou

I can live with .0001 accuracy, because you could easily be there reason for the trivial discrepancy

How do you stop the crank from rotating slightly as you torque up the big ends?

That is a very well-done video good near ration to.

Plastigauge shines for checking/controlling gross errors, and checking out clearances on an engine before you commit to a complete teardown. It has its place. Maybe not on high dollar builds, but it has its place.

Great Video. it seems to me if you're careful, you'll be ok. I think I'd use an infrared thermometer to make sure the crankshaft's at room temperature. Check the bearing temperature too. However, I think I would only be comfortable if my reading fell close to the middle between the maximum and minimum allowable clearances. This allows you plenty of wiggle room. I would not trust it at all if you have a reading close to the limit. At that point, time to buy the expensive equipment or bring it to a trusted machinist to double check measurements. lol

Your readings with a dial bore gauge will usually be a little bigger than plastigauge because the tips of the bore gauge dig into the soft outer babbit layer of tri-metal bearings. I've seen heavy and expensive Sunnen bore gauges read 3 -4 tenths inaccurate when used for clearance checking. Fresh plastigauge works great. I asked a Sealed Power/Speed Pro engineer about this and he said I was correct. The H series racing bearings have a harder or thinner babbit layer and using a bore gauge with them is a little more accurate.

Use brake cleaner to remove used plastigage (yes, this IS the correct spelling) off of crank journals. It wipes right off. You have to be a little careful when wiping the stuff off, because you can leave a trace of plastigage on the journal. You have to wait for the brake cleaner to completely evaporate so that the journal is dry, and check for small smears of the plastigage left over when you wiped it off the journal.

Must I do one by one or 2 by 2? Thanks.

Stephan papadakis makes similar video few weeks ago, plastigauge is pretty accurate, bad reading or prepare on measuring tool makes wrong number

Works OK if you RTFM. set the clean dry crank in the clean dry bearings. Torque mains without moving the crank at all. Remove caps, read clearance. same with rods. No oil at all.

Are you torquing 1 rod cap to torque to check the plasti? Thought you were supposed to tourqe all the rod caps evenly in sequence.

Thanks for the comparison. What if the clearance is off, what should be done if anything?

What is nice with plastigauge is that you get an measurement across the whole bearing surface, in theory, very nice. And should you not hold your micrometer by the insulated pad?

The main benefit of plasti gauge vs a mic besides being able to check across the whole bearing surface is that with a mic its fairly easy to scratch the journal if not used properly. Even if you can afford the tools you probably not well versed in handling then. Now bore mic not as much a concern. So average builder or even weekend bracket guy plasti gauge works great without risk of scratching journals. Also just use a little lacquer thinner on a rag to remove plasti gauge.

Back when most things were still made in USA, old timey toolmakers who really knew what they were doing used Plastigage for things more critical than this. If it reads different than a barrel mic, you might not be using the mic properly, or it might be out of calibration. This can very easily give you several ten-thousandths of an inch of error. You really should check your mics every day. How often do you calibrate that dial-bore gauge? Those are notorious for error. Something else to consider, if something is off-centre, your clearance on one side will be different than the other. So measuring the diameter will always give a different result than Plastigage for that. The last time I had a crank ground, I measured it myself with great precision, and took it back to the shop that ground it. I greatly offended the guy who ground it. He blamed his old "non-CNC" grinder. I wanted him to let me show him how to use it, but he wouldn't.

.0022 IS slightly bigger than .002, so the plastigauge is more accurate than he said in the video.

Nice job on this subject. Plasti-gauge is sold under several brands, but it’s patent goes back to the 40’s. So, it may not be your grandfathers Oldsmobile (Or anyone / use to own a nice RB98) but it could be his plastic gauge. So, for many who don’t have $4-5k in inside/outside mic sets, plastigauge will be a general guide and place anyone in the ball park. Note; The newer the engine, the oil recommended by the manufacturer is synthetic down from 5W-20, to 0W-10 gets tighter in bearing clearance specs. Example; 2003 iron block GM 5.3L is 5W-20 and rods specs from GM production (New) 0.00009”-0.00025”, while service is 0.0009”-0.003”. This has a lot to due with the oil and bearing clearance as synthetic may cost more but has a much better cold flow, viscosity control over all heat ranges, etc. Just remember, this thin film is like tiny ball-bearings between metal crank to babbitt material. Use the correct clearance and oil. Yes, it cost more, but so due engines. Short drives to work, shopping or everyday use kills oil, so it needs driven on the highway at temp, once per week or change it at 2-3k miles. Raw fuel, water vapor, egr (Some models) but carbon particles as hard as rocks, float in the crankcase and can be boiled of if you get the temps up, otherwise it stays in the oil and this mixture become more acidic. Don’t let this happen! Change you oil and insist on an OEM filter. ASE Master Tech since 1978 - Retired Like & subscribe !!!

Hmmmm........... Mic's read just over 2 thou, plasty guage reads just over 2 thou, sounds the same to me.

You don't need to clean the platigauge off when your done, you can leave it on. It will not do any damage to the bearings and is designed for exactly that. I have always used plastigauge and a buddy of mine strictly uses bore gauges - neither of us have ever had an issue so really it comes down to personal preference. At the end of the day we're building engines and that's what's fun!!

I wonder, when was the last time he had his gage's calibrated? Has he ever dropped his gage?

is the plastigage measuring the gap on one side of the journal ? or is it preloading the journal , and measuring both clearances together ?

Video starts at 3:46

I've had machinist that worked for me that used a mic as if it were a C clamp. I would always measure 2-3 tenths more then they would when they were concerned about to much clearance. So maybe Plastigauge isn't so much off.

My opinion is that the plastic shows true oil film in assembled/running condition just I want to see it. My race bikes are always plastic checked before assembly and my Yamaha R1 runs better and longer than the so-called race shop engines that I compete against. I'm more than happy with my results but my track rivals aren't as they pay huge bills to have someone build their engines for them. I love my track days at Sebring Raceway Florida.

Plastigauge also works great in scenarios where you're not in a complete teardown and can't measure the clearances with conventional tools. For example, I had a buddy with a Mustang, 4.6 3v, break a cam cap when he was swapping the cam. He was able to get a used replacement from a guy on a forum, but I wasn't sure whether the different cam cap had slightly different dimensions, or if the one had had been lined bored with the cam, etc. So we fit it up, used some Plastigauge, and tolerances checked out within factory spec. There would have been no other way to ascertain the measurement without pulling the head off.

(Walter Brennan voice): back in my day,...right after they invented iron,....I schtarted buiding engines,...I'm 160 yrs old now,....been building engines since before I was hatched....we never used gauges,....we just liked our finger and held it up in the wind to see what the right clearance waszzzz.

plastiguage is the only way to set up babbit and shim style engine bearings

To get the Plastigauge off a part, just spray a little carb cleaner on a paper towel, gently rub the plastigauge and it disappears.

Dial bore gauges need to be set with gauge blocks to be accurate. You seting the micrometter on the journal is not a transfer standard since the frame of the micrometer flexes a little.

I would challenge you to do a blind test and measure your crank and your rods multiple times to see how much error you have in your measurements. You also are only measuring in one spot you’re not actually measuring the cylindericity of the Crank or the rod. I would venture to say that plastic gauge is a more real life measurement of the clearance, and if there’s any variation it’s more than likely the way you measure it with your gauges.

Damn! Gas prices must've been up then to get$140... Hell after accumulating junk from automotive repair, having hundreds of lbs in steel rotors,brakes, radiators etc, I'll get $70 on good days! Loading my small sonoma approx over 2,000 lbs.

Of course plastiguage is accurate - as if there's any doubt! OK, so the plastiguage isn't the most accurate we can be, but what actual difference does it make to the home engine builder - the tool's intended use? I contend none. If used for its intended purpose as a checking tool, it confirms your clearances are in the ball park to a high degree of accuracy. If you're assembling the engine yourself and want to check your machinists work then platiguage is perfectly fine, but no machinist would ever use a plastiguage as a primary means of determining journal size and therefore clearence so I'm unsure of the point of the vid? I don't know of any machinists that machine crankshafts using plastiguages.

You confirmed what I always believed..... good to know, thanks for the video. Now I can tell my buddies to get off my back when I bust on plastigauge...! lol...

I think less chance of mistake with plastic gauge

You can also do this with Soldering Wire and then measure it with a Vernier Caliper

So what do you do now that you have measurements. What is the purpose of knowing clearances?

Nobody here is going to work to "tenths", you would have to have a CMM and be damn good with that to get reliable results. You can give two guys the same micrometer and have them measure the same thing and they will come up with different dimensions. One ten thousandths of an inch is in another world compared to even one thousandth of an inch.

Never turn tfe plasti guage crooked on the journal, more accurate when straight

Back in the in the 90's I built and tore down to check my own Sprint car engines and always used Plastigage. Did I ever blow one up? Yes, kicked out of gear twice with my foot on the back motor plate a few years apart, they were wound tighter then a ducks fart! Back to your video, if the Gage is wider than .002 than it would be higher than .002 and not smaller correct? I believe posited the the opposite in the vid.

I like that comment about the European stuff😂My man...the imperial system rules the roost👍🏾👍🏾

Plastigauge is just fine for the average builder. It's been around for 70 years and going to be around for another 70. BUT I'm curious, being a mold maker for many years. How you can read .0001 on a dial indicator only accurate to a half thousand (.0005). Everything in between is just guessing. You would need another dial indicator accurate to .0001.

Plastigauge is pretty damn close. If you're building a mild engine under 400 hp this will work. Once you start punch over 500 hp I would use precision tooling. One big thing I like about plastigauge is you can visually see if you have taper on your caps. It's cheap and works just fine.

Well, how do you measure the crankshaft bearings' clearance using that one dial gauge? By the way, just stumbled upon your videos and they really inspire me. I'm a Mercedes-Benz trainee in Germany, so your little series does help me out a ton.

Спасибо за перевод на русский!)))

Not trying to be rude, but the 3min 45 seconds at the beginning of the video wasn't needed. I clicked on the video for the title. I didnt want to waste almost 4 min watching somebody make a scrap run.

Not necessary to wipe off spent plastigauge. It is oil soluble.

Anyone want to bet that the guy in the cab of that loader didnt speak enguish

Isn't 0005 that 5 tenthousand

Jump to 3:44 to get to the plastigauge bit :p

I think a lot of people see this as plastigage vs. micrometer, including the host, but thats missing the point of it all. No, plastigage is not as accurate as a micrometer, but it has it's place. The guy (or gal) that's NOT an engine builder and doesen't have fancy tools, its absolutely better than just slapping an engine together. I mean, if you are aiming for .002 and its closer to .001 or .003 you definitly know something isn't right. However, if you are building something more serious, chances are you have a lot more knowledge and own or can borrow a set of tools. Remove plastigage whith acetone or brakeclean and a rag.

I'd say that's close enough

That crank could have been polished a little better

Plastigauge has never let me down and saved my bacon more than once.......

Plastigage is ok stuff. Is it as good as a micrometer, and a dial bore gauge? No! But for most street applications it’s perfectly fine. If you’re having machine work done, and your having it done at a reliable shop. There is really no reason to waste your time on Plastigage.

(6:42) 2.2 thousandths of an inch, (8:40) that metric stuff I don't understand. 🤣🤣🤣🤣 Then don't use a decimal in your first measurement and see what that looks like. Metric is SOOO much easier to understand and more accurate. The day the imperial measurement dies forever will he a good day. Great video though. 👍🏻

Its not the question if it is accurate or not, what will you do if the clearance is off? Is it the bore? The crank? Are the parting lines stepped? How do you determine if the bore is round and you have the radial clearance, how does the bearing crush look? Is the rod ovaled out? Its great if you "want to know" but its not an engine builders tool, its a hobby tool for knowing the clearance at the exact place you placed the plastigauge. Those are the engines that you take apart and the parting lines are down to the copper.

Hey I needed those doors

Plasti-gauge is fine for 99.99999% of home built engines. It cleans off easily with a paper towel and some brake cleaner.

Could of done without the first 3.5 minutes of this video but otherwise informative.

Why would you check clearance on worn parts to be machined, other than checking bearings brand loyalty or machine shop reputation?? Do another video on how accurate Plasti gauge is AFTER your parts are machined for rebuild . I bet the Plasti gauge readings come in a hell of a lot closer to your precision tools then..

Plastic-gage .....high school auto shop technology, no thanks.