Plasti-guage Use

super99 · Jan 1, 2020

Every time I have tried to use plastiguage to check bearings, it ends up embedded in the crankshaft and bearing. I have seen video where they use it and when they take bearing cap off, they lift it off and hold it up against the package to read it. What am I doing wrong? Thanks, Chris

Super H Mike · Jan 1, 2020

That's the way it looks when I use it too. I run it straight across though, not at an angle like that. Then I scrape it off with a fingernail or wipe it off with brake cleaner and a rag. Use the package at the crank to measure.

rustred · Jan 1, 2020

Make sure the brgs and crank is lubed first.

Janicholson · Jan 1, 2020

I stick it on the bearing using a tiny dab of engine oil either way measuring across th width of the squished thread is critical. Good explanation, Jim

fixerupper · Jan 1, 2020

Jim I read that oil takes up space making for a false reading on the plastigage. I usually do it your way though, just a little dab of oil somewhere along the thread to stick it down.

Janicholson · Jan 1, 2020

Clean journal, tiny dab. The smashing leaves no oil thickness at the plastic (at least not but a few molecules). Jim

tim s · Jan 1, 2020

Is it possible that the crank is being turned a bit to "Mush" the plasti-gauge on the journal??

kencombs · Jan 1, 2020

One thing often overlooked is supporting the crank up to the top of the bearing bore. I use a paper/cardboard shim under two journals not being measured. That supports the crank upward. If that?s not done the weight of the crank mashes the plastic age before pressing it against the top of the bearing. Wrong reading and causes a lot of pressure which sticks it to the crank

And straight across not angled.

Janicholson · Jan 1, 2020

Absolutely not. Careful use requires the journal to be stationary. On mains with the engine in the car, I was taught to use shims on the main bearings to assure the crank was being held up in contact with the upper shell. Jim

rustred · Jan 1, 2020

Yes , but on An engine rebuild it?s in an engine stand and engine is rotated upside down on assembly. Checking clearances is more critical having crank turned and rods resized when installing brgs.

guido · Jan 1, 2020

Hello super99

You measure one at the time, while all the others are tight. Plastigauge will stick to the crank, and as you have seen the package has the clearance scale. It is intended to be used where both surfaces are dry, so it spreads properly,

Guido.

Super H Mike · Jan 1, 2020

I have always used it dry also and believe that is the correct way.

guido · Jan 1, 2020

Hello super99,

It also appears that the plastic gauge is on a slant. You need to put it across the journal, or from the back to the front of the engine. Cut it a bit short of the size-lenght of the bearing shell,

Guido.

guido · Jan 1, 2020

Hello Super H Mike,

That is the correct way to measure clearances with plastic gauge. I worked with a mechanic that would lube the back of the bearing shell. Could not get through to him, that it would decrease proper bearing to crack clearance, and probably remove part of the bearing shell's wear layer, and 100% not necessary,
Guido.

tom upton · Jan 1, 2020

Plastigauge needs to be on top laid parallel to crank. So if looking at end of crank with motor upside down plastigauge in the 12 oclock position. If it is not it gets smeared as you tighten down the cap. Make sure you wipe surface clean before putting strip on. Use correct range of plastigauge. Measure on the crank.
If you are doing much rebuilding I would suggest investing in a bore guage and mic. KBC tools has bore gauges on sale from time to time for $100 or so.

matthies · Jan 1, 2020

Looks like it really got smashed, there is red and green plastiguage also, I would try using a different color/thickness. They are made for different clearances.

jd man wis · Jan 1, 2020

It looks like you spun the crank over did you. You check it across the cap at the bottom of it stroke.

37chief · Jan 1, 2020

Looks like you have it upside down, so the crank is not hanging down. I wish I had a clearance like that in the past. I usually scrap it off with my finger nail. I have always had it stick to the crank, or bearing. Maybe because I do it dry. Stan

T.R.K. · Jan 1, 2020

The way I was taught to use it in the '80s was to put the shell in the cap, lube the inside of the shell so the plastiguage won't stick to it, lay the plasti-guage on the dry crank parallel with the shaft, put the cap on and torque the bolts to spec. Then remove the cap and measure the plasti-guage with a portion of the wrapper. I was told that you lube the inside of the bearing so the plastiguage won't stick to it.

You run the piece of plastiguage allmost all the way across the journal to be certain that the journal doesn't taper from side to side.

I only skipped that step on one engine. After all, the crank was reground, right? As soon as I torqued the front main cap, the crank froze tight. Checking with Plastiguage would have told the story.

It turned out that the thrust bearing faces had worn on the crank so that when you pressed in the clutch, the crank moved forward enought that the timing gear could rub the front main bearing boss in the block. It had actually worked the last 1/4" of the bore inward enough that the new cap would clamp tight on the block. I had to get the block align bored at one shop and have another machine shop weld up and re-grind the thrust face on the rear crank journal.
This was a late 206 engine in a Minneapolis Moline tractor.

coshoo · Jan 1, 2020

Sure looks like you're rotating the crank after you put in the plastiguage. It has to remain stationary- remove cap, put in plastiguage, put cap back on, torque it down, then remove cap and compare width to the scale on the package.

gregww · Jan 1, 2020

In my late teens and early 20's I rebuilt 2 small block Chevrolet engines using on Plastigauge to measure for new bearings. My engines were mounted on engine stands. Never had the trouble you seem to be having. This was over 40 years ago now, doubt I would remember how to rebuild an engine today. The last time I saw those 2, they were running strong. Of course 40 years ago, so was I.

teddy52food · Jan 1, 2020

plastigage is soft enough that it will not hurt the crank or bearing. It will end up in the oil filter if you don't scrape it off.

super99 · Jan 1, 2020

Tried it again, motor is on a stand turned upside down. It?s out of a Oliver 550. Dab of oil on crankshaft, torqued the cap and took it off. Think I need smaller plastiguage, it is wider than the marks on the package. I was able to get the stuck piston to move, cleaned up the sleeves and got one of the better pistons out . Thanks, Chris

gregww · Jan 1, 2020

Have you possibly mixed up the caps, or turned them around backwards from what they were? In a perfect engine, this may not matter. If this was a perfect engine, you wouldn't be doing this in the first place

pete 23 · Jan 1, 2020

As spread out as that gauge looks I would say to use the smaller size plasti gauge.

super99 · Jan 1, 2020

That is the only one that's been off. took off and put right back on. When I picked up the Plasti guage, that is the only size they had right then, they had all the sizes in the warehouse but only one in the store. I'll try to get a smaller size and try it again. Chris

Bob · Jan 1, 2020

(quoted from post at 21:18:32 01/01/20) That is the only one that's been off. took off and put right back on. When I picked up the Plasti guage, that is the only size they had right then, they had all the sizes in the warehouse but only one in the store. I'll try to get a smaller size and try it again. Chris

I can't think of a single use for .004" to .009" plastigauge in any common auto or tractor engine.

Did you get it at industrial supply house the probably stocks it for a reason, or at an auto parts store that doesn't know what they are doing?

teddy52food · Jan 2, 2020

Get the green instead of the blue.

Hobo,NC · Jan 2, 2020

Use a plastic credit card to remove it :wink:

dr sportster · Jan 2, 2020

That is what happens when you put .004 plastigauge in a .002 " situation.

Ozlander · Jan 2, 2020

At least you know it's tighter than .004, maybe .003.

620 John · Jan 2, 2020

Check your specs to see what kind of clearance you should have. I'm guessing you're gonna need .003" for that journel????? With that being said you'll need probably green plastigage (.001-.003") or red (.002-.006"). Find the spec and pick the color with your measurement in the middle of the range.

Recently I did a little experimenting using plastigage with and without lube on the journels. I did one measurement on a main journel completely dry and did the same journel again with a little bit of a synthetic assembly lube. The measurement I got with using a little bit of lube was NOT noticeably different as the one dry. I thought maybe with a little bit of lube it would tighten up the measurement but I couldn't tell a difference.

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