How to - use Plastigauge on Datsun engines

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How to - use Plastigauge on Datsun engines

#1

Post by BLUE » Sat Oct 04, 2014 4:31 pm

This is just a few pictures/words describing how to use plasti-gauge to check main bearing , and rod bearing clearances on your Datsun engine.
The engine in the picture below is a L28ET (Datsun 280zx Turbo 2.8 6-cylinder).
Pretty basic procedure or process , so don't sweat if you're a worried first timer.

(STEP 1:) --- Consult , purchase , or obtain main bearing as well as rod-bearing minimum , and maximum wear tolerances. Examples are Nissan factory service manuals , Haynes repair manual , or a Chilton repair manual. Some repair manuals/specs are in inches/metric , and others are just simply metric.

(STEP 2:) --- After consulting my repair manual I obtained the correct "Green Plasti-gauge" size from my local NAPA auto parts house. Plasti-gauge is color coded in several colors to indicate the size range in which the material is designed to test. It is best for me to let YOU do your homework on what size you need (or color) as a general statement since not all sizes fit one in this case. Pretty easy just a couple of extra minutes on a search in google at Jegs , Summit or a call to a local parts house.

Image020 by 71240z, on Flickr

(STEP 3:) ---- Assuming your oil pan is off. Take off either the rod-bearing cap or main bearing cap that is desired to check. The procedure is the same for both.
I'm using a 14mm on a 1/2" drive breaker bar to take off an crankshaft main bearing cap.

Image022 by 71240z, on Flickr

(STEP 4:) ---- The main bearing cap is off ... try to be as clean as possible (relatively). You don't want to have excessive oil residue or oil in general on the journal being testing.

Image023 by 71240z, on Flickr

(STEP 5:) ---- All you're going to do next is cut a strip off your green plasti-gauge ... lay it like it's shown in the picture below. While leaving the bearings in place place the main bearing cap back on carefully. Next torque the bolts down in at least (3) stages minimum via the torque specifications outlined in your repair manual or book. The torque spec used for this engine is right around 4oft lbs , but you need to look up the exact specifications yourself since it's very important to know them from the source :) . Un-torque the main-bearing cap in (3) stages minimum then pull off the cap as shown in the picture below. Hold the ruler on the side of the Plasti-gauge wax paper up next to the crushed piece of plastic gauge. The closest green or white bar on the ruler held next to the squished piece of plasti-gauge on the crank is your crankshaft main-bearing or crankshaft rod-bearing clearance. Repeat the same procedure for all the bearings on the crankshaft carefully with attention to torque specs.

Image040 by 71240z, on Flickr

Image026 by 71240z, on Flickr

Image033 by 71240z, on Flickr

(STEP 6:) ---- Clean off all the plasti-gauge residue in the least harmful way possible. An old credit card or fingernail are relatively harmless. Don't use metallic objects or tools to clean off the residue. Especially in the bearings (soft) or the crank where it can get scored or scratched.

This can be used on lots of different engines/makes/years as well if you were curious.

Have fun.

(may need editing).
DRIVEN » Sat Oct 11, 2014 10:24 am wrote:
1. Make progress until broke.
2. Go make mo money.
3. Repeat.

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Re: How to - use Plastigauge on Datsun engines

#2

Post by DRIVEN » Sat Oct 04, 2014 5:04 pm

Good tip on the old credit card.
Plastigauge is a great way to check your work. When I first started turning wrenches I worked for my uncle. I remember the first engine he let me freshen up for a longtime customer's old Chevy truck. Basically a reseal with rings and bearings and a valve job. I took measurements when I tore it down and ordered new parts because the old bearings were not marked as STD or undersized. I ordered STD rings, rod and main bearings because that's what i THOUGHT I measured. Was putting it together and decided to check the clearances with Plastigauge. Good thing I did because for some reason the rod journals were standard but the mains were .010" under and I mismeasured. There were no obvious signs that the engine had ever been open before and .010" extra clearance in a main bearing is a lot less obvious than a rod bearing that is that sloppy -- especially to the inexperienced eye. Plastigauge saved my ass.
When the only tool you have is a hammer every problem starts to look like a hippy.

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Re: How to - use Plastigauge on Datsun engines

#3

Post by BLUE » Sun Oct 05, 2014 1:22 pm

That's an excellent point DRIVEN !!! I've been in that situation (reverse on the sizes needed , and it was a SBC) many moons ago when I was learning to make engines work properly after I had touched them :D :rofl: (I was a kid) . Very glad I did the plasti-gauge process , and as a learning curve it's a great basic practice to do. Takes a little extra time , but very worth it. Very cheap insurance all the way around !

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DRIVEN » Sat Oct 11, 2014 10:24 am wrote:
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2. Go make mo money.
3. Repeat.

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Re: How to - use Plastigauge on Datsun engines

#4

Post by Laecaon » Sun Oct 05, 2014 2:49 pm

Yep, always plastigauge after assembly too. I have heard too many stories coming from not doing that.

I usually just rub the plastiguage off with a bit of oil and my finger. I figure oil and plastic are the same thing.

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