When using plastigage

[Jon K]

When you sing plastigage, I am to clean everything with no oil. Lay a new bearing in the journal (block upside down)? Where do I place the plastigage? What side of the crank shaft? Torque to torque and then remove and look at plastigage. This is with the new bearings in, right?

[bsell]

When you sing plastigage, I am to clean everything with no oil. Lay a new bearing in the journal (block upside down)? Where do I place the plastigage? What side of the crank shaft? Torque to torque and then remove and look at plastigage. This is with the new bearings in, right?

Right on top of the crank, where the new bearing (in the cap) will contact it. It is vital that you do nothing to smear the plastigauge, either by bumping (twisting/spinning) the crank or rocking the bearing/cap into place.

Yes, torque as specified, then remove the bearing/cap as gently as possible so the plastigauge is not disturbed from the original, torqued, squish.

The plastigauge should come with a 'gauge' to read the squish. Match up the width of the squished plastigauge with the markings on the 'gauge' to see how much clearance you have.

Patience is key as you have quite a few bearings to check. Doing the rods will drive you crazy if you don't have the pistons connected and in the bores.:(

Brian

[Jon K]

Thanks! So, if the block is upside down (bores down) I can put the plastigage on "top" which is actually where the oil pan would be?

Next question, what are the damn clearances haha.

[Turbo Ready]

Jon, I don't think it makes a difference if the block is upside down or not, the crank rotates so not important. The clearances are in the Bentley.

I have attached a few pics illustrating how I did an m20 bearing clearance check a few weeks ago.

[Turbo Ready]

this is what the wax strip looks like after the bearing has been torqued and removed.

[Jon K]

Awesome thanks! Do you do all of the bearing surfaces at the same time? Meaning, torque the whole crank down with plastigage under each bearing shell?

[Turbo Ready]

I did them one at a time, no need to all at the same time.

Remember to mark each piston position and direction to the intake or exhaust as you remove them from the block. I placed an arrow to point towards the intake side of the block as shown in pic.

[Turbo Ready]

It's also important to check for the crankshaft end play. I used a mid priced machinist dial gauge and magnetic base to check for the crankshaft end play before I removed it from the block.

[winfred]

.0012 - .0028 if i remember right, to the tight side of that is good, might i suggest a cocaine scale from ebay to balance the rods and pistons, got my ohaus 2610 for like $36 delivered, my rods were 4gr difference and pistons were 2.5gr, if the bad ones got together that could be 15-20 hp lost, i got em all within 1/10th of one another

[Jon K]

.0012 - .0028 if i remember right, to the tight side of that is good, might i suggest a cocaine scale from ebay to balance the rods and pistons, got my ohaus 2610 for like $36 delivered, my rods were 4gr difference and pistons were 2.5gr, if the bad ones got together that could be 15-20 hp lost, i got em all within 1/10th of one another

no need to rotate balance? I don't want to take the pistons/rods out of balance and have the crankshaft + piston assembly be off.

Winfred - M50 non vanos, the exhaust valves are smaller than the intake valves -- I didn't mark which way the pistons went in... is there some way to tell?


Also winfred - the circlip type deals that hold the wrist pin inside the piston - do I need new ones if I seperate them? Where do ya get em?

[winfred]

if you are worried balance the pistons/rods before having the crank balanced they just need one assembled piston/rod/rings/bearing to set the bob weight right, a few grams off ain't going to screw with it but having the stuff that changes directions and swings around far from the centerline of the crank balanced will help

it's been a while since i was into the bottom end of a 50 and can't remember but theres probably a arrow or something on the piston, i can't remember if the valve relief cuts are matched to the valve sizes

i reused the clips on mine, as long as you don't tweak them so that they loose strength or bend them i don't really see a problem with reusing them

heres my slugs after i balanced them
http://www.fileden.com/files/2006/11/26/427251/pistons%20and%20scale.JPG


no need to rotate balance? I don't want to take the pistons/rods out of balance and have the crankshaft + piston assembly be off.

Winfred - M50 non vanos, the exhaust valves are smaller than the intake valves -- I didn't mark which way the pistons went in... is there some way to tell?


Also winfred - the circlip type deals that hold the wrist pin inside the piston - do I need new ones if I seperate them? Where do ya get em?

[Jon K]

So winfred did you also balance the crank?

[winfred]

i had the machine shop do it but i was having some other work done on it so i don't really know how much it was off in stock form, i had the counter weights bobbed to clear the m20 pistons

[Bill R.]

If you're going to balance it ,you have to balance it all or else your wasting your time... The rods have to be balanced at each end , you have to hang them in a special fixture and weigh the piston end and balance and then weight the big end and balance and then balance the weight overall. The ends each travel in different circles. And the crank, flywheel, clutch pressure plate and harmonic damper all need to balanced as an assy with the rod/pistons.
I learned on a stewart warner shadowgraph back in the early 70's. It was accurate on balancing rods/pistons to less than 1/10 gram. Here's a pretty good link on how to build a rod balancing fixture that is similar to the factory stewart warner setup (http://www.angelfire.com/ca4/CorvAIRCRAFT/RodBalance.html)

[Bill R.]

There's an arrow on top of the piston to indicate the direction of the piston on the m50 like so.








no need to rotate balance? I don't want to take the pistons/rods out of balance and have the crankshaft + piston assembly be off.

Winfred - M50 non vanos, the exhaust valves are smaller than the intake valves -- I didn't mark which way the pistons went in... is there some way to tell?


Also winfred - the circlip type deals that hold the wrist pin inside the piston - do I need new ones if I seperate them? Where do ya get em?

[Bill R.]

the rod bearing specs are as follows...The metric spec is in the pic. The US spec is .00078 inches to .00216 inches.