Plastigage issues.. what am I doing wrong??

[Rengar18]

Trying to check the main bearing clearances with the red and green plastigage and my results are 4 of the journals are unreadable (the plastic gets bigger then I can measure. Bigger then .002 on the red gauge and bigger then .001 on the green gauge). I've gotten 1 (my first try) where 4 the journals came out to .0015 and one was .001 but I overtorqued the bolts.

The process i'm doing is I lay the plastigage in each journal and lay the main bearing cap with all the bolts in it. Hand tighten each bolt in the proper sequence then tighten each bolt again in sequence until i feel a little resistance in the wrench (about 5 ft lbs or less) manual says tighten the bolts in 3 steps so I assume this is step 1?

After that I tighten each bolt to 16ft lbs(step 2?)then after all 10 are 16ftlbs I do a additional 90 degree(12 o clock to 3 o clock) on all 10 (step 3) again both these steps in the correct sequence

I must be doing something wrong (also the crank is a brand new stock crank not cut or anything and i'm using std bearings) hopefully somebody can shed some light on whats going on.. Thanks

 

[g4ebguy90]

I assume that's a 7 bolt.

If the plastigage is getting bigger doesn't that mean it's a tighter fit.
Usually people plastigage used stuff. So my crank with 170 k will have a smaller plastigage because clearances are not tight. I will check right now on my plastigage if bigger is better.

 

[DSMN]

you may have to have the caps milled down to fit the new crank. the machinist will set it up in the jig and measure the center line (line hone) and they'll cut depending. the crank seams to be a little snug in there. just verify the bearings are what there supposed to be. also make sure when you put the caps over the plastiguage don't pre smoosh it . because the crank is new its obviously not worn down and the clearances are tight. one other thing. i like my clearances to be around 1.5 -2.0 thousandths

 

[g4ebguy90]

Well I just looked at mine, Bigger does mean there is less clearance, which is usually a good thing, there is less play and chance for wear. I would expect this buying a uncut crank, and new standard bearings honestly.

 

[talonDSMerr]

Are you cleaning off all the residual plastigauge off the bearings/journals before trying it again? The slightest bit left will throw your measurements off. Also, be very careful removing the main caps so as to not squish the plastigauge any further.

 

[Indian]

Make sure your not doing this with in hot tempatures as the plastic will seem to melt and skew the readings.

 

[Rengar18]

Are you cleaning off all the residual plastigauge off the bearings/journals before trying it again? The slightest bit left will throw your measurements off. Also, be very careful removing the main caps so as to not squish the plastigauge any further.

Yes i've been cleaning it all off after every test (on the crank journals and off the bearings in the cap) Using a old credit card and my nail plus a rag and some spit .

Yea im working on the motor in my room so its not too hot haha. So G4ebguy90 I actually never realized since its smashing the plastic so much its extremely tight.. is that a good thing? I just want to have piece of mind before I assemble this and these results not being concrete has me worried...

Oh and yes its the 7 bolt out of my 97 Gsx forgot to mention that

 

[g4ebguy90]

I mean how much bigger is it then the plastigage marking??? and whats the spec for your clearance?

 

[DSMN]

tight clearnaces are nice but thats very tight. having that close of clearance heats the bearing quicker because the oil cant properly lube the journals that well IMO like i said previously 1.5 -2.0 thousandths is what i like to run.

 

[99RedGs]

Make sure the crank isn't rotating when you install/remove it. That will smear it and give false readings

 

[Rengar18]

Its about 30-40% wider then .002 with the red gauge. I bought more of it to test further to see if 100% the results are the same everytime. But the process i'm doing to tighting the bolts is correct? I thought I must have been tighting them wrong?

 

[Achelea]

What they are referring to is Step Torquing.

IE you take a torque wrench and set it lets say 50% of your final torque. then 75% of your final torque, and then finish it off with 100% of your final torque.

IE it says 100 in/lbs, toque it first at 50in/lb, then 75in/lb, then 100in/lb.

You need to be doing this with a torque wrench. Considering you are estimating your torques, I'm guessing you are using a socket. If you're not careful you can twist what you're working on.

Calibrated tools are vital, especially with something like this.

But what do I know, I'm just an aircraft mechanic.

Edit:

Also, your above method of torquing might stretch bolts and make them innacurate. On some things you can go quarter turn for torque specs, but when you are that deep in the engine, each turn ramps up the amount of torque exponentially.

 

[Rengar18]

What they are referring to is Step Torquing.

IE you take a torque wrench and set it lets say 50% of your final torque. then 75% of your final torque, and then finish it off with 100% of your final torque.

IE it says 100 in/lbs, toque it first at 50in/lb, then 75in/lb, then 100in/lb.

You need to be doing this with a torque wrench. Considering you are estimating your torques, I'm guessing you are using a socket. If you're not careful you can twist what you're working on.

Calibrated tools are vital, especially with something like this.

But what do I know, I'm just an aircraft mechanic.

Ah fair enough. No i'm using a torque wrench but I actually never thought of setting the wrench to a lower setting to ensure there all at the same gradual torque at all times. Cool ill try 8ftlbs, 16, then the 90 degree turn.

 

[Achelea]

Ah fair enough. No i'm using a torque wrench but I actually never thought of setting the wrench to a lower setting to ensure there all at the same gradual torque at all times. Cool ill try 8ftlbs, 16, then the 90 degree turn.

No, DO NOT do the 90 degree turn, put it at the final torque required. For all you know the 90 degree turn could be under torque, or over torque.

Trust me, I think I know what I'm doing.

Besides, going past where the torque is required is over-torquing your torque wrench and throwing it's calibration off, meaning it won't be as accurate when you need it to be.

 

[g4ebguy90]

Wait you are not using a degree tool. To go 90 degrees?

 

[Rengar18]

No, DO NOT do the 90 degree turn, put it at the final torque required. For all you know the 90 degree turn could be under torque, or over torque.

Trust me, I think I know what I'm doing.

Besides, going past where the torque is required is over-torquing your torque wrench and throwing it's calibration off, meaning it won't be as accurate when you need it to be.

Dude i'm just going with what the service manual says which is to torque it to 16ftlbs plus another 90 degree turn in 3 steps. And to use paint to mark the bolts/bearing cap to ensure the 90 degree turn is dead on. Also i'm using a breaker bar to do the 90 degree turns not my torque wrench

No G4ebguy90 just using the paint method explained in the service manual. Thought that would be enough . Also i'll have more results tomorrow trying the step torquing Achelea suggested. Thanks again guys for the help so far

 

[Achelea]

Ah, alrighty. My apologies then. ^.^

 

[dj-t]

I say find someone with a micrometer/bore gauge or take it to a reputable honest machine shop and have them mic it for you. If you take it to a machine shop just have them record each measurements for each journal for your records. $60-$100 (around my area) for their service is cheaper than having a bearing or worse things give out on you down the road.

So you have gotten .0015mm on 4 of the journals and .001mm on the other or is it in inch(red strips). Don't the dealer offer different bearing size that you can get? Did you measured the journals on the crank?

 

[Rengar18]

Zzzz somehow the number 2 bolt for the bearing cap snapped the first test I did while I was loosening it after I had torqued all 10.. but on the flip side this test came up good doingthe step torque....0015 on four of the journals and .001 on the stout journal. This is with the green plastigage btw. Ill test it a few more times and post results once the new bolt arrives.

 

[Achelea]

*Thumbs up* Cool.

 

[tcouty87]

Just got done building an engine n had the same problem. Even though ut bearing caps come in standard, most machine shoos will do a little cross hatching on these as well to help with initial breaking and oil clearances. Like the aircraft mechanic said a t-bore gauge n micrometer will be best.

 

[Rengar18]

Alright, new bolt is here and I did a few more test.

Looks likes final results using the step torquing and such are

From Stout to flywheel end: .0015, .001, .0015, .001, .0015

Ive gotten that result pretty consistently using the green gauge. Which according to the service and haynes manual is within spec (.0008-.0016 In.). So I think im good to go. Thanks for the tips guys.

 

[Frickadella]

Pessimist that I am, I'd be worried about all of your cap screws having been stretched. That one of them broke is a sign that your 1/4 turn technique may have fatiqued all of them - and is why you were getting unreadable plastigauge. The spec is 18 ft.lbs, and I can be pretty sure that 1/4 turn is going to add a lot more than 2 ft.lbs.

I should also point out that torque is a measure of the friction on the threads, so whether you use lubrication or leave them dry makes a difference as well. Rust will also increase friction. More friction means less clamping or shearing force on the cap screw for the same torque reading. In other words, lubrication allows you to turn the cap screw further before reaching a torque spec... snap! Most mfr specs are dry & clean unless otherwise stated.

I was taught to lightly oil under the head of the cap screw to reduce shearing force.

If you like peace of mind, I'd suggest you get the ARP stud kit. With studs you don't have to worry about the shearing forces applied to the cap screws. As a note, you'll need a torque wrench that goes over 75 ft.lbs for the ARP studs, if memory serves.


Also, there is no cross-hatching done to mains. Bearings don't move and nothing is breaking in. Oil flow behind the bearings should be minimal or non-existent. Cross-hatching would only be a by-product of the the align honing, and not an objective.

 

[Rengar18]

Pessimist that I am, I'd be worried about all of your cap screws having been stretched. That one of them broke is a sign that your 1/4 turn technique may have fatiqued all of them - and is why you were getting unreadable plastigauge. The spec is 18 ft.lbs, and I can be pretty sure that 1/4 turn is going to add a lot more than 2 ft.lbs.

I should also point out that torque is a measure of the friction on the threads, so whether you use lubrication or leave them dry makes a difference as well. Rust will also increase friction. More friction means less clamping or shearing force on the cap screw for the same torque reading. In other words, lubrication allows you to turn the cap screw further before reaching a torque spec... snap! Most mfr specs are dry & clean unless otherwise stated.

I was taught to lightly oil under the head of the cap screw to reduce shearing force.

If you like peace of mind, I'd suggest you get the ARP stud kit. With studs you don't have to worry about the shearing forces applied to the cap screws. As a note, you'll need a torque wrench that goes over 75 ft.lbs for the ARP studs, if memory serves.


Also, there is no cross-hatching done to mains. Bearings don't move and nothing is breaking in. Oil flow behind the bearings should be minimal or non-existent. Cross-hatching would only be a by-product of the the align honing, and not an objective.

Thanks for the reply.. yea while I did measure all the bolts length and they came out in spec (under 2.79 in.) I did not use a straight edge to see if they were worn in the middle

Also Id say I torqued them down about 15 times trying to get a consistant reading. Anyways after I final torqued them the endplay came out to .003 and the crank spins freely and the bolts were the same drill to tighten so I think i'm good. Hopefully this doesnt come back to bite me in the ass at a later date after the car is running(knowing dsms that is very well possible ) really dont have $60 for studs atm but that is a good idea.

Would i be able to pull the oil pan after the motor is assembled in the car and running and switch the bolts 1 by 1 much like how head studs are done?