PLASTIGAUGE Vs MICROMETER !!!!!!???????

[OldSkool69]

Ok guys,

As u might know I been cleaning every inch of my engine to rebuild it!!!!

Just finish doing that......and here I was in the weekend placing the 3/4 but before as dady at 7 y'o' hit me with his torque wrench told me..."first you measure all the clearence in all the bearings, you can't trust machinist here, then you meassure again bearing clearence, after that you measure again bearing clearence, all with tools, and last but not least you check it with the plastigauge, just to make sure you aint reading bad the tool"

Don't know if it was his kind words or the hit in my head that always makes me remind this !!!????

Anyway, I did this with my 5.3L. As u all know the crank went .25 on 4 mains and .30 on main #5.
Rod went to .2.

I check and re-cheked this with the micrometer, and the measures where totally consistent, machinist did a great job in accuracy in all the lobes.

Then, I checked twice with the greenn plastigauge ant the measures came out tight in respect to the micrometer....4 mains on .20, #5 main on .25, And the rods came on .15.

After that I tried one with the red plastigauge that has a 2-6" tolernace and same result as the green on the mains only.

I was like WTF, but some times happend to me in other rebuilding, even thou as it where inside the specs I always rebuild with no problems.

As this engine u know is for kicking ass, I want to be totally sure.

Now, as my old man tauch me (not hit on this one) I always "FEEL" the engine turning the crank to see how smooth it goes, and it goes smooth as silk.

Question: who is giving me the correct clearence?????, anyway both get into specs, but I want to make sure, so I use the right Oil Weigth.


Hope you experts share some light on me.

Gabe









Image Gallery with PicTiger

[Bowtie70SS]

I would trust a calibrated micrometer way more than a little stick of clay(plastigauge). Plastigauge will get you in the ballpark, but I would trust the mic. Also you already said it turns nice and smooth so there you go.

Dave

[RedHeartbeat]

I always mic it in three locations around each journal plus check for taper end to end on the journal. Blueprinting your crank and rods is very important when you know you are going to brutalize them.

[misterp]

Agreed; Plastiguage is not reliable enough for a blueprinted build. The only thing that can check a mic is another known good mic. If you are going to push it to the ragged edge then RedHeartbeat's advice is the only one to take, take an extra day and measure/verify taper in addition to clearance. RE crank rotating smoothly is only valid after you've capped the mains; once you begin stuffing cylinders in my experience doesn't mean a damn thing. Several of the most reliable short blocks I have assembled had ring packages with pretty high tension and were very stiff to turn over (50+ ft-lbs after the pistons were in) and I've also had others with low-tension rings that would turn over with 20 ft-lbs. Use a known good mic, you can get a Mitutoyo digital caliper for $50-75 on eBay.

Mr. P.

[02CHEV]

car craft just did a thread on this

[OldSkool69]

I'll look for it ant the net dude, if u have the link better.....no Car craft around here sadly

[02CHEV]

i looked on carcraft.com and they did not have the article on this. sorry cant help. thought it would help out but not

[OldSkool69]

Thanks anyway for the time dude...really apreciated

Gabe