BradleyScott

I want this rebuild to last a lot longer than my first attempt did years ago (95 LT1 M6 ~ 50mi.), so I'm try to go slow and do it right BUT for as cheaply as possible. I don't have access to every tool so I'm buying them as needed. Can I torque all my caps down one at a time with the new bearing(s) installed, use a micrometer and measure the average i.d. of say 3 measurements. Then subtract from that the average o.d. of another 3 measurements of my crank journals in order to find my clearances? Or is that not accurate enough? I know they make dial bore micrometers just for this purpose but could I just use one of the basic digital, slide types (unsure what they're actually called).

Toocool

Buy some plastigage, it makes it simple.

Charlie Jones

. If you are on a limited budget , one of the best tools you can use is Plastiguage . It's only a few bucks and will tell you your real bearing clearance .
(As opposed to a theroretical clearance based on measurements )

edzolz

I'm not opposed to using plastigage but your statement about measurements being theoretical is totally wrong. I was a tool and die maker (one of my many professions) and actual measurements are not theoretical. Using a dial bore gage is the most accurate way to measure the ID of the bearings. And using a micrometer is the most accurate way to measure the journals of the crankshaft. The measurement you get using Plastigage is, at the best, a theoretical measure because of the possibly inconsistent diameter of the ribbon of the plastic and comparing the mashed ribbon to a piece of paper that is printed with the width of each supposedly bearing clearance. I do agree that Plastigage is the best measurement method if you do not have access to accurate mechanical measuring tools.

oddball

I never had good results with plastigauge, but it is better than nothing. One thing I don't like is everything has to be completely dry - any oil film will throw off the plastigauge.
The common cheap dial bore gauge is about $60 and is decent. Takes some practice. You can buy a single caliper of the right range (2"-3") for under $50. Those will get you within 0.0005", but there is a "touch" to using those tools. But this setup has been good enough for me to catch a tight rod and a tight align hone. Buddy's 4.6 mains had less than 0.001" clearance when we got it back from the shop. Apparently 0.001" is the low end of the spec on those aluminum blocks, but I told him to send it back.

joe_padavano

Plastigage is notoriously inaccurate.

As for the original question, well, sorry but if this is what you think is the way to measure bearing clearances, well, I understand why your first build failed. There is no "average" clearance. You MUST measure the clearances of every single journal (mains and rods) to verify that EACH ONE OF THEM is within spec.

cjsdad

Don't sugar coat it for him Joe!

Dood! Tell him why his question is flawed for goodness sake.

In one way, Joe is right, you cannot take an "average" measurement, but you do need to take "multiple" measurements for each bearing surface. Engines with high mileage or heavy wear can get out-of-round journals so you have to measure them at multiple points to find out. If the bearing surfaces are too worn, they need to be re-ground to make them reliable.

Plastigauge needs to be used the same way. Multiple measurements on each bearing journal for maximum accuracy. It is not perfect, but can be close enough for a simple refresh of a running engine. Always cut the plastic, if you tear it you ruin its ability to measure properly.

There are acceptable limits of wear on an engine and that is why rebuild guides give minimum and maximum clearances for everything. Engine performance and life will suffer the closer you get to the maximum tolerance. If you are not having the engine block cleaned professionally, get an engine brush kit and scrub the beejeesus out of it with warm soapy water! Clean ALL of the oil passages including the pushrods and the holes in the crankshaft. Any debris left in those passages can damage a new bearing in just a few miles! Oil all machined surfaces after drying so they don't flash rust.

Cleanliness is next to go... Oh wait, that is for another forum, cleanliness is an absolute must for engine assembly. Any grit or heavy dust can damage new bearings especially if it gets between the block and the back of a bearing. I learned that on youtube! Watch all of the engine assembly videos you can stand. All makes! There will be repetition in most of them for a reason and a few little gems along the way that will be AHA! moments.

You will get a lot of negative comments from the rogue's gallery here about not throwing down wads of cash for a complete remanufacture of the engine but if you are meticulous enough you can build a decent engine without dropping 5 grand on it.

83hurstguy

If you're trying to measure the crank journals with a "digital slide type micrometer," it sounds like you are referring to a digital caliper? While those can be accurate, they are not accurate enough to measure bearing clearances. You could buy a conventional screw-type, non digital micrometer, then buy a dial bore gauge, and that will get you measurements. However, doing this still takes practice to obtain repeatable/accurate results. I recommend you have someone with experience helping you through this build.

JohnnyBs68S

Faro Arm.

J/K. We use this at work, but like any other measurement device, you have to be proficient in its use to get good measurements. This would be overkill (and impractical) for an engine rebuild when much simpler, more straight-forward and much less expensive measurement methods work just fine.

BradleyScott

I was thinking about a caliper tool in my mind's eye even though I called it a micrometer. Thankfully, google set me straight about the difference. From my new understanding of the differences between the two tools; micrometers are far more accurate down to ten-thousandths (0.0001) or lower, whereas calipers typically have an accuracy in the thousandths (0.001). Also, apperently I wasn't clear enough in my statement because I did mean an sverage of 3 measurements for EACH surface individually. I didn't mean like take my measurements and then average them out as a whole or set (mains, rods, p.t.w., end gap, ect.) or anything like that. I understand that once everything is clean, I will be assembling and unassembling each component multiple times before I'm ever ready for "Final Assembly". I was just needing reassurance that I got the basic process down right before I attempt this again. On my 1st motor, I did have a machinist helping me along the way until break-in. He told me that I should break in with a stock cam/pcm but I didn't listen. Instead, I decided to use a mail-order tune, open headers, and a high lift cam (.570 in. / .576 ex.) Everything went fine until it was time to drive it to the exhaust shop (1.5 hr runtime apx.) By the time I got there, I had a bad knocking soumd and tons of gas in the oil. Looking back, I believe the scavenging effect from the headers was causing fresh O2 to be read by the sensors (3-4 inches away from the openings) resulting in massive amounts of fuel to be dumped by the injectors. i should have had it towed there but alas my penny pinching bit me in the butt. I was young and reckless.

So let's go over how I think it should be done, and those of you with the experience, let me know if I'm on the right set of tracks.

Mains: Start with cap 1 clean and ready to go. install dry bearing. torque to 100 ft/lbs, take 3 measurements of i.d. in 3 different spots, write them down, disassemble while keeping cap/bearing as a "set", then repeat for remaining caps.

Crank: Take 3 measurements of o.d. for first main journal. write them down. Repeat for remaining main journals.
Then take 3 measurements of first rod journal being careful to make sure I measure where each rod actually sits. write them down. Repeat for remaining rod journals.

-----In order to set the front to back clearance, and then measure it; I need some insight.-----

Rods: Clean and dry install bearing. Carefully clamp in vise and torque cap to 80 ft/lbs. Remove from vise and take 3 measurements from different areas of i.d. of bearing surface Write them down. Disassemble being careful to keep each rod and bearing as a "set" from now on. Repeat for remaining rods/bearings.

Cylinders: Clean and take 3 measurements from upper area of cylinder 1. Write them down. Take 3 measurements from middle area. Write them down. Take 3 measurements from lower area. Write them down. Repeat for remaining cylinders.

Pistons: Clean and take 3 measurements from o.d. of skit area of piston 1. Write them down. Take 3 measurements of o.d. of ring land area (middle part). Write them down. Take 3 measurements of piston crown. Write them down.

Rings: Lubricate top ring of piston 1. Insert into cyclinder 1 about 2-3" down. Using a feeler guage, measure end gap. Write it down. Repeat for remaining cylinders. If it's too tight, file to fit. If too loose, STOP and try swapping around ring(s). If no good, I can try buying new rings or buy new ring/piston set in a bigger size; machine to fit and start all over.

After I have all my measurememts, I intend to calculate the minimum, maximum, and averages for each. Depending on results, I may try to switch around certain bearings (switch tighter ones with looser ones) in order to get the "spread" to tighten up or just leave everything alone and begin assembly. I do plan on double checking my measurements by installing each main bearing alone ( one at a time) with oil and making sure the crankshaft glides freely after being torqued. Basically, I just want to make sure one doesn't seem to have more resistence than the others. After the crank is done, I may check each piston one at a time in the block too. So long as I don't get super impatient. If there's a main or rod that does cause more resistence than the others, I plan on taking it to a local machine shop and pay for their opinion/fix.

cjsdad

Perfect plan! Just remember Mike Tyson's words about a plan...

“everyone has a plan until they get punched in the mouth”.

69455

You can also use a snap gage with a micrometer.
Less expensive than a bore gage

BillK

Bradley,
One more thing you can try just to verify your measuring method. You can only do this in the front main bearing but it will tell you if you are close. Sit the crank in the block, put the main cap on but dont tighten it yet. Then get a .002" feeler gauge and slide it in between the crankshaft and the main cap bearing. Then start tightening the main cap a little at a time. If you can torque it all the way down and you can still move or pull out the feeler gauge you know you have at least .002" clearance. If it gets tight and you cant pull it out you can try it again with a .001" feeler gauge. Same thing the other way, try a .003"

This isnt real scientific but if you use your preferred measuring method and come up with .002" clearance and yet you cant get a .002" feeler gauge to be a snug fit, then you might be doing something wrong. Like I said, you can only do this on the front main but it is one more way to check yourself.