[Unclepennybags]

My supposedly "tight" crankshaft, is crowding the limit on the loose side. Two journals are past the loose spec!

The only problem that I can see on my end is temperature. It was a fairly mild day (60's), and I had the heat on in the garage for 4 hours before I began measuring. ***The mic had been stored in the garage also, so it was the same temp as the crank.***

I realize that when measuring pistons in their bores it is essential that all parts be "soaked" in the same room for 24 hours before measuring, and the measurement be taken @ 70 deg F. How important is it (70 deg F.) in the case of a crankshaft measurement?

I'll also be checking my Starret mic against a standard today at work,

but wanted to ask this temp-expansion question too.

Thanks!
Mike

Update: Had my mic calibrated. It was .0002" off - it was reading big, so the crank is actually over the limit on the loose side.

 

[engineguy]

Mike,
I don't think that temperature variation was the problem in your case. If the mic and the crank were stored in the same area (garage), then they were both the same temperature. The difference between optimum temperature (72*) and your garage temp after running the heater for a few hours is probably very slight. Due to the mass of the crankshaft, slight temperature variations will not have an affect.

 

[Unclepennybags]

Should I send it back? The spec for a .010" under crank is 2.0890" - 2.0900" on the rods, and 2.4384"-2.4393" on the mains.

This crank came in @ 2.0891" on the rod journals with one at 2.0889". The mains were 2.4384" with one @ 2.4382"

I had specifically asked for a tight crank. While I am sure that this one would be "ok", it's not what I asked for, and in fact exceeds the specs on two journals. Am I being a hard-@**?

Mike

 

[engineguy]

I have an idea that your crank grinder will tell you that .0009" is the closest he can hold tolerances on a crank and that the .0001" to .0002" variation you are encountering can be attributed to the person reading the mic, and/or micrometer accuracy. Probably wouldn't hurt to ask him and see what he says. Bill K., what do you think??

 

[mls48341]

Mike,
I would think that the .0001-.0002" is not going to be a problem for you.As you found on your tools, a slight calibration error, or the individual user could easily account for a .0001"
difference.
By the way, have you found a use for that 283 block?
Mark

 

[Unclepennybags]

Originally posted by mls48341:
Mike,
I would think that the .0001-.0002" is not going to be a problem for you.As you found on your tools, a slight calibration error, or the individual user could easily account for a .0001"
difference.
By the way, have you found a use for that 283 block?
Mark

Mark,

Haven't found a use for it yet, but I will.

My contention is not about being .0001" out of spec, it is that it is not even within the loose end of the spec.

Talked about it with my machinist. He was really cheesed. At first he was kind of p!ssy about it, but in the end,I did get him to acknowled that it was at the loose end of the spec with my mic, and that he would be more likely to trust my mic over his due to the fact that mine was nearly new and had just been calibrated in the AM. He did make some snotty remarks about leaving my mic behind so that he could finish the machine work to my mic, but he calmed down later. He did call the crank shop to have them verify the crank.

I'm a little concerned about him possibly doing a number to the rest of my parts, but what is the point of measuring stuff if you aren't going to investigate when you find a discrepancy??? I never once raised my voice or questioned his ability. In fact I pointed out that he had done some great work so far, and that I trusted him, I just don't know/trust the crank shop. I pointed out that all I know about the crank shop is what I can measure with the micrometer.

Mike

 

[BillK]

Mike,
Did you buy a "crank kit" or have your crankshaft reground ?? The guy that does our cranks keeps all the journals within a "tenth" and usually right in the middle of the range unless I ask otherwise. I will say that he is unusually good, I dont know what I would do if he decided to retire. I have seen other guys that can barely keep all the journals in spec, never mind all the same. If you purchased a crank kit, you will probably not get any better, and you would probably scare yourself if you checked the strokes

 

[Unclepennybags]

Bill,

It wasn't a crank kit. They took the crank that came with that engine and sent it out. It was originally standard/standard. Knowing that I wanted to be in the tight side oil clearance wise, they sent the crank out to get turned 10/10, rather than polish it.

 

[1968 hot rod]

Uncle Penny Bags
this is all dependant on what your bearing
inner dia check.what are your clearances??

 

[Unclepennybags]

1968 hotrod,
Don't have the block back yet. I realize that the bore id of the main caps and rods is part of the equation when determining clearances. I will also be checking the main bores and the rod big ends with an inside mic. However, I don't want to be starting out with a crank that isn't within GM's specs.

If you were in a restaurant and ordered a well done steak and instead you get something that had been cooked 30 seconds on each side and served, I would hope you could point out that you didn't get what you asked for without anyone taking it personally. This guy was turning red and telling me that if I don't run enough clearance, he couldn't stand behind his work. That's fine, but I simply told him I wanted a crank ground to the middle of the spec or higher. I am sure that if I stay within GM's specifications (out of a GM Overhaul manual) I'll have enough oil clearance. Funny thing is, everyone agreed to it before we began work. When the owner came into the back room, the machinist said that, "the crank was at the mid point with my mic, and at the low end with his." So the owner said, "Well, he asked for a tight crank, why not just give him another one - H*ll, it's a SBC - they must have five of them there!

We ended up sending the crank back for a re-measurement by the crank grinder. They are going to remeasure it, but the machinist was steamed.

Mike

 

[jpete]

I don't know too many machinists who don't get offended when you question their work. If you point out that something isn't right, what you are really asking is,"Are you SURE you know what you're doing?" Even if he didn't PERSONALLY grind the crank, you are questioning his supplier and the wisdom of using them. I know when I point out to some of the guys that I work with that MAYBE paper towels and shop rags shouldn't be used to shim a part on a fixture, they take all kinds of offense

Just remember George Carlins words...Somewhere out there is the WORST doctor, and...someone has an appointment with him tomorrow!
KNow what I mean?

 

[Unclepennybags]

Crank shop is supplying the machine shop with another crank. This one will be documented and tight.

Machinist is spitting nails, and getting nasty. Talked to the shop owner. He told me not to worry about it. He says that the machinist gets testy. Bottom line: I'm not going to talk to the machinist any more. I'm going to deal with the owner only. He's a good guy and we've been doing business for a couple of years. Best of all, I can say that I insulted no one, never swore, and didn't get nasty/personal. Too bad the other guy can't say the same.

 

[Wooderson]

Hey Uncle, this is somewhat unrelated to the topic, but I got curious at work and checked some bores on an iron casting after I got it out of the washer. The temp before was around 70 degrees, and out of the washer the temp is unknown, but is so hot you can't touch the part for long. A 1.5" bore grew .0007" A 3.5" bore grew .0015" and a 6.750" bore grew .003" .

 

[Unclepennybags]

Wooderson,

Thanks for that information. Always wondered just how much cast iron changes with temp.

Mike

 

[1968 hot rod]

Uncle Penny
cast iron expands approx the same as steel
steel .000006 millonths per degree per inch
alum .000012 millonths per degree per inch
good luck