Crank measurement question

[Groovy911SC]

Using a venier caliper, I measured the crankshaft main bearing shaft (D1) and the rod bearing shaft (D2) in multiple points. The result for the main bearing shaft #1-7 is 2.360" or 59.944mm. The result for the rod bearing shaft #4 is 2.081" or 52.857mm, the remainder of the rod bearing shafts measured 2.084" or 52.9336mm.
The rod bearing shaft measurements seem to be at the wear limit. Is this an indication of the crank having been ground previously?
This may be a silly question to ask. I am trying to learn the machine process in order to have correct expectations of this complex endeavor. Any help would be appreciated!!

[snowman]

Quick answer - a vernier caliper isn't accurate enough. I don't care it it reads in millionths of an inch. You must use a micrometer to make this measurement.

On the good side, even the cheepo harbor freight $10 micrometer set will do the job.

Also consider buying a micrometer with a digital readout. The blasted analog, vernier scale is just to easy to make mistakes with.

Another good investment is an inside snap guage set. very inexpensive. A little hard to learn to use, as it is a transfer guage, but highly accurate.

As a final check of bearing clearences, you can use something called plastiguage. Its near foolproof, only costs a buck and is generally avilable at most auto shops.

On the subject of ground cranks. Cranks are generally ground in 0.010" increments, nothing smaller. so a typical crank may be std, std or 10 under, std or 10,10 or 20,20 or std, 20 for examples. The meanings refer to the size of the main journals and the size of the rod journals. each are independant. some cranks have std crank journals and 10 under rod journals or both crank and rod journals are 10 under, ie 10/10. In some bastard cases only a single journal may be a differen't size.

[Groovy911SC]

Thanks Jack for your reply! I thought my method for measuring was flawed... I am in the process of finding someone in my area who can work on german cranks. There are many folks in my area who have machine shops, however all are nascar fans and seem to have difficulties with the metric system. The closest is 4 hours away in Memphis.... may just have to take a road trip!

[William Miller]

Let them measure, you convert!

[Wayne 962]

Jack's 100% right here.

One note - I don't recommend reusing cranks that have already been ground...

-Wayne

[MikeB]

Jack/Snowman

Um, what is an inside snap gauge?

[jgparker]

snap gauge pic:



They can be problematic for a novice, since you have to transfer the measurement to a micrometer.

JP

[rick-l]

Are the ends of those snap guages round to match the radius of the smallest bore you would measure or are they a point?

[William Miller]

You can also find realitivly inexpensive dial bore gauge set now which are a little easier to use.

[ChrisBennet]

Originally posted by William Miller
You can also find realitivly inexpensive dial bore gauge set now which are a little easier to use.

Speaking as a novice, I found the snap guages impossible to use i.e. I could not get consistent readings. I find the dial bore guage very difficult but at least possible to use.
-Chris

[Wayne 962]

Dial Bore gauge is great - we sell several:

http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?command=DWsearch&description=dial+bore+gauge

-Wayne

[snowman]

I can't disagree that the inside snap guage is difficult to learn to use, but you can do it and you can even do it, accurately, to within a few tenths of an thousandth of an inch. And the price is less than $15 for the set. Plus you have to have micrometers, which you have to have anyway.

To answer your question about the ends, they are radiused, not pointed.

I think is is good to learn to use this instrument, because it teaches you to have the correct feel needed to use almost any other instrument properly. If you can't get a good number with this one the numbers you get with a bore guage are also suspect. The main difference is that you can get readings much more quickly with the dial indicator bore guage. Said another way, if you can't get a good reading, even though it may take a while, with a snap guage, then don't beleive that quick reading you got with the bore guage. Its a lot like learning to ride a bike, real simple once you have mastered it, but learning can be a bit painful.

To use the snap guage properly you have to do several things at the same time. First insert the guage into the center of the cylinder to be measured, release the snap so the ends make contact. Next wiggle the guage both up and down as well as back and forth and lock in place. After locking in place check and see if the back and forth is negligable, it it isn't try and ascertain the center of the back and forth wiggle room and release the guage into this area and re lock it. repeat as necessary to insure you no longer have any up and down or back and forth wiggle room. this is the trickey part. After you have done this, remove the guage and measure it with a micrometer. Repeat the measurement until you get consistant results. Once you have mastered a consistant measurement you can lock the guage in very securly and then quickly check other cylinders or more places in the same cylinder to see if they are, smaller, bigger or the same. In this way you can find the smallest areas, largest areas and make several measurements and record them. Sounds like a whole lot of effort and it is. Once mastered though it can be done almost as quickly as the bore guage for practical purposes.

PS Waynes bore guage is a bargain, well worth the money. I would buy both the snap and bore guages, both have their plus and minus es.

[Groovy911SC]

Thanks Jack for your words! One of the most challenging aspects of my re-building project is getting up to speed with the tools I am not familiar with. Actually, getting new tools is half the fun. Getting comfortable with new tools takes a bit of time. This forum certainly helps with information like what was given above. Thanks!

[Wayne 962]

One of the problems with using tools like this is having the right setup and workbench too. I used to make measurements like this all the time in college, but we had marble, flat-tables with the right holders and clamps. Very often, I'd use a milling table to make measurements, because I had spent hours setting up the machine and I knew it was parallel. I have found that I have had problems making these measurements in my garage (which is lacking a mill or a flat, marble table). Taking measurements yourself is a good learning experience, but unless you're setup to do it well and complete, I suggest at the minimum having a machine shop confirm your results.

-Wayne

[William Miller]

Wayne, I'm glad to see you are now selling the tools!
I had to buy them elsewhere a year ago!
Good work on "One-Stop-Shopping!"
Mine is the Fowler with the 2 ranges. Well worth the investment and saved having to pay someone to do it. Much easier than the snap gauge. Once you get it calibrated you can measure the Cylinder in many different spots in seconds. You can find the center by watching the dial get to the smallest point.

[Wayne 962]

Originally posted by William Miller
Wayne, I'm glad to see you are now selling the tools!
I had to buy them elsewhere a year ago!
Good work on "One-Stop-Shopping!"
Mine is the Fowler with the 2 ranges. Well worth the investment and saved having to pay someone to do it. Much easier than the snap gauge. Once you get it calibrated you can measure the Cylinder in many different spots in seconds. You can find the center by watching the dial get to the smallest point.

Actually, we had most of them a year ago, but not easily visible on DriveWerks. The new search engine incorporates all of our products from all of our sites, all in one place...

-Wayne