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By grovedawg - 15 Years Ago
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I'm going to try to describe this to the best of my ability without having a picture, or a way to measure the grooves. I took my crank over the the machinist who was going to narrow my aftermarket rods. I mentioned earlier that I wanted to verify the stroke against what the crank grinder said it came out at. I didn't really ask him to do it, just said I was interested.
Well, in the midst of all his machining he decided to take my cherry, freshly ground crank, and set the main rods on these two wierd SHARP metal pedals that he had and spin it will measuring the stroke with a dial indicator to check the stroke. When I picked it up he said that the lines made from the spining of the crank on the pedastals would polish out and that I shouldn't be worried about it.
WELL I AM! I'm not a machinist. This is my first engine build. But why would a machinist place my crank on metal, not a bushing, and spin the crank through each stroke leaving a nice little groove in the two outside main rods!?
I can't feel the groove with just my fingertip, but if I gently glide my finger over the grooves I can feel it catch. My guess is that it's a nice little groove about .0005"-.001" of an inch deep!
Should I be worried? It's a 312 that's just barely been ground down to 292 mains. I would really, really, really not like to grind another .010" off the mains just to clean up the guys mistake.
But I don't want to have a nice oil dam, or uneven oiling of an engine that I'm rebuilding! What should I do? I can take some pics tonight and post them so you guys have a better idea, but right now I'm clueless as to what the groove would do if left unchecked, and frustrated at the prospect of redoing work that is costly. Thanks, Ryan
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By rick55 - 15 Years Ago
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He is probably right that the scratches will polish out and not be a problem, but if that's the case why didn't he do it before he gave you the crank back?
I would take the crank back and get him to polish it to confirm that the scratches come out OK before reassembling the engine. It will always be in the back of your mind when the engine is in the car.
If the scratches don't come out a 0.010" undersize crank won't pose any problems for you in the future.
This sounds like one of those two steps forward, one step back instances.
Regards
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By crenwelge - 15 Years Ago
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A lot of it depends on your expectations. If you are a perfectionist and it will worry you, it might be better to turn it now. From a practical stand point, it will probably not make a bit of difference. I have been in the trucking business for over 45 years and have always reconstructed trucks from wrecks and sold salvage. I am constantly faced with decisions of what to replace or what to run. It wouldn't bother me a bit to run a crank with a small nick on the journal. I see them run every day in Cummins engines that are set to develop 1650 ft. lbs. of torque at 1200 RPM.
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By grovedawg - 15 Years Ago
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Here are some pics, let me know what you'd all recommend: 
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By 46yblock - 15 Years Ago
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It sure would piss me off!
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By mctim64 - 15 Years Ago
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OK! Here's my opinion for what it's worth. I've been grinding cranks for 27 years now so I have a little experience, It will be fine!  On the other hand I do think the guy was a little careless with your crank, I can check the stroke on any given crank in the grinder clamped in the chucks and only just touch the journal that I'm checking the stroke on. I don't think those scratches are going to polish out completely but it really wont hurt anything, just make sure it doesn't drag on your bearing. On the other hand if you get it back from him and the grooves are completely gone I would be a little suspicious that he polished the crank too much, so check the clearance with some Plastigauge to see if it is correct or if you have a Mic and know how to use it that would be better.
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By grovedawg - 15 Years Ago
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mctim64 (7/28/2010)
OK! Here's my opinion for what it's worth. I've been grinding cranks for 27 years now so I have a little experience, It will be fine! I am a total newb, so I just wanted someone like you, with a little bit more experience (27 years) to chime in and tell me what you think. Thanks Tim! I am a little pissed off, but if it'll be ok then I'll just turn my perfectionist brain off and let it go. Thanks for the response to my post!
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By mctim64 - 15 Years Ago
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One other thing I noticed in your pix, who ever ground the crank did a nice job on the radius.  Most shops wont take the time to dress their stones in this area so you get a square corner and a great place for a crack to start. If the radius in your rod journals looks as good as the mains your crank should take a lot of pressure. 
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By Ted - 15 Years Ago
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What Tim said X2. Sounds like sloppy work and from your description, it’s difficult to call the guy doing the checking a machinist. The guy performing the stroke check of the crankshaft is obviously not the same one that turned the journals undersized for you. The V blocks I use for that have teflon pads for the crank to sit on while some of the other V blocks I’ve seen have brass inlays. Regardless of the material, the key here are V block surfaces that are both clean and wide that will not hurt a machined surface when turning the crankshaft. A little bit of oil also goes a long way in protecting freshly turned journals when doing a check of this nature. At the very least, the guy doing the checking (just can’t call him a machinist) should have taken it upon himself to correct any issues rather than creating the problem and just passing them on to you. I’ll mirror what Tim says in repeating that polishing the crankshaft to the point of removing the blemishes is likely going to leave you with an excess of bearing or oil clearance.
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By grovedawg - 15 Years Ago
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mctim64 (7/29/2010)
One other thing I noticed in your pix, who ever ground the crank did a nice job on the radius.
You've got a good eye. My crank grinder was highly recommended, it's Casey's Machine shop in SLC. The radius is 1/8th inch. Because we were taking soooo much meat out of the crank I asked him to leave as big of a radius as possible. He thought that an 1/8th was about right.
If the radius in your rod journals looks as good as the mains your crank should take a lot of pressure.
The radius in the mains are the same- 1/8th inch. 
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By grovedawg - 15 Years Ago
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Ted (7/29/2010)
What Tim said X2.
The guy performing the stroke check of the crankshaft is obviously not the same one that turned the journals undersized for you.
Nope, they're not the same two machinists. I've actually got 3 different machinists who've helped out throughout the project. My main machinist is Steve Flatt, who owns the Machine Shop in Lindon. He recommended the crank grinder, Casey, who also did a great job. And because neither had the right fixture, lathe, and set up required to narrow my aftermarket rods and bearings Bill Jones was recommended for the job.
What sucks, is that I didn't even ask him to check the stroke. I just mentioned that I was curious about verifying the stroke length against what Casey had said before I decked the block. I probably shouldn't have mentioned it. Completed my align hone, and bore, stuffed the crank in with the rods and pistons and measure to determine how much to deck. Oh well.
It's all part of the process of building a motor I guess!  It's too bad I love it so much. I really am having a great time putting this Y together. I'm a convert.
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By 46yblock - 15 Years Ago
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The passing of time does well curing anxiety. At the tail end of quite a bit of block work I was present for the milling of the deck .028. It required successive small cuts taken by the huge machine. After the 3rd or 4th pass I was looking almost straight down on a block corner, and there was a crack running from a water jacket hole into the upper, end, head bolt hole! It wasnt there before. Worry, indecision, a whole bunch of bad feelings are now nothing more than a story. It all worked out great.
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By John Mummert - 15 Years Ago
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Ryan, if it is any consolation we find that when using Clevite bearings we usually have very little oil clearance. You will probably want the main journals close to 2.4980". Most crank grinders will shoot for the middle of the spec which is 2.4984". You might want to measure the crank first or plastigauge it and will likely find it needs to be a little smaller. More good news. Your bellhousing is done.
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By Y block Billy - 15 Years Ago
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I tried to mention this the other night but got knocked off. I had a good crank and just had it polished to use .001" undersize bearings. they are not all that common but they are out there if you want to have that scratch polished out.
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By grovedawg - 15 Years Ago
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More good news. Your bellhousing is done.
YYYYEEEESSSSSSSSSSSSSSSSSSSS!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Then I'm going to write you a big check because the bores are going to be rough cut this weekend to determine the final size, and I'll order the pistons, pushrods, and timing crap on MONDAY!!!!!!
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