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 Bent crank question
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Merrik66
Cochise

USA
370 Posts

Posted - 14 Jun 2014 :  5:24:57 PM  Show Profile  Reply with Quote
Ok, so I've accumulated most of my parts but my crank seems to be bent. I found this out as I had placed all bearings which are 010 in spot and torqued everything down but when I rotated it it had a slight bind in a spot. Something worth noting was that I had checked all my clearances with bearings in place and then checked journals. I came out with about .025 and .028 clearance. I thought that was acceptable but I think it was an early indicator possibly. What I just did now was I pulled things apart and set the number 2 and thrust bearings in the block then gave em just a drop of oil and layed the crank in. I didn't bother putting caps on. I set my dial indicator to read the thrust journal first. Needle didn't move. I then went to the nose of the crank. Set my indicator up on the first journal. It moved from 0 to .003 and back again. I then went to the rear journal. It did the same thing upon rotation. I double checked and all the readings did the same thing. I would assume I've got a bent crank somewhere around the thrust journal area. Does my logic sound correct? And if so, is straightening the crank an issue for shops? Or should I use a spare which I have and have it turned for 100$. Otherwise this "bent" (possibly) crank is fresh..it's an "N" crank. One more piece of info..it had tipped over on concrete a while back and I cringed at that loud "Ding" but I asked a few forums if it would be ok and most all said it'll be fine..I'm thinking that's how it's happened. Thanks ahead of time for any and all feedback.

Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 14 Jun 2014 :  11:25:44 PM  Show Profile  Reply with Quote
Hard to tell. Main clearance should be in the .002 to.0035 range. I will continue as if the above is a typo. Install the front and rear bearing half only and check main run-out in the middle being careful to not thrust forward or back. I would use a liberal amount of assembly lube.
Make sure it's not and assembly issue. Assemble the crank and caps. Does not have to be full torque value. 50 lbs or so. Leave the thrust only snug. Smack the crank forward and backward a few times with a dead blow hammer or block of wood & steal hammer. Don't go crazy. Torque all caps. Check thrust. .007 to .012 if i recall. Check for binding. If it still binds, consult machine shop. It could need a line hone or crank shaft.

What type rear seal are you using?


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Merrik66
Cochise

USA
370 Posts

Posted - 15 Jun 2014 :  12:09:00 AM  Show Profile  Reply with Quote
Yeah, Blue...typo acknowledged. My runout was fine at .008 had went though that procedure. Rope was my seal but now it's out. Cleaned everything back up. I'm going to call the shop on Monday and explain to them what I found and ask them if they straighten cranks. Is that a stupid idea? But, like I mentioned above, I do have a spare which only needs a .010/.010 cleanup which would let me use the bearings I've already got. Sucks to throw away a crank which I have 200$ into but if it's dumb to try to fix it then so be it. Thanks guys again for any foresight/insight.
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Merrik66
Cochise

USA
370 Posts

Posted - 15 Jun 2014 :  12:18:00 AM  Show Profile  Reply with Quote
Just reread your post blue, I must be tired, you explained it clearly but I'm brain dead. Thought you were talking about thrust bearing end play at first. You addressed that later in your reply. I will go through the procedure you described in the morning. End play was fine...came in at .008.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 15 Jun 2014 :  12:20:10 PM  Show Profile  Reply with Quote
sometimes i will install the flywheel with 2 bolts to use as a convenient handle or lever. It makes it easy to spin the crank. The crank should spin freely (without rear seal) and not stop in the same spot twice. I've never worked in a machine shop so i don't know the options available. If you don't think it's right, then certainly ask more questions.

I would NOT use the rope if its from the felpro gasket set. Im using the teflon/graphite rope. 500 miles and so far so good. There is a new one piece lip seal available form BOP that looks promising. But i have not seen much feedback
As a review I'll post this rope seal install video.
http://www.youtube.com/watch?v=kSQWlnvAIbI



Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Merrik66
Cochise

USA
370 Posts

Posted - 16 Jun 2014 :  01:35:58 AM  Show Profile  Reply with Quote
So I cleaned everything and then installed number 1 and number 5 bearing with crank in position including a little moly lube. I left 2,3, and 4 off. I torqued both caps to 50 lbs. I then measured 2,3, and 4 individually during very slow rotations. Both number 2 and number 4 main journals measured over .001 runout. Number 3 was .002 runout. BTW I kept the crank from moving back and forth because of no number 4(thrust) bearing in place by using some clamps, shims, and flat stock at the front of the number 1 journal. It really looks like I've got a bent crank. Any additional feedback? I'm going to call the machine shop in next couple days but I don't want to trust an answer from them which may not be the right way to go. I have no idea what is common or reasonable in an approach to a bent crank problem or the threshold on how bad my runout is? Toast? Or easily bent back with proper shop expertise? In hindsight I should have also measured the max runout for each of those 3 journals in terms of crank degrees to really understand how it's bent. May do it just for good practice.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 16 Jun 2014 :  7:10:23 PM  Show Profile  Reply with Quote
If run out is .002 and the clearance is.0025 then it should not bind in the saddles.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Merrik66
Cochise

USA
370 Posts

Posted - 16 Jun 2014 :  7:14:31 PM  Show Profile  Reply with Quote
So I talked to the shop today, they said it shouldn't be a problem to "unbend" the crank. They have about a .002 max that they're comfortable with tweaking into straight. 45$ should do it. Gonna have them double check some other things involving the block too. Still asking you guys though..is this a stupid plan? I do plan on rechecking everything once I get it back, hoping to drop everything off this week unless someone here chimes in with opposing views and experience. Thanks.
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bnorris_74
Crazy Horse

USA
1442 Posts

Posted - 06 Jul 2014 :  07:12:54 AM  Show Profile  Reply with Quote
TTT
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Merrik66
Cochise

USA
370 Posts

Posted - 09 Jul 2014 :  01:26:54 AM  Show Profile  Reply with Quote
Blued, somehow I missed your reply. I haven't done a darned thing with it. Too much other stuff goin on. What you say makes sense..it also introduces the issue of maybe needing a line hone after all. I asked the machine shop to check it for straight a long time ago. They didn't do it...said it would be fine as there was no noticeable trauma. In any case, this has been one of those projects that's been in and out of mothball. I just need to bring it all in ...do a main line hone..clip caps if needed., check the damned crank recheck it all again. Now back in mothball as I'm now trying to get full custody of my son, gonna be a while.
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Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 09 Jul 2014 :  11:47:30 AM  Show Profile  Reply with Quote
Fathers right are very slowly being recognized by the courts. Automatic default to the mother is no longer a forgone conclusion. Hoping the judge finds in favor of whats best for the kids.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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Mr. P-Body
Running Bear

USA
2258 Posts

Posted - 10 Jul 2014 :  7:57:14 PM  Show Profile  Visit Mr. P-Body's Homepage  Reply with Quote
Merrick,

What state are you in? I raised my three kids after a court battle. She wasn't the better parent, and that's what Arizona was concerned about. In VA, it's the "old" way as B&P describes. Mom gets the house, the car, the kids, the check, and Dad gets the shaft. Get a female domestic law specialist...

As for the crank, make sure the shop is willing to buy the crank when they break it. It's NOT a good idea to "straighten" a cast crank.

Your measurements are scewed by the clearance in both ends. You need a pair of V-blocks (you can make them from wood). The clearance causes a slight amount of deflection, and your crank could, in reality, be "bent" as much as .008-.010, based on clerances and "leverage".

Unless your crank was damaged by a bearing, it's probably "straight". Large-journal blocks are notorious for align-bore issues. 400s aren't as bad, but not "immune".

If the crank is only a "little" bent, and the snout and hub are still "in line", just grind the mains...

Jim
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