Should a newly installed crank be tight? - Page 2 - Off-Road Forums & Discussion Groups
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post #11 of (permalink) Old 07-25-2000, 08:49 PM
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Re: Should a newly installed crank be tight?

I agree, the joint between the main cap and block should be seamless. I've had some blocks that I was able to catch a finger nail on, but the crank would turn freely. I would not use a block that had a less than perfect seamless fit for a daily driver. If it was an engine that was for weekend fun, that would be a different decision all together. I will say that getting a crankshaft with all the correct bearing clearances is no doubt the most important part of the engine building process. I don't mean to say that the other critical engine part clearances are not important. It's just that for long engine life and good oil pressure the crank has to be correct with all the clearances. If a piston is off by plus .001", the engine will run and most likely not even smoke out the exhaust. If a main journal is off by plus .001" the engine just lost 15 PSI of oil pressure, if a main journal is minus .001" there's a very good chance of spinning out a bearing. I usually shoot for .0018" clearance on main bearing, then after a few thousand miles, the clearance will grow to about .002" which is going to help make an engine last a very long time with regular oil changes.
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post #12 of (permalink) Old 07-26-2000, 05:35 AM
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Re: Should a newly installed crank be tight?

Very good point dave.

post #13 of (permalink) Old 07-26-2000, 07:58 PM
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Re: Should a newly installed crank be tight?

Update:
I took the block to a diffrent machiene shop today. I showed two of the guys what I had. They felt them, then measured it with a telescoping gauge and caliper, and some other long tool with a dial? They said the seam was OK since it was so small and the mains checked out to be within acceptable limits (what ever that is).SO I am guessing that the caps got out of order somehow, thats why the crank wouldnt turn at all. After re-arangeing them it will turn if you push on a rod journel with tow fingers. Im going to talk to the shop that did the work tomorrow and tell them what I have (not going to tell them that it was their work at first) and see if they say it is acceptable. If so then Im going to go ahead and start building it I guess. And I found the tag that came with the block. It was line honed, not bored.
Another question...what does line honeing do for a block? Does it just help hold in the bearings in? Would a block like the 305 that I cant feel any seams need it?
Thanks for all the help! If all goes well Ill post back and let you know how good it runs in a couple weeks!
Mike

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post #14 of (permalink) Old 07-26-2000, 10:18 PM
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Re: Should a newly installed crank be tight?

Line honing is to get the main journals round again. As the crank spins, there is some twisting action. The twisting action of the crank can cause the main journals to go out of round. It's only a small about, usually measured by the .0010" scale. The main caps sometimes will not sit flush with the block, so a little material is removed from the main cap to make the main cap flat again. Then a light hone will make the main cap round after the main cap is flat. Here in the rainy Northwest, blocks are often cleaned with a hot oven to bake the rust off the blocks, including the inside of the block as well. The heat of 500 degrees will tend to warp the mains some, so it's common practice to line hone the mains after the block has be oven cleaned.
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post #15 of (permalink) Old 07-28-2000, 08:58 PM
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Re: Should a newly installed crank be tight?

I called the shop that did the work and told the owner what I had. He said there should be absolutely no seam if It came from his shop. Im going to take it to him tomorrow. Its good that they are makeing right on thier work, but if it is going to take any longer Im going to have to put a new clutch in real soon (tomorrow). Im going to have to atleast drop the T-case anyway to put a gasket between the tranny and T-case. If I put the newly ballanced clutch and flywheel on the curent motor, shouldnt it be OK to switch the clutch and flywheel to the rebuilt one when it is done?


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