Question about machining the crank

[khartley]

Alright, so the crank in my Talon is f*cked - I have a spare 4g63 engine with a stock crank in it. The crank that was in the Talon was at .25 under.

My question is if I can put in the stock crank along with stock main and rod bearings. I ran my finger along the journal of the stock crank, and it's like glass. I just don't see the point of having the stock crank machined if I don't have to.

 

[khartley]

No ideas, links, anything?

 

[myblack98gst]

you shoudl at minimum check it against factory specs.... since you are asking this question I would take it to a machine shop and have it polished and checked

 

[1fast97gsx]

yes you can use your factory crank just make sure you use the main caps off of the block you are putting it in. Also replace the bearings with new standard sized bearings while you are in there. ( measure first and make sure standard is what you need but it probably is )

 

[khartley]

yes you can use your factory crank just make sure you use the main caps off of the block you are putting it in. Also replace the bearings with new standard sized bearings while you are in there. ( measure first and make sure standard is what you need but it probably is )

So if I can just use the factory crank without having it machined, why is everyone telling me that I need to? If the journals were scarred, then yeah it would need to be machined before going into the new engine. But they aren't.

Someone said that it needs to be machined, because I am using the factory crank with different rods and pistons. Is that why?

Just clear things up for me, please! I'm confused.

 

[1fast97gsx]

So if I can just use the factory crank without having it machined, why is everyone telling me that I need to? If the journals were scarred, then yeah it would need to be machined before going into the new engine. But they aren't.

Someone said that it needs to be machined, because I am using the factory crank with different rods and pistons. Is that why?

Just clear things up for me, please! I'm confused.

I don't see why .. my friend did a 6 bolt swap and his block didn't have a crank so he just got one from someone else and put new bearings on it. As long as the surfaces are good on the crank just measure it and see what bearings you need and be sure to replace those.

 

[lacroixdp]

IMHO, I would never put a crank back in an engine without at least having it micro-polished and checked for bends. The nice thing about having a crank ground down is it works out the bends in the crank at the same time. If you do a very light cut, you will keep the nitrite coating in tact. It's up to you, but I would never put in a crank without having it checked; kinda defeats the purpose of rebuilding an engine Make sure that you also use plastigage to verify the bearing sizes. It's not all that uncommon for there to be different size bearings on different mains to compensate for block defects.

 

[bastarddsm]

This is why your motors blow up all the time. there are no shortcuts to building a motor. you either build it right or you scatter it.

you need to have a good quailty micrometer to check for roundness. if any journal is out of round by like .0001 (not sure on the factory spec) it needs to be ground if the journals are worn too small then it needs to be ground.

plastiguage is not an accebtible way of measureing clearances to build a motor correclty you need $1000's of measureing equiptment. and thats if you have someone else do the machining

 

[khartley]

So I should take the crank out and take it to a machine shop and have them measure everything and check for bends and get it 'micropolished', if not machined.

I should probably have that same machine shop get the bearings and measure them also, huh?

And I'm not trying to cut corners, I just want to understand why it's necessary, if it is.

 

[lacroixdp]

Respectfully, that's what I would do if it were my motor. Now, while I agree that Plastigage isn't the most accurate way of measuring bearing clearance, I wouldn't call it unacceptable. You can have the machine shop measure the clearances for bearing sizing if you don't feel comfortable doing it yourself. At the very least though, you need to have the crank mic'd, micropolished, and checked for bends. If it were my engine, I wouldn't be using the same pistons that came out. In all my rebuilds I change out the pistons and have the block bored out; just a little preference to my rebuilds. Most importantly, I would check up on the machine shop doing all this work for you. Make sure you ask for a few references and inquire with them on how good of a job they do. Nothing sucks more than going to a machine shop that performs bad work. If you want a lead and are willing to pay for it, I can direct you to someone that I use in Indiana that I have used for several years. While he is rather expensive, he does some damn good work.

 

[khartley]

Respectfully, that's what I would do if it were my motor. Now, while I agree that Plastigage isn't the most accurate way of measuring bearing clearance, I wouldn't call it unacceptable. You can have the machine shop measure the clearances for bearing sizing if you don't feel comfortable doing it yourself. At the very least though, you need to have the crank mic'd, micropolished, and checked for bends. If it were my engine, I wouldn't be using the same pistons that came out. In all my rebuilds I change out the pistons and have the block bored out; just a little preference to my rebuilds. Most importantly, I would check up on the machine shop doing all this work for you. Make sure you ask for a few references and inquire with them on how good of a job they do. Nothing sucks more than going to a machine shop that performs bad work. If you want a lead and are willing to pay for it, I can direct you to someone that I use in Indiana that I have used for several years. While he is rather expensive, he does some damn good work.

See, that's why my crank is f*cked to begin with - bad machining from a low end shop that didn't care. So now I don't know who to trust to do the machining, which is why I asked if it needed to be done.