Crankshaft questions..

[ZoomZoomZoom]

So lucky me, I've been informed that my crank won't balance likely due to a bad harmonic balancer. Finding a used 7m crank is very difficult, finding info on bad cranks even more so. I've read a post about all cranks being "crooked" and should be straightened. My father-in-law asked if the garage doing the balance has done imports before and it made me think that perhaps there is a bit of know-how to balancing the 7m crank. Thoughts? Suggestions? I'd like to keep this crank because overall, it looks pretty good, not abused, just needs polishing.

thanks!

 

[IJ.]

7M cranks are 0 balanced meaning they don't need the Damper, Flywheel/Flexplate as each is also 0 balanced.

 

[lewis15498]

Look for a new machinist before you look for a new crank.

 

[suprarich]

Super easy to do a high speed spin balance on a in-line 6 crank. Your machinist is hitting the crack pipe

 

[ZoomZoomZoom]

7M cranks are 0 balanced meaning they don't need the Damper, Flywheel/Flexplate as each is also 0 balanced.

What does that mean? I have a crank never had a spun bearing, so what steps should I take before reinstalling it?

 

[IJ.]

What does that mean? I have a crank never had a spun bearing, so what steps should I take before reinstalling it?

Just means that the shop is talking shit about the balance Tracey, Mic it up and if it's in good condition and within spec just order up the correct bearing shells from Toyota.

Toyota use a select fit bearing system, there's a chart in the TRSM that give the Rod/Block sizes and the Crankpin sizes in an X/Y Format, you follow an X line for say the Rod ID across to the Y line for the Crankpin diameter and where they meet is the exact bearing you need to order.

 

[nsngarage]

^

Not an externally balanced crank, your machinist isn't balanced

 

[mecevans]

If you cant afford OEM bearings you can have the crank polished to all the same size. Then order a set of standard size celevites and be good to go.

 

[ZoomZoomZoom]

Ok, I'm sorry I was so vague with my original post, I'm just learning. I got some clarification on the issue. The original harmonic balancer is bad. It was not tight. It caused abnormal wear on the snout. I can get material welded back on, but the guy who is rebuilding the engine thinks its chancy given the time and $$ put into this engine rebuild. He believes the weld would be a weak point. If done, I would have to check the crank and balancer on a regular basis. But, if the balancer went bad in the first place, sounds like I need to check it regularly even if I had all new parts. I did go out and buy a brand new OEM harmonic balancer for alot of $$.

What do you guys think I should do?

 

[IJ.]

Just replace it with a good one, there are plenty about in the US.

 

[ZoomZoomZoom]

Just replace it with a good one, there are plenty about in the US.

Just hop on a plane and show me where!! I keep finding 6m cranks. And I know the difference between the 6m and the 7m cranks, but I am looking for a 7m. And the guy doing the rebuild is picky - he doesn't want one from a rebuild-em assembly line shop, or one that has suffered great abuse. I can find the cars in a junkyard, but pulling the crank is not something I can readily do without a pile of tools and a lift and a big chunk of time. And if I do get it, its likely that the crank has been abused or is a 6m.

Sorry, I'm crabby - this crank issue has side-lined my rebuild for 2 months now. Mostly because I cannot find a decent 7m crank!

 

[IJ.]

Take a look at later model NA Cressida's, more chance of finding one that hasn't been abused

Don't stress about the crabby thing I went through all this shit here during my build and ended up spending mega $ to ressurect a dead 7M crank so I understand fully.

 

[fasttrac64]

torque it and used red loc-tite on balancer bolt thats what i did and no problems since but i replaced the crank and balancer with new used and turned 2nd crank

 

[hvyman]

Balencer is 198ft lbs.

Just use a 6m crank and have it counter balenced. It will do the same thing.

 

[nsngarage]

^ +1

 

[ZoomZoomZoom]

torque it and used red loc-tite on balancer bolt thats what i did and no problems since but i replaced the crank and balancer with new used and turned 2nd crank

So I should use loc-tite on my *new* balancer to prevent this from happening again?

---------- Post added at 12:06 PM ---------- Previous post was at 12:03 PM ----------

Balencer is 198ft lbs.

Just use a 6m crank and have it counter balenced. It will do the same thing.

If I have it counter-balanced, that means adding weights? Weights that could potentially come loose or off?

 

[IJ.]

As long as your old crank isn't totally trashed on the snout you could have the shop spin it up and polish it then buy and fit an ATI Damper as an upgrade, they're TIGHT as a very tight thing on a stock crank!

Drop of 262 loctite on the bolt only + 198 ft/lbs and it'll never come off/loosen in use.

 

[hvyman]

No. The take matieral off in certain places to balance.

 

[ZoomZoomZoom]

As long as your old crank isn't totally trashed on the snout you could have the shop spin it up and polish it then buy and fit an ATI Damper as an upgrade, they're TIGHT as a very tight thing on a stock crank!

Drop of 262 loctite on the bolt only + 198 ft/lbs and it'll never come off/loosen in use.

I already purchased a new OEM harmonic balancer and that cost me an arm and a leg. So I need to use it. Will do the loctite though, thanks for the suggestion!

No. The take matieral off in certain places to balance.

My shop really doesn't want to use this crank.

 

[jstricker]

Just means that the shop is talking shit about the balance Tracey, Mic it up and if it's in good condition and within spec just order up the correct bearing shells from Toyota.

Toyota use a select fit bearing system, there's a chart in the TRSM that give the Rod/Block sizes and the Crankpin sizes in an X/Y Format, you follow an X line for say the Rod ID across to the Y line for the Crankpin diameter and where they meet is the exact bearing you need to order.

IJ's bearing selection instructions are correct ASSUMING you have a virgin crank that's never been turned in a machine shop. You find that out by doing what IJ said when he told you to "Mic it up". WRT balancing, stock Toyota balancing is just fine for 99% of the cases. Where you might start having some concerns on getting the assembly balanced is if you're going to add a lot of aftermarket parts.

An aftermarket flywheel + aftermarket rods + aftermarket pistons + a turned crank = a good candidate for a professional balance

Another case will be if you intend to rev the engine well past that 6000 rpm mark, then factory stock may not be good enough. If you do get the ASSEMBLY balanced the shop will need the crank, rods, pistons, pins, clips, flywheel, and balancer to do it right. As I said, though, normally this isn't necessary.

John Stricker