6M/7M crankshafts

[toy fanatic78]

Exactly when did they change the crankshaft?How do you tell the difference?I bought a hard wrecked 88 for the engine,my 86.5 was knocking lightly.The 88 runs good,car has 110k on it,but the PO said the motor had been changed,and he thought it was from an 87.Pros and cons of the different cranks.

[figgie]

6m is not counter balanced.
7m is counter balanced

7m weighs more than the 6m but does not "whip" as much as the 6m.

SupraRich has pictures of both.. look him up.

[TheNewRed]

6m cranks are labeled "6M" on the edge of one of the middle weights, they also have weird markings(they look like Japanese symbols?), that i did not see on my 7m crank. You can just tell, the 7m crank is a lot more beefeier!

[Nick M]

6M is counter balanced. All crankshafts are. Not all crankshafts are balanced to zero by drilling or weighting.

[IJ.]

6M
http://ij.supramania.com/crank01.jpg (http://ij.supramania.com/crank01.jpg)

7M
http://ij.supramania.com/crank02.jpg (http://ij.supramania.com/crank02.jpg)

[92nsx]

IJ in with the best post again!

[toy fanatic78]

6M
http://ij.supramania.com/crank01.jpg (http://ij.supramania.com/crank01.jpg)

7M
http://ij.supramania.com/crank02.jpg (http://ij.supramania.com/crank02.jpg)

:bowdown::bowdown::bowdown::bowdown::bowdown:
Thanks IJ.I like pictures:icon_bigg.Which crank would you prefer for an na that might eventually go na>t?

[Doward]

Lightened and knife edged 7M crank :)

[AJ'S 88NA]

Lightened and knife edged 7M crank :)

+2

[suprarich]

7m
http://img.photobucket.com/albums/v487/rich1969/ebay-2057.jpg

6m
http://img.photobucket.com/albums/v487/rich1969/ebay-2065.jpg

7m above, 6m below

http://img.photobucket.com/albums/v487/rich1969/ebay-2052.jpg

[TheNewRed]

Nice! I have a question now, if you look closely at the 3-5 rod journals on the cranks in Suprarich's pictures, you can notice a slight discoloration right outside of the journals. Is this a sign of heat fatigue? i see a lot of cranks like this, 6&7M alike.

[suprarich]

The rainbow color you see on all stock cranks is from heat treatment at the factory.

[IJ.]

"Induction hardened"

[Tanya]

I'm using a normal, but balanced 6M crank with my 6M engine and have no idea what this "whip" is that you say IJ.... my 6M has 10:1 compression and is rev happy with the internals balanced and machined stock flywheel


*shrug*


My preference would be to use the 6M crank > 7M for an NA build but for a turbo build, 7M would probably be better.

.... but don't listen to me, Im just a girl :D

[IJ.]

Tanya: Once I got to 500rwhp I started seeing really odd wear patterns on the Main bearings that I can only put down to crank flex/whip when turned fast for extended periods.

ie: Long pulls above 8000 rpm at high boost.

Not the normal situation for these engines and might apply to .05% of members here but figured I'd report my findings as I'm just a guy :icon_razz

[Tanya]

Ah, gotcha. I really thought that the 6M crank "issue" was apparent at all specs, whether stock or not. I thought I had read somewhere that you can feel a difference between engines running the different cranks.

I only have experience driving one 7M car, with the 7M crank, and I didn't "feel" it acting any "smoother" than my 6M.

Or maybe I just didn't care to notice *shrug*

[IJ.]

I ran my motor with both cranks identically prepped within 2 weeks of each other (one of my Pauters tapped the Oil Pump AUX shaft and chattered the #1 and #2 crank pins during an 8500rpm experiment)

The 7M is smoother across the board from idle to 6000 once above 6000 I couldn't feel a difference, the 6M while not "bad" was harsher, the 6M accelerates MUCH quicker due to it's lower PMoI.

This is what prompted me to cut down the 7M to around the same weight as the 6M.

http://ij.supramania.com/crank03.jpg (http://ij.supramania.com/crank03.jpg)

[wiseco7mgt]

I ran my motor with both cranks identically prepped within 2 weeks of each other (one of my Pauters tapped the Oil Pump AUX shaft and chattered the #1 and #2 crank pins during an 8500rpm experiment)

The 7M is smoother across the board from idle to 6000 once above 6000 I couldn't feel a difference, the 6M while not "bad" was harsher, the 6M accelerates MUCH quicker due to it's lower PMoI.

This is what prompted me to cut down the 7M to around the same weight as the 6M.

http://ij.supramania.com/crank03.jpg (http://ij.supramania.com/crank03.jpg)

Did you cut down the counterweights? is there a weight to ask for with the machine shops? or is it done on an individual crank basis.?

[IJ.]

My Crank shop used their CNC to do the work based on a Cosworth counterweight profile, we removed as much as possible without upsetting the inherent balance of the I-6 crank.

Once you get to this point it's a bit of a juggling act weight wise, remove too much and you get a funky balance requiring heavy mallory metal inserts.

[TheNewRed]

There is a lot of good info in this thread, thanks guys!

[gofastgeorge]

Don't use the 6M if your going to build a high rev 7M.
(I'm talking up to 8500 rpm)
I did, and constantly broke off flex plate bolts,
not to mention welding the harmonic balancer to the crank nose.

I have done in 2 sets of ARP bolts, and one set of stock.
ARP suggested a stronger bolt,
but they want $100 per bolt & 3 months to do up customs.

So out comes the light weight 6M crank,
(as soon as I get the damn ballancer off)
and I have a ballanced 7M crank ready to go in.
I also dowel pinned the flex plate to the crank, to take some of the load off the bolts.

I may even loosen up the accumulator springs in the trans,
so that it allows a little more slip when it shifts.

I am getting real tired of dealing with this one weak point,
and don't want to shake another flex plate off.

By the way, anybody running an automatic as I am,
ARP has a shorter bolt than the 4AG ones that most Supra places sell.
It is p/n 254-2901, and is .800" long.
The 4AG bolts, p/n 203-2802 are 1.050" long,
and can only be used by bottom tapping the crank holes, and running the ATI flex plate (which is much thicker than the stock one).

[IJ.]

I use a dual flex plate and arp bolts and haven't had an issue 6 or 7M cranks to sustained 8300 George.

[gofastgeorge]

I use a dual flex plate and arp bolts and haven't had an issue 6 or 7M cranks to sustained 8300 George.


Damn,
Then I may not have the problem figured out yet.......
I wonder if my converter is way out of ballance ?

[toy fanatic78]

not to mention welding the harmonic balancer to the crank nose.
I had this problem with the 6M crank also,balancer spun the key and transferred so much metal onto the front of the crank that I could hardly get the old one off,let alone the new one back on.And with slight rod knock(which may have been the balancer "wobbling" on the crank)I had pretty much decided to go with a crank in better condition.Pulled the motor from the parts car apart a couple weeks ago and was glad to see a 7M crank in it,probably send it out for lightening/balance next month.

[toy fanatic78]

My Crank shop used their CNC to do the work based on a Cosworth counterweight profile, we removed as much as possible without upsetting the inherent balance of the I-6 crank.

Once you get to this point it's a bit of a juggling act weight wise, remove too much and you get a funky balance requiring heavy mallory metal inserts.

Would you happen to have the specs on said profile?Like maybe the CNC program coordinates,or what cosworth profile.

[gofastgeorge]

I had this problem with the 6M crank also,balancer spun the key and transferred so much metal onto the front of the crank that I could hardly get the old one off.

I am about to start cutting this one off........
It's loose, and moves around,
but will only pull out about .020" before it locks up.
Even with a big ass puller & heat.
I have had this happen on high reving 2-stroke bike engine flywheels too.
So much metal transfers from one piece to the other, it ends up acting like a key, keeping the two from coming apart.
I had to cut those off also.

[suprarich]

Damn,
Then I may not have the problem figured out yet.......
I wonder if my converter is way out of ballance ?


Bolts backing out? Worn out holes on the flexplate? Threads in the crank messed up? The converters are self balancing being full of fluid, but it could be off center. In most cases of off center, the transmission input shaft bearing will fail before the flexplate assembly.

[suprarich]

Once you get to this point it's a bit of a juggling act weight wise, remove too much and you get a funky balance requiring heavy mallory metal inserts.

IJ is right on with that. If you are just going to lighten the crank, take even amounts of weight off each counter weight going straight in towards the center. This will remove a good bit of weight from the counter weights, but will still leave mass on the outside edge of the counter weight. Like in the pic below, the crank on the left is lightened by 5 lbs, but was cut straight in without knife-edging the counter weights. Leaving the weight on the outside of the counterweights disturbs the balance less.
http://img.photobucket.com/albums/v487/rich1969/ebay-2051.jpg


Now in the next two pics, this crank was lightened and knife-edged. Most of the weight was removed from the outside portion of the counter weights. This really played hell with the balance, which we fixed later with 100.00 dollars worth of 2 mallory metal plugs drilled into thhe counter weights. I eventualy got that crank back to within 1 gram of zero balance.

http://img.photobucket.com/albums/v487/rich1969/ebay-2063.jpg
http://img.photobucket.com/albums/v487/rich1969/ebay-2064.jpg

Long story short, take metal from inside the counter weight and less from the ouside edge and you will have less headaches later trying to balance it.

[IJ.]

Would you happen to have the specs on said profile?Like maybe the CNC program coordinates,or what cosworth profile.
Remind me in the new year and I'll see what I can get.

[TheNewRed]

Long story short, take metal from inside the counter weight and less from the ouside edge and you will have less headaches later trying to balance it.

Excelent tip, i will have a long talk with the person who does mine, about this.

[toy fanatic78]

Remind me in the new year and I'll see what I can get.

I will do that.Thanks.

[gofastgeorge]

Bolts backing out? Worn out holes on the flexplate? Threads in the crank messed up? The converters are self balancing being full of fluid, but it could be off center. In most cases of off center, the transmission input shaft bearing will fail before the flexplate assembly.

"Bolts backing out?"
Nope,
Clean breaks right under the heads.

"Worn out holes on the flexplate?"
Nope,
each time it was a different, but either new or excellent condition flex plate.

"Threads in the crank messed up?"
Nope, threads in great shape, even after the head failures.

But I am planning on having the converter checked out.

Everything points at a harmonic problem, or the fact that the 6-bolt crank just can not take 8500 bang shifts.
Hoping that the dowel pins will help take care of the extra shock loading.
And the 7M crank taking care of any vibration issues.

But it is still a weak point.
Toyota didn't go to 8 bolts on the 1JZ/2JZ for no reason.

Sent an e-mail to Crower to see if they can still make a 7M crank.
If so, I'll have them put in the 2JZ bolt pattern.

Anyway, it's back to the garage for me.
I finally had to split the harmonic balancer to get it off.
So hopefully I'll have the 7M crank in the block sometime tonight.
Maybe have the engine back in the car by Monday.

[BlackDynamite]

when i had my 88 black supra, i rebuilt the engine because of spun bearings and i came across the same issue. IJ gave those EXACT 2 pictures!

As i did research, I put in the 7m crank for durability and it was the only one i had available for cheap, but noticed a COMPLETELY different rev pattern than the 6m....The 6m in my supra now, revs more than twice as fast as the 7m in my old supra.

[suprarich]

"Bolts backing out?"
Nope,
Clean breaks right under the heads.

"Worn out holes on the flexplate?"
Nope,
each time it was a different, but either new or excellent condition flex plate.

"Threads in the crank messed up?"
Nope, threads in great shape, even after the head failures.

But I am planning on having the converter checked out.

Everything points at a harmonic problem, or the fact that the 6-bolt crank just can not take 8500 bang shifts.
Hoping that the dowel pins will help take care of the extra shock loading.
And the 7M crank taking care of any vibration issues.

But it is still a weak point.
Toyota didn't go to 8 bolts on the 1JZ/2JZ for no reason.

Sent an e-mail to Crower to see if they can still make a 7M crank.
If so, I'll have them put in the 2JZ bolt pattern.

Anyway, it's back to the garage for me.
I finally had to split the harmonic balancer to get it off.
So hopefully I'll have the 7M crank in the block sometime tonight.
Maybe have the engine back in the car by Monday.


You have to have some sort of other problem then. There really is no issue with the 6 bolt 6m or 7m cranks not being able to handle power or shock loads. The 4age uses 8 bolts also, but it was not for strenght issues, just a different design.

If you really feel you need a billet crank, try Moldex. I would not want to mess with the year long lead time from Crower or the Minimun 5 crank purchase from Brian Crower.

I don't feel anyone needs a billet crank under 1400 hp, as the stock crank has been proven to that level already with shift points over 9k rpm

[gofastgeorge]

You have to have some sort of other problem then.... try Moldex. I would not want to mess with the year long lead time from Crower or the Minimun 5 crank purchase from Brian Crower.


I'll check out Moldex, thanks.

As far as BC, I wouldn't use jack from him, even if he paid me......

[4U2QUIK]

Remind me in the new year and I'll see what I can get.

I'd be very interested also. a nc or cad/cam file would be even better.

[wiseco7mgt]

Asking for trade secrets guys? tsk tsk lol

[IJ.]

Asking for trade secrets guys? tsk tsk lol

LOL none of it is a secret I'm happy to share if I can get the files, only problem there is the code is usually generated for a particular machine so unless you have access it's not going to be of much use.

[wiseco7mgt]

LOL none of it is a secret I'm happy to share if I can get the files, only problem there is the code is usually generated for a particular machine so unless you have access it's not going to be of much use.

Ever thought of sourcing 7m cranks and selling a performance crank based on your own spec? Would this spec also be applicable on a 2jz crank.

[dan0311]

what size is the standard rod bearings? some places say its .25mm, but my rod bearings say .75mm. what does that mean?

http://i108.photobucket.com/albums/n1/dand6577/001.jpg

it says .75mm.

http://i108.photobucket.com/albums/n1/dand6577/002.jpg

[4U2QUIK]

LOL none of it is a secret I'm happy to share if I can get the files, only problem there is the code is usually generated for a particular machine so unless you have access it's not going to be of much use.

that's what reverse post is used for.
plus the geometry would still be the same. usually a good programmer can adapt a program from another machine quickly.

[IJ.]

Ever thought of sourcing 7m cranks and selling a performance crank based on your own spec? Would this spec also be applicable on a 2jz crank.
Nope never considered it Pete ;)

The 7M crank is the prototype for the 2J so I can't see why the same treatment wouldn't work.


that's what reverse post is used for.
plus the geometry would still be the same. usually a good programmer can adapt a program from another machine quickly.
Never used anyone elses files in my machine so didn't know that was possible :) (self taught and haven't had a need to learn that bit yet)

[4U2QUIK]

lol, most people aren't aware that a reverse post exists none the less actually know how to use one.
I'm self taught also, but I've been in the right places at the right time to learn some very advanced techniques. I can program just about anything you throw at me. 3rd 4th and 5th axis.

[tekdeus]

My car came with a JDM 7MGTE. Did these only come with the 6M crank? Any chance it might be a 7M?

[IJ.]

Depends on the year

[speedfreak426]

My car came with a JDM 7MGTE. Did these only come with the 6M crank? Any chance it might be a 7M?


My JDM 7MGTE came with a 7m crank

I believe its from a 1992 becasue of the shifter knob that was on the trans, and it was a gray plug harness

[speedfreak426]

http://jblmk3.com/cars/crank_comparisons.php

Lots more info there

[tekdeus]

My JDM 7MGTE came with a 7m crank

I believe its from a 1992 becasue of the shifter knob that was on the trans, and it was a gray plug harness
What year did the 1JZ become available? Did buyers have the option to choose which engine they wanted?

[JDMMA70]

What year did the 1JZ become available? Did buyers have the option to choose which engine they wanted?

Late 89 is when the 1JZ became availiable they were sold as 90 models though. After that you didnt see anymore 3.0 Supras in Japan after 89, just your 2.5 and 2.0 models.

[speedfreak426]

Late 89 is when the 1JZ became availiable they were sold as 90 models though. After that you didnt see anymore 3.0 Supras in Japan after 89, just your 2.5 and 2.0 models.

another question.... I know my engine is a gray plug, 7m crank, and it had a digital dash....
any idea on the year?

[JDMMA70]

another question.... I know my engine is a gray plug, 7m crank, and it had a digital dash....
any idea on the year?

I would say mid 89