6M crank

[whenmunkysfly]

Ok so never really looked at it until now but after building my engine and having it ready to put in i relized that the old crank i have is a 6M crank. my question is do you think its worth it to have it machined. the guy i bought the car from had spon two rod bairings and it damaged the crank but not extremaly bad. so is it worth it to fix the crank or just trash it?

 

[Superjustin13]

well Used cranks are still used.

Take it to a Machinest and have him look at the damage, might be able to Polish it, or Grind the journals down and get thicker bearings

 

[starscream5000]

Yep, take it to a machinist first. They will be able to tell you if it's sill good to go .

 

[NashMan]

thicker bareing are all wasy not worth the tiem i find there just wekaer and the 7m bottom end is a spinner

 

[Superjustin13]

thicker bareing are all wasy not worth the tiem i find there just wekaer and the 7m bottom end is a spinner

eh?

what?? if the machinest has to grind the journals up to be able to use the crank, you'll have to get thicker bearings, the person paying is not really giving up any time putting it back in, just putting thicker bearings in due to the machinst grinding as much as lil off as possible on the crank, then you wont be able to use STD bearings you'd have to get .10 or .20 etc over

 

[jdub]

Here is the specs on the crank...this will tell you if it's worth turning or not. Note, the amount of material that can be removed is small..as previously noted, a machinist should be able to tell you based on these specs:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&Page=83

If you have the crank turned, make sure the journals and rod pins are polished. I would also have it balanced...especially a 6M crank.

The 6M crank is lighter, but is not a well balanced as a 7M crank. The difference is in the counter weights on the crank itself...thay were reconfigured on the 7M. IMO, the 7M crank is better to use.

 

[Superjustin13]

7m Crank is more counter balanced on cylinder number 2&5 which is why the redline is 250 less, not the only reason its lower, but its part of it

depending on what you want to do to your car, use a 6M or 7M crank on what kinda conditions you want

 

[whenmunkysfly]

i forgot to mention that it is blued from the heat of trashing the bairing. how would this effect the crank

 

[jdub]

That blue color is on one of the rod pins correct?

Sounds like the heat annealed the steel and compromised the hardened bearing surface. The crank definitely needs to be turned...replaced if the damage is too severe. I'd take a close look at the rod and main bearing cap oil clearances here:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&Page=68
and here:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&Page=71

The journals and rod pins should be nitrate hardened IMO. Inspect the caps and rod ends for damage. I'd also have the rod ends inspected to ensure they're concentric and resized to spec.

 

[whenmunkysfly]

nope the crank it self is blue from one main bairing up to the rod bairing and then back down to the next main bairing. its blue on the cast surfaces not the flat ones

That blue color is on one of the rod pins correct?

Sounds like the heat annealed the steel and compromised the hardened bearing surface. The crank definitely needs to be turned...replaced if the damage is too severe. I'd take a close look at the rod and main bearing cap oil clearances here:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&Page=68
and here:
http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?Section=EM&Page=71

The journals and rod pins should be nitrate hardened IMO. Inspect the caps and rod ends for damage. I'd also have the rod ends inspected to ensure they're concentric and resized to spec.

 

[jdub]

Wow...it had to get pretty hot to do that. Find a good machinist, have the crank closely inspected and point that out. I'm not too sure I'd want to use that crank :icon_conf

 

[89turbosupra]

If the casting part is blue form the heat I would not trust it.

thicker bareing are all wasy not worth the tiem i find there just wekaer and the 7m bottom end is a spinner

Actually its an old hot rod trick to turn your crank to the limit. It reduces bearing speed to you can rev it higher without spinning a bearing. It also frees up some horsepower due to the slower speed and less friction.

 

[whenmunkysfly]

that what i was thinking. its pritty bad. when i took this engine apart i looked at how bad this guymessed up the car and the only thing i was thinking is how could someone ever let their car get this bad. huge dent in the oil pan lead to low oil level and he prob. lost oil pressure and didnt know so the bairing almost disapper. but his words where "i pulled over as soon as it started knocking". it almost hurts me to see how he abused my baby.

If the casting part is blue form the heat I would not trust it. Actually its an old hot rod trick to turn your crank to the limit. It reduces bearing speed to you can rev it higher without spinning a bearing. It also frees up some horsepower due to the slower speed and less friction.

 

[NashMan]

runing bigger bareing is no no but that is just me

as for bluing and truning caps/rod black can tell yae right now that crank will most likly be toast as in my stander's you only cna drive on rod nock for so long tellt eh damge is to big

as or the 6m crank and the 7m crank both do there job well why was the 7m cank made my biggest guess what toyota tryign to make the 7m smoother kidna like the rx7 but it never will be aka filled motor montes and new crank it did make it smoother but really it's 7m not a 1j or 2j