Blue spots on crankshaft

Booner7M

Booner7M

Sleepy bitch
Apr 9, 2005
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Quebec City
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Hey guys,

Last month I heard the sweet sound of rod knock so I immediatly stopped using my car to check out the rod bearings..!!! I found one faulty bearing.. it was ripped bad (large scratches, like debris that passed by). Since i still dont know the reason of that failure I am wondering if this could be detonnation...??

We checked the crank and rods and there was blue spots on the crankshaft .. because of overheating?? But still, i checke dthe picture i had of the crank when we rebuilt it and there was blue spots on it as well... so anyone know about these.. is this a heat treatment or the crank suffered from detonnation?

Ill check all the plugs and make a leak down test if one look poor!

thnx for any tips
dave

here is the pic of the crank during rebuild.. there were blue spots on it before
 

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Kruso

2J>7M
Jun 9, 2007
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SugarLand
You either have to be abusing the heck our of your 7M or be running some crazy power to get a rod knock by detonation. The blue mark is a burnt mark on the crank. Sounds like you've had a rod-knock before, did you use the same crank?

Kruso
 
Booner7M

Booner7M

Sleepy bitch
Apr 9, 2005
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Kruso said:
You either have to be abusing the heck our of your 7M or be running some crazy power to get a rod knock by detonation. The blue mark is a burnt mark on the crank. Sounds like you've had a rod-knock before, did you use the same crank?

Kruso
Click to expand...

I used the engine (JDM) for a little while before the rebuild and it was not knocking but it ran lean for some time...

When I did that rebuild we sent the crank (from that JDM engine) for polishing and balancing, there were blue spots on it then. Do you think that this crank is still good???
 
K

Kruso

2J>7M
Jun 9, 2007
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SugarLand
The crank is NOT good and I wouldn't look into rebuilding that crank. I used to post alot along time ago on SupraForums but have been out of the loop for a while. Unless other Supra MKIII owners are able to tell you other wise with good proof to back it up with. If I absolutely had to reuse the block, I would atleast change out the crank with a virgin crank. I've had a VERY bad experience with 6+ "rebuilt" cranks on several motors with crazy money invested in them each time.

Did your machine shop resize the crank? What size of bearings did you use? Where did you obtain the bearings?

Kruso
 
Booner7M

Booner7M

Sleepy bitch
Apr 9, 2005
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Kruso said:
The crank is NOT good and I wouldn't look into rebuilding that crank. I used to post alot along time ago on SupraForums but have been out of the loop for a while. Unless other Supra MKIII owners are able to tell you other wise with good proof to back it up with. If I absolutely had to reuse the block, I would atleast change out the crank with a virgin crank. I've had a VERY bad experience with 6+ "rebuilt" cranks on several motors with crazy money invested in them each time.

Did your machine shop resize the crank? What size of bearings did you use? Where did you obtain the bearings?

Kruso
Click to expand...

Like I said that crank has already been use to rebuild the engine, its been running good for 2-3 years but I heard rod knock 1 month ago and then found one bad bearing. I used toyota bearing and did not resize the crank. Im going to put a new toyota bearing in place and hope for the best... if you say that its not good then maybe its the cause of that bearing failure but since its been running good for some time ill give it an other try !!!!
 
Booner7M

Booner7M

Sleepy bitch
Apr 9, 2005
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IJ. said:
7M Cranks are induction hardened this turns parts of them blue........

If it were from running a bearing the Journal and Bearing shell would be destroyed.
Click to expand...

right and they look good.. I think its still good !!

any toughts about how these scratches could have been done??? like debris or anything.. where could that come from??
 
TurboWeenie

TurboWeenie

7M-GTblownheadgasketE
Jul 22, 2007
32
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KS
If a 7m crank gets scratched up, is it ok to have it polished or ground (if polishing doesn't clean it up)? Will the setup last?
Kruso seems to be of the opinion its new crank or nothing.
 
Suprapowaz!(2)

Suprapowaz!(2)

New Member
Apr 10, 2006
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Booner7M said:
right and they look good.. I think its still good !!

any toughts about how these scratches could have been done??? like debris or anything.. where could that come from??
Click to expand...


Are you refering to the large grooves (scratches) on the walls of the counterweights??
 
TurboWeenie

TurboWeenie

7M-GTblownheadgasketE
Jul 22, 2007
32
0
0
KS
TW, lol that's a first. I like it.

What do you mean by 10/10 and 30/20? I've heard u can grind .01" off. Does this weaken the crank at all or affect life expectancy? Sorry, I'm a nub, so embarrassing... :1zhelp:
 
I

IJ.

Grumpy Old Man
Mar 30, 2005
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I come from a land down under
Rich: LOL yep I'm trying here ;)

TW: 10 thou undersize on the Rod and Main bearing journals = 10/10

Anymore than this and you grind through the hardened outer shell of the crank and get into the soft core and the slightest touch will transfer bearing material to the crank and total failure is only hours away.

As I said mine is ground 30 rods and 20 mains but it's had a LOT of expensive work to bring the surface hardness back to spec.
 
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