Crankshaft Question.....

[Bruno Molly]

to make a long story short, Old engine, 89 7m-gte booted #3 rod out of the block. Machine shop says crank can't be saved. Not new to engines but never had a crank that couldn't be turned. He said it was 60 thousandths out. Is my crank a Boat anchor now? Or can a machine shop Add metal, then grind it to spec? Would that change the Hardness spec in that region and create a weak link? Trying to rebuild on a Budget since it belongs to my son who is a student. I have a machined block +.020 but got hit with the bad news about the crank yesterday...

Thanks
BM

 

[Bruno Molly]

ANyone know where i can get a 7M crankshaft in decent condition? Is there a Big difference in a 6M and 7M?

 

[Bruno Molly]

No love on the Crank? A little history, we have the block back from the machine shop but now we need a Crankshaft. Just trying to rebuild my son's MKIII basically back to Stock before making any mods. Reliability is the Keyword in this rebuild.
Looking at pulling the Crank from an 89 NA..... Was also looking at a Reman from O'Reilly's which is reasonably priced and comes with the bearings.
I may be misguided but no one has replied to my questions as I am sort of lost in which direction to go
Not looking to spend $1G for a New Crank, just would like to know :
Where is a good source for a 7m-GTE crank decently priced ?
Reman vs used? (measured and checked for operability).
Where do you guys get your Cranks from?
Is it worth the Hassle to hunt down a 7M crank vs a 6M? I understand the differences in the 2 cranks with the balance and all..
Went to Supraforums.com for help and can't even post...WTF man....Geeze.
Thanks in Advance for any direction from you veterans on this subject.
-=BM

 

[CyFi6]

Theres a lot of info on here about the 7m/6m crank differences. Theres really no reason for a 7m crank if you are on a budget, the 6m is much easier to come by. Look around on the forums here, they pop up quite frequently in the for sale section. Any 6m/7m crank will work. You will have to measure it yourself and determine if it needs work once you get it. Most people will sell them any show pics but you are not likely to get measurements before you buy it. They really are not that expencive, avg price for a good 6m crank is probably $100. Ive done some reading on the reman cranks from autozone/checker etc, general concensus is to stay away from them.

 

[Bruno Molly]

THANK YOU!! Thats what I was looking for. I have read the difference in the cranks with the Balance, Redline #'s etc., and the limitations / pros and cons of both. So now i guess we'll be looking for a good used crank that doesn't need machining.
I guess the reman cranks from Autozone or Oreilly's are regrinds with oversize bearing eh? Would the reason to stay away from machined cranks at say .010-.020 have ground most of the hardness out of the journals?????
What if any other reason would be to stay away from Crank Kits? Seems to me that finding a Used crank will most likely need machining as well..... Going now to pull a motor and check it out. But I wanted some answers before I go hunting.
A little about me so you guys can get to know me...I am not new to cars at all. I am in my 40's, Have built many engines, Toyota SR5,22R's, Triumphs TR7's, MG's, Volvo 740 Turbo, 855R <----My daily driver, various other Nissan, Datsun, LUV, Buick V6, GM V8's etc over the years. Never have ran into such particulars as this 7M-GTE. I can bring alot of Electronic knowledge to this forum having sharpened my teeth owning a TR7 waaaay back in the day. Some of you guys weren't even born then. Anyway,
Paint and Autobody is my other specialty. Once we get over this Engine rebuild for my son, I want to design an LED Tail Light System and Light Show with a code driven microcontroller and will share my design here... Its not rocket science once you learn the particulars. The hardest part is writing the program to do what you want it to do. But, I will share what I know as this is the place to do so. Supraforums.com.....I have to shake my head..everytime I try to post it says I don't have permission. Sobeit...I have been a member there for almost a year now and still can't post...WTF... Ok...Going wrench spinning. I will post some pics and start a Build thread this weekend.

thanks for the Info.
-=BM

 

[suprarich]

What does your shop meen when he saysit is 60 thou out? Journal size? Straightness? I have seen some pretty bad cranks in my day, but needing to go .060 under on a rod journal to grind a crank I have never seen. YES your crank journal can be welded and machined back to a std size, but the cost will be more than buying a good used crank and then having it re-finished. Most machine shops do not have the equipment to weld and resize cranks like that and it is usually sent to a crankshaft specialty shop. You can call me at 330-541-1122 if you have any un-answered questions. The rpm limit between 6m and 7m cranks is in the ECU, not a physical limit of the crank. I have customers spinning both cranks to 10K rpm

 

[Bruno Molly]

What does your shop meen when he saysit is 60 thou out? Journal size? Straightness? I have seen some pretty bad cranks in my day, but needing to go .060 under on a rod journal to grind a crank I have never seen. YES your crank journal can be welded and machined back to a std size, but the cost will be more than buying a good used crank and then having it re-finished. Most machine shops do not have the equipment to weld and resize cranks like that and it is usually sent to a crankshaft specialty shop. You can call me at 330-541-1122 if you have any un-answered questions. The rpm limit between 6m and 7m cranks is in the ECU, not a physical limit of the crank. I have customers spinning both cranks to 10K rpm

I totally understand. I am thinking about using another machine shop. Seems like everything i take to him he says is either Junk or I need New this or that. To me I think the crank is still usable after a regrind. I don't even think he put the crank on a machine and checked it. He also said it was probably bent and will eventually Break if I get it ground and redone...Ha ha ha...

I have seen worse cranks repaired my self. I will call you Suprarich..I also need some direction on my Camshafts. Never have I had such Headache getting an engine rebuilt...Geeze! Well except that damned Triump TR7 I had in college.....NIghtmares all over again. CYl Head!..uuugh!

 

[bmoss85]

I totally understand. I am thinking about using another machine shop. Seems like everything i take to him he says is either Junk or I need New this or that. To me I think the crank is still usable after a regrind. I don't even think he put the crank on a machine and checked it. He also said it was probably bent and will eventually Break if I get it ground and redone...Ha ha ha...

I have seen worse cranks repaired my self. I will call you Suprarich..I also need some direction on my Camshafts. Never have I had such Headache getting an engine rebuilt...Geeze! Well except that damned Triump TR7 I had in college.....NIghtmares all over again. CYl Head!..uuugh!

If you can't get your crank situation figured out I've got a 7m crank ready to go.

 

[Bruno Molly]

If you can't get your crank situation figured out I've got a 7m crank ready to go.

Thanks Bmoss.... I got one last week. Its being polished... So now I need to decide which one to use, the 6m or the 7m. Once I get my camshaft ordeal over with...decisions. Good looking out though. How much would you want for your 7m crank?

 

[bmoss85]

$50 picked up

 

[Bruno Molly]

$50 picked up

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