7 bolt cranks suck

[dsm_eclipse]

ive got a 98 gst, it spun a rod bearing so i got the crank turned now i cant get any bearings for it. has anyone else had this problem or should i just buy another crank or do a 6 bolt swap

 

[donmagicjuan]

You mean like these? http://www.slowboyracing.com/shop.php?sid=&cat=3945

Most vendors sell standard as well as a few undersized main and rod bearings for this very reason. Looks like they even have them for the 7-bolt.

 

[andymoraitis]

If you have trouble getting bearings for a cut crank from Slowboy, you can also try Jackson Auto Machine. They're listed on our site sponsors page. Be prepared to hear a lecture about using a cut crank, but they do usually carry bearings for them.

 

[D_Eclipse9916]

Why did you turn your crank....argh!!!!

 

[94awdcoupe]

If you plan on using a 7bolt cut crank, you are looking at spinning a bearing very quickly. My advice is to junk that crank and buy an unmolsted 7bolt crank and have it nitrided. All you are doing with that cut crank is shaving the bearing surface right off of it, which is what is happening when you spin a bearing.

Do it right the first time to save yourself the hassle of doing it again. Even cutting a 6bolt crank is downright retarded.

 

[hereitcomes]

I spun a rod bearing on #4 cyl. on my 7bolt. I was also holding the car in 3rd gear @ 6k for about a good 10 seconds, so....ya. Wasnt the motors fault it was my fault. Get a fresh 7bolt and you should be good for a long time.

 

[DNA666]

Nothing wrong with a cut crank.

 

[92DSMErdrick]

I'm starting to realize that a cut crank comes down to a matter of opinion. Depending on different engine builders, they will recommend different things. The 4g63 crank is not suppose to be servicable. . .yet they make different size bearings for it. If the car is going to be used for a Daily driver than a cut crank should really be fine. If your going to be modifiying your engine to be a crazy beast than you might want to go with a uncut crank and keep with standard stuff. Recently I've been researching this and most results I've gotten from people are just opinions. There are plenty people out there running cut and uncut cranks with no problems. Your choice.

 

[Defiant]

I'll stick with what Mitsubishi says. The 7-bolt crank is a non-serviceable item, and is never to be ground.
YMMV.

 

[InvaderGSX]

Yeah I am a 7 bolt guy because I have an automatic. I've been through a lot of motors not because it was a 7 bolt, but because I went through a lot of trial an error and a lot of crappy machine shops. Now my last time out I spent the bucks and bought a 7 bolt Eagle crank. If your going to stay with 7 bolt just buy a new crank. Not a reman. A brand new one! If your on a budget go with the Topline crank. Same price is what people sell remans for.

 

[MyBeatGSX]

I'd like to nominate this for "obvious thread title of the year".


I spun a bearing and swapped a 6 bolt. Screw that 7 bolt crap.

The 4g63 crank is not suppose to be servicable. . .yet they make different size bearings for it.

Aren't those select fit bearings to make every individual bottom end fit together perfectly when new, not nessesarily for a rebuild? That was my understanding...

 

[XtremeRS2gnt]

I'd say if you are really worried about it, just bite the bullet and get the new crank. It is a lot more money, but i suppose it worth the peace of mind. Just as info though, i've built quite a few engines now(2 4g63's), and several of them(420a's), have needed the crank's to be turned. To date, these engines are still running strong(one is a 420A turbo). If you plan to have a crank turned, it's best to go about it a certain way. First off, before anything, find out what oversize bearings you can obtain. In most cases, you will find 2 main oversizes available- .25mm and .50mm(approx .010" and .020"). Once you know this information, take the crank to a reputalbe machine shop to have inspected. Get their opinion on how much material will need to be taken off to get the spun journals back into shape. I personally would not go over .010, as this is already quite a bit of material, and if the crank journal is spun that bad, i'd opt for a new piece. If they say .010 will clean it up nicely, then tell them you want that, and that you can get the bearings in that oversize. If you are assembling the engine, you MUST at a bare minium plastigauge ALL journals for proper oil clearnce. I cant stress enough how important this is. You may find that people that have had ground cranks spin bearings again, have left this out. Ther is NO reason that providing proper oil clearnce, installation, and of course oil lubrication, that you spin a bearing. Bearings spin because of oil starvation, or super dillution from foreign materials such as antifreeze, or clogged oil journals from other engine parts failure. Anything that can cause metal to metal contact, will spin bearings, and do it in a very quick fashion..it only takes seconds! If it were me, and i was building a higher HP engine, i'd get the new crank. If it were just a stock or lower HP daily, then turn it. Since it is a 7 bolt crank, that "crankwalk" fear is greater, so that may sway me even more to get a new crank as well...tough decision when on a tight budget.

 

[drivemusicnow]

Actually what it really comes down to is how the crank was cut. Most places won't radius the edges of the journals like they should, or do a poor job at it. A properly cut, and radiused crank can be just as, if not stronger than a "new" crank. (no guarantees the factory did it perfectly either)

I would use a cut crank, but only if I knew who had cut it, how, and how skilled they are at the complex machining that doing it right requires.

 

[94awdcoupe]

Bottom line on cut cranks, I dont really care what any engine builder says. Mitsu says in their service manual that cranks are not servicable, so guess what? Obviously, Mitsu knows what is up and cut cranks are for only one place and thats the trash. Be my guest if you want to use a cut crank, but the fact of the matter is you will be opening your engine very shortly thereafter with a cut crank. Spend the money and do it right the first time!

 

[DNA666]

Bottom line on cut cranks, I dont really care what any engine builder says. Mitsu says in their service manual that cranks are not servicable, so guess what? Obviously, Mitsu knows what is up and cut cranks are for only one place and thats the trash. Be my guest if you want to use a cut crank, but the fact of the matter is you will be opening your engine very shortly thereafter with a cut crank. Spend the money and do it right the first time!

Are you posting from personal experience or just spewing recycled posts?

From my experience, the fact of the matter is that a cut crank works fine.

 

[94awdcoupe]

Are you posting from personal experience or just spewing recycled posts?

From my experience, the fact of the matter is that a cut crank works fine.

I am posting from experience. Not my experience personally, but I dont like to cut corners, especially when it comes to an engine. I have several friends that have had cut cranks in their cars, and were built from a reputable shop and the motors spun bearings.

I dont feel like getting into a debate or argument to say the least, so if you feel you are that cheap to put a new or like new crank in your motor and not risk it, then so be it. Go the cheap route and just be prepared to be taking your motor back apart... at least from my experience.

Also, even if I didnt have experience, I would just be better off following our very own service manuals that specifically says right in there that mitsu cranks are not servicable, so right there, Mitsubishi puts that in there for a reason. Do what you want to do, its not my money so I could care less whether you use a cut crank or not. I am just stating facts that cut cranks are completely worthless!

 

[DNA666]

My rebuilt 2.0 worked fine with a cut crank as does my 2.3L 4G64 crank.

My friends has rebuilt 2 2.0's and is currently running almost 400HP on his 2.3L which was cut .70 and it works great as well.

So I will have to disagree that cut cranks are worthless.

You are also talking aobut a 20 year old service manual that only takes into account stock parts. There is better oil, bearings, and treatments available today then when the Mitsubishi service manual was written.

Would you teach Cobalt programming in a computer science class today?

 

[Defiant]

Would you teach Cobalt programming in a computer science class today?

Or, Cobol.

 

[drivemusicnow]

I am posting from experience. Not my experience personally, but I dont like to cut corners, especially when it comes to an engine. I have several friends that have had cut cranks in their cars, and were built from a reputable shop and the motors spun bearings.

I dont feel like getting into a debate or argument to say the least, so if you feel you are that cheap to put a new or like new crank in your motor and not risk it, then so be it. Go the cheap route and just be prepared to be taking your motor back apart... at least from my experience.

Also, even if I didnt have experience, I would just be better off following our very own service manuals that specifically says right in there that mitsu cranks are not servicable, so right there, Mitsubishi puts that in there for a reason. Do what you want to do, its not my money so I could care less whether you use a cut crank or not. I am just stating facts that cut cranks are completely worthless!

I understand what you're trying to do. You've had personal bad experiences that included resized cranks. Cool, we get it.

Making statements such as

I am just stating facts that cut cranks are completely worthless!

Is not helping anyone. You've made your point. It's not like this hasn't been argued before, but guess what? Everyone understands that Mitsu says they are not serviceable, and that some have had bad experiences with them. Let's not get out of hand by making blanket statements such as "I am just stating facts blah blah blah", When in fact, it is not a fact.

People still make huge power and have long lasting engines with "cut" cranks. You know what that probably means?

It means that it is not JUST resizing the rod and main journals that INSTANTLY turn a crank into crap. I'm not an expert on this, you're not an expert on this, so I let my machinist / crank specialist make that decision. He said yes. He also modified it with a few extras that should make it not only stronger than a new crank, but also better for racing conditions.

 

[omegis13]

A point about Mitsubishi and reserviceable parts:

"Rather this can be blamed on Mitsubishi's poor deal with Getrag, the transmission manufacturer. In the agreement, Mitsubishi agreed to consider the transmissions "non-serviceable," and instruct all their dealers to simply replace the entire transmission if there was ever a problem. Indeed, the factory service manual has a single page devoted to the Getrag transmission, saying exactly this. This of course generated significant
increase in sales for Getrag, at the expense of the loyal owners one might add."

A transmission was listed as non-serviceable. We all know that is BS. As for the crank, you'll be fine to cut it. Just make sure the guy who does it knows what he's doing and get the proper bearings.

Greg Heineken

 

[BIGBLAZE79]

I spun the number 2 rod bearing at 107K miles with no crank walk. Had the crank rod and main journals ground, nitrided then micro polished. My engine is running fine with 4K miles so far.

 

[Initial DSM]

i have a cut crank in my 1st gen (.10) under and its fine been in the car for 2 years with 50 track passes and 10k miles on the street ..car runs 11.0@132 making about 550 whp..and i use it almost everyday so who ever says cut cranks are no good don't know what the hell there talking about..end or story

 

[Street Surgeon]

Pick up a used unmolested 7bolt crank, or maybe an eagle crank if you've got some change. They're 699 from summit. A full 100 bucks less than from SBR!

 

[bryanwheat]

Who would take the advise of a company such as mitsubishi who hasn't even released a factory service bullitin on the 7 bolt thrust bearing oiling problem. HMM not me

I have been building these motors for 8 years, now, and personally know a few machinist's very well. There is no reason to not cut the crank.

The reason that peple prefer to not cut the crank is because it will supisodly weeken the journal, and on the 6 bolts it will take the nitrate coating off, it has nothing to do with if it will spin a bearing or not. Only to the overall integerity of the crankshaft.

IF the crankshaft is ground correctly, than it will most likely be better than stock, most cranks from the factory are out of round, especially 7 bolt cranks. Why not cut a 7 bolt crank? You are removing 10 thousand's of an inch of material. That isn't alot, and isn't going to affect the strength of the crank really any at all. Remember that these stock crankshafts are capable of withstanding over 1,000 horsepower. This is because they are a factory forged steel crankshaft. Which is very very strong.

.

IF you have a good machinist, than he will be able to machine your crankshaft much better than it ever could of been from the factory.

There is no reason not to turn a 4g63 crankshaft, and it is not going to cause you to spina rod bearing. That is not the concern.

 

[Black95TSIawd]

I spun a rod bearing on #4 cyl. on my 7bolt. I was also holding the car in 3rd gear @ 6k for about a good 10 seconds, so....ya. Wasnt the motors fault it was my fault. Get a fresh 7bolt and you should be good for a long time.

What do you mean you were holding it in 3rd @ 6k for a good 10 seconds? Do you honestly think a good bearing will spin just by doing that?