Contradictive Pricks

[fivestardsm]

So I pulled the motor out of 1387 tonite and was checking all the tolerances. While I was refferencing my Mitsu manual, I came across two contradictions a page apart. One page says dont grind the main journals of the crank, the other says if the tolerances of the rod's are bad, have the crank reground. I guess my misunderstanding is because the first part says that the crank has a special treatment done. Wouldn't that mean the whole crank had it done and not just the main Journal's? Sooooo which is correct??? You be the judge.


The rods are .05 under, I dont know about the mains yet, And I 'll probably be scraping the crank be cause the rod thrust clearences are at the limit. I think that this is part of the reason why the motor sh*t after a few miles. I am assuming it was bad machineing.

 

[turbowop]

Is that for possibly a different motor, since the manual lists specs for all engines that came in the galant?

I'm feeling too lazy to go thumbing through my manual. /ubbthreads/images/graemlins/tongue.gif

 

[Rausch]

The cranks were coated, which is why they recommend that you do not cut it down. IF you did, and could get the appropriate bearings. etc., you'd have to have it recoated, and it would still be weaker to begin with.....meh.

Thinking they were listing for other motors as well.. /ubbthreads/images/graemlins/dunno.gif

 

[fivestardsm]

Well the manual is actually a laser manual that I had given to me by a friend of mine who owns the local Chrysler dealer. It was sectioned for the 2.0 turbo. so I dont know. I wouldnt belive that they would be different for any of the other models with the 4G63. Im 90% sure that the NA cranks are the same anyway. (I will varify):?

Anyway, I am gonna toss the crank tho, it has some really "iffy" machine work done to it. It was atleast rebalanced. BTW in my first post I stated that the crank was tuned .05, well I ment to type0.5 MM which comes to 20 thousandths. Anyway just wanted clarify.

Anybody want to buy a crank??? /ubbthreads/images/graemlins/wink.gif

 

[Brianawd]

You can cut the crank. It will be fine.

 

[3rdstrikedsm]

I will never use a cut crank and I know a lot of the high hp guys won't use a cut crank either
It will remover the coating and when you cut it you will cut the smooth bevel to a square and that alone will weaken the crank but it most likely dosent matter for people under 500whp.

I would just make a practice of using un cut cranks if it were me.

 

[Brianawd]

Quote:
weaken the crank



How many 4g63t cranks have you seen broken /ubbthreads/images/graemlins/dunno.gif

 

[3rdstrikedsm]

Just 2 but both were cut and on 800 plus hp cars, I have never broke one nor has anyone I know with a street car.

 

[fivestardsm]

Well, cut or not, it is unusable. The shade tree monkey that re-built it (if you can call it that) didn't know his ass from a hole in the ground.. which is sad because that is where he is (R.I.P.) Anyway, the main journals are shot as well because as we all know what happens when you don't put the bolt in the balance-shaft to connect it to the oil pump gear, right??

Well if you dont know, it forces the balance shaft to the journal boss and wears a hole half way through it, and in-turn fuggs up the oil pump which decides to stop working and starves the engine for oil. This inturn causing catistofic (s.p.) bearing failure. I.E., the block is F**ked.

The balance shafts were bot seized to the bearings and they spun. And all of this on about 50 minutes of running from what I was told. Granted, I realize if I just do a balance shaft removal, It should be fine. Just not sure tho.

Now it just comes down to which one of the 15 or 16 motors do I want to tear down to rebuild. /ubbthreads/images/graemlins/dunno.gif

 

None! you want a drop in engine! /ubbthreads/images/graemlins/wink.gif

 

I agree with Brian. I've used this cut crank ever since I bought the car. I beat on it at the track, been through 8 pistons, 32psi (52lb/min) on a 60-1 as a daily driver (lots of water injection /ubbthreads/images/graemlins/smile.gif ). It was fin until the last set of pistons cracked and blew boost into the crank case. pushed enough oil out to kill the bearings and score the crank. But the crank didn't break, though I definately wasn't running 800whp.

However, there were several very high horsepower 4g63s running through SBR and other shops with cut cranks and no failures. I'd like to see where those cut cranks actually broke.

 

[fivestardsm]

I dont have a problem with cut cranks either. I Have run them before. The situation with this one is the poor machine work. The journals dont have the correct thrust clearance, and the end-play is right at the limit. The thing that scares me the most is the re-balance that was done. I found one of the heavy-weight plugs is loose.

 

[Ted Andkilde]

Cutting cranks is a bit of an art -- you need to find a machinist who knows his stuff, knows the engine you're working on and pays attention to detail (things like cleanliness, nice journal radii, etc).

When you can pick up a clean, used, uncut crank for $150 or so, it's just not worth it IMO. In 20 years when you can't get parts, sure.

Also, you can get cranks plasma nitrided after cutting, I don't know if that's the factory coating but it is a good one.

t

 

[G]

^ What he said, depends on who's doing the cutting, balancing & re coating/ treatment etc.....

 

[FlyingEagle]

Only crank I saw in photo form that was broken was LilEvo's back when he had the Maroon 4 door sedan converted to AWD. That crank broke not at the machine work areas, but in a completely separate area IIRC. Sheered clean in half that way, running 400 HP (not sure of torque values).

 

[iceman69510]

Nitriding is a surface, limited depth treatment that does not intrinsically make a crankshaft stronger, it just makes the surface tougher and more wear resistant. The strength comes from the material and proper heat treatment.

That said, cutting the crank must be done properly as others have mentioned above. Correct machining should not result in a compromised piece. Do you necessarily want it in a 700 hp engine? Maybe not, but you are probably pushing the limits of the design of the original material spec anyway at that point.

 

[FlyingEagle]

That's what I was looking for because it is exactly what we are learning in class (my second time around at college, yes I graduated the first!). Nitriding is a heat treatment, not so much a chemical add-on. If you have a good machinist or one that is building high dollar race engines that come back looking good, then consider cutting a crank, otherwise look for pristine examples of used cranks, and have them cleaned up a bit. It's not everyday any Mitsu crank from this generation snaps, whether cut or not, or so has been my experience from reading and seeing on the net. (5+ years).

 

[misterfixit]

gas nitriding as is stated above is a surface treatment. I discovered recently there are two types. the type i'm familiar with is used on rustable steels to increase the surface durability. the surface builds up in the furnace a thou or two, and is converted to be very hard appx 60Hrc. the case depth is about 5 to 6 thou, but this depends on the time in the furnace. you usually leave the substrate in a lower condition 45 to 50 hrc. Once out of the furnace the dense layer on the surface needs to be ground back a thou or so to get the desired surface finish and form.

you need to make sure pre nitriding and post nitriding that the surface is very good 32Ra pre, and thas good corner rads, and post processing you are looking for 4-8Ra, and careful control of where the nitriding runs out in relarion to the corner rads.

The second type i found out about was from dealing with Harmonic drive systems in Japan and is a much quicker process, but is only a couple of tenths deep and is not as hard a case.
Its late and i can't remember the trade name.

if you are refinishing a crank and would want to put a strong treatment on it that is slippy, best go for Titanium nitride. very hard and very low coefficient of friction.

But anyways.. cut crank or uncut crank. depends on who has done the work and how much care is taken over it.

rich