The Top Mitsubishi Galant VR-4 Resource

Join the best E39A 1991-1992 Mitsubishi Galant VR-4 community and document your GVR4 journey.

  • Software Upgraded - Reset Your Password to Login
    In order to log in after the forum software change, you need to reset your password. If you don't have access to the email address you used to register your GVR4.org account, you won't be able to reset your password. In that case, follow the instructions here to regain access to the forum.

lets talk balance shafts for a second.

thecman02

Well-known member
Joined
Nov 3, 2007
Messages
917
Location
Kalamazoo,MI
As far as balanced assemblies. I think I had +- 1g on each rod/piston combo. It still vibrates. Eliminating balance shafts just seems like the right thing to do. If you don't like vibrations don't put the urethane motor mounts in.
 

dsm10o0

Well-known member
Joined
Jun 16, 2010
Messages
680
Location
San Jose CA
+1 on elimination the balance shaft.

Heres a pic of my b-shaft bearing. Idk what caused it, but this was after a couple runs at the track. Found my balance shaft seized and then snapped the belt.

Picture171.jpg
 

jmelocik

Well-known member
Joined
Jul 24, 2011
Messages
126
Location
Cameron, NC
Quoting GSTwithPSI:
My GST has the stock motor with around 160k on it. It is my daily driver and it is lightly modded click . I have never had any issues with the balance shafts themselves, only with the balance shaft belt. To me, the balance shaft belt is the weakest link in regards to balance shafts. Much of the time when the balance shaft belt goes, it can take the timing belt with it.

They absolutely do make a difference with how smooth the motor feels though. It is probably up to each individual how much of a difference this is and how it is perceived, but it would be wrong to say the don't make the engine operation smoother and reduce vibrations some. It could be argued that the difference balance shafts make are negligible, especially depending on how your car is modded, but there's a difference none the less. I would say the reasons to eliminate them far outweigh the reasons to keep them, but I like the smoothness they provide on my current setup, and have opted not to eliminate them.

I will end with a story. I was driving my GST a few years ago when the engine all of a sudden started feeling like it was running rough. It wasn't all the time, but while accelerating through the gears I could definitely feel a vibration which randomly got better and worse through the RPM range. I started to troubleshoot for all sorts of problems. At idle the car hardly seemed different, but as soon as you would rev the engine there was no doubt something was broken and it was running rougher than before. The worst thing was the car ran great still, it just vibrated and felt like sh*t. It felt like a misfire almost, but the car ran too good for that to be the case. After tons of work and troubleshooting, I finally figured out the vibration was caused by a bad balance shaft belt. The timing gears had cleaned all the teeth off the belt, and it was just chillin under the timing cover not doing anything. Luckily it didn't break off and destroy my timing belt. I replaced both belts and called it a day. I tell you this story only to point out, that I could instantly feel the difference in the car without the balance shafts in action. It felt foreign, and without the shafts doing what I was used to them doing, the car felt like crap. I would have never thought they would have made such a difference had this not happened to me. Since that happened, I've always like the idea of keeping them because of the smooth operation they provide. Just my 2 cents.




This is actually misinformation. The reason your car vibrated harshly and felt like sh*t, as you described it, is because you had ONE balance shaft still rotating with the weight spinning.

"Balance shafts are commonly found in inline four cylinder engines such as the Mitsubishi 4G63 which, due to the asymmetry of their design, have an inherent second order vibration (vibrating at twice the engine RPM) which, contrary to popular belief, cannot be eliminated no matter how well the internal components are balanced. This vibration is generated because the movement of the connecting rods in an inline engine is not symmetrical throughout the crankshaft rotation; thus during a given period of crankshaft rotation, the descending and ascending pistons are not always completely opposed in their acceleration, giving rise to a net vertical inertial force twice in each revolution whose intensity increases quadratically with RPM, no matter how closely the components are matched for weight."

This is a quote from someone much smarter than me. Having built several engines though, I understand it and the very small side effect of removing the balance compared to the risk you take of leaving them in. The balance shafts rotate at twice the speed of the engine and yet rely on bearings smaller than either the rod or main bearings. In theory, with good oil pressure, this wouldn't be a problem. But the belt being smaller is a weak link and the tendency for oil pressure to "momentarily" be a little on the low side effects these more than the rods and mains.

I won't build an engine without removing them. The absolutely minimal noticeable vibration is far outweighed by the piece of mind gained from there absence.

Josh
 

LILEVO

Well-known member
Joined
Sep 20, 2003
Messages
195
Location
Wisconsin
I've always run an "AMS style" rear shaft in my engines and never had any issues.


Any vibrations are really non existent with exhaust drone and poly mounts.

rearshaft2.jpg
 
Last edited:

656of1000

Well-known member
Joined
Jan 18, 2005
Messages
292
Location
Phoenixville, PA
Quoting AMS:
In our experience, replacing the front balance shaft with a stub shaft will increase the chances of oil pump failures.


The stub shaft in question is an OE part from a 4G61. That engine, from the factory, has this setup. What I don't like about the AMS shaft is that there is still a shaft that is spinning at twice engine speed, as well as having a bearing that can fail. We had a car in our shop just last week that spun the rear shaft bearing when the customer grabbed 2nd in stead of 4th.

In my opinion, anything more than a daily driven street car must eliminate the balance shafts, but is highly recommended even on the daily driven street car.
 

Street Surgeon

Well-known member
Joined
Mar 3, 2004
Messages
941
Location
Omaha, Nebraska
Don't run em.

Also food for thought, these blocks will core shift from time to time (anybody ever get their blocks line honed?) and you're relying on a shaft that's supported by a bolt-on aluminum oil pump to be true all the way back? Yipes.
 
Last edited:
Support Vendors who Support the GVR-4 Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications RixRacing RockAuto RTM Racing STM Tuned

Recent Forum Posts

Top