Machined Balance Shaft

[Andy_S]

Just got my balance shaft back from being machined down. I know its probably overkill and that the stub shaft would be fine, but I thought that since I have the shaft and a good friend to do it, what the heck. Plus, it makes perfect mechanical sense to me. Anybody else have one and care to share their results such as oil pump longevity? Below is a pic of the finished product. It sure is good to have friends with machine shop and CNC access /ubbthreads/images/graemlins/smile.gif Any comments appreciated.

 

[14u2nV]

I know a guy with a lathe, I may do the same thing. /ubbthreads/images/graemlins/grin.gif Do you just do the back one?

 

[Andy_S]

Yep, just did the back one. No point in doing the other one as it doesn't support anything. I also bought a crank spacer for where the balance shaft pulley goes behind the crank pulley. Its the stock part from the 1.6l.

 

[prove_it]

Stub shafts have been used for a long time with no real complaints, cutting the shaft down has been happening for a while now too. In my opinion, both work just fine. Obviously machining the shaft does add more support, but I don't think it's necessary. Either way it's freed up ponies and that's always good!

 

[turbowop]

Quoting Aspod:
Anybody else have one and care to share their results such as oil pump longevity?



I'll share my results for using a stub shaft... /ubbthreads/images/graemlins/hsugh.gif I've had zero problems with the oil pumps in both my cars using it. I can't even count the amount of 1/4mile passes 1051 has made with the stub shaft, let alone a lot of regular driving.

IMO, the turned down shafts aren't needed, but if it's free, do as you wish.

 

[1990ggsxnj]

Just seems like a whole lot of work for something that can be eliminated altogether with less of a hastle. I haven't seen any facts or experiences where the pump's life was reduced from removing the shaft. /ubbthreads/images/graemlins/dunno.gif

 

[CarRacer]

I think the stub shaft is fine for 90% of the motors on this board. It's my impression that the machined shaft is only beneficial for motors that see extreme RPMs.

Unless you are planning on running over 10k rpm, I don't see the stub as an issue. It's a piece of mind thing for others who want the groundwork necessary to do so.

 

[Hertz]

Isn't another benefit that with the turned shaft you're not going to see excessive oil pressure? Hence saving the effort of porting the oil relief in the housing?

 

[CarRacer]

No, because the shaft itself provides the oiling on the rear one. The front one is the problem shaft as it's oiled by the holes in the block.

 

[Barnes]

CR, Actually, it will reduce oil pressure. The rear shaft is supplied though the oil pump. So it is getting pressure that would otherwise be blocked off with a stub shaft. Since a oil supply is being blocked off, the pressure has to go somewhere. In this case, the rest of the engine.

 

[14u2nV]

I don't get the argument,, yeah maybe it would be debatable if it were a "buy the machined shaft or buy the stub", but for free, there is no debate. /ubbthreads/images/graemlins/dunno.gif

 

[Barnes]

IMO. There is no debate since it is free. The turned down balance shaft is probably more reliable. Granted, compared to something that is already reliable, it will just be... well... really reliable. I doubt it waste much HP anyways.

Any chance you could get the weight of that shaft?

 

[atc250r]

I'd still be worried that the BS bearing would get spit out, even with it machined there is a potential for that rear bearing to fail and send bearing sludge through the rest of your motor. The "more support" argument makes total sense to me but I'd still be concerned about that bearing coming undone.

John

 

[Barnes]

I've thought about it, but you have to ask yourself why do they get puked out in the first place. It does that because there is a radial force the bearing must support. The weight of the balance shaft slinging around at a zillion rpms. So you have cases where the bearing and balance shaft wear (just look at a used one) due to contact. Once both surfaces get rough enough I'd imagine that finally at some time running high rpms the b-shaft contacts the bearing and drags it for a ride. Ta-da, destroyed bearing/shaft/block etc.

Thing is, with the machined shaft, there is basically no load. It just nicely hovers on a cushion of oil and really doesn't make that much of a demand on the bearing. So I don't really see why it would ever seize.

 

[spooling92vr4]

id rather not have balance shafts... one less belt to snap and get caught in things

 

[Barnes]

No. The machined REAR shaft runs directly off the oil pump. The FRONT shaft, which is removed in this case, runs off the belt. Therefore, no issue of snapping the b-shaft belt.

 

[Dialcaliper]

Looks like a nice piece of work.

It's really a tossup

With the stub shaft, you get more oil flow to the rest of the engine. With the turned down shaft, you get better stability. But keep in mind that this is the *driven* gear. The gear with less support and more load (once the balance weight is gone) is the drive gear, which is loaded by the timing belt. The turned down shaft will put more inertial loads on the drive gear, since you have to spin up the shaft. Both have advantages and disadvantages.

Either option will work better than the weighted shaft. If you're going to stick with the original pump and gears, cutting down the original shaft is probably a better idea than just sticking a stub shaft in an old pump.

I think the most important thing is to use a brand new oil pump with brand new deburred gears. The most likely cause of failure is going to be using either used gears or a used pump housing with wear patterns that don't match eachother. Also, stick with the straight cut gears over the helical ones. The latter will be quieter, but will create side loads on the casing. (Helical gears can take higher loads, but you're unlikely to actually break an oil pump gear)

 

[Andy_S]

Quoting BarnesMobile:


Any chance you could get the weight of that shaft?



My digital mail scale says 14.7 ounces. Unfortunately, I forgot to weigh it before the machining took place.

 

[CarRacer]

I actually have a stock rear BS sitting in my car that I forgot to mail VR. I'll weigh it before sending and report the results.

 

[Kenny_Kline]

I did this on my motor and no problems yet and its been a year. AMS does this to ALL there block they build now. Makes more sense to cut the weights off and put it in a lathe. Controlled oil pressure and support for oil drive gear.