Diff. oil pumps?

[stupidweirdo]

I've got a couple oil pumps that are diff. One has straight cut gears the other has helical.
Anyone know why they're diff? Both out of turbo 6-bolts.

 

[atc250r]

The helical were a "fix" for customers complaining of noise from the motor which turned out was due to the straight cut gears. There was even a Service Bulletin from Mitsu back in the day.

JOhn

 

[3Diamond]

Is straight cut one more efficient? Or are they the same?

 

[CO VR4]

Watch out for this, guys! The straight cut gears AND the straight cut gear case were the original equipment on the pre-93 cars. After 93, the helical gears AND the helical gear case replaced the straight cut gears, in order to keep the "whine" to a lower level.

YOU CANNOT USE THE HELICAL GEARS WITH A STRAIGHT CUT CASE! YOU CANNOT MIX AND MATCH. If you use the helical gearset, you MUST use them ONLY in a helical case. Straight cut gears can only be used in a original straight cut case. The case clearances are different.

If you don't abide by this limitation, you'll sieze the oil pump and grenade your motor. Guaranteed.

 

[atc250r]

Good point. I should have mentioned that. If I still had the TSB I'd post it but since I'm no longer at Mitsu I can't. If there is a lot of interest I can get a copy from a buddy of mine.

John

 

[HunterDG]

Quoting CO VR4:

If you don't abide by this limitation, you'll sieze the oil pump and grenade your motor. Guaranteed.



Sorry to bring this back from the dead.. Any idea how to tell the front cases apart? Our GVR4's came with straight-cut right? I'm pretty sure I have the right front case, but I'd like to check if there is a way..

 

[iceman69510]

I just opened up the oil pump on the '90 block I am rebuilding, and it has the straight gears. Is there any benefit or down side to keeping these? I have not checked the clearances yet, but if they are OK, I plan to use this oil pump. Seeing as how you can't get the old cases or gears anymore, just wondering what arguments there would be against using this.

 

[BoostedAWD91]

that is good to know, i never knew that there was 2 different types

 

I don't see any down side besides the noise, but your old enough I don't thing you can hear anymore anyways. /ubbthreads/images/graemlins/grin.gif

We use straight cut gears in our engine all the time and they last well over a million miles. I say if its within spec go ahead and use it.

 

[solidviper89]

I remember when I did the balance shaft, I had helical gears, I think, maybe the previous owner replaced the pump?

 

Straight cut gears are stronger, but noisy. Helical gears are slightly weaker, generate thrust wear, but are quiet. Not a big deal in an oil pump, but a big concern in transmissions. Anyone who wants to sample the noise need only put their car in reverse. A "dogbox" transmission uses straight cut gears for strength.

 

[Barnes]

Actually, helical gears are stronger. My guess would be that straight cut gears are common in aftermarket gear sets because they are (I'm assuming) much easier to make. That and/or the fact that the need to reduce thrust load is greater than the need to have stronger gears.

 

Alright now I'm putting together a car right now and I was about to install new straight cut gears in a case that had helicals. I have the same part number for the front case up to 4/92 (7 bolt switch) but obviously different gear part numbers for helical or straight.

So I do not understand why I cannot swap gears as long as the housing is fine and my clearances are on.

 

Quoting CO VR4:
Watch out for this, guys! The straight cut gears AND the straight cut gear case were the original equipment on the pre-93 cars. After 93, the helical gears AND the helical gear case replaced the straight cut gears, in order to keep the "whine" to a lower level.





This post is incorrect! Straight cuts were only used in 90s!

Heh the front case is already on the car gasketed, rtved, and locktited down. So we'll see in the near future how long my gear swap lasts at 80/lbs min of airflow.

 

Low oil pressure has never really been a problem for the 4G63. I have had the opposite quite a few times until I found the fix for it.

 

[3rdstrikedsm]

Quoting unior:
Quoting CO VR4:
Watch out for this, guys! The straight cut gears AND the straight cut gear case were the original equipment on the pre-93 cars. After 93, the helical gears AND the helical gear case replaced the straight cut gears, in order to keep the "whine" to a lower level.





This post is incorrect! Straight cuts were only used in 90s!

Heh the front case is already on the car gasketed, rtved, and locktited down. So we'll see in the near future how long my gear swap lasts at 80/lbs min of airflow.

\

Correct straight cuts were used in 90 only and are the usual choice for high hp high rev motors as the helical gear sets are kind of known for eating the case and thus destroying the oil pump /ubbthreads/images/graemlins/frown.gif

 

[Street Surgeon]

Correct, straight cut gears are stronger, and AFAIK only came in the '90 cars.

 

[Barnes]

Maybe I have tunnel vision but, when you guys keep saying that straight cut gears are stronger, are you only referring to this particular situation. I.E. Straight cut oil pump gears are stronger than helical oil pump gears. Is that what you guys are saying? /ubbthreads/images/graemlins/confused.gif

 

[Rausch]

NO.:
TSB-92-11-002 REVISION 2

DATE:
November, 1992

MODEL:
See Below

This bulletin supersedes Technical Service Bulletin # TSB-92-11-002 REVISION (Dated June, 1992) and Advance Technical information Notice # ATIN-92-11-001 (Dated July 31, 1992). Please discard the superseded TSB and ATIN.

New information includes:

- Deletion of 1983-89 2.0L Truck from Vehicles Affected list.

- Addition of new drive gear for 1983 Cordia/Tredia (1.8L and 2.0L, SOHC), 1985-87 Galant (2.4L, SOHC), 1987-90 Van/Wagon (2.4L, SOHC), and 1990-92 Truck (2.4L, SOHC).


PURPOSE

This Technical Service Bulletin describes a new oil pump/gear assembly that may reduce engine noise on some 1.6, 1.8, 2.0, and 2.4 liter 4G6-Series engines.

VEHICLES AFFECTED

1983-88 Cordia/Tredia (1.8L and 2.0L, SOHC)
1987-90 Van/Wagon (2.4L, SOHC)
1985-87 Galant (2.4L, SOHC)
1989-92 Galant (All)
1989-92 Mirage (1.6L, DOHC)
1990-92 Eclipse (2.0L, DOHC)
1990-92 Truck (2.4L, SOHC)
1992 Expo 2.4L, SOHC)


DESCRIPTION

On some vehicles equipped with the 4G6-Series engine, you may receive customer complaints of a high-pitched whining noise coming from the engine. This noise most likely originates from the engine's oil pump and is particularly noticeable during cold starting.







To help reduce the noise, a new oil pump is available. The new pump has helical gears as opposed to the former pump's spur gears. In addition, modifications were made to the engine front case to accommodate the redesigned gears.

All 4G6-Series engines built from 6/11/91 with identification code LX8939 and up, have been assembled using the new oil pump gear set and front case assembly.

When installing the new oil pump on a vehicle, be sure to replace the drive gear, driven gear, and front case as a set. These parts are not interchangeable with the former ones.

For information concerning the replacement of the engine oil pump, refer to the applicable service manual or engine overhaul manual.







PARTS INFORMATION

WARRANTY INFORMATION
Position Code: 121010.
Use standard warranty procedures.

 

[Dialcaliper]

Not quite.

Helical gears themselves can actually take higher loads and higher speeds(i.e. transfer more power) before they will break, since the load is spread out over more area, and they engage more gradually (less shock loading).

The caveat is that yes, they produce side-loads on the bearings, where straight gears do not. Dogboxes use straight cut gears because they are much less expensive to manufacture on a mill or lathe, which is how most low-volume gear parts are made. Less machine time, less precision required, and you only need a manual indexer, rather than a continuous one.

In the end, that means your race team can afford to have more ratios to swap out for different tracks/courses/stages.

Helical gears also happen to run quieter.

What usually happens in automotive transmissions is that while you can put in stronger gears, you can't really upgrade bearings other than choosing higher a quality part. A typical bearing performs much better with radial loads than thrust loads. Bearings usually have plenty of load margin in the radial direction to give longer lifespan.

In the case of helical gears, the side loads go up as well, where they do not with straight gears. Either the bearings fail (usually the cages holding the balls in place deform) or the transmission case flexes, and when that happens, the gears become misaligned and turn into kitty food.

Just as in the case of the oil pump, the limitation is actually the housing and the design, not the gears themselves. Even though the helical gears are better at high speeds, the aluminum housing simply isn't up to the job of handling the thrust load. In this case, the design was better to begin with, but the later helical design was driven by NVH concerns, not performance. Aka, people complaining that "my engine is making funny noises when its cold".

For our specific oil pump, any rebuilt engine is usually better off with the straight gears, since more than likely, it will be pushed beyond its original design, which the housing can't handle. Anyone who is willing to put up with no balance shafts is unlikely to care about a little bit of gear noise in the oil pump.




Quoting 687OF2000:
Straight cut gears are stronger, but noisy. Helical gears are slightly weaker, generate thrust wear, but are quiet. Not a big deal in an oil pump, but a big concern in transmissions. Anyone who wants to sample the noise need only put their car in reverse. A "dogbox" transmission uses straight cut gears for strength.