Concentric shaft.

 

We were running this same mod in Starions (4G63 SOHC non US model) 20 years ago you guys are a bit slow on the uptake

 

It's been a while since I've seen the oil pump gears, and I remember there being at least two different types of gears for the 1G/2G DSMs. If I recall correctly, isn't one a straight tooth gear and the other a helical cut gear (or possibly just an angle on the tooth axis)?

 

There were straight cut gears on the early 1Gs, which were later changed to helical cut gears. The straight cut gears fit in their specific front case, and the helical gears fit in another case. They were not interchangeable, according to the factory service bulletin.

The shaft modification that AMS is recommending has been available for years in the 1G/2G field. Some say that it decreases oil pump failures. Others disagree that shaft "wobble" is the cause. Either way, there's no harm in using the turned down shaft, and it may solve the problem, in whole or in part.

What is clear is that most pump failures seem to have as a common component the gears "digging into" the case on the side closest to the outside of the motor. Whether or not you use a stubby shaft or a turned down shaft, it is considered essential that you deburr and polish (maybe even slightly radius) that top outside tooth of the oil pump gears before you assemble them into the front case, thus reducing the likelihood that if the gears contact the case, they will start the cutting process that damages the case and the gears...

 

Are the Evo gears straight or helical gears?

I ask because the helical gear is going to have an axial load that will force the gear into the case. The straight tooth gear on the other hand will not have that axial load. I have to wonder how many oil pump failures happen in the helical gears compared to the straight tooth gears.

 

Mitsubishi has been using helical gears starting in the 1991 model year.

Someone asked about the bearings and the possibility of converting their motor from a stub shaft to a support shaft. The bearing that supports the shaft we modify (the one coming out of the oil pump, not the one driven by the belt) doesnt have an oiling hole in it therefor has no need to be rotated. The oiling for this shaft is fed from the oil pump and carried thru the shaft to the bearing, similar to the supply to rod bearings. If that bearing wasen't touched and is undamaged, you should be able to install a support shaft.

Only the bearings that support the belt driven shaft (that one that gets eliminated), supply oil and need to be rotated to prevent oil pressure loss, similar to main bearings.

 

just got my 2.3l short block and stage 4 head from jam and they highly recomend running there balance shafts ...
now i know y they highly recomend them ...
thanx for the gr8 thread eric.

 

You can just replace the stubby shaft with the new race balance shaft, because the oil for the bearing is supplied through the shaft, and not from the block and through the bearing.

 

Just my observations. I have personally seen 2 oil pump failures using the stubby shaft in an evo. 2 events is not enough to say it was the cause, but it happened. I went with the AMS style shaft on mine although I did it myself buy turning it down on a lathe to save some $$$.