Air Pump removal, Something you need to know.
 

The first thing most people do when upgrading their car is to remove the Air Pump and throw on some under drive pulleys. The problem with this is now the contact patch on the water pump pulley is greatly reduced and most find that they can turn it with their fingers even with the belt tightened above stock tension. What most people then do is over tighten the belt to stop the slipping.

The rotary engine uses hydrodynamic journal bearings to support the eccentric shaft. The way it works is by flowing oil under pressure between the bearing surface and the shaft and basically “floating” the shaft through the fluid dynamic effect. Increasing the lateral load to one side on the shaft reduces how well the journal bearing can do its job of “floating” the shaft and results is metal on metal contact and accelerated wear. Over tightening the belt creates just this type of lateral load.

Pictured below is just one example of excessive bearing wear caused by running under drive pulleys without the air pump and over tightening the belt to compensate. The first picture is of the front bearing on two motors with a similar history. Both ran Mobil 1 10w30 most of their life and were autocrossed. The 99,800 mile motor stayed in stock form until it met its end due to a water jacket o-ring failure. The 66,000 mile motor had the air pump removed and under drive pulleys install around 53,000 miles. It also met its end to a water jacket o-ring failure.

The front stationary gears are in their correct orientation so what you are looking at is the top of the bearing as it sits in the motor. The copper color area is the wear.

http://www.tweakit.com/rx7/b1.jpg
http://www.tweakit.com/rx7/b2.jpg

The next image is of the rear stationary gear bearing. The picture is upside down to the way it installs in the motor so you are looking at the bottom of the bearing surface.

http://www.tweakit.com/rx7/b4.jpg

Close up of rear bearing wear:
http://www.tweakit.com/rx7/b5.jpg

As you can see the bearing wear is exceptionally worse on the 66,000 mile motor and the wear pattern on the bearing clearly shows the extra load applied by the lack of an air pump or idler in its place is the cause.

The only solution is to keep the air pump or replace it with an idler pulley. Currently there are three companies that have a solution available now or in the near future. They are:

Pineapple Racing: $179.00 + shipping
Requires removing two bolts out of the water pump housing to install.

http://www.pineappleracing.com/Produ...20IMGP2241.JPG

Tweakit Racing: $142.00 shipped
Bolts to Air Pump stock mounting points
http://www.tweakit.com/rx7/pulley.jpg

Garfinkle Motor Works: Will be released soon. Price to be determined, but estimated below $200
Bolts to Air Pump stock mounting points
http://www.tweakit.com/rx7/garfinklep.jpg

A worthy mod for those without the air pump.

FYI a local tuner (Portland OR) actually cracked the E-shaft by using too much belt pressure in his personal 600+ HP car.

He probably added the pulley following that.

I would be in on the group buy, but already have Pineapple's kit.

*cough* shameless plug *cough* :D All kidding aside, this is a great product. I had a chance to check it out at the shop a while back. I will more than likely be getting one of these in the near future. Dan and crew(Brian and Andrew) are very knowledgeable... just about as knowledgeable as they come. Dan is one of the few people that I will let work on my car due to piece of mind that it is going to be done right.

When my OE motor "met its end due to a water jacket o-ring failure", Dan was top on my list of builders for that reason. I'm going to get one from Tweakit because they're so close, and he can "supervise" my install.

as far as these go thats all well and good but some of those "idler" pullies may get in the way of peoples single turbo's. so im kinda curious if anyone has a replacment waterpump pulley that has ribs in it to run the belt around it instead of on the back of the belt? wouldnt the ribbing give you the extra "grip" you need to prevent slippage at the correct belt tension?

z

ya sorry guys i thought about this one for like ten minutes before still posting it and then did anyway....oops

BUT i do have a picture on my home computer that has it run exactly this way so maybe he has a different impeller or is just waiting to blow his motor i wish i could post it here as the rest of the setup is pure track...

It would run the water pump in the opposite direction ;)

i would love one but it seems that with the GT42 i have little to no options when it comes to this, the only one that i think might fit ix the pineapple one, it seems small but im still not sure it will fit.

I have a question: Don't most people remove the air pump to make room for piping or a single turbo?

Will Garfinkle's kit allow for this?

Thanks for the post this is really good info.

It just depends on how your single is mounted. On Brent's single turbo car there was about .0003" of clearance between the thermostat housing and the turbo :D. None of them would have worked for his.

Dan

Dean, I think those are actually your 99K bearings in the picture. Your motor was surprisingly nice inside when we disassembled it.

It's not just for single turbos anymore. ;)
I still run stock twins, but for me the point of removing the airpump was for (after emissions delete) the room, weight reduction, convenience and looks. It's been said before, but the advantage for an idler pulley is to keep the stock belt in full contact with the waterpump without having to go to an over-sized (under-drive) pulley set. I autoX but don't track. So I don't spend extended periods of time at high RPM and I don't have a need for the under-drive aspect. Same situation for guys that only street their cars. Not to mention the possible issues during periods of heavy electrical loads at idle.

Chadwick's post is just more reason why I'd rather spend my money on a good idler pulley than an underdrive set. Although I hadn't considered accelerated bearing wear, I have personally seen a guy way over-tighten the belt on his under-drive pulley set because it kept squalling at cold start-up. You could have played a tune on the belt, but hey...they were much prettier than mine. :D

Great. I won't change my driving habits then.
redline, here I come :driving:

lol!

I just put my name on the GB for your idler pulley. Can't wait for this to go through!

hey they look like it could fit with a single on the tweak it set...