ky7

Maybe it's just me, but I hate the damn things. Too delicate, especially when installing the tranny with the car on jack stands and the clutch bolted to the flywheel. It also can be a monumental bitch to get out when stuck in there. I think a simple brass bushing is a better design. I can't see why this would not work given a good grease and perhaps a special lubricating brass, save the fact that the bushing wall thickness would be quite small, and of course subject to wear. Personally it wouldn't bother me if I had to drop the transmission every 30k miles to check / replace.

Are bushings available which are a suitable direct replacement for the pilot bearing in the 13B?

Any thoughts in general?

now

iTrader: (1)

or better yet teflon

ky7

Indeed, or Kevlar. Seen these used in performance Ford engines. A list of ideal bushing materials would be great. I can't remember the name for that particular type of Brass which is self lubricating (as it wears it releases lubricant).

Main thing is.. are there any suitable bushings available "off-the-shelf" that will fit the 13B (FD) e-shaft and input shaft correctly or will I have to get one made?

RXBeetle

You mean one of these (see attached pic) It's made of oilite which is just oil impregnated bronze I think. It came with my Kennedy Rotary engine adapter kit. It is the same size as the needle bearing too. You can also order oilite round stock and take it to your favorite machine shop and have them turn you one.

RETed

Actually, in terms of lower friction, it's hard to beat the needle bearing.
The bushing might be more reliable...


-Ted

RXBeetle

The needle bearing only works as a bearing when the clutch is in so I could care less about friction then, especially on that small of a shaft. Those needles aren't that hard to break when installing and engine and when they bind after that you're doooooomed. It also always bugs me that I always see the needle bearings packed with clutch dust instead of grease when I pull the engine. Not that the bushing is immune to the same contamination but at least the bushing wont lock up from the grit. The only worry I have is that the Oilite bushing is not happy taking that high of an rpm/load combination (high speed shifts or screaming clutch drops). It would be very obvious if it was a problem though (galling and bushing wear) Needle bearings are awesome with rpm/load when they are clean and intact.

RETed

Isn't the trans input shaft always in contact with the pilot bearing / bushing?

I know what you mean about the engine installs killing the pilot bearing.
I've gotten my technique down good enough to avoid this problem now.


-Ted

drago86

the bearing is spinning all the time, not only when the clutch is in,..

It is there to support the input shaft, the bushing would just wear a little and no longer do tht job. Not to mention the increased friction ted talked about (adding drivetrain loss anyone?)

Just replace it whenever you pull the trans if it worries you.

now

iTrader: (1)

the bearing is only spinning around the shaft when your foot is on the clutch
when your foot is off the clutch the shaft is turning the same speed as the motor

REVHED

Only if you're clutch is slipping all the time. lolol

ky7

After some useful points being made above.. like RXBeetle, I am still not convinced the merits of the needle roller bearing outweight the merits of using an Oilite bushing for example. It's a lot less hassle eliminating one less pain in the *** thing by replacing with a simlple bushing, when installing the tranny.

Removing the transmission to check / service the bushing every once and a while would be an afterthought if it wasn't for that damn needle bearing. Especially when it seems you got to "pull" the transmission the last inch or so, the bell housing never "closed up" for me like other boxes with just a push, even tho the input shaft is clearly in the splines. You're always concious of that damn needle bearing.

If the the stock bearing is only rolling on the input shaft when the clutch is in (disengaged).. why then does the grinding / rumble sound of a bad bearing continue sometimes when the clutch is partially engaged? Sometimes a bad bearing only makes sound at this point, and not when the clutch is fully in (disengaged)?

drago86

I stand corrected. I guess it really doesnt matter to much then.

sereneseven

Cause when one is ingaging the clutch is when the pilot bearing is being loaded the most, when the clutch is fully disengaged the pilot bearings under very little load it just free wheeling. another thought to add to this is that using a bearing allow you to run a much tighter tolerance whearas the use of a bushing would mean you will need to open up the input shaft tolerences a bit which will add to the amount of inpute shaft bearing load, intermediate bearing load do to out of center clutch ingadgement.

ky7

Thanks sereneseven for the good info, that's food for thought.

I'm thinking of making my own bushing and I was going to match exactly the tolerances of the new bushing with the stock pilot bearing. What do you think, considering the above comments?
Update - got this response from the very helpful guys at Kennedy Engineered Products...

They charge about the same as a new pilot bearing for these.

I don't have the ID / OD for the stock pilot bearing to compare with the above figures, perhaps somebody else does? Also the diameter of the input shaft if anybody has that figure handy?

RXBeetle

I have the Kennedy Bushing and a brand new needle bearing, I'll check em out tonight for fit.

ky7

Excellent.. will be interesting to know.. thanks RXBeetle.

RXBeetle

Kennedy bushing:
.789 OD
.589 ID

New Needle Bearing
.790 OD
.594 ID (I turned a piece of aluminum down .001 at a time till the bearing went on)

I don't have a mazda tansmission to check clearance on the input shaft, my engine is getting mated to a 901 Porsche transaxle. The needle bearing felt sloppy on the Porsche shaft though. I'm gonna run the bushing.

TonyD89

iTrader: (10)

I just miced the input shaft dia. at .5895". '89 NA. But my mic was a little cold from being in the garage. We'll see after it warms up.

sereneseven

'93 w/60k on it mic's out .5900

RXBeetle

hmm .0005 clearance or .001 interference is not exactly a good fit for a bushing...
I'll double check tomorrow and measure the VW and Porsche trans input shafts just for comparison, They are supposed to be the same size as the mazda. Is there a spec anywhere for the mazda trans input shaft? It is also possible that my mic is out of whack, I'll check it with a gauge ball.

RXBeetle

Remeasured, 2 different mics, same results as above. Porsche shaft is .587 which is why the bushing fits so nice and why the bearing felt sloppy.
The VW box is behind another engine and other car parts I didn't feel like digging through.

ky7

This is turning into an excellent thread, thanks for the above contributions, and your time on this RXBeetle.

Seems that bushing is a bit too tight fitting for the stock input shaft?

ky7

Wow.. I specifically ordered a set of these bushings from Kennedy Engineering, but after paying for the bushings, they have sent me out the stock pilot bearings instead!

I will update once they rectify the situation, I said I'd buy these Kennedy bushings just to see, but I've made up a few bushings from Oilite round stock in the meantime.

rx7306vert

I am going to make my own bearing, I ordered a piece of 932 bearing bronze that has the tensile strength of 35,000 and brinell hardness of 65. I think .002 to .003 clearance would work, not sure of the type of grease but had never seize compound in mind, if anyone would like I could make one for you, also would like some input. leave a phone # I will get back to you

ronbros3

allready beeen done at least 10yrs ago, rx7 came in for clutch job, well on inspection found spun factory pilot, and chewed up the trans input shaft. NOW! what do you do that dont cost a small fortune, simple MIKE the hole in eshaft and mike the pilot shaft, chuck a pc. of oilite bronze in the lathe and make a custom pilot bearing, polish the pilot shaft with endless belt, make it fit a tite press fit in shaft, .002-.004 clearence. still running fine 10yrs. didnt cost a lot ethier. Ron