Is anyone else interested in a bronze pilot bushing? - Page 2 - PeachParts Mercedes-Benz Forum

charmalu · #16 06-22-2010, 08:21 PM

Quote:

Originally Posted by panZZer

I like the idea of a bushing that could have a roller bering pressed in-is there enough room to do this with the bigger 85 hole?

TOMJ did this for his 85, made it on his lathe. i read in a later thread it started to spin in the bushing.

Charlie

charmalu · #17 06-22-2010, 08:37 PM

here is the thread where he turned the bushing.

Need Help - Tranny Swap to Manual

Charlie

winmutt · #18 06-23-2010, 01:15 PM

Quote:

Originally Posted by junqueyardjim

You show me a car running with a ground down pilot bearing and I will show you a junker. Get real, grinding off a half mm from a hardened bearing shell. It can't be done. I would rather go with the correct bearing, that is true. Yet many vehicles have had bronze pilot bushings. Remember, the only time it is in use is when the clutch is disengaged, like when the pedal is in. Not much use!

Worked for me, 2x. I had atleast 15k on mine before I stuck a pre 85 engine in my car. I'd take my chances on a bearing before the crank any day of the week.

OM616 · #19 06-23-2010, 01:48 PM

Quote:

Originally Posted by Stevo

I need to ask you this, please dont take offense, this shop, you know these guys for a long time? From a mechanist point of view, is making this fine a tolerance thing (all of them) a everyday sort of job or what? Such skinny little walls and all

How big of a deal is making such a bushing for those in the know?

Something to keep in mind when designing the bushing is that the ID of the brass/bronze bushing will shrink a bit when the bushing is pressed into the crank.

To say it another way, if you have a close slip fit between the input shaft and the bushing ID, (say .002 inches, that is .001 per side (which is too tight IMO)), when the bushing is pressed in the crank the input shaft may not fit anymore because the walls of the bushing were squeezed toward the center when the bushing was pressed into the crank.

A common way to deal with this is to ream the bushing ID after pressing. But this can be trouble some as if the ID is not reamed square, (straight), the ID will not be true to the crank centerline.

The trick will be to find what the ideal "working fit" tolerance is, and then add the amount of shrinkage that will take place after pressing, so in the end the working fit is with in tolerance.

I often machine parts with less than +- .001 tolerances. Something else to consider is generally, the tighter the tolerance the pricier the part. Any decent machine shop should be able to hold +-.002 with brass or bronze without a problem.

Stevo · #20 06-23-2010, 07:50 PM

Quote:

Originally Posted by OM616

Something to keep in mind when designing the bushing is that the ID of the brass/bronze bushing will shrink a bit when the bushing is pressed into the crank.

To say it another way, if you have a close slip fit between the input shaft and the bushing ID, (say .002 inches, that is .001 per side (which is too tight IMO)), when the bushing is pressed in the crank the input shaft may not fit anymore because the walls of the bushing were squeezed toward the center when the bushing was pressed into the crank.

A common way to deal with this is to ream the bushing ID after pressing. But this can be trouble some as if the ID is not reamed square, (straight), the ID will not be true to the crank centerline.

The trick will be to find what the ideal "working fit" tolerance is, and then add the amount of shrinkage that will take place after pressing, so in the end the working fit is with in tolerance.

I often machine parts with less than +- .001 tolerances. Something else to consider is generally, the tighter the tolerance the pricier the part. Any decent machine shop should be able to hold +-.002 with brass or bronze without a problem.

Thanks, more good info, sounds like too big of a job for the DIYr, but something that a good shop should'nt have a problem with including the "working fit".

Pretty soon someone will put a "kit" together for swapping manual trannys in behind turbo 617s and one of these bushings will have to be in the "85"kit

junqueyardjim · #21 07-05-2010, 12:32 PM

I just purchased 12 inch of bearing/bushing bronze from a metal sales company in Wisconsin. In picking the minds of mechanics who were familiar with bushings, I soon found out that this had to be made very correct or the bushing would not last. Too tight on the pilot shaft or too loose in the big bore and you have trouble. Lots of things could happen and leave me with a handful of junk bushings. So in doing a lot of measuring and it is difficult to get a good reading on the crank bore, I did realize that the bore was actually closer to 35mm then to 34mm. Actually, the best reading we could get on it showed that the bore was 16 thousanths small. Well, 16 thousanths is pretty large when it comes squeezing steel, but yesterday I thought, I wonder what a couple of hours in the deep freezer would do to that bearing. Well, that was 4th of July and then with the fireworks, the bearing sat atop of the wife's favorite "Moose Tracks" ice cream all night. So this morning early, I grabbed the bearing in a mit and with a hard rubber hammer got it started in the hole. I was surprised and didn't think it would go in. So then I pounded it in flush with a hammer and a piece of 4x4 treated lumber and then pushed it all the way with a 22 mm socket and shop hammer. Job done and it was slick and easy and the bearing turns as it should. The only thing that would make me happier is to sell someone 12 inch of 1 3/8 bronze bar stock. This is rated as bushing/bearing bronze, but is not "oillite" or porous bronze. It weighs 7 lbs and I will sell it for $50.00

JB3 · #22 07-06-2010, 11:48 AM

clever solution! It turned fine when it warmed up again? This certainly solves this problem for a lot of people.