Pilot Bushing ID Smaller After Install? What!

[Jack O.]

Might sound crazy but...
I'm using a National #PB656HD (Made in USA) Pilot Bushing with ID of .592". Fits trans input and my clutch Alignment Tool which has a .590 input before install. However, after I install it I can no longer get my clutch alignment tool into the bushing.
Of course I found this out the hard way when I couldn't get my trans installed. I first figured the use of the cheapo plastic alignment tool may have not aligned everything well enough and decided to buy a metal alignment tool and redo. That's when I first found that the metal tool would not input into trhe bushing. Assumed somehow I screwed the bushing up when installing it so I bought another bushing and installed it. Same thing - fits before install but not after. I was very careful when installing and don't believe I did anything to mess it up.

Anyone else heard of such a thing? I've done clutches many times before and have never experienced this. Any suggestions on what to do? Would it be accecptable to open it up a little with sandpaper or something. Shouldn't take much but just doesn't seem right. '69 BB w/ M21 BTW.

Thanks,
Jack

[Bob H.]

Re: Pilot Bushing ID Smaller After Install? What!

Hi Jack:

Never heard of such a problem. Is this without the pressure plate in the way to see what is going on? Sounds you you have plenty of experience but I have to ask if the beveled side of the bearing is out.

[Jack O.]

Re: Pilot Bushing ID Smaller After Install? What!

Bob,
Yes, everything is off so I have a clear view. Nothing visually suspicious. Beveled side is out.
Thanks,
Jack

[Gene M.]

Re: Pilot Bushing ID Smaller After Install? What!

Jack, One of two things is causing problem. The hole in the crank is small or the OD of the bushing is too big. Press fit should be about .001" interference. Any more and the bushing will be too small to fit the tranny end.

[Jim D.]

Re: Pilot Bushing ID Smaller After Install? What!

The last two clutch jobs I've done, I've had to reduce the O.D. of the National #PB656HD bearing in order to get it to fit into the crank. The one time I didn't, it was hard to install and then the input shaft wouldn't fit into the bearing.

[Jack O.]

Re: Pilot Bushing ID Smaller After Install? What!

That's messed up. Maybe I'll try the one available from GM. Not sure I trust myself to reduce it correctly.

[Jack O.]

Re: Pilot Bushing ID Smaller After Install? What!

Anybody had better luck with the GM bearing, part #10125896, or know if its OD is smaller than the National? I've got a question out now to a parts place to get the OD of the GM bearing.

[Larry M.]

Re: Pilot Bushing ID Smaller After Install? What!

Jack:

Info from my files indicate that the original GM oillite bushings were 0.594 x 1.094 x 0.750 inch. I would check any bushing you buy against these specs. The OD can be turned down slightly using a drill press and some fine sandpaper or a very fine file. It doesn't take much. A lathe is even better, but most of us don't have this at our disposal. I believe that desired interference fit into the crank end is about 0.002-0.003 inch. The ID should not be turned (to increase opening) as this will alter/close off the oillite pores that ride against the transmission shaft.

Once at spec, a good trick is to put the bushing in a zip-lock bag in the freezer overnight to shrink the metal. Then install quickly. A bit of light oil should be okay during bushing and transmission install to make things slide easier. Do not grease the bushing ID or the trans shaft.

Larry

[Timothy B.]

Re: Pilot Bushing ID Smaller After Install? What!

Jack,

If you are using the bearing make sure to check the crank to bellhousing alignment. If it's off I don't believe the bearing will last where as the oilite bushing will allow some wear.

[Domenic T.]

Re: Pilot Bushing ID Smaller After Install? What!

I cut the gear off a old input shaft to install the bearing and have found that some needed to be turned down. The input shaft kept the ID from reducing when the OD was pressed in. Also makes a great line up tool. And yes you have to cut it off with a torch.

Dom

[Larry M.]

Re: Pilot Bushing ID Smaller After Install? What!

I cut the gear off a old input shaft to install the bearing and have found that some needed to be turned down. The input shaft kept the ID from reducing when the OD was pressed in. Also makes a great line up tool. And yes you have to cut it off with a torch.

Dom

I agree 500%......... This is the best way to do this job. NO surprises during the transmission install.

Another needed item(s) is having two bellhousing-transmission alignment dowels (about 4-5 inch long bolts with the heads cut off and a screwdriver slot in the ends).

These two items (input shaft and dowels) make all the difference in the world. Especially if you also have a lift . I always had to work off a creeper on the floor or driveway.

Larry

[Jack O.]

Re: Pilot Bushing ID Smaller After Install? What!

I did get confirm that the GM bushing has a slightly smaller OD and larger ID. I'm going with that...
Thanks everyone for your thoughts.

[Bill L.]

Re: Pilot Bushing ID Smaller After Install? What!

I am late to the party but have you checked with Autogear in Syracuse NY?

They make the correct non magnetic pilot bushing. They do have a minimum order amount that will require the purchase of two pilot bushings.

I realize this is an aside but I thought it might help.

Bill

[Dan D.]

Re: Pilot Bushing ID Smaller After Install? What!

Beware of the cheep repro bushings that are magnetic (contain iron). I don't think they will last very long. Original GM bushings are not magnetic.

-Dan-

[Jack O.]

Re: Pilot Bushing ID Smaller After Install? What!

Ok, got the GM bushing. Just to be sure I don't go through this a fourth time, can someone confirm that the attached picture of the bushing is showing the outer side, i.e. away from the crank? The 'back' end of this bushing is different from the other bushings I installed and rather than simply being flat it rounds out from the edg to the center and is only a flat area in the center roughly 3/16" wide. Thanks.

GMBushing.jpg