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MG MGB Technical - Pilot bushing

Getting ready to put my trans back in...before I do I was wondering if there are any tips to check if I need to replace the pilot bushing...I did not change the rear main seal so i didn't really touch anything on the rear of the engine block. I was wondering if I needed to change it now that the motor is out or do I have some years left on the one that is already there?
Peter Murray

I always change the piot bushing when I install a new clutch.

Steve
Steve

Cheap to buy, easy to instal,28? years old.What the heck put one in. Ric
RIC LLOYD

Peter-
I have to agree with the previous posters. The pilot bushing is an inexpensive part, so go ahead and replace it. The three-main-bearing crankshafts that were initially employed with the three-synchro transmissions were fitted with a 1.500” long sintered bronze pilot bushing (BMC Part # 1G 765) that had a smaller-diameter bore size in order to accommodate the smaller-diameter .620” input shaft of its first motion shaft (BMC Part # 22H 56) of the transmission used in conjunction with the three-main-bearing 18G and 18GA engines. This first motion shaft was subsequently redesigned to have a .850” diameter input shaft (BMC Part # 22H 843) of the transmission for use in conjunction with the five-main-bearing 18GB and later engines, and as such required a pilot bushing with a larger diameter. It should be noted that while there are two different lengths of sintered bronze pilot bushings, 1.000” (BMC Part # 22H 1416) and 1.500” (BMC Part # 12H 1630) used to support the input shaft of the first motion shaft of the five-main-bearing crankshafts, the spigot bore of the crankshaft is of the same diameter and depth on all of the five-main-bearing crankshafts employed in the MGB, regardless of whether they are fitted with the long or the short pilot bushing. The shortening of the pilot bushing was yet another example of cost-cutting by the factory. The longer of the two pilot bushings provides a greater load bearing surface area and thus wears more slowly, providing better long-term support for the input shaft (first motion shaft) of the transmission. The pilot bushing's inner diameter dimension is about .002"-.004" larger than that of the outer diameter of the input shaft (first motion shaft) of the transmission. Soak the new pilot bushing in oil for a few days before you install it. The sintered bronze alloy will soak up the oil until it is saturated, ensuring good initial lubrication.
Replace the rear main seal, too. It's also an inexpensive part, and you don't want to have to pull everything out and apart later when it fails. An uprated single-lip crankshaft rear seal that was used in the version of the B series engine found in the Sherpa van will do an excellent job of keeping oil inside the engine over the long term (Rover Part # LUF 10002). Contrary to rumor, this oil seal is not a double-lipped design. A double-lipped seal is essentially a single lipped inner seal shrouded from dirt by an outer second lip. This usually extends the life of the seal and any extra sealing action is purely a bonus. The original seal worked just fine before the advent of sealed crankcases, but the vacuum present in the sealed crankcase of the later engines tends to draw stuff in. Most "double lipped" seals have the outer lip reversed in order to prevent ingress of dirt or air that can damage the seal and thus interfere with the maintenance of the vacuum inside of the crankcase. On the other hand, a true double-lipped seal would have both lips in the same direction, for good sealing against fluid escape. The seal dimensions are: Outer Diameter 4.125”, Inner Diameter 3.500”, Width .375”. Being made of Viton, they are not prone to failure until thermal conditions rise above 450° Fahrenheit. This seal can be obtained from Brit Tek (Brit Tek Part # AHU2242). When you examine the oil seal, notice that one side of the seal has a sharp edged lip while the other side does not. The side with the sharp lip also has a spring around the rubber. The spring holds the rubber in contact with the shaft and the sharp edged lip runs on the shaft. The sharp lip is what seals the shaft. On the spring side you can see that oil under pressure would tend to assist the spring in keeping the rubber in contact with the shaft. Likewise, if installed backwards, oil pressure on the side opposite the spring would tend to lift the rubber and would oppose the spring, defeating its purpose.
Simply pry the old seal out with a screwdriver. Installation of the new seal is quite straightforward. Make sure that the engine backplate is held in place with the bolts only finger-tight so that it can be moved by gently tapping it with a soft hammer. This may be necessary in order to properly center the new oil seal. Clean up the rear of the crankshaft, as well as the hole in the engine backplate. Oil the crankshaft journal, and then slide the plastic adapter that came with the seal over the end of the crankshaft, with its big end first. Oil the outside of both the adapter and that of the seal, and then slide the seal over the adapter until it meets up with the backplate. Do not tap the seal directly with a hammer when installing it onto the engine backplate. Grease the outer rim of the seal and then gently tap the adapter all around its circumference with a small hammer in order to drive the seal into place. Gently tap the seal until it is flush with the engine backplate, and then pull off the adapter. Before torquing the 3/8”-24 UNF bolts of the engine backplate, give the backplate a gentle rotational wriggle to make certain that the seal is absolutely centered onto the crankshaft and is not pre-loaded by means of the engine backplate being slightly offset. Install the crescent-shaped locking plate (BMC Part # 1H 1021) with its four 5/16”-24 UNF bolts, and then bend the tabs up in order to retain the bolt heads in position.
Steve S.

Alright, you all have convinced me. Is there a easy way to remove it?
Peter Murray

Sounds silly but I removed mine by stuffing the hole full of wet toilet paper and then putting a socket about the same diameter as the inside of the bush on an extension bar, You put that into the hole and whack the end with a BFH. Since the hole is filled with water (held in the soggy paper) the force hydraulically forces out the old bush. That was a tip I got off here.

Also before inserting the bush check that it does fit over the end of the input shaft! The first one I had was slightly too small for some reason resulting in much frustration trying to get the gearbox mounted when the shaft was never going to fit at all.

Simon
Simon Jansen

Peter,
After trying several ways(hacksaw blade,packing it with grease)to remove the pilot bush a local club member who runs a repair shop suggested I use a 7/8-9 NC tap. I put an old socket into the crank for the tap to bottom out on. I then ran the tap into pilot bush and when it bottom out on the socket it screwed the bushing right out of the crank. Only took me a couple of minutes and there was a lot less mess.Hope this is some help.
Tony
Tony Shoviak

I second Simon's comment - I'd tried various methods over the years but the wet toilet paper trick is quick and effective (and you don't get a dollop of grease in the eye!).

David
David Overington

"Before torquing the 3/8”-24 UNF bolts of the engine backplate, give the backplate a gentle rotational wriggle to make certain that the seal is absolutely centered onto the crankshaft and is not pre-loaded by means of the engine backplate being slightly offset."

FWIW. The back plate is positioned and centered by two dowel pins in the block (#12-4313 in VB catalog).

Clifton
Clifton Gordon

Clifton-
Yes, I should have said that you wiggle the backplate before pressing it onto the locating dowels.
Steve S.

I has no success removing the pilot bush with hydrolic pressure. It was in there way to tight. I took a long stove bolt and rigged up a simple puller. The lip of the stove bolt catches the edge of the pilot bush and by turning the nut on the other end...out it came like a greased pig. The pictures should help. Good luck.

Paul

T. Schreiter

Here's another picture....could only load one at a time.

T. Schreiter

Before installing the new one immerse it completely in engine oil for 24 hours.
Wipe clean and install as per the info above.

Cheers , Pete.
Peter Thomas

This thread was discussed between 02/03/2008 and 07/03/2008

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