I have heard that when replacing the jackshaft bearings, that the center one should NOT be replaced, that spot should remain vacant.  Could it be that is more of a problem when an aluminum intake manifold is used or is it it just some odd idiocincracy of these cars?  Wilkinson told me it could be because others don't have the "experience"...he has "done lots of them".  I note that there are spacers between the clips and the bearings...I wonder if a wider one in the center (if available) might make a difference.  I'm not against leaving that spot vacant but I'm just trying to figure the "why" of this.

I am also wondering what kind of bolts others have at either end of their jackshaft.  I have the two centers as allen type that are two part, a threaded stud that screws into the part with the allen head having a short thick shaft threaded inside.  The outers are standard long hex head bolts that are difficult to access with the jackshaft in the carrier.  I intend to change those for allens as well but they will be the standard type as only the central two have the carrier designed for those unusual bolt types.  Apparently the carrier was first bolted to the engine then the shaft was slid in while all was on an engine stand.    

Thanks....Terry

 

Original Post

Terry,

 
I have done a few of these jack-shaft bearing replacements now, it's a horrible job. Like you suggest, I get rid of the silly 'cap-head' over stud arrangement and use conventional 5/16th UNC cap heads on all of them under the shaft. That way, you can remove them with the shaft in the casting. Whoever came up with that original design should be taken out back and shot. I do install all 3 bearings, not sure if it would 'whip' with only two? the center one has normally spun on the shaft, I have machined it down and installed a spacer (hot) and then machined it back to 25mm; this works provided it's not worn below the size of the rest of the shaft.  If it's below the size of the shaft you have to weld it up and machine it back. I didn't think I would be able to weld a long shaft in the center without it bending, but a friend of mine who is a 'real' machinest said he could do it. When I went to pick it up he said he built it up with one spot at a time with the MIG and let it completely cool between spots, before doing the same on the opposite side. Throughout the day he kept adding more spot welds until it was ready to machine. It runs true, I will try that myself next time! Don't buy Chinese bearings!!
 
Johnny

if you need new ones, I bought a set from these guys in the UK and they arrived in Texas in two days!  very reasonable pricing too

https://www.qualitybearingsonline.com/

Here's a text clip from an earlier thread with dimensions.  Worked perfect in my case

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Front bearing: 47mm OD x 20mm ID x 18mm Wide. #62204-2RS1 (SKF). $22 (I had a 14mm wide bearing here and a spacer behind my pulley!)

Middle and Rear bearing: 47mm x 25mm x 16mm. #63005-2RS1 (SKF) $20

Rear bearing for LATE cars: (not sure where cutoff is, but if a 47mm is too small.....
52mm x 25mm x 15mm #205-SZ3 MCH? $16

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

MH

 

FWIW, I'm of the school that says the center bearing is the source of most Mangusta drive bearing problems. If you're worried about the shaft whipping from the combined alt/AC load (that from an alt alone on a shaft that size is almost non-existent), use a home-made nylon support bushing in the center position. I suspect that heat-related expansion/contraction of the engine castings causes more distortion in the long, spindly bearing holder than the center bearing can compensate.

Good to see you're working on the old  'Goose, Terry. Let us know when it makes it around the block on its own power and I'll hoist a drink for you!

MH...

Thanks for your info.  I had my jackshaft at a shop who disassembled it and he said there were no spacers in the front, that the pulley was up to the bearing.  He still has all the parts as I sending it out for clean up (media blasting).   Markings on the shaft seem to indicate no sign of a spacer.  That bearing sits next to a shoulder on the jackshaft itself.  It was only 14mm.  I need to talk to him again to make sure there was no spacer but he said there was not when I did talk to him before.  The middle and rear bearings were 12mm with thin spacers inside the clips that are on the outside of those bearing races.  I have been told to not put in the middle bearing and have decided to follow that.  Johnny Woods does replace them but note that said that they are "normally spun" and he has to repair the jackshaft.  Indicates a problem.  Steve Liebenow says definitely to not replace the center one siting problems.  I did place my shaft carrier on a flat counter and found that the center to bosses that are to meet the intake manifold are about a mm+ short of the length of the outer two.  Either the stock intake manifold has that slight step up or thin spacers are needed there.  Have you checked this?  Also, my shaft is bare metal, not painted black like I think earlier ones.  My car is #700.  I have considered thinning the rear spacers to accept a slightly wider bearing like 14 same as the front.  If I don't have a spacer on the front as I was told, I am reluctant to trim the shoulder on the shaft to accept a wider bearing.

Bosswrench...Re "whipping problems or just for appearance, I considered taking a bearing and making the inside diameter slightly larger such that it does not contact the center shaft bearing race but could put a damper on potential whipping if the tolerance was not too big.  Seems it would have to be out of balance to do any whipping.

Is there any choice between double or single row bearings in this application?  Is double better?

Terry     

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