[Healeys] Gaskets and clearances

Bob Spidell bspidell at comcast.net
Wed Nov 22 14:59:23 MST 2017


You may remember the saga of my BJ8 jumping out of 4th gear after an 
engine rebuild.  While sorting out the issues in the gearbox and OD I've 
been pondering why the car would start doing this after an engine 
rebuild when it hadn't done it for over 100K miles before.  Thanks to 
people on the List and the Forum, I've noted some possible culprits:

1) weak detent springs on the shifting forks

2) weak or worn springs or balls in the shifting hubs

3) excessive end play

4) other/all of the above

I don't think it's the shifting forks' job to hold a gear, but it's been 
noted that especially stiff shift lever boots could command an unwanted 
shift, but I don't think that' the issue as my shifting forks, springs, 
etc. are in fairly good shape, and I could feel the shifter fight to 
release from gear when I held it.  #2 is very likely a contributor (I'm 
replacing mine as the small gears that mesh with the synchro are worn).  
#3 is certainly a possible cause, as Dave P and others have pointed out, 
but I think it's a combination of things, and one that just dawned on 
me.  A poster--I believe it was Steve Gerow--has been alerting owners to 
a problem caused by too thick paper gaskets on the rear axle hubs.  
There's a spacer in there, whose job it is to clamp the outer race on 
the bearing to keep it from turning, but the new gaskets are too thick 
and prevent the axle disk from clamping down on the spacer sufficiently 
to apply the necessary pressure to the spacer, and spun bearings can 
ensue (I heard of a shop doing a pretty steady business fixing rear axle 
hubs with spun bearings).

Similarly, there are thin shims at both the front and rear of the 
gearbox that are there to apply pressure to the gearbox front and rear 
bearings.  Magnus K notes in his (excellent) video that these are 
critical to minimize end float in the input and main shafts, which can 
cause the jumping out of gear.   When I split the adapter from my OD I 
noted that the original--AFAIK--gasket was very thin; paper thin to be 
exact (unfortunately, I split the bellhousing and gearbox and didn't 
save the gasket, which was installed at the last rebuild about 130K 
miles ago).  The new gaskets that Moss, and probably others, provide are 
much thicker than this.  The front shims for the gearbox are either 
0.002" or 0.004", and the rear are 'A/R' and none are available (at 
least from Moss).   A random gasket I pulled from the set--which, I 
believe, are also for some MG and/or TR cars--measured 0.019", a lot 
more than the width of available spacers.

Obviously, I can't prove any one cause conclusively, but if the shims 
are for a setup with, say, a 0.002" gasket, then a 0.019" gasket is 
going to eliminate the pressure that should be applied to the bearing 
outer races.  This also fits with the behavior of the box, which had 
jumped out of gear a few times after a previous engine rebuild, but had 
settled in and not jumped for over 100K miles.  And now, the problem is, 
where do I get an 'original style' gasket, which is probably only a thou 
or two thick?  It is not practical to 'roll your own' as these are 
complex gaskets and there are many openings that need to line up.  Note 
these are smooth, machined, non-porous surfaces which should not require 
a thick gasket to fill imperfections like, say, a thermostat housing 
(yet the gaskets appear to be made out of the same thick material).  I 
could use a silicone or other sealant, but I am more comfortable with a 
gasket with a bit of sealant spread on it ('belt and suspenders' as it 

Anyone else seen this problem?  Oh, and I've got 2 gaskets sets minus 
the front and top gaskets for a centre shift gearbox available to a good 
home for postage.


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