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| Toyota Engine Development, Modification & Performance Tuning | ||||||||||||||||||
| :: MA-61 / MS65 Front Hub Upgrade | ||||||||||||||||||
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:: Introduction - MA61 Hub Spec There's about 25 different good reasons you could give for wanting to upgrade the stock ma61 4 stud bolt pattern hub to a 5 x 114.3mm stud hub, but for simplicity here's five:
. image above:: a copy of the toyota manual's diagram of the front hub and brake assembly. it would be worthwhile becoming familiar with the set-up before continuing. the ma61 front assembly is a basic macpherson strut style suspension, with the front hub running on a single spindle mounted to the strut assembly. the hub is maintained by twin opposing taper roller bearings, which are pre-loaded by a lock nut and split pin on the most outboard end of the spindle. the brake disc is mounted on the rear face of the hub, and has its own retaining bolts on a separate bolt circle to the wheel studs. now obviously, the easiest way to upgrade the existing ma61 hubs is to find another hub that slides straight onto the ma61 spindle, bolts up without fouling, uses the same bearings, and is dimensionally identical to the stock ma61 hub - just with 5 wheel studs instead of 4. evidently, that's not so easy, and it wouldn't be doing justice to the effort it took to find such a hub if i give away the solution this early... so, what's so hard about finding a 5 stud hub? answer: the bearing sizes. the bearings used in the stock ma61 hub are as follows:
image above:: at top:: outboard bearing LM11949/910/Q. you can see that the outside bearing diameter (45,237mm) corresponds to the inside machined dia of the hub, and the inside bearing dia (19,050mm) corresponds to the ma6's outboard spindle dimension. at bottom:: inboard bearing LM67048/010/Q. you can see that the outside bearing dia (59,131mm) again corresponds to the inside machined dia of the hub, and the inside bearing dia (31,750mm) corresponds to the ma6's inboard spindle dimension. A complete dump of the Repco (Aust) database for all vehicles using the ma61 stock front wheel bearing part numbers as listed above was done to yield the following list:
:: Option #1 - Crown MS65 Hubs after double
checking these figures with the SKF bearing database http://www.skf.com
it
was confirmed that the only 5 x 114.3mm (5 x
4.5") stud hub variant in that
list was the crown ms65 series I and II, circa 1972.
Surprisingly, every model of crown before and since the ms65 ran larger bearings (to be discussed later) with the ms65 being the odd one out running the same # as the ma61 (possibly due the ms65 being manufactured in australia?). also surprising is the real lack of development toyota show in their hub design between 1970 and 1985. so now we're
on a mission to find the rather rare 1972 ms65 in the
wrecking yards. at this point of the adventure it was yet
to be determined if the ms65 hub was even similar to the
hub on the ma61 despite running the same bearings.
following a tip, an interstate phone call, and double
checking the dimensions of an ms85 model hub (having
learned that the ms85 looked the same as the ms65) the
search began in earnest to locate the elusive ms65.
Packing a pair of vernier callipers,
we eagerly scratched around in the dust of the wreckers
with the newly disassembled ms65 hub, and confirmed that
a) the general dimensions and proportions of the ms65 hub
was similar to the ma61, and b) that the bearings and most
importantly, the hub spindle of the ms65, was identical to
the ma61. this was the moment of truth, confirming that at
the present time, the only known 5 stud hub variant
directly compatible with the ma61 spindle was this, the
ms65 that we held in out hands.
Whilst the overall dimensions of the ms65 hub are basically similar to the ma61, note one important difference is the ms65's greater thickness of the hub flange, pushing the offset of the brake disc inboard some 10mm. more importantly though, the outboard face of the hub flange lies in the same location as the ma61 hub and thus wheel offset is not affected at all. also of
importance is that the depth of seating of both the
inboard and outboard bearings within the ms65 hub is
within 1mm of the spec of the ma61 bearing seats, meaning
that mounting surfaces of the ms65 bearings on the ma61
spindle will be correct (well, within 1mm anyway).
For the present project, these ms65 front hubs are going to be built up with large Wilwood 315mm x 32mm brake rotors mounted on custom aluminium hats attached to the rear mounting face of the hub flange. as such, we're not overly concerned with the increased negative offset that the ms65 hub flange boasts compared to the original ma61. if, however, you are planning to simply upgrade the ma61 hubs to the ms65 units without modification to the stock ma61 braking system, you will have to machine approximately ~10mm off the inboard face of the ms65 hub flange to correct the excessive offset, allowing you to then install stock toyota crown ms112 front brake rotors. with the correct hub machining, the ms112 rotors should bolt up to the ms65 hubs and allow the use of the stock ma61 brake callipers, without any fouling. :: Option #2 - Crown MS123 Hubs an
alternative to the rather rare ms65 hub lies in the use of the more
recent (1983-85), and far more common crown series 110 and 120.
specific models of interest are the crown ms112 and the
ms123: both of these models of hub are identical to each
other. for the purposes
of this article, we used the ms123 items, though all
information also applies to the ms112 units.
The main problem with the use of the ms123 hubs on the ma61 lies in the fact that the ms123 hubs do not use the same bearings as the ma61. the internal machined diameter of the ms123 hub into which the bearings are pressed is significantly larger (~1mm) on the ms123 compared to the ma61, and the inner diameter of the stock ms123 bearings are also significantly larger than the ma61 owing to the larger crown spindle on which they run (see image below). specifications of the ms123 bearings are given below.
image
above:: (note: compare the following dimensions with the
stock ma61 bearings above) at
top:: outboard
bearing LM12742/711/Q. from the dimensions you can see
that the outside bearing diameter (45,974mm)
corresponds to the inside machined dia of the
ms123 hub, and the inside bearing dia (21,986mm)
corresponds to the ms123's outboard spindle
dimension. at bottom::
inboard bearing L68149/111/Q. you can see that the
outside bearing dia (59,974mm) again corresponds
to the inside machined dia of the ms123 hub, and
the inside bearing dia (34,988mm) corresponds to
the ms123's inboard spindle dimension. It should be obvious from
the bearing specifications above, that the ms123 hub and bearing
combo will not
directly replace the ma61 hub. if you were to try and install
the ms123 hub with ms123 bearings onto the ma61 spindle, it would immediately obvious that the ms123 spindle
(from which the hubs were derived) was of considerably larger
(~3mm) dimension than the ma61 model, and the ms123 hub would simply
slop around on the ma61 spindle and never tighten. it soon
becomes obvious (if not intuitively) that what's ideally required in this situation is a totally new bearing that
satisfies the outer diameter requirements (eg 59,974mm) of the ms123
hub, and whose inner diameter corresponds to the spindle dimensions
of the ma61 (eg 31,750mm). unfortunately, despite eyeballing
1000's of bearings, no such bearing specification exists
(if you do find one, please contact me).
There are,
fortunately, two simple solutions to the problem of ms123 / ma61
bearing incompatibility. the first, and easiest IMHO, is to use the ms123 hubs,
with ms123 spec bearings installed, and to press machined sleeves over
the ma61 spindle (both inboard and outboard sections) such that
the dimensions of the sleeved ma61 spindle satisfy the ms123 inner
bearing race tolerance requirements (see http://www.skf.com
for details regarding sleeve dimension tolerances). this is an
easily machined option, adding little complexity to the
hub/spindle set-up. the second solution is to use the
ms123 hubs, but this time with ma61 spec bearings installed. it would be
necessary, however, to have a custom 'thicker' outer bearing race machined
to mate with the ma61 inner bearing + rollers such that the
assembly could be pressed securely into
the ms123 hub. this option is a little trickier as the machining
must be precise, and must be done with hardened materials. note::
some people have mentioned that it might be theoretically
possible to simply make a 'hybrid' bearing by using the inner
portion of the ma61 bearing within the outer portion of the
ms123 bearing. I have been advised by skf that this practice IS
NOT RECOMMENDED as the specific taper of the rollers within the bearings
is matched precisely (microns) to the races on which they run. mixing
rollers and races results in high loads on the bearing surfaces,
and ultimately early bearing failure.
One significant upside of the ms123 hubs is for those who do not wish to do a simultaneous large brake upgrade. as mentioned above, the ms123 hub flange is the same thickness as the hub flange on the ma61. this makes the rearward offset of the brake rotor mounting flange the same (not yet measured, so check) as the ma61, allowing you to directly install an ms112 crown stock front brake rotor without fouling the ma61 brake calliper. as we are doing a large brake upgrade, we haven't checked these dimensions exactly, so do check before going ahead, but we would anticipate everything lining up to within ~1mm. for those of you doing a large brake upgrade, as you'd know, such modification requires the custom manufacture of a rotor mounting hat (as is also the case with the ms65 hubs), and as such, things like flange offset dimensions are trivial. just design around it. :: Brake Options As we are later going to be fitting the m65 hub with a custom 32mm x 315mm brake rotor/calliper assembly, figuring how to retrofit the ms65 / ms123 hubs to work with the existing ma61 calliper has not been a big priority. the fitment of such large rotors requires custom machine work, and is designed specifically around the dimensions of whichever hub you use. for those wanting to upgrade hubs without worrying about the brakes, however, here a few obvious thoughts on fitment... firstly, now that the ms65 / ms123 hubs use a 5 bolt rotor retainer arrangement, you'll need to use a front rotor off a crown ms112 (DBA # 727 www.dba.com.au). these rotors have a total height of 26mm (identical to the ma61 26mm) and when installed on a hub with the same hub flange offset at the ma61, should install without fouling. this brings us to point two (as mentioned above somewhere): given the increased inboard spacing of ms65 hub flange compared to the ma61, this hub specifically requires a serious amount of material (~10mm) to be removed from the inboard hub flange face to move the disc mount outboard some 10mm. this should allow the ms112 rotor to mount directly without fouling the ma61 calliper. fortunately, the ms123 hub flange is very similar to the ma61, and thus does not require such exhaustive removal of material (if any). the ms112 rotor 'should' fit without any major problems. obviously, these modifications have not been pursued by us to completion, and therefore we cant guarantee the accuracy of the above measurements. we would be suprised, however, if things didnt line up to within ~1mm of expected. :: Wheel Options the 5 x 114.3mm (or 5 x
4.5") PCD of the crown series hubs is the same as that used
by ford motor cars ltd. unfortunately, the upgraded hubs do not
solve the problems of the ma61's offset woes, and the car will still suffer from the PITA +8mm offset
requirements which severely
limits wheel choice. on the upside, in australia, EL falcons and
earlier, as well as the XD-XF fairlane LTD's run a similar
offest (+6mm) so wheels designed for these models will work with
minimal increases in ma61 vehicle track. check out www.speedywheels.com.au
for a sample.
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