I don't know all the history as to why they came up with the name Super Series for
the line of motors but there are a few other differences that have not been
mentioned here and they are important aspects of the performance differences
between the motors. All of the "Super Series" engines use cranks that are shorter
on the flywheel side causing the flywheel to be closer to the centerline
of the engine. The coil mounting posts are shorter on the super series blocks
to allow the correct alignment with the flywheel and the ignition system uses a
completely different set of points. All of these differences are improvements
over the "standard" design motors. The flywheels on Mac engines are very heavy
for the size of the crank and there is definately some flexing that occurs in the
cranks so making the distance shorter from the center to the flywheel reduces
the amount of runout that occures at the flywheel. I bet most of you have
seen evidence at one time or another of the flywheel rubbing against the coil
but could not see how as the gap was set correctly. That will occur more often
on the "standard" motors than it will on the "super series" versions. The points
on a "standard" motor are designed with a "Z" shaped bend in the spring while
the "Super Series" motors use points with a spring that just has a long arc.
The "super series" versions are better as they can be set up with more point tension
than the "Z" type. Regards, Steve O'Hara ====================================================================== Flywheel and Shroud covers 10-2005 by Steve O'Hara There are two basic styles of side cover/shroud for Mac engines. For ease of discussion I will call them the "standard" which is used on the 7,8,9,49, 90. 91X, 92,93 models and the "super" style used on the 20, 30, 40, 45, 70, 75, 100 and all 101s. Starting with the 101A the flywheel covers changed in shape on the "super" style but it is interchangeable with any of the other "super" type covers. The flywheel side of the cranks and the coil post lengths are different for "standard" vs "super" configurations so you cannot easily convert one type to the other. ===================================================================== McCulloch Identification Information courtesy of Steve O'Hara Steve's background - 8 time IKF National Champion, Reed Heavy & Reed 125cc 1978 Enduro Nationals, Reed Light and Reed Heavy 1979 Enduro Nationals, Reed Light, Reed Heavy & 125cc Reed 1980 Enduro Nationals)Reed Light 1971 Sprint Nationals Please let me know if you find out more on the port arrangement for the 91A. Like you mentioned, relying on anything we find today can be misleading because we don't know if parts have been swapped around. With respect to the 91 vs 91A boost port layout I have not been able to confirm my memory in writing but here is what I remember.... the 100/90 series motors had single exhaust and "nine port" boosters on the opposite side. When the 91/101 models came out they both had two exhaust ports and the single square boost port opposite the exhaust. The next model change was the 91A/101A and I'm pretty certain that they made both engines with the 2 "acorn" shaped booster ports on the back side but they went back to the single exhaust port on the 101A. Why they abandoned the two exhaust port layout used on the 101 is a mystery to me but they never went back to it. I was always of the opinion that the two port layout was better but it did result in much less material remaining connecting the upper an lower parts of the cylinder. Perhaps they just found too much distortion in the 101 blocks and went back to the one port arrangement. n any event, starting with the 45/75 series of engines I can ID all of them just by looking at the blocks although I have some uncertainty when it comes to the 91A vs. the 91B.... I don't remember for certain when the thick top fin was introduced but I'm pretty sure it was the 91B1. If that is the case, the 91A and 91B blocks may be identical and the changes may have only been in the carb. Here is another tidbit that most people don't know about the motors.... the intake manifolds on the 91/101 series motors are different from all of the other models that came after them. The 91/101 manifolds are about a tenth of an inch shorter and they do not have the letter "H" cast in them. Our research showed a slight performance advantage from the shorter manifold but the reeds would not last an hour without fraying at the tip. Ran across your site tonight and wanted to compliment you for your efforts on identifying the characteristics of the old Mac engines. I share your interest in the species and I will offer up a couple bits of info to help your project. The first bit is to say that my Dad bought me a brand new Mac100 in the box in the spring or summer of 1968. The 101s were not out yet but they arrived very soon after we got the 100... and they were much faster:-( The 100 had the shallow version of the chrome flywheel cover and a chrome head shroud. The intake manifold was the "Reed" sloper with the Go-Power pyramid reed cage and the engine had the small "flat back" carb just like a Mac 45 or 90. The port layout featured a single exhaust port and three "nine-ports" on the back side. The 100 and 90 series blocks were the last ones built with the crankcase passage from the intake manifold area to the ports opposite the exhaust and they had the partition milled away so that the A/F mix from the Reed manifold could find it's way to the boost ports without the need for a "nine-port" type piston. I also noted that your chart shows the 91A as having the same boost port arrangement as the 91 with a single large "window" and a bolt on cover. I believe that the 91A was the first version with the two "acorn" shaped boost ports opposite the exhaust and the block had the thin top fin as earlier models did. I am in California and know Vince as well and I have come to suspect that there were different version of some Mac models sold in different parts of the country. For example, we never saw a yellow and black 101 out here on the west coast but I have seen one sold on ebay as a never touched NOS motor. Also, we had some all chrome 101Bs in the late 70s as I recall. =================================================================== Thanks for the help on this. Looking at the chart there are only two motors that used a 1.5" stroke. One is a Mac 6 and the other is the Mac10. The crank I have is short on the ignition side and uses the big ball bearing on the PTO side just like a Mac45 crank. The Mac 6 looks like it uses the same type of side plate and flywheel shroud as the 7, 8, 9,91... series engines so it doesn't appear that it would be a Mac6 crank. Can anyone here tell me if the Mac 10 cranks were dimensionally the same as the later "Super Series" models such as the 20,30, 40, 45? > The MAc10s had a different ignition point location so I'm wondering if the point cam was in the same location or if the timing of the point cam was different? > Thanks again for the help> Steve |
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