91MC motor identification

[Carl Haydt]

Hi,After reading the story on the 91MC/101MC i became interested in finding out any info on a 91MC that was bought new years ago by my father during his karting years. Enclosed is a pic showing a 91MC with the compression release & 3/4" shaft still installed but this motor came with a chrome (not polished alum) inner shield & a unpainted outer shield. I can assure you he did not have the shroud chromed so does anyone know who might have built this motor & the story behind it? THANKS! Carl

[steveohara]

Carl,

Looks like a motor built from parts, some used and some new. I never saw any M/C motors come with the actual compression release installed. On the west coast the M/C motors had a special plug installed in the CR hole to block it off.
The motor in the pix was definately not delivered as NOS from Horstman or McCulloch with no paint on the shroud and a polished or chromed side cover. It also looks to me like the top plate on the carb is the wrong part for that model carb and the finish on the intake manifold may not be OEM either.
Still looks like a solid motor though... all just cosmetic stuff.
Steve O'Hara

[John Tzortzoudakis]

Steve,
Good example of why trying to ID a motor by it's fan shroud color or chrome is never the Absoulute way to identify a motor.
The McCulloch Engine website is divided in Primary and Secondary features. The Primary features is what you focused on. The secondary features are just like you said; Cosmetic.
http://www.mccullochkartengine.com/McCulloch_91.htm

There is also information on MC motors where Horstman purchased all of them from McCulloch and repackaged them with the Compression Release plug and new tapered crankshaft.
What IKF News said about the M/C engines:
http://www.mccullochkartengine.com/images/MACMC0002.pdf
Horstman Ad showing how the engines were packaged:
http://www.mccullochkartengine.com/images/Mc_MC0001.pdf

I never hesitated buying M/C's when others passed them up since they were not a "normal" mac. I never got used to the Red and White colors my self so I always switched them the the black and yellow.
Here's one of mine still racing in 81'
http://www.mccullochkartengine.com/imag ... tokart.jpg

Here's how to make a compression release plug like Horstman installed on the motor:
http://www.mccullochkartengine.com/Mccu ... ration.htm

[Carl Haydt]

Hi Steve,Thanks for the reply,the motor was untouched by me and remains the way I remember it from the 70's after my dad had "lost intrest" in this motor and was on to some other model Mac. It's possible that it was assembled from various parts by someone who had his own ideas and I was hoping the chrome inner shroud would be a clue to who that was. I have never seen another chrome inner shroud on a "std" series & was hoping someone else had one or knew if there was a story behind it.
Thanks again for sharing your thoughts & knowlege! Carl

[steveohara]

Carl,

I've never seen another chrome side cover like that. I would bet that someone may have had that motor fitted with one of the polished GEM flywheel covers at one time... it would have looked very nice with the both pieces polished or chrome.
I'm kind of surprised that the side cover could be chromed at all.... a lot of the alloys used in the Mac engines have too much magnesium to allow for chrome even with copper undercoating.
Looks like a good motor for vintage karting.... with the actual compression release it could be fitted with a recoil and you could start it without breaking your hand!
Steve O'Hara