stuck a 101...need some help...

[Jeff Campbell]

Can't tell for sure from the photos but it looks promising that the block is repairable, you lucked out. Usually the bottom of the cylinder takes more of a beating from the rod hitting it, with huge chunks taken out on the manifold side and on the opposite side those thin ribs in the transfer port area usually get crushed when the cylinder gets distorted by the rod. Weld up or epoxy the hole and manifold mounting area, cut away the cracked bottom portion on the cylinder and then bore it .. it might be very good then. The crank, stuffer, rod, piston, manifold, reeds are probably all junk.

For those reading this thread, it is real important to limit the RPM's on a 101 and/or set a proper squish (piston to head clearance). Generally, a 101 should be run about 1000rpm lower than a 91, and the 101 squish is too big from the factory. Just before the 101 was introduced, McCulloch had an issue with motors sticking, so they band-aided the problem by sticking in a thicker head gasket, which was carried through the stock class specs for the 101 for all years to follow. The thicker gasket reduces engine temp, but places additional tensile stress on the rod at TDC. Such are band-aide fixes, solve one problem, and create another. The real fix would have been to increase piston-cylinder clearance, add more piston taper and not increase the squish (reduce it if anything). If set up right, a 101 will run and run ... the 101's on my dual Chaparral are on their 5th season without rebuilding... but I do have a box of grenaded 101 blocks, cranks, etc... that was my learning experience! Others may want to search up some of Steve Ohara's previous posts, he figured out these issues many years ago and provided me much help in this area.

Jeff

[Chris Hanly]

well...funny you mention the head clearance issue and the updated head gasket....I had just put a new head gasket on that horrible day...and I noticed that the head gasket made the head sit a small bit taller....my dad and I looked at each other and figured we would compression test and vac. test it...it all checked out o.k...looked at where it seated on the head and block and it all looked good...wonder if that aided in the grenading...also i recently learned (please please don't flame me too bad) that you MUST have the head cover on to cool the engine...I am learning...just too bad i had to blow my only engine to learn...

with the help of some kind EXPERIENCED guys who have my baby now and after they kick butt in Barnsville are going to get me fixed up with a 91 and I will be back...I still need much parkinglot practice before I will get the nerves to get out there with you fellas...I hope to get her back in time to practice at circleville a few times too...and then maybe, just maybe keep up with the vets

I appriciate all those who took time to give a noob advice and help steer my decision...and a big thank you to gary and his bud for getting me set to run...
-Chris

[Larry Collins]

Greetings!

101's are great engines, and even in stock form are pretty potent. If you compare stock '91 rods with stock MC101a or b rods, notice that the only difference is the '101 rods are longer, but not beefier. If you keep the rpm down to no more than 12,000, your '101 will last a long time, but frequent checking the rod for stretch is still very advisable. The failure in your engine is classic; right below the wrist pin eye is where they typically snap off. I have seen this kind of rod failure more often than any other kind with Macs, and is usually due to running RPM higher than 12k.

By now you probably have already repaired or sold off the blown engine, but I have had a number of similarly blown engines successfully repaired. Like an earlier rely advised, you can get the block welded by a guy who is really good with heliarc. Don't forget to pressure test the newly rebuilt engine; any porosity in the repair can be taken care of with epoxy such as Devcon or Marinetex. With judicious grinding and filing, the repaired areas are inconspicuous, especially when the engine is back on the kart.

Save your damaged crankshaft, but for now you will probably need to find a replacement. There are machineshops (rare) which could weld up your crank, then machine the journal back to the correct diameter.

Good Luck with your Mac; don't give it up!

Larry

[Pruit Ginsberg]

Hi Larry,
With respect to the MC 101 rod length, what is the correct factory length of the rod? How much stretch is indicative of impending failure?
Thanks
PRuit

[Larry Collins]

The factory rod length for 101's and 91's can be found in the technical section of this website, and there is a range. The amount of stretch tolerable prior to failure would vary; when building an engine it is a good idea to measure the rod you are using for initial length; that way you have a basis for comparison when checking for stretch later.

Folks like Steve O'Hara probably have a more authoritative opinion based on greater experience, but I would be hesitant to use a used rod that was more than .001" longer than it was initially. Don't let your 101 see over 12,000 rpm and it will last a long time!

Best regards,

Larry Collins

[Pruit Ginsberg]

Thank you Larry for the rod length info. What amount of squish is desirable?
Pruit

[Larry Collins]

Pruitt,

Regarding squish clearance, I personally have had good results running the squish at .015 to .020" in both 101's and 91's. I run mostly alcohol, and Hartman Blimp pipes or similar. Make sure the screw-shell of your spark plug doesn't protrude into the combustion chamber. Whether you run alcohol or gas, be sure to avoid running lean!

Sorry it took so long for this reply.

Best,

larry

[Pruit Ginsberg]

The delay is not a problem. I appreciate the info.
PRuit