Mac Crank Bearing removal and installation

[Lee Heinlein]

Hi all-
I'm rebuilding a few 91's and 101's and looking for some information on how to remove old crank bearings and re-install new ones. Any advice/help would be appreciated.

Happy Holidays-
Lee Heinlein

[Rob Voska]

Install with a piece of tubing just a little bigger than the crank that way you can tap or press if on the crank. Make sure bearing has a larger race than the crank so bearing sits in the correct location.

[Scott Kneisel]

You can use a small gear puller to get them off, they come off fairly easily.

Caution!! When installing the new bearing, make sure you support the crank in the press directly under the shaft between the two counterweights. If you don't you may bend or crack it. Those cranks are forged and heat treated and they are pretty tough but they are also expensive and not always easy to come by so you can't be too careful.

I install mine with a piece of tubing as the previous member explained and use a 1/2" steel plate across the legs of my press to slip the crank onto. You could also do the same thing with a vice and tap the end of the pipe with a hammer. It also helps to heat the bearing to 180 degrees or so in the oven or even with a heat gun if you are careful not to get too close. Leave the crank cold.

Have fun,
Scott

[Randy Forbes]

Harbor Freight has a pretty cheap (aren't they all) 12 ton free-standing hydraulic press that makes short work of pushing the bearings out/in. Lots of uses around the shop, once you have it (sure is better than beating on things with a hammer).

Likewise, I didn't find any bearings in this Mc9 (crank or block) that were much more than a tight push; they came out/off fairly easy.

Where's the best source to get new Mc9/Mc91 bearings? I need both the ball roller and caged needle types to put the Mc9 back together.

[Lee Heinlein]

Randy-
Crank bearings (ball roller type) can be found at Comet Kart Sales. See resource page on this site or use this link:
http://www.cometkartsales.com/store/mc/misc.htm

LH

[Jeff Campbell]

The 6203 ball bearings used on many of these motors are available from many sources. I like the ones that came on the later motors, the bearings with the plastic ball retainers, they are supposed to be a low friction inexpensive bearing. I believe McCulloch in later years, used the FAG 6203.TNH.C3 plastic retainer 6203 bearing. I have found this difficult to find online, and at a decent price. I have been able to find the SKF equivalent, 6203TN9/C3, online at very low prices, I think the last ones I bought were about $6-7 each. Many of the ones available from kart shops have the steel ball retainers, they should work, but would not be my first choice. Also, beware buying 6203 bearings from sources unknown, I bought some SKF bearings years ago, that turned out to be foreign made knock-offs which were absolute garabage with internal clearances and tolerances worse than any bearing I have ever taken out of an engine to replace. IMO, these motors are not easy and quick to rebuild, it takes many hours, I am only going to put high quality parts in when doing a rebuild job.

Does anyone know the specs, equivalent bearing mfg brand part numbers for the 91 series PTO needle bearing?

Also, I'm still trying to find a source for LOW cost high quality loose needle rollers for the Mac rod-crank bearing, anyone?

Jeff

[Scott Kneisel]

I buy all my bearings and seals from either Applied.com or MSC direct. They are industrial supply houses that sell to the public online. Applied has a search engine where you can put in the dimensions and they come up with choices. Real nice.

For the ball bearings, since the RPM in Mac engines can get really up there, ABEC3 or ABEC4 quality bearings should be used or at least have a rating of 22,000 RPM or so. There are a tone of ABEC1 bearings out there for low cost but they are only rated at 5000RPM.

As far as the PTO bearing for Mac standards that use a roller, I buy them from Zoe. She has OEM bearings. Vintagevixsin and I have had real good luck with her since she went out on her own.

Thats my story and I'm stickin' to it!!!

[Lee Heinlein]

Thanks you guys for your help - much appreciated.
LH