I acquired this engine from a friend after he told me he was going to chuck it in the trash! After tearing it down, everything looks to be in good shape. Crank assy. looks good. No discoloration on the rod. Bore is 2.165, the piston is 2.158. Cylinder just needs a light hone. When I put one of the rings into the bore, about 1/4" to 1/2" from the top, the end gap measured at .104. I know this can't be right. Could these rings wear that much or could they be incorrect rings? I am planning on ordering a set of standard rings. Also, I failed to make note of which way the piston came out. Which direction does the open side of the piston point? One other thing has me stumped. I haven't been able to find any identification for the carb. No letters or numbers.It has a squarish plate with a fuel inlet on it. Any chance of torque specs when I go to put it back together? Thanks for your time.
Jim
Mc91 m/c help
Moderator: Rob Voska
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Jim Veenstra
- Posts: 3
- Joined: Wed Jan 09, 2008 2:41 am
- Vintage Karting items owned: 1973 Mc91 m/c engine
Re: Mc91 m/c help
Small Engines Service Manual Item number: 330202307699 on ebay. There are others so look around. I have a 10th edition and it's great and will answer most all of your questions.
Yes Mac rings CAN wear that much. Get a good straight bore not just a light hone so you know what you are starting with.
Yes Mac rings CAN wear that much. Get a good straight bore not just a light hone so you know what you are starting with.
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Jeff Campbell
- Site Admin
- Posts: 580
- Joined: Tue Jun 12, 2007 7:52 pm
- Vintage Karting items owned: 1961 Fox Go-Boy MC20's
Robron Chaparral dual MC101
Margay Cheetah MKIII - Location: West Bloomfield, MI
- Contact:
Re: Mc91 m/c help
this should be helpful.... from page 23 of owners manual >> spec for end gap is 0.051" to 0.091" (remember these are pinned rings, the pin takes up a large portion of that ring gap). I usually size my end gap to the lower end of that range to allow room for wear.
Download McCulloch Owners Manual 91-101 series motors - large file 8.0MB
Thanks go to Jim Waltz for scanning this and making it available.
Jeff
Download McCulloch Owners Manual 91-101 series motors - large file 8.0MB
Thanks go to Jim Waltz for scanning this and making it available.
Jeff
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Jim Veenstra
- Posts: 3
- Joined: Wed Jan 09, 2008 2:41 am
- Vintage Karting items owned: 1973 Mc91 m/c engine
Re: Mc91 m/c help
Hey Jeff. Thanks for that link! It has all the info I'm looking for.
The engine also has a Horstman clutch and a GEM "QT" pipe. I haven't been able to find any pics of this clutch, even from the Horstman website. The body is black with ribs, 3 I believe, running around it. The end cap is aluminun with ribs radiating from the center out with a small breather hole in the center. It has two shoes that mount with three bolts each shoe. It looks to be an oil clutch as it is pretty wet inside. Also, there are no return springs on the shoes. Are there suppose to be some? If so, where are they available? Thanks.
Jim
The engine also has a Horstman clutch and a GEM "QT" pipe. I haven't been able to find any pics of this clutch, even from the Horstman website. The body is black with ribs, 3 I believe, running around it. The end cap is aluminun with ribs radiating from the center out with a small breather hole in the center. It has two shoes that mount with three bolts each shoe. It looks to be an oil clutch as it is pretty wet inside. Also, there are no return springs on the shoes. Are there suppose to be some? If so, where are they available? Thanks.
Jim
Re: Mc91 m/c help
No springs in that one, just oil.