Wanted - +0.040 or 0.050 piston for Mc5/20/49
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Bob Towarnicki
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- Joined: Sat Jun 16, 2007 5:45 pm
- Vintage Karting items owned: 65 Alley Kat Mc91
Narrow Hoop A Bone Mc91B
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Wanted - +0.040 or 0.050 piston for Mc5/20/49
Help. I need a large oversize piston to salvage a Mc5. The engine is in great condition and will restore nicely but it appears to have been run hard. Currently it has a +0.030 thin ring piston and is out of round. Looking for a Mac 53726 or 53727 piston and rings 48978 or 48934. Can anyone help? Cash or trade other items. Thanks, Bob
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Scott Kneisel
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- Vintage Karting items owned: '63 Rupp Grand Prix, 66 Rupp Chappy, Mc6's, Mc8, Mc10's, Mc20's
Lotsa' other Macs - User Agreement: Yes
- Location: Farmington, NY
Re: Wanted - +0.040 or 0.050 piston for Mc5/20/49
Bob,
Other than an original oversize pistons from the early 60's, the only piston I know of that has the correct wrist pin offset for the mc5 and Mc49 and is 2.160" (0.040 over for the 49) is the Mac #61428 which is the standard size piston for the Mac450 saw. The next oversize for that saw is #61426 which is 2.180" which is 0.060 over for a 49.
These pistons have wide rings but I have used them before and I narrowed the rings down to 0.030" by grinding the lower half. They worked well. If you bore the 49 for the 60 over piston the wall gets pretty thin and wouldn't be recommended, I don't know about the 5 or 6 blocks, they may have a thicker liner than the Mc49.
Unfortunately these pistons are really hard to find but they do come up once and awhile.
Just and FYI, the true Mc20 piston is the same diameter as an Mc5, 6 or 49 but has the same wrist pin offset as the Mc7-91 and won't work on the older "3 fin" blocks.
Good luck looking,
Scott
Other than an original oversize pistons from the early 60's, the only piston I know of that has the correct wrist pin offset for the mc5 and Mc49 and is 2.160" (0.040 over for the 49) is the Mac #61428 which is the standard size piston for the Mac450 saw. The next oversize for that saw is #61426 which is 2.180" which is 0.060 over for a 49.
These pistons have wide rings but I have used them before and I narrowed the rings down to 0.030" by grinding the lower half. They worked well. If you bore the 49 for the 60 over piston the wall gets pretty thin and wouldn't be recommended, I don't know about the 5 or 6 blocks, they may have a thicker liner than the Mc49.
Unfortunately these pistons are really hard to find but they do come up once and awhile.
Just and FYI, the true Mc20 piston is the same diameter as an Mc5, 6 or 49 but has the same wrist pin offset as the Mc7-91 and won't work on the older "3 fin" blocks.
Good luck looking,
Scott
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Bob Towarnicki
- Posts: 122
- Joined: Sat Jun 16, 2007 5:45 pm
- Vintage Karting items owned: 65 Alley Kat Mc91
Narrow Hoop A Bone Mc91B
Various restoration projects - User Agreement: Yes
Re: Wanted - +0.040 or 0.050 piston for Mc5/20/49
Scott, Thanks for the heads up. I didn't realize the mc 20 had a different wrist pin offset from the 5. I'll need to find the 61428. Bob
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Bob Towarnicki
- Posts: 122
- Joined: Sat Jun 16, 2007 5:45 pm
- Vintage Karting items owned: 65 Alley Kat Mc91
Narrow Hoop A Bone Mc91B
Various restoration projects - User Agreement: Yes
Re: Wanted - +0.040 or 0.050 piston for Mc5/20/49
Got what I needed. Thanks