Another question....
I just picked up an Mc91A block and piston that really looked great until I cleaned up the bore and measured it. It is egged and has some nasty pits (rust I think) near the top of the cylinder. I think it will take 0.020" to clean it up, problem is that it is already .060 oversize with a bore of 2.225". It already has what appears to be a .010 over Mc70 piston, if I can find a 0.030 over Mc70 piston, can it be bored that big? There appears to be a lot of sleeve left and I was surprised about that because I also have an Mc45 that is 0.070 oversize and the sleeve is thin as tissue on that one.
Any suggestions would be appreciated.
Scott
Mc91A Maximum Bore Size
Moderator: Rob Voska
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Scott Kneisel
- Posts: 477
- Joined: Mon Mar 24, 2008 7:48 pm
- 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
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Dean Seavers
- Posts: 222
- Joined: Fri Jun 22, 2007 3:51 am
- Vintage Karting items owned: '66 Chap, '61 Bug Stinger, '61 McCulloch R-1, '60 Go Kart 800, '60 Bug Wasp, '60 Weirdo
Re: Mc91A Maximum Bore Size
I always thought the Weisco block saver pistons were .070 -over, which still puts you .010 shy. I have no idea if the 91 block will take .080 with any long term success.
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Butch Kavanagh
- Posts: 66
- Joined: Tue Apr 08, 2008 1:11 pm
- Location: pt charlotte fl
Re: Mc91A Maximum Bore Size
happy thanksgiving, our 4.95lb beer can chicken has been cleaned and ready. overbore--akron(oh) karting club in the late 60's-70's was fortunate to operate navarre kart speedway. we ran the time trial system hence bring what you got. track was a short road course and one time a guy brought a twin to race, 1silver and 1yellow engine. he thought the silver engine would improve his low end. anyway we lived in wiseco land. if we lost a wrist pin bearing and put groves up the wall, to wisco we went. keep in mind the mc70 was not that popular. from stock spec 2.165, wiseco would bore .085 to mc75-100 spec 2.250, still had 'some' lining left. pistons were plentiful. now ports has to be somewhat stock as wiseco used a 101 big hole rod, decked the block .060( needed for piston at tdc to be flush ) tom kipp of wiseco(always very helpful) if you wanted to modify ports, go sideways, same timing 25-26 but suggested .020 head gasket alky. .032 for gas. i ran mine stock gas and oil and it ran fine. saved alot of blocks but alas back then, mac parts were eveywhere. we forgot some of the parts we had. the piston could be a '9-port' or stock. we got to race. in today's vintage racing, if you can find the parts at a fair price, you have a ride. so good luck. butch