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| Posted: Sun Jun 10th, 2012 06:20 pm |
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1st Post |
Brian Santee
Member
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I am wanting to learn how to port the Mcculloch engines. I may just be insane with this wish, but I have a Mac 15 chainsaw block I can practice on and a Dremel tool. I was wondering if there are any tips of porting I should know, such as how much material to remove and the like.
Brian Santee
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| Posted: Mon Jun 11th, 2012 02:43 am |
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2nd Post |
David Luciani
Administrator
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brian,
bring the block to Avon and i'll show you what to do after race time.
when i get a minute i'll get a list of tips you'll need.
also ted johnson has a favorite file you should buy to do the exhaust ports.
if you're missing ports bug terry bently he made a nice jig to add ports to mccullochs.
dave
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| Posted: Mon Jun 11th, 2012 11:59 am |
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3rd Post |
| Posted: Mon Jun 11th, 2012 12:27 pm |
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4th Post |
Ted Johnson
Member
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Hey, Brian. The exhaust port file Dave is talking about is a 60 grit carbide flat hand file, 1/8" X 1/4" It's McMaster Carr part No. 81725A11 and is perfect for roughing in exhausts on all engines, and intakes on Clintons and 580/700 West Bends. You have to smooth them out with a regular file after roughing, and I sand them with 180 grit emery cloth strip ripped into smaller strips and glued to popsicle sticks. Get the popsicle sticks at craft stores. MacMaster has other sizes of this file, but I found the 1/8 X 1/4 is really manuverable. http://www.mcmaster.com Take it slow! Use a 3/16" Dia. chain saw file for your corner radii. Chain saw files cut the iron cylinder liner well and are not tapered. Of course, the mill is much faster, but not all of us have a mill, and the 3/16" Dia. cutter you need to use to give a 3/32" radius in the port corners is somewhat flexible, so care is needed in its use. You can use an end mill with a larger diameter shank on some applications, but the larger shank often prevents you getting close enough to the exhaust flange opening to do the top and bottom of the ports. ALWAYS leave a radius in the corners of square ports to avoid stress cracks. Be neat and take your time. Ted Last edited on Mon Jun 11th, 2012 12:28 pm by Ted Johnson
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| Posted: Mon Jun 11th, 2012 07:51 pm |
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5th Post |
Brian Santee
Member
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Thanks for the information. I am going to practice on a Mac 15 block first in hopes of eventualy doing my 300 saw block, it is the same bore and stroke as a MC 49 exept it has 2 ball bearings instead of a needle and ball bearing.
Brian
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| Posted: Mon Jun 11th, 2012 10:53 pm |
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6th Post |
Kevin Brown
Member
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I understand that "porting" done correctly will improve performance. But is there a downside even when done correctly? Or put another way . Why didn't the original manufacturers/ designer/engineer build the engines with the changes?
Thanks. I appreciate the knowledge gained from this site and it's members.
Kevin
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| Posted: Tue Jun 12th, 2012 12:31 am |
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7th Post |
Sonny Gerber
Member
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Kevin, Take it from a guy who has experimented with porting Macs since 1968, there is no free lunch. When you cut on the exhaust and raise it you move the power band higher up the rpm range, with an accompaning loss of lower range torque. Probably, Mac engineers wanted an engine with more torque than high rpms. This was just what chainsaw owners wanted, more grunt or torque at lower rpms.
I would advise you to not touch the intake ports, several famous engine builders have advised this and it's good advice. Macs have far more intake ports than are needed. If you are going to run a dry clutch, raising the exhaust will move the power range above where a dry clutch will engage. Raising the exhaust works best when using an oil clutch, more slip will be needed for the higher engagement necessitated to engage at peak torque. Also raising the exhaust, normally means that you would want to increase the overall exhaust length. When you raise the exhaust, the higher rpms mean the stress on the rod is greater. I have multiple broken blocks to prove this. There is no free lunch, but the experimenting is fun.....Sonny
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| Posted: Tue Jun 12th, 2012 12:31 am |
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8th Post |
Sonny Gerber
Member
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Kevin, Take it from a guy who has experimented with porting Macs since 1968, there is no free lunch. When you cut on the exhaust and raise it you move the power band higher up the rpm range, with an accompaning loss of lower range torque. Probably, Mac engineers wanted an engine with more torque than high rpms. This was just what chainsaw owners wanted, more grunt or torque at lower rpms.
I would advise you to not touch the intake ports, several famous engine builders have advised this and it's good advice. Macs have far more intake ports than are needed. If you are going to run a dry clutch, raising the exhaust will move the power range above where a dry clutch will engage. Raising the exhaust works best when using an oil clutch, more slip will be needed for the higher engagement necessitated to engage at peak torque. Also raising the exhaust, normally means that you would want to increase the overall exhaust length. When you raise the exhaust, the higher rpms mean the stress on the rod is greater. I have multiple broken blocks to prove this. There is no free lunch, but the experimenting is fun.....Sonny
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| Posted: Tue Jun 12th, 2012 01:17 am |
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9th Post |
Ted Johnson
Member
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Brian, I've been building Macs since 1960, and a properly intake ported Mac will eat a stock-port Mac for lunch. The issue is learning to do it correctly, learning correct port timing and not being too radical. I guarantee the West Bend 610's I've had Siamese ported by Dave Bonbright are SO much faster than stock that it's hard to believe they started out as the same engine. I have a Siamese ported 101 that runs very well indeed, also. By the same token, an intake port job that is poorly done will kill the performance quickly. It's a good idea to find some early (1960/1961) Karting World magazines and study Jim Butler's methods. They are simple, easily done and work well. My Pop was helped along by Gil Horstman in 1961, and our engines were Central Florida's quickest in the early sixties. Pop knew Horstman from their racing against each other in model airplane control line speed. The hardest thing on a Mac is matching the back ports to the fronts. We learned to do the back ports first, then match the front ports to them so as not to go overboard on the ports you can more easily see. Start out by squaring exhausts and rounding the sharp edges of the drilled intakes, but not enlarging or raising them. You can experiment with port timing after you get the basics of improving the flow of drilled holes. TJ
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| Posted: Tue Jun 12th, 2012 04:43 am |
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10th Post |
Terry Bentley
Member
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If the Mc 15 is missing any intakes or does not have all three exhaust ports, you may consider following this link for some ideas and closeups. HERE and HERE
Last edited on Tue Jun 12th, 2012 04:46 am by Terry Bentley
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| Posted: Thu Jun 14th, 2012 08:38 am |
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11th Post |
| Posted: Thu Jun 14th, 2012 12:33 pm |
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12th Post |
Ted Johnson
Member
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Kevin, please get rid of this (above) jerk! Another schmuck trying to sell something. TJ
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| Posted: Sat Jun 16th, 2012 02:33 pm |
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13th Post |
Al Nunley
Member
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I built some fast Mc91’s back in the 70’s.
I had the exhaust at 85ATDC with 25 degrees blow down. Open the top of the exhaust way up, square off the transfers and add counter balance to the crank. And of course twin carbs.
My clutch was set at 9200 and the peak RPM was right at 14000.
I won division 7 north, (Northern Calif.) that year. Fast time at every race and won every heat I finished. Also won the Winter Nationals.
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| Posted: Tue Jun 19th, 2012 04:46 am |
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14th Post |
| Posted: Tue Jun 19th, 2012 02:16 pm |
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15th Post |
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