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Anyone have a +.005 Mc 6 thin ring piston to sell? I could also use a +.010 if no one has a 5 over.
Steve O'Hara

Steve-

Are there any other Mac pistons that cross over? I know you like original stuff.

Turns out the bore in the block I was building was a mess so now I need a +.030 piston.
I have a couple NOS Mc 49 pistons that are the correct size and have the right pin to crown dimension but the space for the rod is .450" for the later style rods.
The Mc6 rod is skinny at the top and here is where I'm a bit confused and hoping for some reminders from folks here on the forum so I don't have to tear apart my original Mc 6 to remember what I'm looking for.

What I can't recall is whether the orignal Mc 6 piston is a thin ring or thick ring version and also did it use thrust washers on either side of the rod or just have the bearings closer together???
Anyone have any photos of the correct rod, piston and thrust washers if applicable?
Thanks in advance for any help offered.
Steve O'Hara

Steve-O, replace the Mc6 rod with a 91 rod. Toss the thrust washers. We carefully grind the eye on the 91 rod until there's about .020 clearance between the bosses. It doesn't seem to adversely affect the balance, and makes for a far more reliable setup. All Ron C's early engines are set up that way, and I recently did two Mc7's. They all run great, and we're much more confident in their longevity. Ted

Like Ted said, get rid of the 6 rod and thrust washers. All of the original 5&6 pistons used the thrust washers and a 91 rod is much better, which should work fine with your 49 piston.

The original 6 piston I believe is a thin-ring piston, #48844.

The stock "6" piston IS thin ringed, which is why, even with the little HL-93 carb, it would easily outrun a stock Mc10. If anyone's running a stock stroke Mc10, they should replace the rod with that from a '91. TJ

Guys,

Thanks for the tips but I am building the motor to be a completely correct collector specimin and want to retain the original parts if I can find them.
If I'm not mistaken, a piston from a Mc 7 or 30 will be taller from pin to crown, otherwise it would be the same as far as the bearing spacing and use of thrust washers. If I'm wrong please let me know.
Anyone have a 30 over Mc 6 piston??

Happy Holidays!
Steve

Steve, Scott Kneisel has a lot of the early Mac goodies. If you don't have his contact info, PM me. Scott's a prince of a guy to deal with. Ted Johnson

Steve,
The original Mc6 piston had thin rings and the original rod is the same thickness at the pin as the 91 rod. The thin top rods came in with Mc7-Mc40.

I have a very nice original rod if you want it but a 0.030" over piston that uses spacers will be almost impossible to find. The Mc49 piston is perfect and will fit the original rod.If you want to use spacers, just push out the bearings and mill additional clearance in the bosses to allow for the spacers. I think you can find needle bearings that are slightly narrower and I may even have them but have to check.

The original Mc6 piston had shallow square recesses on the outside of the pin bosses so the wider bearings fit.

Send me an email if you want the rod...no charge to you, just let me know.

A couple pics of an original standard size Mc6 piston on an Mc9 rod.
Going into one of the Mc6's I am doing for Dick Teal's latest surprise next season!!