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Whats the diff between a medalion crank and a td crank?

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Old 04-21-2013, 03:07 PM
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TampaRC
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Default Whats the diff between a medalion crank and a td crank?

Are they interchangeable at all?
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Old 04-21-2013, 03:49 PM
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Default RE: Whats the diff between a medalion crank and a td crank?

Yes-the external physical dimensions are the same-the porting arrangement is different. The TD has a large rectangular valve port, the Medallion a circular one of significantly smaller area. You can interchange them, but there will be some effect on performance either plus or negative, depending on which way you go. The difference in performance between a TD and a Medallion is not just the crankshaft-the two engines use different cylinders, different heads and different carb setups-and all of these differences have some effect on performance.

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Old 04-22-2013, 09:55 AM
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Default RE: Whats the diff between a medalion crank and a td crank?

Yes & no actually, depending on the year of manufacture if memory serves.

I used Medallion cranks in my "big prop" TD's some years back. I'd have to drag one down off the wall & strip it down to report the exact difference but I think it was in the prop driver to crankcase nose clearance area.

Some cranks drop right in to a TD, others require a matching Medallion crankcase. It may have been some of the old stuff I was working with at the time though. My being a lifetime Cox engine piddler gives me some fairly ancient parts to play around with.
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Old 04-22-2013, 11:38 AM
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Default RE: Whats the diff between a medalion crank and a td crank?

I must have been lucky then-I've never had any issues-and I've done it with 049, 09 and 15 Medallions-normally replacing a Medallion crank with a TD one as part of a 'rebuild' which essentially made TD's from Medallions by replacing the appropriate parts. [For a period-late 70's-mid 80s TDs were hard to find in NZ-but there were 'parts set' Medallions -essentially the whole bottom end of the engine available from time to time-so by adding a TD cylinder and head you got something with more power than a Medallion-but less than a TD. Then as I randomly acquired other bits, shafts etc, the bottom end got upgraded to TD specs]
....probably about a third of my existing TD 049/09/15 fleet were produced in this fashion.....

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