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Discussion Starter · #1 ·
In my TNT, the original engine tag states it is Type 641 vs. my Nordics both have Type 640. As you can see, all the numbers regarding bore and stroke are the same.

I'm needing a crankshaft for the TNT, and wondering if the difference is referring to heads, compression ratio, dual carbs, timing etc, that gives the TNT 641 more power. Does anyone know if the crankshafts are the same? Yet to tear-down the Nordic engine.
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Hi there, yes the cranks are different as the 641 has an extra PTO bearing making the case a little different. That being said you dont have to use the same bottom end - you could go with an entire bottom end from an older 640 with the single bearing like a 70 640 engine, or the newer ones too. Other things that are different are the cylinder transfer ports are much larger in your tnt engine, the pistons use the L top ring, and pretty sure the heads are a little different as well. The 72 also has the dual carbs.
 

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Discussion Starter · #3 ·
Thanks for the post. My thoughts after reading your post: I really don't want to use my 640 bottom end unless absolutely necessary. I may use the entire 640 engine until I'm able to (gotta be a 641 crank out there) rebuild my 641. I'm trying to track down pistons and that is even a chore.
 

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What's wrong with your 641 crank? If its just bearings they can be replaced easy enough (I replaced the two outer bearings on mine). Try Goose for parts if you haven't already.
 

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Discussion Starter · #5 ·
When I split the case, it was packed with sediment and rust. One of the connecting rod bearings is froze in place. The crank bearing on mag side is so rusted and damaged it came apart in pieces. I can locate main bearings, but not connecting rod bearings. I'm wondering if 640 and 641 engine ran the same bearings? If the crankshaft can be saved I need to get to shop so the crank can be disassembled.

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