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914World.com _ 914World Garage _ Flapper Box Clamp Bolt 914-6
Posted by: DennisV Aug 18 2026, 07:40 PM
Is this the correct bolt to secure the flapper box to the heat exchanger on a 914-6? Part number 901-211-631-00. Appears to be NLA. Paired with square nut.
It is what I removed from a pair of used flapper boxes I bought. I tried installing it on a new Dansk flapper / heat exchanger and it appears too short. Even if I try various clamps to compress the flange and close the distance.
Posted by: Puebloswatcop Aug 18 2026, 07:51 PM
Dennis, I tried looking it up in the PET and other resources and it doesn't give a length. It sould be an M6 bolt although that is an assuption based on the fact that it shows the nut on it is M-6. Sorry its not much help, but you can at least check if its M6. if the one you have doesn't meet that spec, then you'll know its not right.
Posted by: bdstone914 Aug 19 2026, 03:29 AM
Is this the correct bolt to secure the flapper box to the heat exchanger on a 914-6? Part number 901-211-631-00. Appears to be NLA. Paired with square nut.
It is what I removed from a pair of used flapper boxes I bought. I tried installing it on a new Dansk flapper / heat exchanger and it appears too short. Even if I try various clamps to compress the flange and close the distance.
I assumed the 4 and 6 flappers took the same bolt. But thevpart number does start with 901.
I can check if a 4 flapper fits a 6 exchanger. Im sure i have those bolts to check.
Im betting it is the Dansk flapper that is the problem.
Posted by: rgalla9146 Aug 19 2026, 07:50 AM
[quote name='bdstone914' post='3268916' date='Aug 19 2026, 05:29 AM']
[quote name='DennisV' post='3268892' date='Aug 18 2026, 06:40 PM']
Is this the correct bolt to secure the flapper box to the heat exchanger on a 914-6? Part number 901-211-631-00. Appears to be NLA. Paired with square nut.
It is what I removed from a pair of used flapper boxes I bought. I tried installing it on a new Dansk flapper / heat exchanger and it appears too short. Even if I try various clamps to compress the flange and close the distance.
[/quote]
I assumed the 4 and 6 flappers took the same bolt. But thevpart number does start with 901.
I can check if a 4 flapper fits a 6 exchanger. Im sure i have those bolts to check.
Im betting it is the Dansk flapper that is the problem
I agree. The bolt on my flappers is 32mm
If the Dansk parts do everything else as they should a longer bolt will do the trick.
If you choose to go with OE 6 flappers I have a pair of beauties
Oh, one more thing.
The bolt extends through the elongated hole. The square nut goes on the round hole side. The round hole side keeps the nut from turning.
And one more. Put a flat washer on the elongated hole side to keep the clamp from getting bent.
Posted by: johnhora Aug 19 2026, 04:51 PM
Dennis...here is a picture I took today of my OEM original six flapper boxes
Posted by: johnhora Aug 19 2026, 04:52 PM
Posted by: DennisV Aug 20 2026, 08:30 AM
The bolt extends through the elongated hole. The square nut goes on the round hole side. The round hole side keeps the nut from turning.
And one more. Put a flat washer on the elongated hole side to keep the clamp from getting bent.
Thanks for that detail.
@http://www.914world.com/bbs2/index.php?showuser=107 thanks for the photos and dimensions.
Maybe it's the end of the Dansk heat exchanger that is causing the problem. When I put the old and new flappers side-by-side, I don't see any notable difference in the diameters when relaxed.
Original on the right. New Dansk 914-4 with hole cut and painted gray on the left.
Posted by: aturboman Aug 22 2026, 06:25 PM
Here is an NOS valve and retainer bolt/nut. Interestingly the replacements were black oxide type finish with the unique locking nut. 
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