Fat Boy 4 - Muffler Repacking Installation Tips

All Models

SPECIAL NOTE: When working on your Fat Boy 4 exhaust be sure that the exhaust system and engine have cooled down. Working on the exhaust when HOT, can and will result in a possible injury.

REPACKING SCHEDULE: For proper exhaust performance and to keep noise level consistent it is recommended to repack your Fat Boy 4 exhaust every 20 hours of usage. Under extreme riding condition packing could need replacement in as short as 10 hours.
The repacking used in your Fat Boy 4 exhaust is a perishable item. (Similar to the oil in your engine). It is designed to suppress the exhaust note of your engine while maintaining proper exhaust function and maximum performance.

Failure to repack and maintain your exhaust system can and will result in engine power loss and excessive db noise levels. Running the machine for prolonged periods with burnt, worn or low packing will also cause damage to your Fat Boy 4. Core, body and end cap damage may result. (This unnecessary damage can also effect your manufactures limited warranty)

BASIC REPACKING TIP: It is recommended to repack your Fat Boy 4 muffler when it is removed from the machine.
· It is best to unbolt muffler from chassis and remove at tail pipe slip-fit joint.
Once muffler is removed it is easiest to unbolt the muffler from the tail section. The muffler is attached with 3 or 4 (depending on model) with 6mm s/s allen bolts. Use a good quality allen wrench and reuse of these bolts should be OK. If the screws are not in good condition once removed, replace with new (use exactly the same bolts).
*NOTE: When repacking is finished and muffler is reinstalled onto tail pipe it is mandatory that the muffler screws be secured with LOCTITE 242 Blue thread lock.
You will also want to check that the o-ring used between the tail pipe and the muffler is in good condition. If it is not ripped, torn, broken or damaged in any way it is reusable. If in doubt it is best to replace it with a new o-ring.
· Next you will want to remove the (4) s/s 6mm allen screws that secure the rear end cap into the muffler. The screws are located on the top, bottom and both sides of the back of the muffler. Again check screws, if good reuse, if not replace.
· To remove the rear end cap (it is engraved Fat Boy 4) once screws are removed it is easiest to use a rubber or plastic mallet (DO NOT USE STEEL HAMMER) to tap all around the end cap until it slides away from muffler body.
· Remove perforated muffler core and old packing as one unit. Slide it out. Once out remove core from packing. Clean with a scotch brite pad or soft wire wheel. Inspect closely for any cracks or other damage. Replace if necessary.
· Clean out inside of muffler. Use rag to wipe out or scotch-brite. Also clean rear end cap, Make sure side of the end cap where it touches muffler body is clean so that it can slide back into body without obstruction.

· Reassembly-Slide core into center of new packing roll.
NOTE: Sharp edge on muffler core can catch on packing roll as core is slide through packing it is advisable to wrap a piece of duct tape around the end of the core before attempting to
Slide core through packing. After core has been slide through packing remove duct tape and discard.
· Slide packing/core assembly into muffler body. Make sure that the core slides into the slot in the front side if muffler.
NOTE: When core is installed properly the backside of core will be flush with rear end of muffler body. Also when you look through core there will be no obstructions.
· Reinstall rear end cap. Do not use loctite on the (4) screws that secure the end cap into
the body.
· Install muffler back on to tail pipe. Make sure to use o-ring and to loctite the screws.
· Reinstall muffler and tail pipe assembly onto headers.
* Make sure to seal the slip fit joint with a thin coat of Hi-Temp silicon.

FAT BOY REPLACEMENT PARTS: DRI stocks all the replacement parts for Fat Boy 4’s.
Call DRI or see website for details.

HOUR METER: It is recommended to install and hour meter on your machine. This device can come in very handy keeping track of packing life, valve adjustments, oil changes, top end service, etc. A number of manufactures offer them for under $ 50.00. Installation is simple.


Replacement Parts

FB4-RP950-Repacking Kit (9.5)
FB4-RP110-Repacking Kit (11.0)
FB4-RP135-Repacking Kit (13.5)
FB4-RP165-Repacking Kit (16.50)

FB4-OC110-Muffler Core- (11)
FB4-OC125-Muffler Core- (12.5)
FB4-OC150-Muffler Core- (15)
FB4-OC180-Muffler Core- (18)

FB4-4A020-End Cap; (2.0”) Vertical
FB4-4AH20-End Cap; (2.0”) Horizontal (LTR-Outlaw)

FB4-4A250-Turndown Fitting CNC/Welded w/O’Ring (optional bolt-on)

FB4-85-012-Screw; 6mm x 12 S.S.(End Cap Profile)
FB4-85-512-Screw; 5mm x 12,S.S. (Attach Turndown)
FB4-85-620-Screw; 6 x 20 (Muffler to Tail)
FB4-85-6512--Pack of 12 (4 of each size)

FB4-80-33-O’Ring; Muffler -Tail (3-Bolt)
FB4-80-36-O’Ring; Muffler -Tail (4-Bolt)
FB4-80-37-O’Ring; Turn Down