B&S 35HP Offset Key for Flywheel - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
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post #1 of 7 (permalink) Old 01-04-2020, 12:45 AM Thread Starter
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B&S 35HP Offset Key for Flywheel

I have an 05 Scag w/a B&S 35HP that I changed the alternator & it requires an offset key for the key way on the flywheel. It needs to go in the right way or the opposite will throw it out of time. If I am standing at the rear facing forwards; does it offset to the left or right. I went to the local Scag dealer; but they had NO manual on it & gave me a guesstimate!! I cannot find anything on line.
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post #2 of 7 (permalink) Old 01-04-2020, 08:28 PM
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I find the notion of an offset flywheel key intriguing, like where's the strength come from?

The flywheel keys that the Briggs illustrated parts list for an arbitrary 35HP Vanguard engine, 613477-0039-J1 (in this case), has either an aluminum or a steel flywheel key, depending on date code.

Parts list 613477-0039-J1 says
24 222698S KEY, Flywheel
-(Aluminum)
-Used Before Code Date 07122800
24 796335 KEY, Flywheel
-(Steel)
-Used After Code Date 07122700

When I look those part numbers up in Google images, both look like conventional rectangular flywheel keys. Neither appears to be offset.

Yeah, there are different variations between models in any given displacement category, but radical differences in flywheel keys ? ?

Exactly what model engine do you have that lists an offset flywheel key?
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post #3 of 7 (permalink) Old 01-04-2020, 09:38 PM Thread Starter
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Info

Engine: 6131770114-E1 Code 04110512
Partstree info below for that Engine code indicates an offset key.

Armature-Magneto

Part# 843860

Note: (Includes Offset Key) Used Before Code Date 06113000
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post #4 of 7 (permalink) Old 01-05-2020, 02:52 PM
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I had heard of using offset keys to advance timing on racing kart engines but I had no clue that an OEM used offset flywheel keys.

Kohler uses an offset key, but someone explains how that key inserts for the correct timing:
https://i.postimg.cc/nhyh3Jc6/Kohler...structions.jpg

I can't find a similar advice in a web search for Briggs engines. Hopefully someone here will pop with some experience so you don't have to experiment to find out.
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post #5 of 7 (permalink) Old 01-07-2020, 01:41 AM
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The factory box includes installation instructions on a printed piece of paper, as shown in this photo of the contents of the factory box that I found in Google search:



Note that the instructions reference B&S Service Bulletin #740, but good luck trying to find a copy.

Here's my best attempt at interpreting the text:

------------------------------------------

2. Replace flywheel key with the a____ key _____ ____ ___

3. Install flywheel key with pa___ed (painted?) end facing out toward flywheel nut

Important: Install offset flywheel key sticker to a__ __ _____ cover in a conspicuous spot.

See B&S Service Bulletin #740
------------------------------------------


Any other takers on the word starting "pa____" is?


What is the different on one end of the offset key than the other that would indicate that end faces out? Is there a dab of paint on one end?
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post #6 of 7 (permalink) Old 01-08-2020, 03:07 PM
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Quote:
Originally Posted by Tater50 View Post
I have an 05 Scag w/a B&S 35HP that I changed the alternator & it requires an offset key for the key way on the flywheel. It needs to go in the right way or the opposite will throw it out of time. If I am standing at the rear facing forwards; does it offset to the left or right. I went to the local Scag dealer; but they had NO manual on it & gave me a guesstimate!! I cannot find anything on line.
If it is supposed to advance the timing, install the key so it moves the flywheel to the right.
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post #7 of 7 (permalink) Old 01-09-2020, 09:46 PM
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Here's the Briggs & Stratton Web site's Customer Forum reply to the question of installing an offset flywheel key:

Question:

35HP engine 613177-0114-E1 uses replacement armature/magneto 843860 that includes offset flywheel key 843837.

Which way does the offset key insert for proper flywheel/mag timing? Does the flywheel install CW or CCW of a 'vertical' position?

Answer:

The offset flywheel key must be installed in a specific manner depending upon the color of the bands on the spark plug wires at the ignition coil. If the bands on the wires are black, install the offset key with the painted end facing in (engine side). If the bands on the wires are blue, install the offset key with the painted end facing out (flywheel side). The flywheel will run CW.

https://www.briggsandstratton.com/na...community.html
Search For a Question: search term: Magneto 843860
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