Bottom oil seal F series engine - Lawn Mower Forums : Lawnmower Reviews, Repair, Pricing and Discussion Forum
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post #1 of 7 (permalink) Old 06-22-2016, 10:21 PM Thread Starter
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Bottom oil seal F series engine

How can I keep this seal in place? Can I change it without removing the engine.
Thanks.
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post #2 of 7 (permalink) Old 06-23-2016, 01:59 AM
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If the seal is falling out then it needs to be replaced. On some engines the seal can be removed with the engine on the deck if you have the seal removal tool. More than likely you will need to remove the engine from the deck in order to get the seal out. If it is already out you can install the seal without removing the engine from the deck. If you have the old style seals without the rubber coating you can use a small amount of blue Loctite but it is usually not needed. The newer seals have a rubber coating so no Loctite or sealant needed. You can make a seal driver from a piece of PVC pipe that just fits over the crankshaft. Clean the crankshaft completely and put some two cycle oil on the crankshaft. Drive the seal in so it is about 3/32" below flush. Here is a link showing the seal removal and installation using the Lawnboy tools so you can get the idea. Any questions, let us know. Bill

Lawnboy Crankshaft Seal Replacement Pictures - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information

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post #3 of 7 (permalink) Old 06-23-2016, 11:46 AM
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The seals are quite cheap in cost. If you are replacing one, you should replace both. On most Lawnboy 2-cycle mowers, which include the "F" engines, the top seal is identical to the bottom seal. Just replace them both and be done.
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post #4 of 7 (permalink) Old 06-28-2016, 08:49 AM Thread Starter
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I know I should have replaced both,I just did the bottom. No time to tear anything else apart. I will change the top seal this fall. Changing that seal changed the way that thing was running, took a couple of clockwise turns on the fuel air mix adjustment before it started to sound right.
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post #5 of 7 (permalink) Old 06-28-2016, 12:10 PM
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Glad you got the seal changed and the mower is up and running. The upper seal rarely fails but if you have the mower apart for a good cleaning it is not hard to pull the flywheel and change it as well. Keep in mind when tuning a 2 stroke to turn the adjustment needle in until it is running the smoothest. Continue to turn in a bit at a time until it starts to falter and then back off to a point that was just before smoothest running. You never want to tune a 2 stroke to best lean running. It should have that "burble", almost as if it is running rough. It's the sweet spot that keeps these running for a long time. Bill
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1968 Lawnboy 3054 Mower
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post #6 of 7 (permalink) Old 02-07-2020, 11:26 PM
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Lawnboy F series engine bottom seal replacement. BEWARE ! I just replaced mine on my 1989 S21BSN. Upon removing the original seal, that was falling below the shaft, I noticed in the seal cavity two small brown drops on opposite sides inside the cavity. Looking closer they turned out to be flashing from the original epoxy glue that was used at the factory to seal the head of the engine to the casing. That is the reason for the failure, the seal does not seat on the champher seat flush.. Be sure to inspect the bearing cavity prior to inserting a new seal. Carefully scrape the flashing out with a small device.
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post #7 of 7 (permalink) Old 02-07-2020, 11:57 PM
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It is always a good idea to clean the bore where the seal goes before installation. I usually spray some Gumout in there and use a Q-Tip to clean it out to make sure there is a good, clean sealing surface. I would question, however, based on what I know and have learned on the Forums, whether what you found in the bore was left from the factory. As I understand it, the case halves were assembled and then line bored as a set which is why it is not recommended to mix and match case pieces from different engines. The parts diagram clearly shows only one part number as related to both case halves.
Are you the original owner of the mower? If so, then the seal has stayed in a good long time. If you bought the mower from someone else, perhaps the issue was caused by something they did or someone else did in the past.
Let us know what the history is of the mower. Thanks for sharing your observations. Bill

1968 Lawnboy 3054 Mower
1973 Lawnboy 8231 Mower
1975 Lawnboy 5024 Mower
1975 Lawnboy 5273 Mower
1976 Lawnboy 5274 Mower
1977 Lawnboy 5024 Mower
1980 Lawnboy 7268 Mower
1982 Lawnboy 5247 Mower
1982 Lawnboy 5247 Mower
1972 Lawnboy 1015 Edger
1972 Lawnboy 1015 Edger
1987 Lawnboy 1400CL Trimmer

Where there's a will, there's Mr. Bill!
They don't call me MacGyver for nothing!
I have LBAD and DCAD!
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