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post #1 of 20 Old 06-02-2019, 02:26 PM Thread Starter
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Oil Seal or Muffler leak?

Hello everyone! Hope all of you are having a good Sunday.

I had my 5273 out on mowing duty today and I noticed a film of oil on the muffler plate around the crankshaft. I was wondering if this is a sign of a bad oil seal or the muffler gasket leaking? The engine starts and runs normally and was rebuilt last year so I'm leaning more on leaky muffler. But then again the rubber oil seals seem to have mixed reaction on here so any input is greatly appreciated

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Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #2 of 20 Old 06-02-2019, 02:57 PM
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Re: Oil Seal or Muffler leak?

Meffler bearing is leaking oil.
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post #3 of 20 Old 06-02-2019, 04:53 PM
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Re: Oil Seal or Muffler leak?

I donít see any evidence at all of a crank seal leak. When they leak from the seal it is very obvious after shutting down the engine. Donít worry about a little oil film being slung around from the exhaust, itís perfectly normal for a 2 stroke.
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post #4 of 20 Old 06-02-2019, 08:00 PM Thread Starter
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Re: Oil Seal or Muffler leak?

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Originally Posted by Lawnboy77 View Post
I donít see any evidence at all of a crank seal leak. When they leak from the seal it is very obvious after shutting down the engine. Donít worry about a little oil film being slung around from the exhaust, itís perfectly normal for a 2 stroke.
Thank you for clarifying that for me! I figured it was something related to the exhaust because it runs perfectly and starts easy hot or cold. All the grime on the adapter and around the crank had me worried.

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Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #5 of 20 Old 06-03-2019, 08:02 PM
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Re: Oil Seal or Muffler leak?

There shouldn't be any oil in that area. If the oil is on the crankshaft the seal is leaking. Also there shouldn't be any oil in the muffler to leak out. Of course it will still run with a slight seal leak but it will eventually get worse.
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post #6 of 20 Old 06-04-2019, 12:33 PM Thread Starter
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Re: Oil Seal or Muffler leak?

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There shouldn't be any oil in that area. If the oil is on the crankshaft the seal is leaking. Also there shouldn't be any oil in the muffler to leak out. Of course it will still run with a slight seal leak but it will eventually get worse.
That's where I had my suspicions. Usually if the muffler is leaking the sludge is on the outer side of that lip. Took the blade and blade adapter off after mowing yesterday and the oil sludge looked to have gotten worse. Guess I know what I'm doing today. It makes sense why the engine was running too rich at normal carburetor adjustment.

Lesson learned don't use the rubber oil seals, they're awful and fail often.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #7 of 20 Old 06-04-2019, 03:29 PM
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Re: Oil Seal or Muffler leak?

On a 2 cycle engine if a crankcase seal (crankshaft seal) starts leaking usually the engine will idle rough or not at all. The engine will normally run leaner due to too much air being sucked into the crankcase and the engine may overheat and seize if run at wide open throttle under a heavy load.

The seizing is due to the piston expanding into the cylinder wall due to heat build-up due to not enough fuel hitting the piston. (too much air) What is misleading is at first the engine may actually seem stronger and rev to higher rpm's.
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post #8 of 20 Old 06-05-2019, 09:10 PM
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Talking Re: Oil Seal or Muffler leak?

I have been using the rubber coated seals from Toro/Lawnboy for a fairly long time now with no issues. Are the seals you have been using OEM or aftermarket? Bill

1968 Lawnboy Model 3054******1973 Lawnboy Model 8231******1974 Lawnboy Model 5023
1975 Lawnboy Model 5024******1975 Lawnboy Model 5273******1976 Lawnboy Model 5274
1976 Lawnboy Model 8234EX****1977 Lawnboy Model 5024******1978 Lawnboy Model 5269G
1979 Lawnboy Model 7268******1980 Lawnboy Model 5247******1982 Lawnboy Model 5247
1982 Lawnboy Model 5247*******1972 Lawnboy Model 1015******1972 Lawnboy Model 1015
1987 Lawnboy Model 1400CL****1995 Lawnboy Model 61638

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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post #9 of 20 Old 06-06-2019, 12:36 AM
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Re: Oil Seal or Muffler leak?

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I have been using the rubber coated seals from Toro/Lawnboy for a fairly long time now with no issues. Are the seals you have been using OEM or aftermarket? Bill
Iíve been using those Toro/Lawnboy seals as well with no issues. The only seal leakage I have experienced was from an NOS seal (metal reinforced), or from converting a 1973 D-400 single bronze bushing crankcase to a dual bronze extended snout without swapping the crank. It was just a matter of polishing the new sealing surface on the original crank and it sealed fine afterwards. I would also stay away from seals that are advertised as NOS, they may not work at all due to the rubber having an expired shelf life.

In regards to the OPís issue, it is still my opinion that his lower seal is functioning fine. The pics look perfect to me. If itís running rich itís not a lower seal issue. 100% of the oil is not going to burn with the fuel, this is normal and good, and this is exactly why we cook those F series mufflers on the grill.
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post #10 of 20 Old 06-06-2019, 01:02 PM Thread Starter
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Re: Oil Seal or Muffler leak?

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Originally Posted by Yard Nazi View Post
I have been using the rubber coated seals from Toro/Lawnboy for a fairly long time now with no issues. Are the seals you have been using OEM or aftermarket? Bill
I use OEM seals. Don't really trust aftermarket. I've had those fail a few times too even with correct preparation. It makes me scratch my head since these ones were brand new OEM.

Quote:
Originally Posted by Lawnboy77 View Post
Iíve been using those Toro/Lawnboy seals as well with no issues. The only seal leakage I have experienced was from an NOS seal (metal reinforced), or from converting a 1973 D-400 single bronze bushing crankcase to a dual bronze extended snout without swapping the crank. It was just a matter of polishing the new sealing surface on the original crank and it sealed fine afterwards. I would also stay away from seals that are advertised as NOS, they may not work at all due to the rubber having an expired shelf life.

In regards to the OPís issue, it is still my opinion that his lower seal is functioning fine. The pics look perfect to me. If itís running rich itís not a lower seal issue. 100% of the oil is not going to burn with the fuel, this is normal and good, and this is exactly why we cook those F series mufflers on the grill.
I removed the engine and my suspicions were true unfortunately. The seal was indeed failing. I've had the exhaust leak before but any leakage is on the outside of the muffler snout around the crank. This leakage was inside that area where only the crank resides and the crank did have oil all over it. I usually second guess these things because I always want to not think the worst.

Running rich indeed indicates a bad seal as well. Having to lean the adjustment out to make it sound okay means one is compensating for some additional air entering the vacuum cycle. I always check other probably causes for rich running and if they all check out it's most likely an oil seal failing.

I tend to stay away from anything that isn't a metal part listed as NOS. I know that means it's likely old and not "plug and play". All seals I've gotten have had been new and OEM. I just don't trust the rubber ones anymore.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #11 of 20 Old 06-06-2019, 03:33 PM
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Re: Oil Seal or Muffler leak?

For an excellent oil seal use the C/R 8624 with the green bore tite coating on the metal. Lawn Boy used this seal for many years. The high quality rubber used in oil seals stays resilient and usable in storage or NOS, it's not a problem.
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post #12 of 20 Old 06-06-2019, 03:48 PM Thread Starter
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Re: Oil Seal or Muffler leak?

Quote:
Originally Posted by Mike72 View Post
For an excellent oil seal use the C/R 8624 with the green bore tite coating on the metal. Lawn Boy used this seal for many years. The high quality rubber used in oil seals stays resilient and usable in storage or NOS, it's not a problem.
Noted and thank you! I think I have some of those in my stock somewhere. I've heard good things from posts on this form about the 609342/8624 seal before so I should've used them in this rebuild. I just had some rubber ones I wanted to use but that didn't end to well. I opened the top end of the engine to examine the other seal and it was pushing itself out.

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
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post #13 of 20 Old 06-06-2019, 04:26 PM
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Re: Oil Seal or Muffler leak?

Do not see any 2 cycle engine lawn mowers around this neck of the woods? Are they much of a pain to keep running?

Wonder how often they get straight gassed.
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post #14 of 20 Old 06-06-2019, 05:12 PM
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Re: Oil Seal or Muffler leak?

Quote:
Originally Posted by Mike72 View Post
For an excellent oil seal use the C/R 8624 with the green bore tite coating on the metal. Lawn Boy used this seal for many years. The high quality rubber used in oil seals stays resilient and usable in storage or NOS, it's not a problem.
I respectfully disagree. There is no miracle rubber that doesnít age. The shelf life program is taken very seriously in the commercial aviation world, and with good reason. Obviously we are not dealing with airplanes here, but the principle is the same. Good luck with those 30 year old rubber o-rings and seals in general. If I do that at my job I run the risk of jail time. We, as certified mechanics, turn in certification documents on every seal that we install on an aircraft that states, when it was produced, lot numbers and FAA approval, manufacturer and most importantly, the expiration date. You guys do what you want, there is no safety risk here, itís just a lawn mower right. I would be laughed out of the courtroom for stating something like, ďshelf life doesnít apply to quality rubberĒ.

Last edited by Lawnboy77; 06-06-2019 at 05:22 PM.
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post #15 of 20 Old 06-06-2019, 06:29 PM Thread Starter
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Re: Oil Seal or Muffler leak?

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Originally Posted by Forest Gump View Post
Do not see any 2 cycle engine lawn mowers around this neck of the woods? Are they much of a pain to keep running?

Wonder how often they get straight gassed.
They do require a service every once in a while and most mechanics don't like messing with them. Lawn Boys are great mowers and have powerful engines but two cycle mowers seem to have fallen largely out of favor with most of the public. On the subject of straight gassing, its sad to think of the large amount of these machines sent to the scrapper from being straight gassed. Probably some nice desirable/rare models too,

Mowers:
1970 - 5239 (D-408)
1973 - 3058 (D-433) (Rebuilt)
1974 - 8251 (D-480)
1975 - 5273 (D-601) (Rebuilt)
1982 - 7071 (F-101) (Custom)
LawnBoy90 is online now  
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