Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing - Page 3 - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
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post #31 of 53 Old 02-18-2011, 04:15 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Interesting read. Glad you bumped it up Nick.

I've never messed with two strokes to any extent but we had a few around on hay elevators and a couple of pumps. The ones on the pumps ran pump jacks that would operate a sucker rod up and down in the well. These were heavy load/zero load situations as the rod was pulled up and then allowed to fall back down the well.

The two strokes would have a problem with the constant up and down load until my Dad added a flywheel to the crankshaft pulleys on them. After that they just sat there and did their thing. As I recall these engines had a long intake runner, maybe 8" long, between the carb and the cylinder. This was supposed to make them run better with more torque at the fairly low speeds involved which I'd guess was something around 2000 RPM.

I've not seen one of those two cycle pump setups in a lot of years, probably fifty or more.

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post #32 of 53 Old 02-18-2011, 04:46 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

That would be interesting.... make a longer intake manifold for a LB engine to optimize power and torque for 3000-3300 rpm or so.

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post #33 of 53 Old 06-29-2019, 09:33 AM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

I don't see any pictures.

First time F engine rebuild.

Lawn-Boy Gold Series Walk-Behind Mower, 1994 (SN: 4900001-4999999)

Model Number 10515

Serial Number 4905787

Discovered flywheel was rubbing on top of engine, about 1/4" of vertical movement of crank, no spark.

Is the self propelled crankshaft the same as push? are flywheels the same on all F engines?
Thank You
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post #34 of 53 Old 06-29-2019, 10:49 AM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Quote:
Originally Posted by 27grains View Post
Lawn-Boy Gold Series Walk-Behind Mower, 1994 (SN: 4900001-4999999)

Model Number 10515

Serial Number 4905787

Discovered flywheel was rubbing on top of engine, about 1/4" of vertical movement of crank, no spark.

Is the self propelled crankshaft the same as push? are flywheels the same on all F engines?
Thank You
Yes the self-propel crank and push cranks are the same for that era of the F series engines. Not all of the Self-propel and push cranks from an F series are interchangeable though, some of the real early ones were gear drive and had a worm gear machined directly into the crank.

The flywheel is kind of the same deal, looks like there were at least 3 different ones over the 20 years or so of the F engine production. I went and looked at the parts catalogue and from about 1991 and on the F series used flywheel p/n# 683580.

The latest F series engines (mid 1996 through the end of production) had thrust bearings and washers installed at the lower end of the crank (pn# 252-76 thrust bearing, and 252-80, thrust washer) to combat the problem of excessive vertical play in the crank. It might be something to consider, and they are still available. You can look at models like the 10401 (latest version), or 10401C see those parts in the diagrams. If memory serves me correct those bearing sets (1 ea stacked) measure about .062 inch, so it may take a couple of the washers to shim you back into specs with yours having approx .250 inch of play. I have yet to incorporate these thrust bearing sets in an engine not originally equipped with them, but the part numbers are the same for both the crank and the crankcase, so it should be doable.

Below is the parts catalogue link that I use to check parts effectively and interchangeability for different model of mowers.

https://www.partstree.com/parts/lawn...nd-lawn-mower/

Last edited by Lawnboy77; 06-29-2019 at 10:57 AM.
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post #35 of 53 Old 06-29-2019, 11:55 AM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

If I understand what you are suggesting is that I can add the thrust bearings and washers to my 1994 F engine without modification to case or crank?

What would wear to allow the crank to drop enough for the flywheel to hit the engine and wear away one of the fin tops? From pictures online I see the lower bearing has a short pin that fits in a slot machined into housing. Is it possible the pin snapped allowing the crank to drop or does the housing wear?
Thank You
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post #36 of 53 Old 06-29-2019, 02:53 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Yes I think you could install the thrust bearing and washer(s) in yours without modifications. Just based on the amount of wear you said you have there should be room, and then some...might have to add multiple washers.

In regards to the question about what would cause the wear in the lower crankcase; I'm not real sure, but I tend to think it's a couple of issues. The first being just dirt, grit getting into the crankcase and mixing with the oil and depositing in the bottom where it acts like a grinding compound and will fairly quickly wear the soft cast aluminum crankcase cover assembly. I've had problems with dirt bypassing these F series rectangular air filters in real harsh conditions, for me it happens real early in the season when I'm scalping the dormant grass. I really think a remote air filter is the way to go for F series use in harsh conditions, and yes I have one on my wish list.

Secondly, I have noticed that all these instances where folks have reported excess vertical crank play it has been self-propel engines. This would indicate to me that the belts might not be aligned perfectly and kinda pulling the crank down. In the case of the worm gear drive cranks it is pretty obvious that when you have angled gears you are going to have the crank being pushed up, or down vertically as it's rotating. Nothing scientific here, just my 2 cents worth.

Now the question I have been asking myself for the last couple of years is why I only have air filter bypassing on the rectangular F series and nothing even close to that with the old round D-400s? I run these old small round D-400s where it's gets pretty thick with grass/ debris on the outside and I'm thinking to myself that I hope none of this debris bypassed the filter, and after a quick removal for cleaning, or exchange for a clean one, I notice that it's perfectly clean on the inside of the filter, just like it should be.

Edit: If you want I would like to donate a thrust bearing and washer out of an old engine from a 10401. I don't think I'll need them since all my mowers are pushers and the vertical play just doesn't seem to be a factor with them anyway, furthermore I'd like to see if fits, and if it does great! and it's yours free of charge, if it doesn't fit, you won't have wasted any money. Let me know and if it's a go, I'll go out and dig them out of the shed. Hopefully still have them.

Last edited by Lawnboy77; 06-29-2019 at 03:14 PM.
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post #37 of 53 Old 06-29-2019, 05:19 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Wow, what a kind offer. Yes i would like to try it.
my email is [email protected]

Thank you
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post #38 of 53 Old 06-29-2019, 05:47 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

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Wow, what a kind offer. Yes i would like to try it.
my email is [email protected]

Thank you
Sounds good! I'll get out to you Monday.
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post #39 of 53 Old 06-29-2019, 08:10 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Lawnboy 77, you do have the plugs ( 611545) installed in the two round holes at the back of the rectangular F carburetor air box?
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post #40 of 53 Old 06-29-2019, 08:35 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

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Lawnboy 77, you do have the plugs ( 611545) installed in the two round holes at the back of the rectangular F carburetor air box?
You beat me to it! That's what I was thinking too.
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post #41 of 53 Old 06-29-2019, 09:00 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

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Lawnboy 77, you do have the plugs ( 611545) installed in the two round holes at the back of the rectangular F carburetor air box?
This one doesn't have those plugs (611545) in the filter box. I think those plugs you are referring to are on the older OMC F series carb boxes. Mine is a 1993 model 10420 with the metal Walbro carb. I'm glad you mentioned that though because I think you are on to something. I need to check to see if that air box/base is warped enough to cause this because I don't think I have a gasket between the air filter base and the carb. The IPC doesn't call for a gasket there and I usually just stick with whatever the parts catalogue says, but obviously if the surface is warped I would need some way to get a good seal there. I don't think there is any other way for dirt to bypass the filter, other than the two mounting holes, but the screws heads have those holes covered well enough I suppose. I should have checked that out the last time I had that carb off. There probably should be a gasket there anyway because who knows what happens when it heats up. It could be sealing okay when I look at it cold, but when hot the plastic may expand and create openings. I had mistakenly thought that it was just a bad design and the fix would be a remote filter, but that may not be necessary. Thanks guys!
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post #42 of 53 Old 06-29-2019, 11:57 PM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

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Originally Posted by Lawnboy77 View Post
Yes the self-propel crank and push cranks are the same for that era of the F series engines. Not all of the Self-propel and push cranks from an F series are interchangeable though, some of the real early ones were gear drive and had a worm gear machined directly into the crank.

The flywheel is kind of the same deal, looks like there were at least 3 different ones over the 20 years or so of the F engine production. I went and looked at the parts catalogue and from about 1991 and on the F series used flywheel p/n# 683580.

The latest F series engines (mid 1996 through the end of production) had thrust bearings and washers installed at the lower end of the crank (pn# 252-76 thrust bearing, and 252-80, thrust washer) to combat the problem of excessive vertical play in the crank. It might be something to consider, and they are still available. You can look at models like the 10401 (latest version), or 10401C see those parts in the diagrams. If memory serves me correct those bearing sets (1 ea stacked) measure about .062 inch, so it may take a couple of the washers to shim you back into specs with yours having approx .250 inch of play. I have yet to incorporate these thrust bearing sets in an engine not originally equipped with them, but the part numbers are the same for both the crank and the crankcase, so it should be doable.

Below is the parts catalogue link that I use to check parts effectively and interchangeability for different model of mowers.

https://www.partstree.com/parts/lawn...nd-lawn-mower/
I have found things differently. The crank on my c21zpn and on my former s21zpr did not have holes drilled for the self propel pulley so those are another one to add along with the capstan drive crankshafts that will not work if you want the drive system to function.

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post #43 of 53 Old 06-30-2019, 10:32 AM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

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I have found things differently. The crank on my c21zpn and on my former s21zpr did not have holes drilled for the self propel pulley so those are another one to add along with the capstan drive crankshafts that will not work if you want the drive system to function.
Yes you are absolutely right! I was thinking that hole for the self-propel was present on all those cranks, but just checked a couple of my original pushers this morning and the hole was not there. I do know that you can use the self-propel crank on a pusher though, so it's a one-way interchange. I did just that on my 10420 a few years ago. Thanks for the correction Ben.

During my hunt this morning for some parts for a fellow member I ran across another F series crank that I had forgotten about. It's a blade brake version I suppose, If anyone needs one let me know. I think it's NOS as well. It was on a NOS short block that I used for another pusher and swapped out the crank to make it work for the pusher.

Last edited by Lawnboy77; 06-30-2019 at 11:52 AM.
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post #44 of 53 Old 07-04-2019, 08:37 AM
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Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Where can I find crankcase housings for my F engine?
Is my post in the correct forum section?
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post #45 of 53 Old 07-04-2019, 12:01 PM
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Originally Posted by 27grains View Post
Where can I find crankcase housings for my F engine?
Is my post in the correct forum section?
I assume you mean the halves of the engine. The cylinder and reed halves are a machined fit. Meaning you can' take the cylinder from one engine and use the reed plate off another. Personally, I'd look for another F engine machine on craigslist and rob the engine off that.

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