Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing - Page 2 - MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information
Walk Behind Mowers We all use them from time to time... no seats on them.. but they get the job done!!!

Reply
 
LinkBack Thread Tools Display Modes
post #16 of 53 Old 06-08-2009, 11:29 PM
Decesaed (R.I.P.)
 
tgore3's Avatar
 
Join Date: Aug 2008
Location: Eureka, KS
Posts: 1,957
Send a message via Yahoo to tgore3
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Wow, i can't read all this. But I've had good luck with some porting and port/gasket matching on F engines.
tgore3 is offline  
Sponsored Links
Advertisement
 
post #17 of 53 Old 06-09-2009, 01:52 AM Thread Starter
Senior MTF Member
 
Join Date: Jun 2009
Location: South Dakota
Posts: 310
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing


and

These images show how well two crankshaft seals fit within one end of an F-Series Lawn-Boy engine crankcase bore. The second image shows part of how we can "safety wire" them in place so they can't slide out of their case bore. Sorry for the soft focus. I'm not familiar with this specific camera.
LoveLearn is offline  
post #18 of 53 Old 06-09-2009, 07:44 AM
Senior MTF Member
 
Mike72's Avatar
 
Join Date: Dec 2005
Location: IL
Posts: 425
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

John, welcome to the forum. All my Lawn Boys have lapped reed plates, I've been doing this for the past 6 years. I made small lapping plates from cast steel for both D and F models. I consider this a standard procedure when I build a new engine or rebuild an old one. I does make a difference with better crankcase sealing and cutting down on fuel fog. (reverse flow).
I have been considering getting a piston coated by Swain Technology for a test engine. As you know the piston is the critical part in a two stroke and anything that can shield it from heat is a big plus.
Most of my work with Lawn Boys has been to identify wear points and excessive manufacturing clearances, then make corrections. I think the Lawn Boy engines are excellent, but can use some finishing touches.
About 4 years ago I started making new throttle shafts for all my D models. The original shaft fits too loose in the carburetor body and hence wears quickly and gets even looser, allowing air to enter.


Mike72 is offline  
Sponsored Links
Advertisement
 
post #19 of 53 Old 06-09-2009, 12:57 PM
Senior MTF Member
 
Ferrstein's Avatar
 
Join Date: Apr 2009
Location: Beautiful, sunny Akron, OH
Posts: 175
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Quote:
Originally Posted by LoveLearn View Post


...shows part of how we can "safety wire" them in place so they can't slide out of their case bore...

Well now you see that right there is just a great idea. Thanks for posting!

My Current Stable:
Lawnboy 22241
Lawnboy 22240
Lawnboy 10515
Lawnboy 10415
Lawnboy 10545
Ferrstein is offline  
post #20 of 53 Old 06-10-2009, 02:46 AM Thread Starter
Senior MTF Member
 
Join Date: Jun 2009
Location: South Dakota
Posts: 310
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

This image shows how an F-series crankcase bottom can be modified by drilling four safety-wire retaining holes. A single drilling operation at each end cuts two holes since they are aligned on the same axis. Observe the drill bit left passing through the two holes at the right end which I left to produce this instructive photo.

John
LoveLearn is offline  
post #21 of 53 Old 06-10-2009, 03:11 AM
Senior MTF Member
 
Join Date: Aug 2006
Location: Wisconsin
Posts: 373
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

I've never had a problem with the seals dropping out of the crankcase on an F engine. All the ones I've rebuilt have gotten a smear of Loctite around the edge of the seal prior to installation though. I made a homemade tool to drive them in once the block halves are assembled, and never had a failure, except for the one L21ZPN that needs new seals again. The small engine shop that I bought the seals from sold me B&S seals that he claimed were the same ID and OD as the Lawn-Boy seals, except they had an all plastic body to them as opposed to a regular metal body like the original. The lower didn't drop out but sounds like it's leaking when I turn the engine over slowly.
Live and learn, I guess...I should have just gotten the seal number off the original and got them from a local bearing and transmission parts house or even NAPA or Carquest for that matter.

But I digress...That one needs to come apart to get refreshed, so at that time I might do a little tweaking to it too.

My current fleet:
8073
10201
10301
S21ZPN

Always on the hunt for more!
TheDodgeGuy is offline  
post #22 of 53 Old 06-10-2009, 08:53 PM Thread Starter
Senior MTF Member
 
Join Date: Jun 2009
Location: South Dakota
Posts: 310
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

TheDodgeGuy wrote,
"I've never had a problem with the seals dropping out of the crankcase on an F engine."
I think your personal experience sample size is too small to reflect these failures. Next year, if my driving skill and luck hold out, I will have driven 50 years without an auto insurance claim against me. Yet I don't see that as a compelling reason not to buy auto insurance. I know that my personal half century sample size is too small to support that opinion and I know from field reports by others that accidents happen. Lawn-Boy crankshaft seals sliding up from the engine top and down from the engine bottom have both been repeatedly reported and discussed in this forum.

"All the ones I've rebuilt have gotten a smear of Loctite around the edge of the seal prior to installation."
That sounds like a very worthy idea. But if someone decided to add new seals and resoften and reuse their old seals with some grease between them, as I described earlier in this discussion thread, that grease would tend to defeat the outer-edge Loctite smear's grip on the case bore. I think safety wires are justified for a double-seal installation as I described.

I'm convinced that hundreds among the thousands of 2-cycle Lawn-Boys set out by curbs before trash collection days arrived there due to these seal migration problems. Both of our solutions seem like improvements compared to the factory repair manual's description, which is essentially, clamp both seals in place with a press-fit and then just hope that you won't become one of the unlucky few who experience seal migration induced failures. Opting out of that lottery seems prudent to me just as does buying auto insurance.

Other discussion treads mentioning crankshaft seals have suggested that we have more options. One thread said that Toro had been running larger (wider?) softer seals on late models, which seals that writer thought wore out more quickly but might seal better before failing. Another thread mentioned "green" "Oregon" seals which that writer thought fit more tightly than stock Lawn-Boy part seals. I have no experience with either of those. I hope that anyone reading this with experience-based observations about those or other choices will report anything useful about these seals that we haven't discussed.
John

Last edited by LoveLearn; 06-10-2009 at 09:58 PM.
LoveLearn is offline  
post #23 of 53 Old 06-10-2009, 09:29 PM
Decesaed (R.I.P.)
 
tgore3's Avatar
 
Join Date: Aug 2008
Location: Eureka, KS
Posts: 1,957
Send a message via Yahoo to tgore3
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

I see those exterior rubberized seals popped out all the time. There's no way these green Oregon seals I use are going to pop out, they go in tight like a seal should.
tgore3 is offline  
post #24 of 53 Old 06-10-2009, 10:28 PM
GTP
2000 Posts and climbing!!!
 
GTP's Avatar
 
Join Date: May 2009
Location: Greensburg, PA
Posts: 2,420
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Quote:
Originally Posted by Toby View Post
I see those exterior rubberized seals popped out all the time. There's no way these green Oregon seals I use are going to pop out, they go in tight like a seal should.
Make those for Duraforces?
GTP is offline  
post #25 of 53 Old 06-11-2009, 12:00 AM
Decesaed (R.I.P.)
 
tgore3's Avatar
 
Join Date: Aug 2008
Location: Eureka, KS
Posts: 1,957
Send a message via Yahoo to tgore3
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Quote:
Originally Posted by GTP View Post
Make those for Duraforces?
Have no idea, I just got them accidentally one time and now I keep ordering them. I get them from TEW. Might check and see if Oregon makes a seal for the DF.
tgore3 is offline  
post #26 of 53 Old 06-11-2009, 03:53 AM
Lawnboy Green
 
sharkey's Avatar
 
Join Date: May 2008
Location: Pittsburgh, Pa
Posts: 633
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Hi John,

I enjoyed your write up about the lawnboy performance tips. Ive done some work with chainsaws. I understand the port timing area equations as expressed by Gordon Jennings. Ive found that some of the others that work with saws will use a ceramic coating on the piston crown and combustion chamber to produce a little more power. Their school of thought would be to prevent combustion heat from entering the piston or cylinder through this coating. I had never thought of Barbecue paint, what color would I use if I wanted to try this?

For what its worth, the published differences in the lawnboy cylinders that gives them their different horsepower ratings is based on their compression ratio. The original D600 engine had a greater compression ration than the D400 series, and this was continued with the later F and V engines that Toro made.

Great idea on the safety wiring of the lower seals because Ive found engines that these are missing or blow out of. It does seem though that most curb finds that Ive come across are there not because of missing seals but instead because of plugged exhaust ports.

Welcome to MTF and I look forward to reading more of your thoughts.

Best wishes,
Bob
sharkey is offline  
post #27 of 53 Old 06-11-2009, 06:53 AM
Collector of many tractors

 
Kbeitz's Avatar
 
Join Date: Mar 2005
Location: Northeast Pennsylvania
Posts: 15,244
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

This sounds like a good place to sell my small engine dino...


Kbeitz is offline  
post #28 of 53 Old 06-11-2009, 07:45 AM
Senior MTF Member
 
Mike72's Avatar
 
Join Date: Dec 2005
Location: IL
Posts: 425
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

The oil seals with the green coating rarely drop out. The green coating is called Bore-tite. Lawn Boy used seals made by different companies over the years. The ones with the green coating are made by C/R (Chicago Rawhide) and are a standard number seal.
Mike72 is offline  
post #29 of 53 Old 06-11-2009, 03:27 PM Thread Starter
Senior MTF Member
 
Join Date: Jun 2009
Location: South Dakota
Posts: 310
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

"I understand the port timing area equations as expressed by Gordon Jennings."
Cool, I met and corresponded with Gordon Jennings. We are poorer for his loss, but his writings about many design issues are still some of the most easily understood. I think discussion participant "mtgrs737" could benefit greatly by reading how tuned exhaust systems must be configured as Gordon so clearly explained them. Earlier in this discussion thread, mtgrs737 said, "Did you realize that the DF engine uses a tuned exhaust and a rear boost port?"

Here's my analysis of that statement.
Code of Federal Regulations Title 29, Volume 5 Revised July 1, 2005 limits "Hand and Portable Powered Tools and Other Hand-Held Equipment," which includes lawn mowers with this language: "The maximum tip speed of any blade shall be 19,000 feet per minute."
That's 316.67 feet per second. Here are some common mower nominal blade lengths:
18 inches, 19 inches, 20 inches, 21 inches and 22 inches. Circumference = pi x diameter.
Their respective diameters are 4.629, 4.974, 5.24, 5.50, and 5.76 feet.
Division yields legal limit rpms for these blade lengths:
4105, 3820, 3626, 3455, 3299 rpm

So if a Lawn-Boy engine is spinning a 21" blade, it's federal safety limit rpm is about 3,455 rpm.
A Lawn-Boy Duraforce specification sheet claims its 21" blade's maximum tip speed is only 17,700 feet per minute which implies 3218 rpm rather than 3455 rpm needed to obtain 19,000 feet/second tip speed.
That seems to identify the Duraforce engine's design speed pretty well.

If a Duraforce Lawn-Boy engine has a tuned exhaust system, that exhaust system needs to have a half-wave length tuned pretty close to 3200 rpm, which is 53.33 cycles per second. I haven't seen exhaust gas temperature readings for low-speed continuous-duty piston-controlled port 2-cycle engines, but I think we can assume they are not too different from otherwise similar 4-cycle engines. We need that value to approximate the speed of sound through that exhaust flow. I used to run these calculations fairly often for projects. I can assure you that a tuned exhaust system that resonates at 53.33 cycles per second is going to be pretty damned long to coil up onto a walk-behind mower. The Duraforce exhaust exits above rather than below its deck. How many times do Duraforce exhaust tubes wrap around its mower deck to create these long tuned lengths? Must be some invisible pipe. Unless physics rules have changed or some new exhaust system design that behaves according to some unfamiliar predictive model is used, DuraForce mowers do NOT have tuned exhaust systems. They have nice broad fairly flat torque curves over a wide range which enables them to recover after short overloads. Tuned exhaust systems' efficiency peaking effect near their resonate frequencies produce peaky torque curves which would, in my opinion, not be suitable for a non-racing walk-behind mower.

As to Duraforce engines having a "booster port," I don't care how some advertising department writer names an extra transfer port. It's still just one more transfer port to me. Earlier I said, "I doubt that we can tweak an F-series engine to become as powerful as a DuraForce which has a larger air cleaner, an extra transfer port and more displacement."

I'm a little surprised that nobody has focused on my suggestion to fill in stock F-series transfer port intersections with JB Weld, then smooth those curves so these ports flow better. I expect that would generate real power gains with little cost or effort. Maybe I'll generate and post a CAD view of this so the idea can be more easily understood.

Sharkey continued, "I've found that some of the others that work with saws will use a ceramic coating on the piston crown and combustion chamber to produce a little more power. Their school of thought would be to prevent combustion heat from entering the piston or cylinder through this coating. I had never thought of Barbecue paint, what color would I use if I wanted to try this?"

An ideal color would be shiny like silver or aluminum paint. But there are several complexities which may prevent any shiny surface confining combustion from remaining shiny. Heat and light are only different in terms of their wave length. They are two names for the same phenomena. Only our body's sensory equipment bandwidth limitations cause us to reference them with different names. Shiny is reflective. We want to reflect combustion heat from cylinder heads and piston tops. But how can we prevent the least volatile combustion gases from condensing out of the flow, forming a mostly-carbon film on cooler combustion chamber surfaces? If the insulating surface we apply quickly becomes covered with black carbon film anyway, there is almost no added utility to be gained by having a lower contacting layer be shiny or white. Thirty five years ago, the highest temperature rated paints that I found were claimed to be able to endure 1750-1800 Fahrenheit. A quick on-line search revealed one Tech paint claiming 2000 Fahrenheit durability, but that is only available in black.

Other issues I'd like to touch on relative to combustion chamber coatings. Most discussion group participants focus on combustion gas temperatures rather than combustion chamber surface temperatures. It seems to me that focus has lead many of them to wrong conclusions.

Let's go back to basics. If a potential fuel like carbon is heated above its ignition temperature in the presence of available oxygen, combustion is triggered. Carbon's flash point is listed at 400 degrees centigrade which converts to
752 Fahrenheit. We know that combustion temperatures within combustion chambers go over 2000 Fahrenheit.
In diesels, lots of excess oxygen is present except at full throttle and during over-fueling conditions. Yet they develop and sustain the familiar solid carbon layer. It not only endures, it grows. Put on your Sherlock Homes hat for a moment and consider this. We know that if carbon is heated much above 800 Fahrenheit in the presence of excess oxygen, it will burn away. Yet these carbon deposits persist. What does that tell us? To me it says those carbon coatings are not getting that damned hot. Just as a large leaf folded to hold liquid water does not get to its flash point when held above a flame. The water boils, limiting the leaf's top surface contact temperature to 212 Fahrenheit. The leaf is thin and wet so its thermal transmission rate to its bottom surface is pretty good, which is why the leaf doesn't burn. Does that sound familiar? I think it should. That, according to my analysis, is very comparable to what's preventing carbon film coatings inside combustion chambers from self-cleaning and burning away. The gas is very hot, but the surface is not that hot.

Ok, before I go on, let me disabuse some readers about their opinion that all combustion chamber carbon deposits lower engine performance. I'm not talking about how it partially fills the un-swept combustion chamber volume at top dead center, which compression ratio effect is a different issue. I'm talking about its thermal conductivity rate compared to bare engine metals.
http://www.engineeringtoolbox.com/th...ity-d_429.html
Aluminum = 250
Carbon 1% Steel = 43
Carbon = 1.7
Balsa Wood = 0.048
We want low thermal conductivity combustion chamber surfaces to preserve piston-pushing pressure. Bare clean aluminum is a thermal conductivity disaster for that engine performance goal. But as internal combustion engines get a few hours on them, they develop thin carbon coating layers which drops surface conductivity from 250 to about 1.7. I would greatly prefer to have it dropped down closer to balsa wood's thermal conductivity, but rumor has it that balsa wouldn't make a very durable combustion chamber coating. (silly humor)

If we entrain a lot of tiny hollow glass or ceramic balls which act as thermal insulators within an extreme temperature tolerant paint, we can create an application-suitable matrix coating that drys or cures forming a thin but effective thermal barrier. These tiny balls are commonly referenced as micro-balls, micro-spheres, nano-spheres or cenospheres. Paints sold for application to exhaust headers seem like possible suitable candidates to hold these insulating spheres to combustion chamber surfaces. Since 800-Fahrenheit-tolerant carbon films endure within that environment, 1700 to 2000 Fahrenheit rated paints should easily be able to survive there too if they bond well to the available substrate which can be carbon that we know bonds tightly to aluminum.

It seems possible to me that the same people who have developed the current body of information about super hydrophobic and super hydrophilic surfaces may someday figure out how to create combustion chamber surfaces to which combustion product precipitates can't adhere. We already have self-cleaning glass. If we can have surfaces like that combined with low thermal conductivity, horsepower-hours per fuel gallon will noticeably go up.

We MUST keep cylinder walls cool enough to sustain a molecular lubrication barrier. You pay dearly for fuel to generate heat because internal combustion engines are driven by heat. Don't dump heat where doing so does no good. Cool those cylinder walls and cool that piston's bottom and insulate its top from absorbing needed gas-pressurizing heat within the combustion chamber.

From a practical view, I'd currently go with black paint mixed with lots of micro balls. The piston should run cooler, the head should run cooler, the cylinder should stay cool enough to maintain it's lubricity and power out should be a little higher.
John

Last edited by LoveLearn; 06-11-2009 at 03:42 PM.
LoveLearn is offline  
post #30 of 53 Old 02-18-2011, 11:28 AM
2 stroke addict
 
nickzom's Avatar
 
Join Date: Jul 2010
Location: Latrobe,pa
Posts: 1,101
Re: Potential Lawn-Boy tweaks - hand-lap reed, double crank seals, crankcase stuffing

Just wanted to bump this thread and see what ever came of these mods??

-Nick
nickzom is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the MyTractorForum.com - The Friendliest Tractor Forum and Best Place for Tractor Information forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome