The "M" series is a better mulcher and has much more power but is slightly clunkier than the d400. The "M" series has a magnesium deck. If you want classic Lawn-Boy the D series is the one but if you want a sophisticated Lawn-Boy get the "M" series.

"The "M" series has a magnesium deck"

Most likely the D400 also has a magnesium deck. IF so, the work Magnesium will be in raised letters on top of the deck, probably on the left side.

Walt Conner

The one with the d-400 will no doubt be much lighter by leaps and bounds, self propelled or not.

Get both!

The 'D' engine has bushings for main bearings and has to have a 16:1 mixture (smokey). The engine in the 'M' is much more advanced, with all roller bearings, but has a finicky oil-injection system. You can, however, 'unplug' the oil injection and just use a regular mix in it. If you plan to actually use it week in and week out, I'd say get the commercial. If you plan to bag clippings, yes, you will need a bag.

"The 'D' engine has bushings for main bearings and has to have a 16:1 mixture (smokey)."

Saxman, surely you know that only a small per cent of LB D400 used the 16:1 ratio ending by 1970. Unfortunately, that is when they went from 2 bottom bushing to one bottom bushing also. The D400 will be much lighter, mine weights about 45 lbs, and IF you really plan to use it, and the bottom bushing is bad, it can be bored out and replaced with a needle bearing from an "F" LB. I have some info on that.

The "M" is not a "real" LB to me.

Walt Conner

Good stuff, Walt. No, I wasn't sure when they started putting rollers in the 'D' and using the 32:1 ratio. Thanks for clearing that up. That definitely makes the older mower a legitimate option, particularly with the mag deck.

The "D" does not have rollers in the lower end. Its an "option" you have to do yourself. You will need to bore the "D" series bushing out and replace it with the needle bearing/race from an "F" series engine.

The older mower will always be a legit option for me. I ran a 1966 lawnboy d-400 for almost three hours straight through except to fuel up yesterday. I love the early spring and fall weather as its the only time of year my "C" and "D" series engines can handle the lawn. (thiner and dry)

Neal

Having a bushing in the bottom of the crankcase has nothing to do however, with whether you need to use 16:1 or 32:1 oil mix. You only need be concerned about boring out the bottom bushing and replacing with needles *IF* your bottom bushing is worn out to where the seal will not hold.

Walt Conner

Curiouser and curiouser. We have read for years on here that the 16:1 was because of bushings rather than roller bearings, now it's no longer true. Okay, then what is the reason for 16:1 (I have no idea why I care, since I will never own one)?

"Curiouser and curiouser. We have read for years on here that the 16:1 was because of bushings rather than roller bearings, now it's no longer true. Okay, then what is the reason for 16:1 (I have no idea why I care, since I will never own one)?"

You will note that I say the BOTTOM bushing. The D400 had needle bearings on the top end. The switch in mix spec came when they went to the 2 ring piston AND the needle bearings on the wrist pin end of the connecting rod, perhaps this was the bushing others were referring to which you may have misinterpreted. These parts can be interchanged and I have done it often only the connecting rod with needle bearings on the wrist pin end must be used with the 2 ring piston.

As for never owning one, reminds me of someone I know who says he will never own a Ford.

Surely most people know that the bottom bushing continued thru the D600 series which used 32:1 mix and all of these LBs had the mix written on them though in early years it was a decal which eventually became illegible. Some had the mix molded into the shroud.

I would note that there is a difference between "needle bearings" and "roller bearings". LB, until DuraForce, used needle bearings unless it was the "M" with which I am not familiar.

As I have said before on this and other lists, if you are uncertain what mix you should use, clean your exhaust ports and while you are at it, count how many rings are on the piston as you look thru the clean exhaust ports. Three rings = 16:1, 2 rings = 32:1.

Walt Conner

I'm afraid I disagree with your reasoning Walt. The three ring vs 2 ring piston is not why oil mix ratios changed.

The reasons mix ratios changed over the years can be traced to several things. In the 50s and 60s most manufacturers recommended high oil ratios for there 2 cycle engines because they were well aware that a large majority of users were running plain old automotive motor oil. In fact that was the recommended practice because a lot of the manufacturers had no oil of there own. Two cycle oils were not commonly available so they new they better recommend ratios like 16:1 to compensate for the oil that would be used. Nobody cared about smoke back then. In the later 60s and 70s much better 2-cycle oils became commonly available. The oil technology improved every decade. Lubrication technology improved dramatically. Synthetic oils were introduced. Less oil was needed and was also a desirable goal to help satisfy the pollution standards.
The 80s, 90s and beyond saw the introduction of many new fantastic oils that could lubricate at higher mix ratios like 50:1 and higher. Engine manufacturers tend to recommend somewhat conservative ratios to cover themselves in the event a customer uses a somewhat less than good oil. And the better oils are somewhat expensive too.
Anyway, today, in 2008, there is no need for 16:1 mix in any 2-cycle engine if you use the best oils available. If you use basic motor oils like Texaco Havoline or Shell X100 you better go with 16:1 and hide from the EPA.

I have three Lawnboys which require 16:1 ratio. I have used 32:1 with no noticeable issues. I actually prefer the older D-400 and "C" series Lawnboy mills that require 16:1. They have a much more stout lower bushing reducing the chances of bending the shaft because there is a "sleeve" completely covering the length of the lower pto. This has pro's like mentioned but also a con. If you do hit an object really hard with the blade you will risk shattering the armeture housing or flywheel breaking. I've never seen it happen but I've heard it could.

As for oil ratios, the old three ring pistons had a bushing on the piston end of the rod. Later "C" and D-400's had the needle bearing on this end and thus requiring a two ring piston. I have converted one of the older long bushing and three ring engines to a two ring piston and newer rod and now run 32:1.
Initially I agree that both oil quality and better parts led to higher ratios.

BTW, when I run 16:1 I really don't have much noticeable smoke. Its all how the carb is tuned.

Neal

The change with Lawn Boy lube spec. occurred when the changes I mentioned took place and of course the number on rings had nothing to do with it, the number of rings is only an indicator of the presence of the update.

Walt Conner

Ok, I see what you're saying now. I thought you were saying that the 3 ringed pistons could not tolerate 32:1 because of the fact that they had 3 instead of 2 rings.

Sounds like the d400 is more reliable, but the M is great if you enjoy the unique lubrication system. Is there a "best " lawn boy push mower?

"Is there a "best " lawn boy push mower?"

I like these. This is a 10515 with an "F" series engine, three speed tranny and aluminum deck.
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