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I have what I believe is a model 5233 and the rod/bearing assembly failed. I bought a used D400 engine and after I completed moving all the parts to the new long block assembly I noticed a difference that has me worried.

If you look at the picture, the failed block on the left has a bearing extension to support the shaft almost to the blade. The new engine has a shorter shaft with no bearing extension. The OD of the shaft is the same to theoretically I can put the old shaft in the new block but I wonder whether the engine/shaft will work with the shaft unsupported.

What I am wondering is whether this is how the newer engines were? Or was there a seperate lower bearing that the new engines used. Any comments would be appreciated.

I am not sure if I qualify in answering your question fully. I do know that the newer D engines like yours have a different style lower shaft end that also allows the engine to run at 32:1 vs. 16:1. I have a 5233 just like yours that has the longer lower end which I believe has a dual bronze bushing. Is one better than the other? I own mowers with both styles and I find that they are all very good. In my buying experience, I have noticed a lot of D engines have excessive play on the lower end of the crankshafts, but then again, nothing lasts forever and with years of use, everything wears out.

I want to compliment you on the cosmetic condition of your mower. Personally speaking, I think they are sort of eye catching in a funky 1960's kind of way. Mine runs very sweet and quiet and is a joy to use. I don't know if you are aware that originally, the flywheel screen was painted the same shade of blue as is the fuel cap, starter handle, the end of the speed lever and the on-off switch. I found this little bottle of paint in a Walmart store and used it on my screen. It is not only holding up well, it is a near perfect match.

Thanks for the reply, I think it is as you said, they just went to a shorter style bearing. At this point I've nothing to lose in trying it.

The I bought the mower in an antique center. It appears to not have been used too much, all the stickers are original. And it came with a brand new side bag. You are correct, somehow these mowers are reflect the high point of american manufacturing. beautiful castings, and an elegant adjustable carb and speed control. Of course in today's $$, it probably cost a $1000 so maybe that explains a lot.

It was a joy to use, I could pump it 10 times and it would start right up everytime.

It tossed the rod/bearing assy just came apart. while being used the last time I mowed the grass last year.

Yes those D-400 extended snout (dual bronze bushing) crankcases are interchangeable with most of the newer D-400 mower crankcases with the single bronze bushing. Your newer single bearing crankcase should work just fine on your model 5233. 1970 is when they started producing the D-400 single bearing crankcases for the residential mowers, the commercial D-400s continued with the dual bronze bushings for their entire production run. It is also the same time that they went to an all-needle bearing connecting rod which changed the fuel/oil mix requirement from 16 to 1, to 32 to 1. I think you did good! About the only time you run into an issue when interchanging those crankcases is when you go from a single to a dual without swapping the crank, then it puts the lower crank seal riding on a roughened area of the crank and makes it nearly impossible to make a good seal. In that case It's better to install a crank from a dual bearing engine, or just install a new crank.

Oh yeah, that 1965 model 5233 you have looks awesome, probably one of the best looking ones that I have ever seen. Same goes for yours 2smoked, you both have near perfect examples of one of my favorite Lawnboys.

I believe the "C" series engines had the extended "snout" too.

Racinbob said:

You are correct, somehow these mowers are reflect the high point of american manufacturing. beautiful castings, and an elegant adjustable carb and speed control. Of course in today's $$, it probably cost a $1000 so maybe that explains a lot.

It was a joy to use, I could pump it 10 times and it would start right up everytime.


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In my opinion, although the "F" engine is a very fine engine (came after the "D" engine), the "F" and the "V" engines were designed to be much simpler to manufacture, less costly to manufacture. It is quite obvious that the "V" engine, as on the Silver Series mowers sold at big-box stores in the 1990's is a cheaper "F" engine. Same piston, rod, crankshaft, seals. They also, over the years started compromising on the mufflers, going from cast aluminum to heavy steel to cheap steel, and they got louder every time!

Phototone said:

I believe the "C" series engines had the extended "snout" too.

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Yes you are correct, the dual bronze bushing crankcases were pretty much standard on Lawn-Boy engines prior to 1970. The only exceptions that I know of were the specialty engines like the edgers where there just wasn't room for the extended snout crankcase due to the pulley mounted just below the engine mounting tabs. According to former employees and various internet forum members the reason for the change in 1970 was just cost cutting. It wouldn't seem like it would cost that much to have such a small amount more of materials, but I suppose when you are talking about millions produced then the savings could be substantial. As far as whether they are better or not, well in my opinion the extended snouts are a little better. I think they offer more support to the crank when that small machined area fits snug down into the hole of the muffler plate, and it would seem they tend to last longer before the wear limits are exceeded.

Phototone said:

In my opinion, although the "F" engine is a very fine engine (came after the "D" engine), the "F" and the "V" engines were designed to be much simpler to manufacture, less costly to manufacture. It is quite obvious that the "V" engine, as on the Silver Series mowers sold at big-box stores in the 1990's is a cheaper "F" engine. Same piston, rod, crankshaft, seals. They also, over the years started compromising on the mufflers, going from cast aluminum to heavy steel to cheap steel, and they got louder every time!

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I totally agree, I remember seeing the Ads that bragged about the F series engines as having the fewest of any parts of all the Lawnboy engines. From what I understand it was a very competitive time for walk-behinds. All the manufacturers were cutting corners, and it continues today, hence the reason for what we see today in the big box stores compared to what we saw 20 or 30 years ago. Cast aluminum is almost unheard of now except for the commercial units. I think I'll stick with the old equipment, it should last me until I get to the retirement home. People laugh at me when I give such a generous quote on the value of a "Well maintained" 40 or 50 year mower, but I still think they worth more than going to a box store and spending 300 on a 5 year disposable unit. The key words here are "Well maintained".

Lawnboy77 said:

Cast aluminum is almost unheard of now except for the commercial units.

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All of the common 4-cycle engines on the walk-behind mowers at the big-box stores uses cast aluminum crankcases. Some, like Lawnboy did, have steel sleeves for the cylinder. Cast aluminum is not the criteria for quality, rather engineering is.

Phototone said:

All of the common 4-cycle engines on the walk-behind mowers at the big-box stores uses cast aluminum crankcases. Some, like Lawnboy did, have steel sleeves for the cylinder. Cast aluminum is not the criteria for quality, rather engineering is.

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I know I didn't specify, but the "Cast aluminum" statement was meant to be in reference to the deck material, not the engine...and most definitely a cast aluminum deck is a real good indicator of quality.

Lawnboy77 said:

I totally agree, I remember seeing the Ads that bragged about the F series engines as having the fewest of any parts of all the Lawnboy engines. From what I understand it was a very competitive time for walk-behinds. All the manufacturers were cutting corners, and it continues today, hence the reason for what we see today in the big box stores compared to what we saw 20 or 30 years ago. Cast aluminum is almost unheard of now except for the commercial units. I think I'll stick with the old equipment, it should last me until I get to the retirement home. People laugh at me when I give such a generous quote on the value of a "Well maintained" 40 or 50 year mower, but I still think they worth more than going to a box store and spending 300 on a 5 year disposable unit. The key words here are "Well maintained".

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I agree totally.

2smoked said:

I agree totally.

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gents - I am pleased to say the mower is back together and works fine. Once I got the carb filled it started on the second pull and settled down to a nice idle. I just ran it 20 minutes without a hiccup.

If any of you have a spare carb/reed plate that you would like to sell, I'd like to buy it. Mine was broken by the crank and my crude fix of filling it with gasket maker and retaining it with strap is effective for the time being. But I note it was wet underneath and it may blow out at some point.

Also if anybody has a need for the original piston, barrel or that crank that came with the new engine, let me know. The original piston bore got notched by broken crank but my bet is it would not affect the piston function. I'll send it with a return envelope. Pay me UPS + $5 for the hassle and I am fine.

Glad it's back up and running, I'll check for that reed plate tomorrow and let you know. I'm pretty sure I have a spare or two.

Thanks, that would be a big help. By the way, my new best tool is my M20 Milwaukee power ratchet. It's really handy like when you are sitting on the back step, with the deck across your legs and you are tightening the bolts that hold the engine to the deck.

Lawnboy77 said:

Glad it's back up and running, I'll check for that reed plate tomorrow and let you know. I'm pretty sure I have a spare or two.

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By the way, I found this plate on ebay that looks to be it. If you want to avoid the hassle, I can just by the ebay one. let me know

Racinbob said:

By the way, I found this plate on ebay that looks to be it. If you want to avoid the hassle, I can just by the ebay one. let me know
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Okay yeah that sounds good, just go ahead and get one off of ebay. It seems like those are going for a very fair price. Thanks, it's kind of a busy time for me right now.

Looking at the ebay listing, I see a bunch of seemingly identical reed plates having different numbers. My plate is 604233. There are several who's numbers are close but not exactly the same. Soooo.

My old plate works on the new mower, and the passage seems to be the same. Are there differences?

Here is an Ebay ad; LINK

I really don't see any differences but the numbers are different.

Just curious for your opinion, are these casting numbers or is there some difference that beats the eye.....
Here's my improvised fix.