OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S motor for SB45

Hi all, doing up an SB45 at the moment. Chassis is all in the process of being sorted, time for the engine.

Started to wonder why bother with my old original engine so had a look at what I could replace it with. On the B&S site the best option displacement and power wise seems to be the "550 Series" which has a layout similar to the Honda GX120/160 engines with the tank on top.

Further browsing online has discovered an(I guess) superceded model in the 91200 series that is 3.5hp and mimics the layout( tank behind and low down) of my original motor.

Anyone know where I might be able to get my hands on one of these? Or if B&S has a current model that has a similar look to mine? there seems to also be a 5hp version, that would be even better.

Pics of mine are in my post at this link:

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=32611#Post32611

David, the first question is why you want to discard the original engine? There are modern engines that are at least as good, but there are also plenty that are not nearly as good - and they are not the original engine, which itself is an argument against putting them on a collectible mower.

The fuel tank placement is just a question of whether you have gravity fuel feed or a suction-type carburetor. I think only Briggs used the suction carburetors, and they used them for their smaller engines, less than 10 hp. In recent years they have been switching the small engines to gravity feed. The relative merits of the two are probably in the eye of the beholder. Gravity feed is simple and faults are easy to diagnose. Suction feed is safer - fuel cannot feed unless the engine is running, so there is no fuel tap, or indeed any place to put one.

A new engine in the 3-5 hp class that you buy now will be made in China, and there are indications that Chinese producers are still on a fairly steep learning curve with regard to production quality. You can read about some cases on this site if you do a search.

The choice of what engine to use is of course up to you. If you replace the original one you will reduce the value of your mower, especially in the longer term, but if you feel it will become more convenient to use, that may be more important to you than maintaining it as a collector's piece.

Thanks again for the help Grumpy.

I think my ideas about changing from the original engine came from just getting lazy. The original donk does run well and will keep the mowers originality, it just needs work to present as well as the rest of the machine and I thought I could save a lot of effort by just getting a new one that at least superficially appears like the original.

This mower is being built to work and ease of starting, fuel consumption, etc are important. I thought that a modern engine would be better in theses areas.

David, you are not wrong about being able to improve on the fuel consumption and ease of starting of the Briggs 80202. Because it is a first generation Briggs design your carburetor has a really nasty choke, and like all side valve mower engines I can think of, it has a compression ratio of only 6:1 so fuel consumption is relatively high. However despite the nasty choke it should always cold start with three pulls. Pull once or twice with the choke closed and it will chug then rich-load and stall. Then open the choke wide and it will start first pull and run until the tank's empty if you don't turn it off. Also, despite the poor thermal efficiency of low compression engines, because a reel mower has a low power requirement compared with a rotary mower, you'll still find the cost of fuel is extremely low.

There is one engine that will outperform the 80202 on both starting and fuel consumption: a small overhead valve Honda from the days when they were still made in Japan. If kept in perfect tune it should start first pull, and with its compression ratio of 8.7:1 for early production and 8.0:1 for later production, it will probably use 20% less fuel for the same power output. However it would look wrong on your mower, and pretty much eliminate its collectibility. Parts are also notoriously expensive, and professional repairs prohibitively so. Since you would be buying the engine second-hand, it sounds a risky proposition for trivial gains over the engine you have.

Of course if you want a more advanced engine, you could simply fit an OHV Honda and put the Briggs into storage so the mower can be restored to orginal condition at some later time. Because the engines are physically interchangeable, this is easily done. However I suggest that you avoid Chinese-made Hondas, and even more rigorously avoid Chondas (unlicensed near-copies of Hondas made by Chinese firms). Also avoid side valve genuine Japanese Hondas, because they have no fuel consumption advantage over the Briggs.

Thanks Grumpy,

I would not be throwing away the original Briggs, so the option would be there to re-fit it at a later stage if I want to go back to original.

First choice would be a Honda, but they're pretty expensive new. I saw that I can get a B&S 550 series for only $269 delivered on ebay. Would this be a chinese made engine?

Are all the modern Honda motors made in China? I recently bought a new HRU196M1 with the commercial GXV160 motor, has run flawlessly in the 7 weeks I've had it(as it should for $1k). Gonna be pretty upset to find it has a Chinese motor.

Would love a Honda GX160, they're rated at 4.8hp, if I did decide to cough up Honda's ask price of $533.56 would I have problems with the SB's clutches being able to handle the extra grunt?

I don't know which Briggs or Honda model is made where, David. Joe Carroll or someone else will be able to tell you the answer, or what physical properties of the engine to examine to find out.

With regard to engine size and power, I doubt you would be able to make any use of anything more than say 3 hp for a 17" mower: the machine will just accelerate to the speed that corresponds to 3,500 engine rpm (the maximum speed the engine's governor will allow) whatever engine you use, unless you are on a fantastic slope. Reel mowers will not cut long grass, so you won't be able to overload it that way. Essentially the original engine was sized to suit the task that mower can undertake. However if you did find a way to exert more load, the clutches would suffer a higher wear rate, especially the drive clutch which is used a lot more than the cutter clutch. There would also be a possibility that the cutter clutch would slip while fully engaged, due to overload - especially if its spring has been in use for quite a while.

Thanks mate.

Getting un-lazy and sticking with the original. Your advice has been great.