OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers SB45 - Kirby to Briggs or ??

Hi all
I have a Scott Bonnar 45 with 17inch reel.

https://www.outdoorking-forum.com.au/forum/u...amp;Main=6404&Number=30812#Post30812

The Kirby (2.5hp)is on the way out so would like to understand if i could fit the 2.5hp B&S from my SB diplomat. Would it be a straight swap or require much to change it over?. Or am I better off looking to a new engine(and what would it likely cost)
I'm relatively handy but haven't done much mechanically so not sure if it would be extending my ability!! I've seen the you tube footage of removing the reel, but not an engine!

Any advice or info would be much appreciated....

Thanks
Barry

Hi Barry, this is a curly one....presuming that the output shaft free end of the Briggs is the same diameter as the Tecumseh; that the mounting holes for the Tecumseh line up when the Briggs is placed in the same position, this would not be a difficult swap.
Before we get the tools out, can you please post some pics of both engines and particularly the cutter clutch attachment to the engine shaft of the 17" machine and how the Diplomat is connected .
We can then work out a plan for you to proceed.

Barry, Briggs have two different engine output shaft sizes in the 2 to 3 hp range. Essentially, the 2 hp 60102 has a 5/8" shaft, the 3 hp 9 series engines have a 3/4" shaft, and in between is the 80102 which is probably the engine on your Diplomat. I don't know which size that 8 series engine has. I suggest you add these items to the pictures Deejay has requested:
- full series of numbers stamped on the cooling air cowl of your Briggs engine
- measure the output shaft diameter of your Kirby-Lauson engine where it goes into the clutch
- measure the output shaft diameter of your Briggs engine where it goes into the clutch.

Note we need the smaller diameter of the output shaft at the free end which slips into the bore of the clutch. We don't want the larger diameter of the shaft right up against the engine, where it goes through the oil seal and into the engine.

Hi grumpy, if you click on the link to pics in the first post of this thread, you will see that without removing the motor, measuring the free end of the output shaft would be nigh to impossible because of the position of the cutter clutch being so close to the engine. If the output shaft of the Tecumseh is stepped down, it will be full contained inside the inner clutch half.

Barry, it sounds as if it will be necessary to at least partly remove the engines from both mowers to measure the shaft sizes. Taking a good engine off a Diplomat to replace a bad engine on an SB45 does not, on the face of it, sound like the most economical way to replace the sick Kirby Lauson on the SB45, since it leaves a partly wrecked Diplomat behind. The engine SB fitted to the 17" Model 45 was the Briggs 80102, but I can't guarantee that it had the same output shaft size as the Kirby-Lauson engine, because SB seem to have had clutches with both 5/8" and 3/4" bore sizes. It will be useful for our archives if you measure both output shafts, and post the results here.

To measure the shaft sizes, you will need to loosen the clamp pin in the boss extending from the clutch on the engine side, if your model has a clamp pin. (Some had a grub screw holding the clutch boss to a key - if you have a grub screw, just loosen it a turn.) If you have a clamp pin, do not try to remove the pin, just loosen the nut and tap the nut end of the pin with a block of wood to loosen it. Then remove the four bolts holding the engine down to the mower deck. Hopefully you can then slide the engine half an inch away from the clutch to measure the shaft. Sometimes the engine shaft has rusted and jammed in the clutch bore. If that has happened you will need to put some Penetrene on the shaft and wait an hour, then try again.

Hi grumpy, this is why I asked for pics to be posted in my first post...to ascertain which clamping method is used by both machines....I have just posted in another thread how to remove the engine simply, step by step, and can re-post that here once we know the shaft diameters.

Regarding the swap, I feel that he wants to get the 17" Model 45 machine up to speed, and he may be able to source another serviceable 80102 for the Diplomat at another time. Providing the engine mounting point on the twin rails is the same for both the Tecumseh and the Briggs, even if the shaft diameters are different, all he would need to purchase, is a new inner clutch half.

Hi guys
Will take some pics on the weekend plus engine numbers.
Deejay, your correct that I'd like to get the SB17 running as my main mower, and will then consider what I do with my diplomat
Thanks

Hi Barry, having a look at the Parts List for the Diplomat, the engine shaft is secured to the output shaft of the Briggs with a 6mm grub screw....we need a pic of the inner cutter clutch half to see how that is secured; as grumpy said with a captive cotter pin or grub screws.
Looking forward to seeing the pics!

Well, Ive had a bit more of a look and taken pics.
Pretty sure the Kirby is a 3/4 shaft and the Briggs a 5/8...

You cant really see from the pics of the Kirby's.









So am really not sure if its worth the effort or the new LHS piece to put an old B&S on it...

Ive seen a few new engines on evil bay, brand new, thoughts ?
http://www.ebay.com.au/itm/Briggs-S...pt=AU_Lawnmowers&hash=item1e706759a1

Most of the ebay engines are Chinese ones. So far the cases we've seen suggest that the Chinese-made genuine Briggs engines are not yet as durable as the American Briggs engines we are used to. I haven't seen enough reports on Chinese-made genuine Hondas to reach a view on their quality. The unapproved Chinese copies of Briggs and Honda engines so far seem to have fairly serious issues that lead to short operating lives, or a lot of new parts, or both. They don't necessarily run badly when new, but there are reports of early problems with fuel system and ignition parts, and rapid wear on starters and engine controls. Most likely all this will be sorted out in due course and the engines will become desirable, but we don't seem to be there yet, based on the reports both here and on other sites.

There may be an alternative to buying a new clutch-half if your existing one, from the Kirby-Lauson, turns out to be 3/4" bore. You may be able to bush it down to 5/8", depending on whether it has a captive cotter pin or a key and grubscrew. However that kind of rework mostly appeals to people who have a lathe at home and enjoy making things.

Unfortunately the pic of the SB45 does not show the captive cotter clearly, I think I can just see the nut of the cotter, underneath the inner clutch half in the 2nd and 3rd pics. I would still like to know the exact diameter of the Kirby shaft free end...but I have a feeling Barry will be right, and it will be 3/4"....I have just checked the output free end of my Honda G100 and it is 5/8" the same as the Briggs and Stratton.
So....we may need a new inner clutch-half in any case (or modify the existing one) to fit a new (or second hand) engine....Honda, Briggs, Chonda, et al....

thanks Deejay and Grumpy

Im 99% sure the Kirby is 3/4. I could fit a 3/4 spanner between the inner clutch and engine, and was the right size for the shaft. Its also significantly bigger than the Briggs 5/8...
So couple more questions
-if I chose to go the inner clutch change, how do I remove current and refit (I can take pics of the captive cotter, is this the screw that holds the inner clutch to the engine shaft (is it also called the Engine Shaft Clamp pin???)
-secondly, Im leaning towards not relying on my old Briggs, as I not confident the old engine is reliable etc.. What/where/how much would other options of replacement be (vs the Chinese Briggs) ?

thanks again.

Hi Barry, seeing that Briggs and Stratton and Honda's are now being manufactured in China as complete engines, and spare parts as well....it is hard to advise you which way to go. A popular choice is the Honda GX120 and from what I can find, it has a 3/4" shaft.
As for prices Barry, you would be wise to shop around reputable dealers.

Thanks all..

So i have a budget of around $300
I have seen
-briggs (new) 3.5 on eBay -around 270
-Briggs (new) 3.5 local mower shop $400
-second hand Honda gx120 $250
-new Honda gx120 $542 (out of my budget)

Thoughts?

The new Briggs may be made in China. Our cases on Chinese Briggs engines suggest that initially they had serious quality control issues in the assembly plant, but this may have improved over the last year or more. However earlier this year Joe Carroll experimented with a recent Chinese Briggs engine and found that, with proper maintenance, it ran properly for 370 hours - but was then worn out. See this thread:
https://www.outdoorking-forum.com.au/forum/u...7178&Words=Chinese&Search=true#Post37281

The old American Briggs engines seem to have lasted considerably longer than this - but 370 hours' use is a very long time for a suburban lawnmower.

I have a high opinion of the Honda GX120, but a second hand engine may have problems, or may have been used commercially (which will eventually wear out even a GX120).

My personal choice of those options would probably be none of them, and I'd look for a GX120 that had some silly tuning problem that had caused the owner to despair and sell it. However when you do that, you have to be ready to make the necessary repairs however complex they turn out to be.

Hi Barry
I just purchased a Honda GX 120 and got it cheaper than $542
from memory and I would have to confirm
If you want to PM me at anytime happy to give you details.

I have a secondhand original Briggs from my SB45 that needs a bit of a restore. I am wanting to sell.
Not sure if that is an option for you.

Ok, well I have taken a punt and gone for a new Briggs engine. Time will tell if I've made a good or poor decision.

Whilst looking in detail at the engine, I've noticed a crack on the front engine deck rail. Hmm!!!!!
So decided to strip the lot, and fix/restore the frame and replace the engine in one hit.

Stripping The mower has been fun! Well mostly... I've got the reel and rear roller out, but engine is proving slightly difficult. One of the engine bolts has\was\is rounded and hence can't get it off... Ive enlisted the help of Neighbour and going to try and weld a nut ontop of the rounded nut to try and get it off.. Not sure there is any other way?? I've tried wd40 with different spanners and vice grips to no avail..

For bastard nuts, I have a tool here I use, not exactly know what to call it, but it has "jaws" stamped on the handle.

its like a stilson wrench, with sharp hardened steel teeth and a built in ratchet in the handle that makes it clamp down harder the more you try and turn it, Since enlisting this tool nothing has been a real issue.

Thanks joe, wouldn't be able to take a pic for me?

There is some writing on the side I forgot to write down, dont let its size fool you I have undone bolts as small as 8mm in fairly confined spaces without too much drama.

EDIT: Oh dear part of my "new toy" has been caught on camera for all to see