OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Model 33 - Kirby Engine - Replacement Engine?

Hi. I bought a model 33 mower about 6 months ago and have been using it ever since I got it, however the original engine gave up on me this morning. Can someone please help me by recommending what I can use for a direct replacement?

I will post pics later when I get near a computer if required.

Regards

Brett

Its a Shame,I got an Engine sitting doing nuffin...But Im in Sydney...Should be a Briggs 3.5.Just Hang on as there are some serious SB Reel Experts here,Im sure They will be able to help you with the info you require fairly quickly.

sikpupy, please post pictures of the mower and its old engine. Are you looking for:
1. Any engine that will suit the mower well?
2. An engine the same as the old one?
3. The "best" engine (in somebody's opinion) for the mower?

Also, what was the old engine, and what went wrong with it? The Model 33 seems to have been built with two or three different engines over the years, and some of them do not die easily - most faults are not difficult to fix.

You might enjoy the pictures of a restored Model 33 in this thread:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=16085

Hi Brett, and a warm welcome to the forum. It's great to have another Scott Bonnar owner on board.
Here's some info:

The Model 33 Mark 1 Scotty was first introduced in 1960 and is a 16" machine with a Villiers 98cc, Mark 3 'Midget'...2 Stroke engine and all chain driven and a segmented wooden front roller.

The Model 33 Mark 2 (also 16") was fitted with a Kirby Tecumseh HK25, 2.5Hp... 4 Stroke engine and was belt and chain driven and the metal front roller and alloy end caps.
Which one is yours?

Hi guys and thanks for the reply.

It is definitely a mk2 As it is belt drive and has the metal front roller. I believe it has a 4 stroke engine fitted to it and it is the original.

Engine siezed on me today. All I really want is something to replace the old engine with something that is suitable for the machine whether it be new or used.

I was hoping that it was going to last longer than it did but it is a really old machine and the engine was tired. I know it is probably easy to fix if I were to pull it apart but in the short term I just need it working over summer so I can keep my lawn looking good.

The local mower shop told me to scrap it but its tooooo good for that.

We need to see pictures of your mower and its engine, to verify that it is as we are visualising it. Most likely the 4 stroke engine is a Kirby Lauson, probably an HK25 (2.5 hp). Most modern 4 stroke horizontal crankshaft engines are interchangeable with the HK25: they have the mounting bolts and the output shaft in the same places as that engine, so they will bolt straight on in place of it. However, the Kirby Lausons had 3/4" output shafts, whereas the equivalent size Briggs and Stratton engine (model 80102) had a 5/8" output shaft, which would involve you in extra hassles to replace the pulley that mounts on the output shaft. So, as Bluegmhtmonaro said in the first place, your easiest solution is to fit a 9 cubic inch horizontal crankshaft 3.5 hp Briggs (model number will begin with 9 instead of 8 - example of a suitable current model is the 93432, but older models are just as suitable) mainly because most of them have a 3/4" output shaft. You could equally easily fit a Honda GX120, an even nicer engine but a more expensive one. Note that where the HK25 was only 2.5 hp, the 9 series Briggs is 3.5 hp and the GX120 Honda is 4 hp - both have plenty of power for the job, and both should be smoother, quieter and easier to start than the Kirby Lauson.

Because both the 9 series Briggs and the Honda GX120 have optional 5/8" output shafts, you need to verify that the one you get has a 3/4" shaft.

Both engines are readily available second-hand, for much less money than a new one. Note that these engines had more than one output shaft length, but one length is usual (approximately 2.5"). Be sure you do not buy an engine with the optional built-in reduction gear between the output shaft and the engine's crankshaft - these are less common than the direct drive engines.

This may be unwelcome and gratuitous advice, but it is quite unusual for Kirby Lauson engines to seize unless they are allowed to run out of oil. 4 stroke mower engines have an oil sump like a car engine, and it is essential that the sump be kept filled to the correct level with clean engine oil (yes, it has to be drained and replaced every year or so). Please do not fit a nice new engine to that nice old mower then seize it up through neglect.

Hi Brett, I do agree with grumpy a second hand Briggs in good running order, may be the answer. There must be some out there...2.5HP, 3 Hp and 3.5Hp and all will fit your machine with a little effort.
Here's a pic (sorry about the quality, its the only one I have)

If you could source a Briggs, and there is a problem with the output shaft size, you could replace the engine side clutch housing with the 5/8" model ; it is available in the online store and will fit the Model 33 as they both have the same cutter clutch. See HERE

Thanks again for the replies, here is pictures as requested. I might buy a new engine for it next week once I have worked out exactly which one to use but I think I will use a B&S engine, at least this will keep the old girl going for another 50 years.

Grumpy, it didn't sieze due to lack of attention. I have only used it a few times since getting it back from the mower shop after new bearings, belt, bottom blade and a sharpen. I think they even changed the cork on the clutch as well. The engine unfortunately when I bought it was tired to start with, although it was extremely easy to start, it had hardly any compression and didn't sound too healthy. I did drop and change the oil before I used it the first time but I dont think there was much life left in it. I am going to give it a birthday over the next few months and have started drawing up the catcher so I can fabricate a new one.

Thanks for clearing that up, Brett. From time to time an engine seizes despite sufficient lubrication. In cases of extreme wear, for instance, a piston ring can have become so thin radially that it slips out of the groove in the piston, and jams between piston and cylinder bore. An extraordinary case of "dusting" (running without an air filter, leading to dust being inhaled with the intake air, and then acting as an abrasive between piston and bore) can also cause seizure. So can running with no cooling fan, or with cooling fins blocked by dried grass clippings or wasp nests.

While I don't like those Kirby Lauson engines, I have no complaints about their durability - they last just as long as Briggs or Honda engines. However, in my limited experience with them, it seems even longer than it is. If you get the right Briggs engine, you should be pleased by the change.