OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Scott Bonnar Original Engine - Rebuild or Replace?

Hi,

Just after some idea's or thoughts.
I have a Scott Bonnar 45 17" with the original fit Kirby/Tecumseh H4-4A. Because of the age of the engine it may be a costly excercise to completely rebuild it, so should I replace or rebuild? If replace, with what engine?

Cheers
Tony.

It depends, does the original engine require rebuilding?

It all comes down to if you want it original or not, you could recondition the old engine fairly easily if it was not too worn and needed just a simple set of rings and gaskets.

Otherwise you could get a similar type of horizontal shaft engine new off the shelf like a honda, etc and put that on.

Deejay on this forum is running a honda on his SB instead of the original B&S motor, maybe ask him if there was any drama swapping to a different brand.

Hey Joe, spot on advice there mate. They are exactly the considerations that TrajkulaSB45 should be thinking about.
In my case the decision was easy, my original B&S was becoming so unreliable and my concern was not originality but functionality....and my machine only had 2 probs; one was called Briggs and the other.....
I went for a Honda replacement because of their reputation; first pull starting and reliability.....It's the best decision I ever made. It was easy to fit, even the bolt holes lined up; and the Honda engine drive mated to the Scotty clutch assy perfectly. My engine is a G100 2.5hp.
TrajkulaSB45 may like to have a look at some pics of my machine in the topic "Old Mower Pictures" thread "Scott Bonnar Model 45 restored.

Thanks for you advice. I'm keeping the original Kirby and decided to install a slightly new B&S I aquired for free. Only downside is I had to install extender brackets to clear the handlebars from the fuel tank on the briggs.

Great restoration! I'll upload some photo's of my current 45 and some of a 45 I restored for my brother in law.

Hi TrajkulaSB45, I'm glad you're keeping the Kirby, and the Scotty will be original with the B&S.
Can't wait to see the pics of your projects.

When I read this ebay listing I keep thinking of you and your thoughts on B&S when I see this one

http://cgi.ebay.com.au/3HP-SCOTT-BO...fGardeningQ5fEquipmentQQsalenotsupported

Hi guys, sorry to dig up and old post but I'm in the same predicament at the moment after my Scott Bonnar started spewing out smoke and leaking oil badly.

I'm tossing up getting a rebuild but leaning towards a Honda replacement after reading a few posts here.

How much should a Honda G100 cost and are they still available? I have been searching around for prices and only come across the GX100.

Are they really as easy to fit as stated above?

Thanks in advance.

Cheers
Peter

Hi Peter, and a warm welcome to the forum. It's nice to have another Scott Bonnar owner join us, as we all love to learn new things and tinker here.
There are 2 things to consider here Peter, one is originality and the other functionality....You don't mention your SB model or what make of engine you have on your machine, so I'm presuming that it is a Briggs; in that case the older Briggs are a good strong engine and quite repairable with the help of our moderators and members here, and will keep your machine original.

On the other side of the coin, replacement of engine is sometimes the best option, as in my case. Unfortunately the G100 is no longer made, and I have not heard how easy (or not) it is to fit a GX100. Another consideration is that Honda engines are now made in China and some consider not up to the build standard of the Japanese made Honda's...yet!

So Peter, you have some decisions to make...no doubt you will receive further replies to help you.
Once again,

Other options to consider would be the Fuji Robin 3hp or the Kawasaki FJ 100d. However I don't know what the parts supply situation would be like for these donks judging by the experiences of locating parts for the FA130D. It is interesting that the Star SB 17" clone uses a Chinese GX 120 clone on it. I know it might sound strange but it appears that Honda has kicked an own goal by off shoring production to China judging by the amount of clones out there, or is it the case of the Genuine article having the cast iron sleeve hence why Honda can command the bigger $$$.

Greg, I suspect the Chinese clones would have been made whether Honda moved its own production to China or not, so their only choices were cease production of small portable engines, or establish their own Chinese connection. My personal guess is that Honda is capable of getting their own Chinese engine manufacturer to produce a quality product. It may take time, or it may not.

Interesting with that being said the Honda GC/GS series of engines are actually made in the US not china. With the US dollar collapsing over the long term how long will it be before production is shifted from China to the US. (There is a lot of pressure being applied for China to move to a fully floating currency away from the present which is pegged to a percentage of the US dollar)

The last lot of Kawasaki engines that I had a look at seem to be still made in Japan for the smaller stuff

Greg, the future value of the US dollar is an interesting topic but this is the wrong venue, so I won't comment. I didn't know that Honda was assembling mower engines in the US - I wonder where the parts are made?

Looking at the GSV 190 that I have I would say that all the ignition and carbie parts are from Asia.

Hi Fellas, Interesting stuff....but the question is, should Peter rebuild or replace his engine?

Deejay, the symptoms he has described (smoking, and blowing out oil) are both probably due to worn piston rings. If it is a Briggs & Stratton, that is a minor problem and on its own is fairly easily fixed by replacing the rings. However if the bore is damaged (usually due to having been seized up at some time, after running out of oil) he will need to replace the piston and cylinder at the same time (hopefully with free ones from a nearby junked B&S engine). I think what I would be doing in his place is identifying the engine (if its a B&S, and he gives us the numbers stamped on the air cowl, we can do that for him). If it is a B&S, he should consider its overall state of wear, to see if a minor overhaul will be sufficient. If it's a Kirby-Lauson (Tecumseh) I'd junk it: lousy engine, and parts too difficult to get except for collecting purposes. B&S engines that haven't broken the connecting rod are usually fairly easy to tidy up sufficiently to run well for a number of years, using second hand parts from wrecked mowers except for gaskets, fuel pump diaphragm, and rings, which of course should be bought new.

Thanks grumpy, good advice there...Over to you Peter...can you post you Scotty model number and mower number plus all the numbers stamped on the engine cowling...this will give us the year of manufacture and model of the engine.

Thank you all for your responses.

The mower is a Scott Bonnar 45, model # 14659, the engine is a 3HP B&S and has 8C stamped on it. I can't seem to find any other identifying numbers.

It has never seized before and has been serviced regularly, last service I was told the the carby would need to be replaced soon but otherwise it was in good condition.

My father inherited the mower from the original owner when he brought a house in 1986, I took possession of it 2 years ago after my father passed away. It spent approx. 5 years being unused due to my father�s illness before I got it and had it serviced.

Recently the mower had been difficult to start, usually it would start first or second time, It was flooding easily but when started would run fine.

I was half way through mowing the last strip when smoke started pouring out of the exhaust and oil started running out of the carby and over the top of the fuel tank.

You referred to the engine flooding, which seems impossible unless it has a gravity-feed fuel system. However you also referred to oil running out of the carburetor and over the top of the fuel tank, which would imply that it has a Briggs & Stratton vacuum carburetor, not gravity feed. (Gravity feed engines have the fuel tank above the carburetor, while B&S vacuum carburetor engines have the fuel tank below the carburetor.) Can you tell us what kind of fuel system it has, or post a picture of the engine please? And can you also have another look for the B&S engine model number? It would be on the air cowl - the piece of pressed tin that extends over the cylinder head and down around the flywheel. The number would be above the carburetor/muffler area, and is stamped onto the tin (air cowl), 19 digits long.

We need to clear up those points so I can interpret what you have told us.

It is a Vacum Carburetor.

Found the numbers required as well, Model: 80202 Type: 087901 Code: 80091503.

OK, we have a 130 cc engine made on 15 September 1980. (Your mower was probably made just a few months later.) It is a first-series vacuum carburetor engine with horizontal crankshaft, plain main bearings and a rewind starter. It has breaker-point ignition. It has a Chok-A-Matic carburetor, and in your picture the choke is applied, so it may be maladjusted, causing seriously over-rich mixture.

Now, is the smoke it emits black (petrol) or blue (oil)? If it is black, we can start by focusing on your choke mechanism. If it is blue, we need to look at your breather system.

The smoke emitted was blue.

So, the engine is burning oil and liquid oil is running around the top of the carburetor and fuel tank. You can see a black hose in that area, connecting to the carburetor just below the air cleaner. Is that where the oil is coming from? That is the breather hose. If the breather is malfunctioning, crankcase pressure can push oil up that hose. If that happens, chances are some of the oil will leak out and run everywhere, while most of it will go through the hose into the carburetor air intake, then be burned by the engine, causing blue smoke from the exhaust.

If oil is passing through the breather hose, you will need to take a look at the crankcase ventilation valve. This is part of the valve chest cover, which is screwed to the side of the engine below the fuel tank. If you remove that, you can see whether it is stuck in some way: it is a simple disc valve on the inside of the cover. Please post a picture of it after you remove it, and we'll discuss it from there. Do not perform any acts of violence on the valve, just show us the picture.

If oil is not passing through the breather hose, we'll need to do some head-scratching and take it from there.

Thanks for your help grumpy, yes it appears the oil came through the hose you stated and also got a little in the air cleaner.

I'll put the sledge hammer away and get the camera out again. I'll post the pictures up as soon as I have done what you suggested.

Cheers
Peter

Hope this it what you are talking about..

Yes Peter, that is the positive crankcase ventilation valve, and it looks completely clean. The disc valve you can see through the hole, is supposed to be able to move back and forth as the pressure in the crankcase pulses. This is what the manual says:

If the fiber disc valve is stuck or binding, the breather
cannot function properly and must be replaced. A .045"
(1.1 mm) wire gauge should not enter the space between
the fiber disc valve and body. (A spark plug wire gauge
may be used.) Check as shown in Fig. 10. NOTE: The
fiber disc valve is held in place by an internal bracket
which will be distorted if pressure is applied to the fiber
disc valve. Therefore, do not apply force when checking
with wire gauge.
Fig. 10 Checking Breather & Fig. 11 Breather Hose

It appears to be stuck on one side as I cannot insert the metal strip.

You should not be able to insert the metal strip anywhere around the fibre disk. If you can, the breather is worn out.

1. Did you clean the breather before taking that picture, or was it already clean?
2. Was the disk stuck to the metal, or could it move back and forth (transverse to the surface of the disk, not laterally)?

If the disk was crudded up and stuck, and you cleaned it and freed it up, we have an explanation for your oil-from-the-breather-hose problem. If it was pristine and working, we cannot blame the breather valve and have to consider uglier possibilities for the problem (like a broken piston, for example, since it happened suddenly).

I can insert the metal strip on most sides and can feel the disk popping back in position.

1. Only oil around the seal of the valve was wiped off. I did not touch the disk area.

2. The disk can move back and forth.

The engine still turns over freely and does not seem like there is any broken parts internally.

Did the smoking and spewing oil begin suddenly or did it happen gradually? If it isn't a stuck breather valve, it sounds like an abnormal amount of blow-by, which gets into the crankcase past the rings or through the piston, and is more than the breather valve can cope with. How does the compression feel, when you pull the starter? Different from a four-stroke rotary mower?

If the problem developed over a period of months or years, it sounds like you need new piston rings. If it happened suddenly, something has broken somewhere.

It happened suddenly, the compression feels fine and is different to my four stoke mower.

How is the compression different from the other mower?