OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Reel-Type Mowers Scott Bonnar 45 Rebuild

Yes, to the center of the clutch mechanism mounting pad, on both rails. That should eliminate the possibility of fatigue cracking of the rail at the inboard end of the gusset.

Hi Grumpy and Boeing,

ABSOLUTELY !, I couldn't agree with you more Grumpy, regarding the length as that is what I intend doing on my 20 inch machine. I wasn't going to suggest it publicly but decided not to say anything until I had done it myself.
Basically the theme is very good, but wherever the gusset finishes is always going to be a higher flexing point, thus that's where the load will inevitably be transferred to. In actual fact the load would basically be put upon the weld joints at the side plates.
The only way to avoid a vibrating Briggs and Rattler causing any issues is to build the chassis like a "Supercut" or replace the power plant with a smoother running Honda or Chonda.

Cheers,
BB

Hello all

In any case, full credit to Mr Jones' Gusset Plate method.
He has offered a relatively cheap solution to repairing and extending
the life of a great design, that has given decades of proud service
to thousands of users.

All very interesting.
---------------------------------
JACK

Are the new Briggs engines a lot smoother?

Are the new Briggs engines a lot smoother?

Hi Boeing,

They certainly are and also are somewhat cheaper than what they used to be years ago due to the Asian competition.

Cheers,
BB

BB,

Think of the rails as a suspension spring in a car, be it a leaf or coil, if you stiffen up that spring, the axle loads transfer to the spring mounts, what will happen to the mounts?

Changing the flexible nature of the rails will only move your problem elsewhere. I would imagine repairing a side plate with a large crack or hole in it would be very costly and difficult.

Boeing,

Comparing the 1970 B&S with the 2015 B&S they both still wobble around. Getting the right engine speed is the key.

Hello all contributors,

BB, exactly what model 2015 B&S are you referring to?
I think a modern B&S slant engine to be pretty similar in smoothness to an equivalent Honda.
Both are 'sloper' designs now. Both are OHV.

It would be great to get input from an engine engineer as to how forces are transferred
in slant versus upright piston travel engines... and how that relates to smoothness.

A Historical Perspective
It's pretty clear that when Honda introduced their small engines that they were superior
to the kool bore Briggs used on 45s. In fairness to Briggs, the 6, 8 and 9 series designs
were decades old - even before they appeared on Scott Bonnars.

For me, what the Japanese did was wake America from its slumber, in a way very similar
to its automotive experience. Britain, for example, did not respond anywhere near enough,
and their famous cars, bikes and engine manufacturers disappeared one by one.

America did respond. The Briggs engines of today are a result of consumer trends and
demands post the Japanese experience - and shock. I'm keen to dispel myth here.
If a customer wants a low-spec. Briggs, they can but one; if they want a high-spec.
Briggs they can buy that too! Honda has not ventured into the bottom end of the
market; The Chondas do that, and they do it well.

Anecdote
One thing I am keen to dispel are the general statements: Honda: good; Briggs: bad.
It used to annoy me when I knew so much of Briggs' poor reputation post Honda
was beyond their control. OEMs were regularly misapplying models not intended
for the purpose, in order to gain sales as the 'cheaper product'.

At the Briggs Engine Application Centre I personally saw Australian manufactured
lawnmowers (including ride-ons) that were shipped over for specific application
matching. In many cases, it would be the simple (and complex) changing of a
governor spring that would make all the difference between a machine that would
fail - or not fail - down the track. In other cases, the recommendations were
extensive - ranging from specific modifications in the machine design to a higher
specification of engine. And, yes, there was comprehensive vibration testing.

I also knew that thousands of small OEMs never took advantage of this free service,
and Briggs would cop the resulting criticism.

The issue of the 45 rail failures is a complex one and I believe its cause is
plural - causes. The SB45 is in a unique position in that, for many, it is not
considered a vintage mower. Many have served continuously over three or four
decades (and beyond), and many owners repair them with the intention that they
will be every-week mowers - not show pieces! Any component failures now should
be considered both understandable and forgivable.

Would I recommend a Honda as a replacement engine on a 45? Absolutely.
Would I recommend a Briggs as a replacement engine on a 45? Absolutely.

All very interesting.
-------------------------------------
JACK

Jack, I explained in another thread how single cylinder engines are balanced and how vibration is controlled. Essentially, all single cylinder engines since the earliest days are "half balanced" unless they have either a reciprocating balance weight or use counter-rotating shafts. Half balancing consists simply of increasing the weight of the crankshaft counterweight to include half the weight of the piston, gudgeon pin, and small end of the connecting rod. Both Briggs and Honda use reciprocating weights or counterrotating shafts on their large single cylinder engines but not on their small ones. So on the small Honda and Briggs engines the balancing technology is the same: half-balancing. However Briggs may do it less well in some cases, by using the same crankshaft on engines with the same stroke but different bore diameters and therefore different piston and connecting rod weights, which would make the half-balancing inaccurate. To be fair, though, Briggs is not the only manufacturer to do this: the Honda GXV120 and GXV140 share the same crankshaft, despite having different bore diameters, and therefore most likely, different piston weights, though I haven't weighed them to verify this. They use the same connecting rod, so that is not a source of balancing error.

I am not aware of tilting the cylinder on a single cylinder engine having any effect on engine vibration: I believe it is done to make the engine more compact, not to make it smoother.

One of the things that gives OHV Honda and chonda engines an advantage over side valve Briggs engines, is that they fire every shot: no misfires. Misfires cause a slight torsional vibration of the engine, and also require the throttle to be opened slightly more to compensate for the missed power strokes. However the main advantage the OHV engines have is that they have a much higher compression ratio - typically 8:1 instead of 6:1 - and so have much less cubic capacity for the same power output. The residual vibration produced by a half-balanced engine is proportional to the weight of the piston, gudgeon pin and the small end of the connecting rod, so OHV engines vibrate less than side valve engines simply because a smaller engine is doing the same job.

The outcome of all this is that provided you select an engine of the same power output, an OHV engine will vibrate noticeably less than a side valve engine. Unless they go overboard with commonising crankshafts across their model range, Briggs OHV engines should potentially be as smooth-running as OHV Hondas of the same capacity.

Hello Grumpy

Thanks, as always, for that succinct re-explanation. I'm sure it
never hurts to reinforce the basic physics of single cyl IC engines.

You will appreciate, then, my argument that 'apples should be compared with apples'
The old Briggs side valve alloy designs, dating back to the 1950s, should not be
used, or applied to, the modern generation of Honda and Briggs engines.

Your last paragraph - in particular - is a salutary reminder to all, and its principle
is clearly applicable to other long-standing 'which is better?' debates. It's best
to avoid general statements; better to compare model for model - apple with apple.

Cheers and thanks.
-----------------------------
JACK

Update,

Began further dismantling and faced an issue with getting the roller sprocket nut loose. A soak with WD40 and then putting a 3/4 ring spanner on it and giving it a sharp hit with the hammer did it. This advise was found in another thread.. Love this site.
Cheers

Hi boeing,

We all try our best to help out as that's what this site is soley based around.
I'm glad you're enjoying it.

Cheers,
BB

All sprockets off, and a bit of the old paint has survived.