OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines B&S 45 no spark

Hi folks,...newbie post with an old problem. I have a Scott Bonnar with a Briggs and Stratton 45, it used to run until I stuck it in my son's shed for 3 years or so. It turns over fine and has compression but there is no spark. Through studious reading of this wonderful site I have followed the tips on tracking backwards through the magneto and have arrived at the points behind the flywheel ( which look in remarkably good condition). I have tested the wires for continuity and breakages and they seem fine however, I think my reading of a multimeter shows the capaciter is faulty (I suppose I'd better get to a question). Do the gurus think its a simple matter of changing the points or have I missed something?

I'd just like to say congratulations on a wonderful site, its only through reading the posts and enjoying the restoration journey's of others that I decided to get the old girl out of the shed (I'll get the mower out tomorrow). I intend to restore it and post as I go along but thought I'd get it going first. Sorry if I'm posting in the wrong topic or making everyone yawn with "not another one!!!" Hope I can get the pics right. Thanks in advance, cheers! Finbar

Trying to post a pic

Hi guys is this right, for pics I mean?

Hi Finbar, and a warm welcome to the forum. I always nice to welcome another Scott Bonnar owner to the forum.
Firstly, yes, you have posted your question in the right forum for questions on your engine, and thankyou for posting the pics.
When you are ready to start your restoration can you please post HERE which is the restoration forum for reel type mowers.

Grumpy is our Briggs and Stratton guru here and I'm sure he will chime in here and help you.
I will assist you with any chassis/clutch/ sharpening issues you may have.
Once again Finbar, to OutdoorKing.

Hi Finbar, there are a couple of things that need to be completely clear before taking the next step in this diagnosis. You will be aware that your ignition system has a "kill switch", which in very early designs consisted of a metal bit that pivoted forward and shorted the top contact of the spark plug to ground. On later machines it shorted the low tension instead of the high tension - on breaker point machines by grounding the non-grounded side of the breaker points, and on Magnatec machines by grounding the floating side of the switching transistor. You need to be completely sure that you had isolated the kill switch when you tested for spark. This usually requires disconnecting the kill wire at its source, not at the point where it is switched to ground by the kill switch, because it is not unusual for the black kill wire to have worn through its insulation and become grounded somewhere en route to the switch. So, please be very sure the kill wire was isolated when you tested for spark.

You also need to be sure that the coil is properly grounded and is the correct distance from the flywheel, and that the wire from the coil to the breaker points is not grounded. Check that the high tension lead from the coil to the spark plug is also undamaged - I once clamped the cooling air cowl in such a way as to pinch the HT lead, which resulted in no spark after an hour or two of use. Check that the flywheel magnet is in place and is still magnetised.

Next you need to check that the breaker points are making good (low resistance) contact when they are closed. Verify that the contact surfaces are clean, not blackened, and are making full-area contact with each other. Check that the non-grounded breaker point and its attached wire are not grounded or leaking to ground.

Once you are sure about those points, there should only be two remaining causes for no spark: either the capacitor (condenser) has failed, or the coil has. Capacitors are much more prone to failing than coils, and are much cheaper to replace, so at this point you should try another capacitor and see if that overcomes your problem. If it does not, you will need to try another coil.

Note that after a lot of wear, the plastic plunger that runs through the wall of the crankcase and operates the points may leak oil into the points compartment, which keeps the ignition from working. If there is oil leakage into the points compartment, replace the plunger and see if that fixes the problem. If it does not, the only cures are reaming out the hole the plunger runs through and bushing it, or switching to Magnetron ignition. You would need to have a special reason for rebushing, since fitting a Magnetron is a great deal easier and tends to produce a better ignition system.

Incidentally I have not found a way to test an ignition capacitor with a multimeter that means anything much. The capacitor experiences a peak voltage of about 150 Volts in service, so you'd need a megger rather than a multimeter. Even then, because of the very rapid voltage transitions that occur in a running engine, the test would be inadequate.

Hi Deejay and Grumpy many thanks for your welcome and replies, feel at home already.
The kill switch on my model is the metal pivot to the spark plug and as far as I can tell does not cause a problem. There doesn't seem to be any oil around the points so I'm assuming the plunger is ok and as far as I can tell the wiring is in good order.
I spoke to my local mower man and he had a set of points for my model so I bought them ($23) which is about right I think. In my haste to get back and try them out I decided to just fit the new condenser side of the points just to see if I could get any sign of a spark (lazy I know). I then reassembled it but still no spark.
As far as I can tell, the points contact is good and they make and break, the wiring is ok but I can't really be definite, the flywheel and magnet are good and I assembled the coil to it using the business card gap system and things rotate well, so I'm guessing the coil?
When I was getting the points from the mower man he said he uses the Magnatron which doesn't require points and I see you mention it Grumpy. He said they were expensive but he has a second hand one, and although I nodded I didn't really understand, I just wanted to go and try me points!
Is it likely that a coil would fail just by sitting for a long time? (Ha, I can't believe I've just written that question. Sorry Grumpy.)
I've managed to find the model numbers on the cowling, are you able to identify this one?
Thanks again guys, regards, Finbar.
B&S model 9250
Type 1029-01
Code 79111325

SB 45 11235

Hi Finbar, I can, from the pics, give you some info on your Scotty. Yours is a 14" cut early model 45...This I can tell from the solid engine deck, alloy end caps on the front roller and the brass ID tag.

The 14" Model 45 was first introduced in late 1967/early 1968 and was manufactured at the Thebarton factory in South Australia. It was fitted with a 2HP Briggs and Stratton painted silver. Some may have been fitted with a 2.5hp. engine.

Your machine has also had a new Briggs fitted at a later stage as your Briggs is a 3 HP. manufactured on the 13th November 1979, which is shortly before the take-over of Scott Bonnar by Rover Australia, and the twin rail engine deck Scotties were in full swing!

PS. I wonder what happened to the original engine...

Hi finbar. Let's start with the easy stuff. Your data indicates that your engine is a 92502, which means it is 9 cubic inches displacement (148 cc), is of the second design generation, has a vertical crankshaft and a Vacu-Jet carburetor, it has plain main bearings and no built-in reduction gear, and it has a radial-pull rewind starter. At this point we have already struck trouble, because your engine has a horizontal crankshaft, not a vertical one. It looks to me as if someone has fitted the wrong cooling-air cowl to that engine, and perhaps has made other changes as well. I doubt there is any point in going into the rest of the information that can be gleaned from the model, type and code, since it seems unlikely they apply to your actual engine. However at least we now know why your Briggs & Stratton 3 hp decal is upside down: it is the correct way around for mounting on a vertical crankshaft engine.

Getting back to your ignition problem, did you try replacing the capacitor (condenser)? That seems the most likely cause of your problem. At this point I have no idea why you replaced the points.

If you try, or have tried, replacing the capacitor and this does not help, it would be time to consider whether to try replacing the coil, or alternatively, fitting a Magnetron ignition unit.

I suggest that you do not buy a Magnetron from a merchant without first asking our members to send you PMs with prices for second-hand units. You could do that through our Wanted forum.

Well spotted Grumpy, I wondered why the decal was upside down.....but herein lies the question...can the original engine (2 or 2.5HP) be fitted with that cowling and are there any other distinguishing marks on the crankcase or elsewhere to identify the model of the engine?

I can't think of a way to tell, Deejay, other than asking finbar to take some pictures of numbers cast into the crankcase, and then asking members who are hip-deep in Briggs engines to compare the numbers with various engines they have.

I think it is not all that likely the engine was replaced, since the "new" cowl is not from a remotely suitable engine. More likely the original rewind starter clagged out and the previous tenant just reached for the nearest available replacement starter that could be fitted with the least effort. If so, it is still the original engine, just with the wrong cowl.

I think maybe you are spot on Grumpy, that was my thoughts as well....what we need now is a member with an early 14" SB with to post here the numbers on his air cowling so as we can narrow down perhaps what is presently on this machine.
Joe Carroll may be able to help here.

Presumably the engine is either a 60102 or an 80102, since those seem to have been the standard engines for the SB45 after the Kirby Lauson phase was finally over. I think both have the same bore but different strokes (i.e. same cylinder/crankcase, different crankshaft) so the obvious way to check which you have would be by measuring the stroke, using the old pencil-through-the-sparkplug-hole trick. However as you said, Joe Carroll probably has both engines ready to hand, and a detailed knowledge of the differences between them.

Thanks for that Grumpy, I am sure Joe will be able to sort this for us.

Hi Guys, sorry for not being in touch,was given strict instructions to keep away from the shed. (son's wedding)
Managed to get back for a quick photo and reply. Many thanks for your info, can't believe people know so much. Seems I have a bit of a mixture of a mower.
I've taken a few pics of the cowling. Now that you mention it, it does seem as though it doesn't quite fit. I can even see a shadow where the original one had been (not sure it comes out in the pics). I can't seem to find any other markings although I haven't given it a good clean yet.
Grumpy;
When I bought the new condenser it came as part of a points set, with plunger etc, so I just fitted the new condenser and gave it a go. I haven't had time to try it all again, with the family thing and all, but if I've put everything back ok it looks like it will be the coil that's the problem.
Unfortunately I'm not going to be able to work on it for a week or so but I'll get back in touch as soon as I can get going on it.

Many thanks guys for your info and expertise, just brilliant.
Kind regards,
Finbar.

It's quite common to replace the standard cowling with one from a 2-3.5hp I have found in the past, either the starters break around the mounting bolts(rare) or the little starter ratchet clutch becomes dried out enough that the friction heat from it melts the starter reel, I am guilty of this modification before as its much cheaper than finding a nre direct replacement.

Finbar, I can see in your new picture that your engine has a spring-loaded device to short the spark plug: the piece of steel sheet springs back when you stop pushing it against the top of the plug. I haven't personally seen one like that since Briggs' WW2 engines. At some point Briggs switched to using a generally-similar device made from aluminium, that pivoted where it mounted to the cylinder head. This meant that when you switched it off by snapping the piece of aluminium into its "down" position, it stayed there and the engine stayed switched off. This was likely to be safer if someone rotated the engine for some reason.

I don't know at this point whether the spring steel device was retrofitted to your engine, or it remained in use much longer than I thought.

looks like the spring steel device was retro-fitted, you can tell because on the opposite side it has all the correct pieces for the correct killswitch.

Might be a silly question, but have you changed the sparkplug?
Also the spark plug lead, is it shorting out anywhere?

How exactly are you testing for a spark? The easiest way is to hold the end of the spark plug on the metal and pull, you should be able to see a spark, and get a nice little shock in the process

Hi Guys, not able to get to the mower just now, as the boss say's " This bathroom won't tile itself y'know!" but do get to read the posts.

Seems I have an engine that has been modified over the years so it might be difficult to establish just what year it was manufactured Great when you think of the life it must have lead, hope I can do it justice.

Hi tezza, saw your reno. Just brilliant! If I can get anywhere close I'll be a happy man, really good job.

Yeah new spark plug! I suppose the frustrating thing for me is I have had this motor running. I bought it several years ago as a runner and through moving houses etc I left it in my sons shed for about 3yrs, and now of course no spark. I've cleaned up the flywheel and points, replaced the condenser and as far as I can tell (visual inspection and multimeter) the coil wiring is ok. I test the spark by clamping the plug to the head (with lead attached) and turn it over. Nothing! So I suppose its pretty much the coil?

It might sound silly but I'd just love to get it going before I strip it all down and start the reno. Think I might have to forgo all that and just get stuck into the reno. After the bathroom tiling of course! :
Cheers, finbar.

A couple of simple points, finbar.

First, "turn it over" has to mean spin it, not crank it. You shouldn't expect a spark below a couple of hundred RPM. Second, before concluding that the apparatus isn't working, you should try it without a spark plug or with a known good spark plug (and these days, a new one is not a "known good" one - there is a decent sprinkling of non-functional new plugs). Just clamp the wire so that the plug's metal connector is about 0.030" from the cylinder head, and see if it sparks from connector to head. The spark should be blue, not red, and appear regularly every second revolution of the engine.

Second, what gap did you set the points to?

Third, what gap did you set between the coil and flywheel?