Briggs Intek engines firing pattern?

[daman]

Does anyone know for certain(not looking for a guess) on whether or not these engines fire once or twice per revolution?

i have a 18.5 hp i need to hook a tach to so i can check operating RPMs i believe there once per rev but not 100% sure any one know for sure??

 

[-Clayton-]

Yes, Once per revolution.

 

[willix]

I don't see any reason why it wouldn't fire on both in. & ex. stroke. Every time around the magnet generates a current.

 

[boraticus]

Most twin cylinder ignition systems that I've worked on are "wasted spark" ignition. That means that both spark plugs fire at the same time. One cylinder will be on the compression/power stroke the other on the exhaust stroke. I'm certain there are some ignition systems that are different but I've never come across one yet.


Are you using an electronic tach that runs off the spark plug wire? If so, it should be programmable if necessary to change the settings. What I would do, is put it on an single cylinder OPE engine that runs at 3600 rpm. Then put it on the twin. If the twin runs at 3600 rpm and the tach reads approximately the same it's good to go.

 

[rclint]

I have never used a timing light on small engines, however I have wanted to, and planned on it for a long time I just never run into a light at the correct price. I know people use timing lights on Kohler Cast Iron series however these have points where yours uses a magneto. I also have a B&S Intek a 24 HP. Can you use a meter to check and see if it fires on the exhaust stroke ?

I'm almost positive that it does not fire on the exhaust stroke, however I can not confirm this, nor give the reason it does not.

 

[daman]

Originally Posted By: boraticus
Most twin cylinder ignition systems that I've worked on are "wasted spark" ignition. That means that both spark plugs fire at the same time. One cylinder will be on the compression/power stroke the other on the exhaust stroke. I'm certain there are some ignition systems that are different but I've never come across one yet.


Are you using an electronic tach that runs off the spark plug wire? If so, it should be programmable if necessary to change the settings. What I would do, is put it on an single cylinder OPE engine that runs at 3600 rpm. Then put it on the twin. If the twin runs at 3600 rpm and the tach reads approximately the same it's good to go.

Right on a twin there's a waisted spark but talking my single here,don't have a twin to try and see the difference so thats out.

Yes just one of them electronic tachs that runs off the spark plug wire is what i'm using it can be set for multiple spark options so i just need to know what i have here,i posted this same question on another tractor forum and got the same response "once per revolution" so i'm going with that,i'll be able to tell if it isn't right.

I thought about a timing light but as fast as this engine turns at idle hard to tell the flashes.

 

[rclint]

boraticus I'm glad you come along to give us an answer. I have not dealt with this issue before. However I wonder if this would also give a cleaner emissions by firing on exhaust stroke as any leftover combustion would then have another chance to burn. Ford made a 2.3 liter 4 cylinder that done exactly this used 8 spark plugs 4 down each side.

 

[daman]

Originally Posted By: rclint
boraticus I'm glad you come along to give us an answer. I have not dealt with this issue before. However I wonder if this would also give a cleaner emissions by firing on exhaust stroke as any leftover combustion would then have another chance to burn. Ford made a 2.3 liter 4 cylinder that done exactly this used 8 spark plugs 4 down each side.

yes good idea,harder on the coil for longevity but never the less..

 

[boraticus]

Originally Posted By: rclint
boraticus I'm glad you come along to give us an answer. I have not dealt with this issue before. However I wonder if this would also give a cleaner emissions by firing on exhaust stroke as any leftover combustion would then have another chance to burn. Ford made a 2.3 liter 4 cylinder that done exactly this used 8 spark plugs 4 down each side.


Actually, the wasted spark will not enhance "after burn". There's not enough fuel/oxygen to cause ignition. The wasted spark system is just simpler to manufacture and implement. Having a spark on every revolution is just so much easier to do and there's no need to interrupt the spark if there's no benefit from doing so.

Multiple spark plugs in the same cylinder will both fire at the same time. Generally, the use of multiple spark plugs in a cylinder is to promote a more even burn in wide bores. As stroke length diminished and bore width increased, engine designers observed uneven burning patterns of the fuel in the cylinder due to the width of the bore. Some tackled the problem by using two spark plugs, others redesigned the cylinder heads and spark plug manufacturers developed more powerful plugs. With EFI and coil on plug ingition, the need for multiple plugs has been pretty much eliminated.

I recall seeing a few motorcycles years ago that had used dual spark plugs per cylinder but not too many.

 

[rclint]

boraticus this was actually for emissions from my research on the ford 2.3l. The plugs on the exhaust side fired on the exhaust stroke, the haynes or chiltons manual stated the reason was to burn off any leftover combustion products. One more note if you unplugged a wire from the intake side which was the main plugs that fired of compression stroke the engine would run as normal, you could tell no difference.

However on the lawn engines I do agree it's a cheaper method, simpler, and for us way less of a headache to deal with than some mechanical (lovely points that everyone loathes ..I hate them myself, however I have them on my old Kohlers and seldom do they give any problem, or wear out as you hear read so much about)or even electrical device to provide spark on power stroke only. ( Compression/power would be very close LOL). I did not know this information on small engines.

Key note on points above, if you have the switch jerry rigged it will burn the points if fire is on them in closed position, and from what I have seen there are huge amounts of electrical engineers in the lawn mower business.. clothes hanger, tape if you name it.

 

[SteveSRT8]

Haynes and Chilton were wrong.

If the mixture has even partially burned the waste spark has nothing to ignite.

It's all about two sparks lighting off more of the mix and getting complete combustion with fewer misfires. It's really covering up some design issues!

All the new Gen Chrysler 5.7's and 6.1's use two plugs per cylinder.

 

[daman]

Well played around with the mower today and good thing i decided to check it,engine always seemed like it was not toping out quit right, put the tach on her and this is what i found.


Hot operating temp NO load from the factory was- 3200 WOT,

Hot operating temp with mower(load applied)engaged- 3,000 WOT.

after my adjustments...

Hot operating temp NO load-3720 WOT

Hot operating temp with mower(load applied)engaged- 3600 WOT, spot on


so it pays to check this stuff




Originally Posted By: daman

 

[rclint]

Originally Posted By: SteveSRT8
Haynes and Chilton were wrong.

If the mixture has even partially burned the waste spark has nothing to ignite.

It's all about two sparks lighting off more of the mix and getting complete combustion with fewer misfires. It's really covering up some design issues!

All the new Gen Chrysler 5.7's and 6.1's use two plugs per cylinder.


This is not the new generation 5.7 I'm talking about 89- (not sure ) for 2.3l 4 cylinders, and I can't imagines you having the courage to say two manuals are wrong !! I could see you telling me I'm wrong LOL, but two manuals, have you ever owned a ford 2.3l with 8 spark plugs ?

These engines ran perfect with single plugs in the years before, and this is a old proven design that the basic core is or was still being used I'm not up to date on this now