OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Quant - fusion

more silly Q's

i've got 2 quantums i'm looking at now

a 3.5hp and a 5hp

but they're both 12 cubic inch (according to the makers plate)

so how do they do it ?

different carbs? valve sizes? valve duration? compression? or exhaust systems?

or are the newer ones just more powerful ;-)

If you post pictures and the full series of numbers (model, type and code) for each, we can try to fit them into a context.

prolly a tomorro job

gotta go get pretty now, then off for a ride my bike to the local boozer for drinks, dames n dancing

cya ...

hi there, got half the info for you

3.5 HP QUANTUM POWER 5 HP QUANTUM XM50

MODEL 121702 12F802

TYPE 019101 1911-B1

CODE 90080957 03090357

the xm50 i bought brand new about 7 yrs ago ... on a victa tornado

the 3.5 is on an old black MASPORT CRAFTSMAN 600-4 LIMITED EDITION that my brother in law gave me when it wouldn't run coz of a blocked aircleaner

no pics, no time today. gotta see mum, dontcha know ?

Here is the illustrated parts list for your 121702, which was made on 9 August 1990:
http://www.m-and-d.com/pdfs/briggs/121700-ms6592-0998.pdf

Here is the illustrated parts list for your 12F802, which was made on 3 September 2003:
http://www5.briggsandstratton.com/eu/en/pdf/illustrated_parts_list/100%5CMS0517.pdf

As you thought, they are both 12 cubic inches displacement (200 cc). The 121702 is a second design generation engine, with a vertical crankshaft, a Flo-Jet carburetor, plain main bearings, and a rewind starter. The 12F802 is a 16th design generation engine, with a vertical crankshaft and a carburetor that was not made by Briggs and Stratton. It has plain main bearings and a rewind starter.

You can look for design differences in the illustrated parts lists, but I doubt you'll find anything very definitive. Essentially, Briggs' 9 cubic inch engines with the Pulsa-Jet suction carburetor were 3.5 hp in the 1970s. With the Vacu-Jet carburetor in the 1980s they were only advertised as 3 hp. The 12 cubic inch engine would have been about 4 to 4.7 hp if it had the same output per litre. Your 121702 therefore had a particularly low advertised hp for its size, while the 12F802 was relatively high. However you should bear in mind that in between the two manufacture dates the engine manufacturers became keener to advertise the highest possible power figures. Back in the old days they used an extremely favourable way of establishing what power rating they would claim, and they may have become even more ambitious in this respect along the way, until they were successfully sued about it fairly recently.

that's a wonderful answer, t/y so much for your effort

but ...

if the blocks are non-repairable, i.e. cannot be bored, why are o/s piston assy's listed in the parts books ?

i'm going to assume that the parts list covers a: iron linered engines, b: o/s's are made available to those who decide to have their engines sleeved or c: engines were made from the factory bored to size dictated by core shift etc

but really, i haven't got a clue

I don't know the true answer to the "why sell oversize" question, but it may be a reluctant response to customer demand. I can't think of any modern engine manufacturer who likes or supports reboring, because results are usually a long, long way short of factory quality standards. However sometimes their official spare parts service peddles the components because there is a dollar in it and their unaffiliated competitors are doing it.

Usually the repair manual is prepared by technical people under the influence of the engineering department, while the spare parts list is prepared by the commercial people in the spare parts department.

another great answer mr.G

t/y again

Thanks hit n miss, I'll close this thread.