OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Quantum Piston ring gap

121702-0191-01
Hi guy's! I need your help again please. I recently purchased a piston assembly. Included was piston, oil rings, compression rings, gudgeon pin and 2 clips.
OEM #493262
Model : For B&S 5.5HP (which confused me straight off the bat, because I thought I had a 4.5HP Quantum)
When testing the ring gap on the 2 compression rings, I could just squeeze a 0.50mm feeler gage between them. So I tested the set I just removed. Top comp ring end gap of 1.10mm. 2nd comp ring end gap of 1.30mm.
So I read the work shop manual and it tells me that the wear limit for compression rings gaps in a aluminium bore is 0.89mm, but it gives no minimum measurement.
Is 0.50mm enough space to allow for those rings to expand when at operating temperature?
And if not, then what is the the optimal measurement?
《I tried without a ring compressor and broke the oil ring, then stepped on the original oil ring and it broke so was unable to measure them, but if anyone knows the measurements for oil ring, I'd appreciate it 》

Hi Dave

Haven't done it myself, but I am sure they say the minimum gap is something like 0.35 mm, so I think you are ok (that spec is on the 148cc)

I don't normally go beyond the cylinder head of briggs since they are so cheap to pick up a whole other running engine (though I will have to rebuild a Quantum 50 eventually due to sentimental reasons)

Thanks for the reply Tyler. My engine is a 120000 Series which according to the manual says its a 190cc. You may be right, but it just looks bloody close. Funny you mentioned sentiment reasons. It was dads and was blowing blue smoke. Next mower is gonna be a Honda.

Hi Dave,
.5mm is a pretty big gap but if that is what you have then just run with it, it will be fine. If you can give it a quick hone, if you don't have a hone then it will probably work fine. Hondas wear our rings as well, I have had a number of smokey Hondas here. They have obviously done a lot of work

Thanks Norm. Here I am thinking the gap is too small. So the original set must have been really shot at 1mmplus Oh well, if you don't ask then you'll never know hey?
Thanks again everyone from Outdoorking. As always you have been a great help.

Here since Briggs didn't minimum gap I used .010" or around .25mm as minimum from the single OHV repair manual for the top compression ring. They list .006 -.012" as standard ring gap.

OHV 120000 series ring end gaps

Ring End Gap (Top) .006-.010 in. (.15-.25 mm) .020 in. (.51 mm)
Ring End Gap (Middle) .012-.025 in. (.30-.51 mm) .020 in. (.76 mm)
Ring End Gap (Oil Control) .020-.016 in. (.51-.63 mm) .035 in. (.89 mm)

But Dave, you must have a mighty short work bench to step on the rings or is a lot more limber than most us. <lol> I haven't able to get my feet on the work bench since I was a kid.