OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Mysterious problem with Quantum engine

Hi I wonder if someone here can help with a mysterious problem on a Briggs Quantum engine I'm working on. I've got the head off for a decoke and this afternoon while turning the flywheel the crank stopped almost dead with the piston half way up the cylinder. I turned it back the other way and the same thing happened. The engine seemed unable to get past the half way up position but after turning the crank back and forth several times it suddenly overcame the 'obstruction' (it felt slightly stiff) and now seems perfectly OK like it was before the problem occurred. I'm completely baffled!

The only thing I can think of which might have caused this is I rotated the exhaust valve while it was fully open. I've had a good look through the sump plug hole and everything seems fine. I also flushed out the crankcase with kerosene and drained it through a filter and didn't find anything. There was nothing caught in the flywheel. Naturally I'm now concerned something is wrong inside the crankcase only everything seems OK now. Has anyone got any thoughts on this? Many thanks Richard

A cam follower may have moved out of place when you rotated the open valve and then righted itself after a bit of back and forth action on the cam. I've got a Honda with a similar symptom except that the cam follower is jammed tight, possibly corroded in as the oil had some water in it.

Thanks for your reply. I think it must be something like that because I checked it again today and it seems fine. I shook the engine and nothing sounded loose or broken so I'll refit everything and see what happens. I hope you manage to get the Honda fixed, is it a GX overhead valve or one of the older sidevalve/flathead engines like my Briggs?

What the model number of the Briggs? And was it one half turn or one turn of crankshaft? Rotating the valve should not caused the problem though. Just looking to see if I see what could have been the problem in theory.

The full engine number is 12T882-1570-21 code 94081258. It was half a turn of the crankshaft so the crank would turn through the bottom half rotation and stop with the piston about half way up the cylinder when turned in either direction. I hope this helps.

It's a GX, on an old Onga high pressure pump. It is a huge heavy cast iron pump that I can barely lift so I am hoping I can get the thing running again, the pump will probably last 100 years.

Hmmm that would put from switching from exhaust to intake on the valves in normal rotation and vica vesa if it was a valve related as it might have been trying to open both valves at the same time.

I would pull the breather cover for the valves and check in there to see if a retainer has came off or not. Just a thought.

I might do that tomorrow. But if a retainer had come off wouldn't that mean the valve would not operate and could simply be pulled out of the block, and the spring and retainer would rattle if the engine was shaken?