How much PSI should a Briggs & Stratton 190cc walk behind lawn mower engine have

[RandyT]

Also keep in mind that the rubber float valve seat will either swell or crumble when exposed to carb cleaner.

 

[WinterDeere]

I have owned a few machines with this Briggs 6.5 hp 675e engine over the years, and several of them shared a common problem, in that the head bolts work loose every few hours. The only one I still own is an Excell pressure washer, but I just finished re-torquing the head bolts on it after about 20 hours of run time. Two were a quarter turn loose, which is typical.

At least on mine, torque is spec’d at 140 in-lb, typical cross-cross pattern. I’ve done it so many times that I have the torque setting memorized. In any case, if left 50 or 100 hours, this could indeed affect compression, and even eat a head gasket.

 

[jpilk99]

Thank you all for info. WinterDeere I’ll definitely check head bolts.

Quick question: I had planned to adjust valves just to eliminate that possibility…but this engine doesn’t have OHV or rockers …is it possible to adjust tappet valves on a flat head motor, or at least an engine with no rockers?

FYI - https://www.jackssmallengines.com/j...r-engine-sump-lubrication-piston-group-valves

 

[WinterDeere]

Better engines like the old ubiquitous Kohler K301 used in all the old 12 horse Cubs, had adjusters on their lifters. But I'd be real surprised if an engine as cheap as the Briggs 675e had them. I'd be willing to bet the only means of adjusting those valves is with a file on the end of the stem to increase gap, or lapping compound on the seat to decrease gap.

These Briggs are almost throw-away engines, cheaper to replace than pay someone to do any serious internal surgery on them. That leaves DIY'ers with good skills and free time without a lot of great options, but that's where market economics has taken things.

 

[jpilk99]

Thank you. I haven’t worked on these types of valves before but …maybe they’re gunked up and need lapping?

Will check the head bolts and go from there.

 

[RandyT]

Better engines like the old ubiquitous Kohler K301 used in all the old 12 horse Cubs, had adjusters on their lifters. But I'd be real surprised if an engine as cheap as the Briggs 675e had them. I'd be willing to bet the only means of adjusting those valves is with a file on the end of the stem to increase gap, or lapping compound on the seat to decrease gap.

Correct.

And they are considered a throw away engine. Even 30 years ago it was cheaper for me to walk into a box store and purchase the entire push mower than it was for me to purchase the engine on the push mower at dealer cost. I won't do a major internal repair on an engine that can be replaced for less than $3K, mainly because if it required boring and oversize pistons and rings and had rod or crankshaft damage the overhaul will set you back close to $2K at this point on a V-twin OHV engine.

 

[WinterDeere]

Thank you. I haven’t worked on these types of valves before but …maybe they’re gunked up and need lapping?

Will check the head bolts and go from there.

The gunk itself can usually be cleaned with scrubbing and solvent, but if left that way for sufficient time, exhaust gas blow-by can cause erosion that might require re-lapping. Since there's no adjuster, aggressive lapping may lead to a need to file a few thou off end of valve stem. All very do-able DIY with the help of YouTube and unlimited time.

1. Tighten head bolts, check behavior.
2. If not good, pull the head, and give everything a visual inspection. Cylinder bore? Valve seats? You can see if they're dirty or pitted by rotating the crank. If all cleans up good, replace head gasket with new, and test.
3. If still poor performance, do a leak-down test, per fuddyduddy's post at the top of this thread. If you can't easily borrow/rent a tester, then just buy a cheap one or DIY your own (see link below).
4. If leak-down reveals a leaky valve, start giving it the love it needs. If leak down points toward leaking piston ring, then we could debate the merits of rebuilding the bottom end of that engine, but it might be a throw-away.

How To Do A Cylinder Leak Down Test - With Or Without A Tester

Doing a cylinder leak down test; can tell you more about your engine than you think. Also, a cylinder leak down test, can pinpoint issues; in specific

dannysengineportal.com

 

[RandyT]

Quick and dirty test for valve sealing. If you have the head off, rotate the crank until one of the two valves is open and then put your thumb on the top of the closed valves and try to rotate it. If it rotates then the clearances are gone and the valve is floating which is common on the older Briggs L-head engines. Then rotate the engine to close the open valve and open the closed valve and try to turn the now closed valve. One the one L-head engines the valve clearances tend to close up to the point the valves don't close. On the OHV engines they tend to open to the point the compression release doesn't work or worse.

 

[jpilk99]

Quick and dirty test for valve sealing. If you have the head off, rotate the crank until one of the two valves is open and then put your thumb on the top of the closed valves and try to rotate it. If it rotates then the clearances are gone and the valve is floating which is common on the older Briggs L-head engines. Then rotate the engine to close the open valve and open the closed valve and try to turn the now closed valve. One the one L-head engines the valve clearances tend to close up to the point the valves don't close. On the OHV engines they tend to open to the point the compression release doesn't work or worse.

I did this and they seem ...okay/good. Thanks! Going to mount up the new head gasket and see what I find. Quick question: Do I use a gasket sealer or no?

 

[WinterDeere]

No, air cooled engine head gaskets generally go on dry.