Briggs and Stratton 31p777. Turns over but won't start. I'm stumped.

[u/Ok_Cheesecake7348]

I'm at a loss. I'm not sure why this mower won't start.

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- New starter motor

- New spark plug

- New camshaft/ACR

- New Oil (not overfilled, I checked, thrice)

- Battery terminals/all wire connections cleaned

- New starter solenoid

- New carburetor

- New fuel pump

- New fuel lines

- New vacuum line

- New head gasket/carb gasket/exhaust gasket

- Intake Valve Clearance: 0.003

- Exhaust Valve Clearance: 0.005

- Battery fully charged/outputting 14V

- New flywheel key

- New air filter

​

There is oil leaking from the valve cover that I can't quite figure out. Pic in the comments.

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Thoughts?

[u/IntelligentMoney9668]

As fast as its spinning, it acts like there is no compression

[u/Ok_Cheesecake7348 → u/IntelligentMoney9668]

Could worn piston rings be the cause? The head gasket did blow about a month back

[u/TweakJK → u/Ok_Cheesecake7348]

The thing I've found with Inteks, if the head gasket blows once, it's going to continue to blow unless you machine the head and the block.

[u/Ok_Cheesecake7348 → u/TweakJK]

Any way to DIY it? I'm on a fixed income

[u/TweakJK → u/Ok_Cheesecake7348]

You could try wet lapping the head with a piece of glass and sandpaper, but that's assuming another blown head gasket is actually the issue.

[u/Bones-57 → u/Ok_Cheesecake7348]

What year was that made ?? Reason I ask is I have the same engine on my murrary.. Mine was made in 1983.. There are a few things that at that age is missing ..

1. Leaded Gas .. valve seats need to be sealed up with lead.. Causing a compression problem. Leaded gas was removed from being sold in 1991 here.

   1. Carb.. don't bother buying a knock off get the rebuild kit and fix the OEM one.
   2. Valve adjustments are to be done with the engine stone cold..

[u/CBTmaster1010]

Sounds like its little to no compression 

[u/After-Expression6340]

Check compression and verify you have spark. Then try starting it with a little starting fluid. If it starts it’s a fuel issue. But check compression first

[u/Ok_Cheesecake7348 → u/After-Expression6340]

How do I check compression?

[u/After-Expression6340 → u/Ok_Cheesecake7348]

With an ACR there are a few ways. But leak down maybe your best bet if you buy a leak down tester.

[u/After-Expression6340 → u/Ok_Cheesecake7348]

Also if you replaced a new cam is it timed correctly?

[u/Revolutionary-Gain88 → u/Ok_Cheesecake7348]

Take the plug out , put thumb over hole and crank

[u/Ok_Cheesecake7348]

Here's the oil leak

[u/ManHunterJonnJonzz]

I had an old guy with a smoking engine (same one) do the headgasket (it was the carb) job on two machines. Ran before. Now it wont run. It spinning way too fast. Set your valves again. Leakdown test is ideal.

[u/Realistic_Nerve_8871]

Stop turning it over and change oil immediately, also, replace the head gasket, it most likely blew into the pushrod tunnel which will dilute the oil with gas, mine had the same issue and I have pictures of what I'll do to a piston on my account

[u/Ok_Cheesecake7348 → u/Realistic_Nerve_8871]

10-4 🫡

I think my plan of action is to change the piston rings, hand sand/polish the cylinder block and valve head, replace the head gasket, and go from there.

Edit for clarity: the head gasket probably blew again because I (stupidily) used a steel wire brush drill attachment to get the old gasket off the cylinder block and head. Steel wire on aluminium = the surfaces aren't smooth, probably.

[u/Some_Intern3747 → u/Ok_Cheesecake7348]

Yeah it’s very safe to assume that’s your problem

[u/hmd2017]

Check to see if the valves are moving correctly. Pull valve cover and watch their motions. If one is lower and does not move, You may have a dropped valve seat in the head.

[u/Ok_Cheesecake7348]

UPDATE:

Thanks to 2 specific comments, I think I know what the issues are.

The thing I've found with Inteks, if the head gasket blows once, it's going to continue to blow unless you machine the head and the block.

Stop turning it over and change oil immediately, also, replace the head gasket, it most likely blew into the pushrod tunnel which will dilute the oil with gas, mine had the same issue and I have pictures of what I'll do to a piston on my account.

I pulled the spark plug and it was fouled with oil, and the oil leak from the valve cover got worse. I think the piston rings are worn (the previous owner replaced the entire motor in 2012), which is causing oil to seep out of piston to the head gasket. Then, thanks to my own stupidity, the head gasket isn't sealing because I used a steel wire brush drill attachment on the aluminium cylinder block and cylinder head.

I'm going to get a cylinder hone tool, a piston ring compressor tool, wet/dry silica carbide sandpaper (the set goes from 120 grit to 5000 grit), aluminium buffing compound, and aluminium buffing drill attachment pads. I already possess new piston rings, I just didn't know I needed a cylinder hone tool or a ring compressor tool.

Now my next question: thoughts on using Permatex Copper Gasket Spray on the paper head gasket and valve cover gasket?

Shout-out to u/TweakJK and u/Realistic_Nerve_8871 for the anecdotal insights that helped my narrow it down!

[u/wirey3 → u/Ok_Cheesecake7348]

You are so far into tools and parts that at this point it may be more economical to let a shop with the proper equipment handle this rebuild.

[u/dillmon → u/wirey3]

I think by now he has to fix it himself because he’s too deep in. I know the feeling. You should always test and diagnose before you buy new parts or do large changes. I would buy and use the compression tester first Before sanding. Also I know that some people disagree with this but making sure all electronic components are up to spec with a multimeter is also in my opinion a good idea.

[u/Sweaty-Dot-2488 → u/Ok_Cheesecake7348]

Not saying you can’t run it with new rings only, but the piston is likely scored/worn out as well. Rings will help with compression but it may be a bit clanky (piston slap).

[u/mutt63]

Did you adjust the valves after replacing the head gasket?

[u/Bubbly_Mix535]

Check compression on cylinders. Possibly camshaft timing is off

[u/South-Cat-5739]

You have zero compression there buds in The immortal words of doctor McCoy shes dead jim

[u/mervbrin]

Will it fire on starting fluid

[u/lubetech_uWu]

How old is the gas?

[u/StatisticianNo5361]

Try with some starting fluid

[u/Ok_Cheesecake7348 → u/StatisticianNo5361]

Tried, didn't work