Briggs & Stratton Compression

[lefty]

09P702-0098-F1 Engine

I received this little push mower from someone who found it on the side of the road. He gave it to me and it looks pretty clean / new. So it seems like a fun little project to diagnose why it won't start. It's an OHV. Do these little engines have a compression release? If not, what kind of compression should I have? I haven't done a leak down yet. On a straight compression test, I'm showing about 45psi.

Thanks

[KE4AVB]

Yes has an ACR. Appear to be operating on the intake valve. As compression most engine are usually around 70 psi with an active ACR and with the throttle vane wide open during the test.

Note some cams are black nylon instead of natural nylon.

[lefty]

It appears to be one of those automatic chokes and throttle, so I'm assuming it's wide open all the time?

I'll do a leak down to see where it's losing it.

Thank you

[creia]

45 PSI seems pretty low. On the old Briggs L-Heads"("Easy Start") we restore from the 1960s-1970s we always check compression. These all have a compression release as well. On an engine that is not worn out past specs we typically get anywhere from 70-90 PSI. It will be interesting what your leak down test shows- please make sure and report back with the results
Michael

[lefty]

Just finished leak down and that seems to have gone well. I put about 95psi in and it held about 90-92psi.

Valve clearances look good I think. Although, I'm having a hard time finding the specs for this. I always struggle with these weird model numbers. 09P702. I can't seem to match it up with the series number. Even when I found the manual for the exact engine, the model numbers referenced don't seem to line up. Point being, I'd like to check the flywheel key while I have the shroud off but can't seem to locate the torque specs for the flywheel nut. Is this a 90000 series? I have that briggs check chart but when I look at OHV it shows 97700-99700 with a torque of 60lb/ft.

If I have a good flywheel key, I'll check spark and if that's good, I'll move on to the carb.

Thanks.

[bgsengine]

seems to me you're diagnosing backwards .. I'd suggest start with a spark check and if you got spark, squirt a bit of gas in plug hole, put plug in and see if it fires, make sure to try with a known good spark plug, and go from there... if it fires and runs on the bit of gas squirted in there and then runs on some gas squirted in carb throat, then compression and spark can be assumed to be sufficient for the time being.. if it turns out to be a hard starting issue but does run on provided gas, then maybe time to consider compression issues - maybe blown head gasket, loose valve seat, etc. if it kicks back hard when trying to fire , then probably sheared key, and yeah the 09P series is the OHV single cylinder service manual and it is a 90000 series in the specs, unless specs have a more specific breakdown.

[lefty]

Understood. The problem I'm running into is that the information I have for flywheel torque shows 90000 series as an L-head. The closets number for OHV is 97700, 99700, which shows 60 lbs per foot. So I'm confused on what torque specs to use.

[bgsengine]

Understood. The problem I'm running into is that the information I have for flywheel torque shows 90000 series as an L-head. The closets number for OHV is 97700, 99700, which shows 60 lbs per foot. So I'm confused on what torque specs to use.

echnical Specifications

Model Series 09P7
Power Lbs/Ft of Torque 5.5
Engine Series 550
Displacement 140
Oil Capacity 16 oz (0.5 l)
Valve Configuration OHV
Flywheel Torque 60 lb/ft (81.5 Nm)
Governor Arm Torque 30 lb/in (3.5 Nm)
Plug Gap 0.02 in (0.50 mm)
Intake Valve .004-.008 in (.10-.20 mm)
Exhaust Valve .004-.008 in (.10-.20 mm)
Idle Speed 1750
Air Gap .006-.014 in (.15-.36 mm)
Flywheel Puller Part 19619
Flywheel Holder Part 19619
Connecting Rod Torque 100 lb/in (11.5 Nm)
Sump Torque 85 lb/in (9.5 Nm)
Head Torque 140 lb/in (16.0 Nm)

*EDIT TO ADD*
This is probably the service manual you want: Covers Single Cylinder OHV horizontal and vertical (not Vanguard) engines including I/C, I/C Pro, Intek, Powerbuilt, and Snow. Part# 276781

[lefty]

Perfect. Thank you.

[KE4AVB]

Also download APSI's 91, 93, and 103 plus DSB 1060. Available in the download forum. APSI 93 shows how to use the flywheel puller.