Briggs and Stratton 7 hp 170403

wizard67 · Jan 19, 2019

Hi,

I have a 1967 Briggs and Stratton 7 HP 170403 that is leaking oil from the breather. I replaced the breather, but am still having the issue. The engine only smokes when the breather starts leaking oil. Any help would be greatly appreciated.

Thanks

Alex

bertsmobile1 · Jan 19, 2019

Run the mower for 5 minutes, shut it off & thn open the dip stickafter the engine stops revolving.
If smoke comes out then you have an internal head gasket failure.
Oil coming out of the breather is a symptom of a problem, it is never the breather itself.

wizard67 · Jan 20, 2019

bertsmobile1 said:
Run the mower for 5 minutes, shut it off & thn open the dip stickafter the engine stops revolving.
If smoke comes out then you have an internal head gasket failure.
Oil coming out of the breather is a symptom of a problem, it is never the breather itself.

Tks Bertsmobile1.

I will do the test.

Rivets · Jan 20, 2019

Check your oil level, if it is high check to see if it smells like gas, you have a problem with your carb. The float needle is not seating properly and fuel is running through the carb into the crankcase.

wizard67 · Jan 21, 2019

Rivets said:
Check your oil level, if it is high check to see if it smells like gas, you have a problem with your carb. The float needle is not seating properly and fuel is running through the carb into the crankcase.

No Gas in the oil. Tks for the info.

wizard67 · Jan 21, 2019

bertsmobile1 said:
Run the mower for 5 minutes, shut it off & thn open the dip stickafter the engine stops revolving.
If smoke comes out then you have an internal head gasket failure.
Oil coming out of the breather is a symptom of a problem, it is never the breather itself.

The test revealed smoke in the Dip Stick. I removed the head found excessive oil on top of piston and valves. Gasket seems ok will replace. Hope it's not the rings.

(Account Closed) · Jan 21, 2019

Sounds like compression rings leaking compression into the crankcase and the oil rings not keeping oil below the wiper ring

A "Leak down test" would confirm this...

*Bert, how would a bad head gasket cause higher pressure in the crankcase forcing oil out the breather? Leakage would just be into the atmosphere, no? Or are you thinking of an OHV engine with compression going down where the push rods would be?

I assume it's a flat head engine..

wizard67 · Jan 21, 2019

SRTsFZ6 said:
Sounds like compression rings leaking compression into the crankcase and the oil rings not keeping oil below the wiper ring

A "Leak down test" would confirm this...

*Bert, how would a bad head gasket cause higher pressure in the crankcase forcing oil out the breather? Leakage would just be into the atmosphere, no?

I assume it's a flat head engine..

Unfortunately that is what it seems to be. Will leak down test to confirm.

Tks SRTsFZ6

wizard67 · Jan 26, 2019

wizard67 said:
Hi,

I have a 1967 Briggs and Stratton 7 HP 170403 that is leaking oil from the breather. I replaced the breather, but am still having the issue. The engine only smokes when the breather starts leaking oil. Any help would be greatly appreciated.

Thanks

Alex

Update, did a Leak down test hot and cold came back normal. Replaced Head Gasket, no kink in hose, but still having the same issue. Wondering if the new Breather is defective.

Removed breather hose from carb and added a section of clear tubing and the oil starts leaking after 30 sec running.

bertsmobile1 · Jan 26, 2019

Oil comes out of the breather for only 2 reasons
1) the oil level is too high so there is oil in the crank case fume
2) there is excessive pressure in the crank case.

The latter can be caused by
1) head gasket broken between the cylinder & pushrod tunnel
2) worn rings
3) cracked head
4) cracked piston
5) cracked barrel

The breather is just a one way valve.
Some do have a small drain hole in them to allow excessive oil to drain back into the engine on the exhaust / compression strokes.
Very rarely a worn crank shaft seal can cause the crank case to pressureize but that only happens at operating speeds.

Excessive carbon build up on the piston can by
a worn inlet valve guide
Excessive crank case pressure
Worn scraper ring
Worn bore
leaking head gasket.

Briggs and Stratton 7 hp 170403

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