Briggs compression?

[sideways]

How many PSI of compression should a Briggs have? My vertical shaft briggs that I'm converting to horizontal shaft (see here for more details) had just below 60 PSI of compression when slightly warm, how much do briggs flattys normally have? I'l get the engine hot and then do it again.

Thanks

Hayden

 

[jr dragster T]

60-80 pounds is pretty normall for a small engine like that.

 

[Kenny_McCormic]

You cannot measure compression on a flatty using normal methods due to the decompression system. You need to crank it over backwards. Briggs doesn't even outline doing a real test, their procedure is to throw the flywheel at the compression stroke, if it bounces back you are good.

 

[sideways]

60-80 pounds is pretty normall for a small engine like that.

Yeah, thats what I thought lol. Thanks

Just got it all hot and now it gets just over 60. Man this thing sounds awesome! Sounds like a dragster It revs real quick with no cutting deck too!

Hayden

 

[jr dragster T]

You cannot measure compression on a flatty using normal methods due to the decompression system. You need to crank it over backwards. Briggs doesn't even outline doing a real test, their procedure is to throw the flywheel at the compression stroke, if it bounces back you are good.

Last time I've seen a briggs 5 hp cam there was no easy start.

 

[sideways]

You cannot measure compression on a flatty using normal methods due to the decompression system. You need to crank it over backwards. Briggs doesn't even outline doing a real test, their procedure is to throw the flywheel at the compression stroke, if it bounces back you are good.

Hmmmm I didn't know that, the Briggs I've pulled apart (a relatively new 3hp flatty, an ancient one with up draft carby and the remains of a mower engine that had smashed a piston) didn't have any form of decompression system? and this mower engine has a approximately 3:1 reduction in the pull starter and you can still feel the compression so I'm sure it doesnt have one. Anyways, we'll see when I pull it apart..

Thanks

Hayden

 

[freakboy]

ive personaly never opend a engine or seen one with a compression release...

 

[Kenny_McCormic]

Its a solid part of the cam, something to do with cracking a valve open.

 

[Russ2251]

Valve overlap...or...intake and exhaust are both open at same (very short) time.
Is easily observed through breather opening or can remove head.
Intake valve begins to open before exhaust valve is completely closed. Becomes a non-issue when operating rpm is reached. Gain is insignificant if this feature is disabled.
Simple stuff.

 

[sideways]

Valve overlap...or...intake and exhaust are both open at same (very short) time.
Is easily observed through breather opening or can remove head.
Intake valve begins to open before exhaust valve is completely closed. Becomes a non-issue when operating rpm is reached. Gain is insignificant if this feature is disabled.
Simple stuff.

Lots of engines do that? Its part of the scavenging system?

Are you meaning on compression stroke or between the exhaust and intake stroke?

Either way, the decompression system sucks (if it is in fact exists) if I got just over 60 PSI

Thanks

Hayden

 

[Russ2251]

Are you meaning on compression stroke or between the exhaust and intake stroke?

No valves should be open during compression stroke.
I mean when exhaust valve is closing and intake valve is opening. Exactly as I stated. This only happens once every 2 complete revolutions.

the decompression system sucks (if it is in fact exists) if I got just over 60 PSI

Exactly the point of "Easy Spin". To ease starting, compression must be lowered (released).
Do as Mr. McCormic correctly suggested. Spin it in reverse!!!

 

[sideways]

No valves should be open during compression stroke.
I mean when exhaust valve is closing and intake valve is opening. Exactly as I stated. This only happens once every 2 complete revolutions.
Exactly the point of "Easy Spin". To ease starting, compression must be lowered.
Do as Mr. McCormic correctly suggested. Spin it in reverse!!!

Okay, yeah thats what I thought. I thought you were meaning both valves were open on compression to act as a compression release which I thought couldn't be right lol. And yes, I know almost all engines have valve overlap, more overlap is better for power, I don't see why any one would get rid of it...

Hayden