almost a tractor

Bob Bancroft · Feb 27, 2013

The B&S 24 HP V twin engine in my mower has always cranked hard. I'm getting it ready for the season, and decided to go after it. I had replaced the four year old battery last year without much effect. My dealer finally convinced me to check the valves. Supposed to be .004-.006". Exhausts were OK. Intakes were .010-.011"! Turns out that when the intakes are adjusted correctly, they don't totally close until the piston is darn near TDC! No wonder they have concerns over all these little engines polluting when they design them like that!

old · Feb 27, 2013

That is there way of having a compression release so it spins over ok. It would be better to have a hand control type compression release but people would not know how to start there machine if they had them

dr sportster · Feb 27, 2013

With a late intake closing it would be of little use to add a compression release.The later the intake closes the more compression is bled off. This effectivly lowers compression when starting already.

JLeus · Feb 27, 2013

Have made some good money adjusting those B&S valves so the thing would start.

cole in mo. · Feb 27, 2013

Briggs started doing that over 40 years ago when some limp wristed yuppies complained about the 2-1/2 hp lawn mower engine jerked the pull rope out of there fingers. And since then, thats how they get different hp engines. They didn't make a different block and crank for each hp engine, they just changed the location of the hold open lobe on the back side of the camshaft. The earlier the intake closes, the more hp. I used to take a new 3hp apart, grind that little lobe off, and I could mow 6in tall grass as fast as I wanted to push the mower.

Bob Bancroft · Feb 27, 2013

Perhaps I will notice a decrease in HP now. It had plenty before, so I guess that won't matter. I've never run into this, but it's been decades since I've worked on little engines. But now I can understand why I notice so much blow back through the carb. on some B&S.

Geo-TH,In · Feb 27, 2013

The exhaust valve on overhead valve engines act as a decompression valve. If you research it, you will find on the larger engines, when running, the cam changes and the exhaust valve stays closed all the time. If the exhaust valve clearance isn't set properly, the starter can't start the engine. It's like the engine is locked up.

huntingreen2day · Feb 27, 2013

On the flat head Briggs and Staton engines there was a hump on the intake valve that held the valve open until the piston was near TDC. When running at full speed this had little effect on the engine performance. At 3600 RPM the easy Spin duration was like 1/200 of a second. If you don't want Easy Spin just open up the valve clearance enough to get rid of it. Then pull a little harder when you want to crank it. Took it out of a lot of engines when racing go karts. We used to juice them little 5 HP Briggs up and turn 9400 RPM using stock cranks and stock valves.

almost a tractor

Bob Bancroft

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old

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dr sportster

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JLeus

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cole in mo.

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Bob Bancroft

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Geo-TH,In

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huntingreen2day

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