Briggs Valves Barley Opening

[darrinster]

Model:31C707-0230-E1

Anyone ever seen both cam lobes worn off? I'm about to pull the engine to check the camshaft and was wondering if anyone knew if something else could be causing this?

 

[Tinkerer200]

Just B&S's bad mistake in going from 1 pc. forged cam to cheap, probably Chinese, segment cam. They are making a fortune on parts.

Walt Conner

 

[motoman]

Even the dealers here say it is common. Some believe it is the lobe material and hardness. This is seen in auto repair as many texts call for measurement of lift , lobe to lobe and against the spec. IMO pushed guides can also contribute with extra pressure of very hard lifter pressed unduly against the softer cam. Add dirt , heat, and marginal or insufficient oil and voila, round cams.

Edit, We know how light the spring pressure is on an Intek. One can compress a spring by hand.

 

[bertsmobile1]

Just B&S's bad mistake in going from 1 pc. forged cam to cheap, probably Chinese, segment cam. They are making a fortune on parts.

Walt Conner

Gees I am going to agree with Walt yet again.
The modern cam is a lot more sensative to the oil you are using than the old cams were.
It gets hot here and I am using a lot more 10w 40 in new mowers that my predecessor did.
According to the recommendations we are in the SAE 30 mower oil territory but when I do a cam replacement I go up to 10w 40 and that seem to stop / slow down the rapid cam wear.
All we used to put 10w 40 in previously was GX 25 & GX 35 trimmer motors.

 

[darrinster]

Both are worn down really far. Pictures:

The other camshaft has a broken compression release.

 

[ken_clifton]

Not to crank up the Zinc or No Zinc discussion, but...

Given the reduction in the extreme pressure additives in engine oil over the last six years, I might fault the oil choice used. I certainly don't want to defend Briggs on their metal quality, but consider how hot these engines run. If you cook the oil to a very thin state, and most of the ZDDP or other EP additives are not there, then it is metal to metal if the oil film fails.

And, this is exactly what the Zinc camp said would happen. I am careful now days to look at how much ZDDP is in my oil choice for air cooled engines. If it is not 1200 ppm, I go with something else. A lot of your standard passenger car oils are now down to about 800-900 ppm of zinc to satisfy the "energy conserving" designation.

ken_clifton

 

[bertsmobile1]

Which should not be a problem if you are using a mower oil as it is formulated for air cooled mower engines.
When I get annoyed is when I convince my customers to use mower oil which down here is twice the price car oil and then the cam still wears round.

 

[Psychlopath]

I had a pretty similar problem on a 31P777-0348-E1 with just under 10 hours on it, but it was only the exhaust lobe; it was worn enough that the valve didn't open at all. When I removed the cam, that lobe looked like it'd been through a machine shop and was smooth enough to the point that it looked like it was intentionally made like that.

The mower shop where I bought the new cam had told me there was a "Run of bad cams," and assured me I shouldn't have the problem again with updated parts. Maybe we'll both have better luck in the future with our engines.

I have about 8 hours on the new cam and the engine still starts easily, so my fingers are crossed hoping for a long life with this new-to-me engine.

 

[Tinkerer200]

I had a pretty similar problem on a 31P777-0348-E1 with just under 10 hours on it, but it was only the exhaust lobe; it was worn enough that the valve didn't open at all. When I removed the cam, that lobe looked like it'd been through a machine shop and was smooth enough to the point that it looked like it was intentionally made like that.

The mower shop where I bought the new cam had told me there was a "Run of bad cams," and assured me I shouldn't have the problem again with updated parts. Maybe we'll both have better luck in the future with our engines.

I have about 8 hours on the new cam and the engine still starts easily, so my fingers are crossed hoping for a long life with this new-to-me engine.

That "Run of bad cams" must of been one H of one.

Walt Conner

 

[Psychlopath]

...must of been one H of one.

May or may not have been. All I know is what I've been told; that comes with as much weight as any of the rumors online.

The new cam I put in my engine has as much lift now as it did when I broke it in, but anecdotes aren't gospel.