Why would the Power Valves Rub on the Piston ?

Rprecision · Sep 1, 2012

Doing a top end on a 09 M8 with 3500 miles. The motor is bone stock.

I was suprised to see that on the left side of each piston is a .010 + groove from rubbing on the Power Valve. A little shiney mark and the tip of the PV's tell the tale.

I have never heard of this before

Any ideas ?

I will work on pictures

Hardass · Sep 1, 2012

Obviously you have the gaskett in there so you have a portion that is wore down? look it over real close

Greengarage · Sep 1, 2012

I have heard of this w/ the 8's and 1000's. Info on this by searching over on HCS. Their remedy is doubling up on the (bottom) gasket. Seems primitive, but plenty cheap, works, and all I've heard for the "fix".

should mention peeps are doing this as a preventive measure as well.

milehighassassin · Sep 1, 2012

Any chance the valves are in upside down?

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backcountryislife · Sep 2, 2012

milehighassassin said:
Any chance the valves are in upside down?

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Can't do that on the M.

I've had it happen with broken valves, but not with ones that are otherwise healthy.

Rprecision · Sep 2, 2012

Hardass said:
Obviously you have the gaskett in there so you have a portion that is wore down? look it over real close

I suppose that is possible

Greengarage said:
I have heard of this w/ the 8's and 1000's. Info on this by searching over on HCS. Their remedy is doubling up on the (bottom) gasket. Seems primitive, but plenty cheap, works, and all I've heard for the "fix".

should mention peeps are doing this as a preventive measure as well.

Thats something I have considered

milehighassassin said:
Any chance the valves are in upside down?

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Can't only go in one way

backcountryislife said:
Can't do that on the M.

I've had it happen with broken valves, but not with ones that are otherwise healthy.

When you say broken valves, do you mean the valve itself was damaged or do you mean the APV system was not working properly.

Hardass · Sep 2, 2012

I'm sure he saying if the shaft on the valve broke below the stop in the cylinder it would let the valve drop onto the piston.

backcountryislife · Sep 2, 2012

Hardass said:
I'm sure he saying if the shaft on the valve broke below the stop in the cylinder it would let the valve drop onto the piston.

That.

Happened to me on my racer a few times (aluminum valves... they save weight for a few miles... then, they don't seem like such a good idea anymore

)

Rprecision · Sep 2, 2012

backcountryislife said:
That.

Happened to me on my racer a few times (aluminum valves... they save weight for a few miles... then, they don't seem like such a good idea anymore)

ahhhhh....I follow now

Mjunkie · Sep 4, 2012

Maybe this sounds like a dumb solution to you but when you rebuild the top end and have the cylinders off, drop the power valves in and use a straight edge to make sure you have clearance between the power valve and the straight edge, and if not get out the die grinder and grind the power valve down to have maybe .020" or so (I have always checked the valves that way every time I've done a top end to be sure and when I've put together a couple big bores). Of course you want to keep the same angle of the valve. I've never seen one of those gaskets wear out. It isn't like the bolts holding them in "should" be loose enough to rub back and forth wearing them out. I know on the M7 motor the valves could go in upside down no problem (and if you did put them in wrong they would rub), on the M1000 they won't go in upside down, not sure about the M8 motor.

Rixster · Sep 4, 2012

I thought I read a post a while back about this. Seams like people were saying the valve seat or stop was getting smashed and letting the valve fall further into the cylinder.

Rprecision · Sep 7, 2012

Mjunkie said:
Maybe this sounds like a dumb solution to you but when you rebuild the top end and have the cylinders off, drop the power valves in and use a straight edge to make sure you have clearance between the power valve and the straight edge, and if not get out the die grinder and grind the power valve down to have maybe .020" or so (I have always checked the valves that way every time I've done a top end to be sure and when I've put together a couple big bores). Of course you want to keep the same angle of the valve. I've never seen one of those gaskets wear out. It isn't like the bolts holding them in "should" be loose enough to rub back and forth wearing them out. I know on the M7 motor the valves could go in upside down no problem (and if you did put them in wrong they would rub), on the M1000 they won't go in upside down, not sure about the M8 motor.

Well, You hit it. This is the plan. I will polish and removed enough to make sure it dosent cause any problems.

Rixster said:
I thought I read a post a while back about this. Seams like people were saying the valve seat or stop was getting smashed and letting the valve fall further into the cylinder.

You called it. When I was cleaning after honeing yesterday I inspected the valve seat which is aluminum. It shows about .020 of wear. This seems to make sense given the valve is steal. Also on one given day I probably have the valves up and down several hundred times.....

Next time, if there is a next time it will need new cylinders

skibreeze · Sep 7, 2012

It might be possible to drill and tap threads in the worn spot and insert a set screw to make up for the worn out spot and the steel won't wear down like the aluminum.

Rprecision · Sep 7, 2012

skibreeze said:
It might be possible to drill and tap threads in the worn spot and insert a set screw to make up for the worn out spot and the steel won't wear down like the aluminum.

I almost threw them up in my mill to do exactly that. Only problem I see is the valve stop boss is very close to the top of the exhuast port. I dont think there is enough metal to do it right

Rprecision · Sep 7, 2012

Heres some photos for those intrested

The PTO side actually wore a small indent in the top of the top ring

The thing that strikes me odd is how its on the same side of each piston

Why would the Power Valves Rub on the Piston ?

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