Piston Slap?

[jimk]

1 hour ago, Inka’d02 said:

Using the screw driver, I can push it back and it returns to taught just fine.

This test should be done with oil in the oil pocket.  Without oil, the tensioner piston has no hydraulics.  And with oil in the pocket and the air pumped out of the tensioner piston, to push it away from the engine (I think you call it back), it should take a lot of force and/or not want to move away at all.

I presume you understand the tensioner works by hydraulics to hold the chain with a ball check, not the spring.

Edited August 4, 2019 by jimk

[Inka’d02]

2 hours ago, jimk said:

This test should be done with oil in the oil pocket.  Without oil, the tensioner piston has no hydraulics.  And with oil in the pocket and the air pumped out of the tensioner piston, to push it away from the engine (I think you call it back), it should take a lot of force and/or not want to move away at all.

I presume you understand the tensioner works by hydraulics to hold the chain with a ball check, not the spring.

To clarify. I checked with the reservoir full then with the oil pulled out. Reason being I couldnt see if the piston is moving freely in the bore when submerged in 1800 mile oil.

[Inka’d02]

2 hours ago, 2002Scoob said:

Ugh. Bummer man, sorry to hear. Was hoping you could diagnose to minor and not have to crack it apart ?


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It is what it is. Brightside is I was planning in doing some upgrades anyway. Thanks Again!

[Hans]

As above, you need to keep oil in the pocket. You don't need to see the piston,  you just need to see the slider shoe that pushes on the chain. Pry it back and forth to bleed out the air and fill the piston with oil. Once bled properly it should be very hard to move. Oil gets into the piston through little holes and there is a check ball inside.

Do I understand you are doing an autopsy?

[m-tuner]

noises , nocking when cold excessive clearance on piston skirts or short pistons as in s38, noise warm valve clearance to wide, bad rockers and shafts, flat cam, rod bearing excessive clearance, low oil pressure, tensioner slap, rist pin bearing bad, those are not forged pistons,  they are made in china ?  if they are thats the first place I would look  Bruce Mtuner

[Russell74Fjord]

a major rebuilder whose name includes the initials MM, says piston #3 runs hot, so it is built with a little more tolerance, (and forged pistons), and so mine also has some rattle, but when run hard and hot, seems to dissipate,,

 

(or since everything else is louder I don't hear it !)

 

isn't that was the radio is for, drown out the worrisome noises. 

 

drive it until it breaks, then fix it,, !

[Roland]

16 hours ago, Russell74Fjord said:

a major rebuilder whose name includes the initials MM, says piston #3 runs hot, so it is built with a little more tolerance, (and forged pistons), and so mine also has some rattle, but when run hard and hot, seems to dissipate,,

A chart offered by an engine builder with similar initials seems to suggest a different conclusion regarding operating cylinder temperatures and optimized cylinder wall clearances.

 

This linked chart: https://metricmechanic.com/wp-content/uploads/2016/07/Piston-Clearance-Chart.pdf   indicates tighter (rather than looser) cylinder wall clearance for the inner cylinders (nos. 2 and 3) possibly suggesting "cooler" operating temperatures and less expansion. Whether these operating temperature conclusions or assumptions are applicable to all E10 engines across the board (with or without forged pistons), or they are only applicable to that builder's end-product is unknown.  A quick look at a typical head gasket supports the notion that the factory considered and addressed cylinder temperature variation when designing the cylinder head water jackets, including location and size of the various cylinder head coolant passages.  It bears mentioning that the temperature variations are somewhat theoretical considering that different engines with different fuel delivery systems and operating conditions and thus operational ranges, will produce differing temperatures.  Setting that aside, piston design and manufacture has not remained completely static since original M10 production.  For all of the supposed benefits offered by forged pistons, they can carry expansion and weight disadvantages.  Conversely, although not as strong as forged, cast hypereutectic pistons suffer less weight and expansion issues, and are less likely to suffer from piston slapping.

 

 

 

 

[Russell74Fjord]

that's my head in the first picture !   (after suffering a cylinder head gasket failure, the gasket showing was the improvement, an M-3 head gasket if I recall correctly, requiing a slight modification to insure it did not spew oil everywhere). 

 

I thought I recall Jim saying hotter, perhaps I mixed up which cylinders he thought were hotter vs cooler. 

[m-tuner]

I have been using forged pistons in my custom built engines for 40 years , they are lighter per the fact that the material is stronger and denser, a lot stronger especially in the ring land hence a smaller ring pack,  hypertectic and cast pistons have no place in any high output engine, they are cheaper to produce, run a smaller side clearance which produces lower oil consumption and noise, but the newer alloys allow clearance s in forge pistons that i use to be about .001 greater than a cast piston.  I have had no failures in any pistons I have used, they will make a little more noise when cold and the oil is cold, which dissipates as the engine warms. the s14 head gasket is for bores greater than 90mm, all my stroker m10 engines are 92mmx88mm and use this gasket  if the deck height of the piston is  zero or above, the stock cutting ring tii head gasket can not be used.   I weigh all components in any build so this is not conjecture but fact and have the component weights  Bruce Mtuner

[Roland]

On 8/10/2019 at 11:33 AM, m-tuner said:

I have been using forged pistons in my custom built engines for 40 years , they are lighter per the fact that the material is stronger and denser, a lot stronger especially in the ring land hence a smaller ring pack,

All things considered, denser does not necessarily mean lighter in weight, unless you are also equating denser with thinner as you seem to suggest regarding a smaller ring pack.

 

I was not touting one piston design over another as I agree that conventional wisdom still holds that "forged" is stronger and more durable than "cast" whether pistons, rods or crankshafts.  However, if there is one historical disadvantage to forged pistons, aside from cost, it is a greater likelihood toward exhibiting piston slap.  This, as you note, is not a considerable impediment to their use.  Reference to hypereutectic cast pistons was only in connection to the cylinder wall clearance chart and the fact that they are an alternative in situations seeking minimal piston wall clearances favoring longevity versus all-out performance on an otherwise stock engine.

Quote

Hypereutectic pistons can be forged, but typically are only cast, because the extra expense of forging is not justified when cast pistons are considered strong enough for stock applications https://en.wikipedia.org/wiki/Hypereutectic_piston

 

Quote

Compared to both 4032 and 2618 alloy forged pistons, hypereutectic pistons are significantly less strong. Therefore, for performance applications using boost, nitrous oxide, and/or high RPMs, forged pistons (made from either alloy) are preferred. However, hypereutectic pistons experience less thermal expansion than even forged pistons made from low expansion 4032 alloy. For this reason, hypereutectic pistons can run a tighter piston to cylinder clearance than forged pistons. This makes hypereutectic pistons a better choice for stock engines, where longevity is more important than ultimate performance. https://en.wikipedia.org/wiki/Hypereutectic_piston

 

FWIW, I have not had any problems with forged and even the lowly cast variety of pistons in M10 and M30 engines that have seen considerable use for thirty plus years.

 

Edited August 11, 2019 by Roland

[m-tuner]

the difference in skirt clearance between a cast piston and my forged pistons is about .001, the fact that the material is stronger means that they can run thinner wall construction, with out steel inserts inside as in stock mahle cast pistons, equates to a much lighter part, and in a stroker motor light means higher rpm, I also use custom rods which are much lighter, 200 grams or more for the piston,rod combo, and  much stronger and longer to maintain a good rod ratio, thats why a stroker motor is 10k, but puts out 230hp with 2 valves and a 100 to 200  lb weight advantage over any  other bmw replacement engine, if I can't build a 2100lb 2002 with 230hp I  am not interested, a s14 build is at 15k for a stock warmed engine if you can find one, they have all been blow up,  they have their own issues, oil pressue and valve contact being some and the big one cost per/horse power, if you are turning a m10  9,000 as I have in racing cast pistons will not hold up, but in a stock application they are very good.  Bruce Mtuner

[Tom Gilpin]

On 8/5/2019 at 12:00 AM, Inka’d02 said:

It is what it is. Brightside is I was planning in doing some upgrades anyway. Thanks Again!

Did you ever figure out what this was? My recently rebuilt engine is doing the same! Thanks

[2ma2]

I have this issue too.  I think it might be a camshaft issue as it has what is supposed to be a 292 grind.  Not sure how well it was contoured but multiple valve adjustments don’t seem to help much and with the stethoscope it def sounds like top end noise.  Car runs great especially at higher rpm’s so I haven’t been in a huge hurry to sort it out.  Will be going back to a stock cam at some point

[Son of Marty]

Are you sure you have your cam timing set dead on if your more than 1 tooth contact with the piston is possible.

[paulyg]

I have also been chasing this issue. De-gunked tensioner piston, wasn’t the problem. Engine is also “recently” rebuilt mile-wise. Noise goes away when warm but can return after a long sit at a stoplight at idle. I’m suspecting a top end oiling issue. I think I will remove and clean the oil spray bar this weekend to ensure that the whole valvetrain is getting a good supply even at idle.