Piston to Cylinder Clearances
- Thread starter 147_Grain
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none that I'm aware of, esp. Alu piston to iron sleeved alu block engines, clearances remained pretty much the same for all these years.
Q.
Q.
Wow, this is actually a good question.
I haven't ever thought about this, but I would say that, due to higher tolerances and increased demand for efficiency, the clearance has decreased.
You can only make a piston as big as the cylinder that contains it so I think that with todays incredibly precise engine machining the limit on clearance has probably been reached. Instead manufacturers are probably spending more time thinking about reducing friction between cylinder wall and piston skirt, as well as attempting to find the optimal ring tension given the engines designed use.
I haven't ever thought about this, but I would say that, due to higher tolerances and increased demand for efficiency, the clearance has decreased.
You can only make a piston as big as the cylinder that contains it so I think that with todays incredibly precise engine machining the limit on clearance has probably been reached. Instead manufacturers are probably spending more time thinking about reducing friction between cylinder wall and piston skirt, as well as attempting to find the optimal ring tension given the engines designed use.
k...here's the scoop RE: piston to bore clearances.
Excessive bore-to-piston clearances, you'll not only get piston skirt rocking inside the bore (similar sounds as piston skirts slapping when cold due to excessive clearances), but you'll also get yourself onto trouble of possible piston seizure due to insufficient piston to bore contacts (yes, it does need to have some "touch" to help dissipate the heat from piston).
On 2T engines: excessive piston-to-bore clearances (typical shadetree mech tricks that still in-use today) will lead to piston seizure; too tight of the clearances may also lead to seizure also.
Optimal clearances have long been established in the area of IC engine designs, and just like piston ring-gap clearances: piston-to-bore clearances hasn't change much during the past 20 to 30 years and I believe these shall remain as-is until they go into the history book.
automotive engine R&D team constantly finding ways to reduce friction (energy saved in friction reduction in engine rotating components equates to fuel savings&/improved energy conversion). Thus the tricks of pulvrerized Moly on piston skirt coatings (Honda), reduction in Piston skirts area, and may other tricks that previously not used, or tricks that previously deemed too costly/unaware of.
Q.
Ask me how I knew this subject for I've done work on Suzuki engines (4cycle, overbore the cylinder bore, lead to cold piston slapping; air-cooled 2T engines overbored which lead to seizure, etc.)
Excessive bore-to-piston clearances, you'll not only get piston skirt rocking inside the bore (similar sounds as piston skirts slapping when cold due to excessive clearances), but you'll also get yourself onto trouble of possible piston seizure due to insufficient piston to bore contacts (yes, it does need to have some "touch" to help dissipate the heat from piston).
On 2T engines: excessive piston-to-bore clearances (typical shadetree mech tricks that still in-use today) will lead to piston seizure; too tight of the clearances may also lead to seizure also.
Optimal clearances have long been established in the area of IC engine designs, and just like piston ring-gap clearances: piston-to-bore clearances hasn't change much during the past 20 to 30 years and I believe these shall remain as-is until they go into the history book.
automotive engine R&D team constantly finding ways to reduce friction (energy saved in friction reduction in engine rotating components equates to fuel savings&/improved energy conversion). Thus the tricks of pulvrerized Moly on piston skirt coatings (Honda), reduction in Piston skirts area, and may other tricks that previously not used, or tricks that previously deemed too costly/unaware of.
Q.
Ask me how I knew this subject for I've done work on Suzuki engines (4cycle, overbore the cylinder bore, lead to cold piston slapping; air-cooled 2T engines overbored which lead to seizure, etc.)
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The big change in clearances happened back when engines (at least some of them) went to hypereutectic pistons from forged.
A forged aluminum slug will contract/expand a fair bit. Subsequently, adequate cylinder to wall clearance must be given to allow for the expansion that happens when the piston is hot.
Cast pistons expand as well, though, IIRC, not as much as the forged ones.
However, with the creation of hypereutectic pistons, which use an aluminum/silicon alloy, the thermal expansion (and contraction) of the piston is greatly reduced. This means that piston-to-wall clearance could be reduced as well.
The biggest advantage here is the reduction in blow-by gasses.
A good example of this was Ford's 302 HO. Engines with the grey oil pan (87 to sometime early 91) had TRW forged pistons. Later (91+) engines, including the one found in the Explorer, had hypereutectic pistons (and a black oil pan). The former engines were desired for their ability to better handle boost. But the change was made for the ever advancing emissions standards, as the hypereutectic slugs made the engine "cleaner" with the reduction of blow-by.
A forged aluminum slug will contract/expand a fair bit. Subsequently, adequate cylinder to wall clearance must be given to allow for the expansion that happens when the piston is hot.
Cast pistons expand as well, though, IIRC, not as much as the forged ones.
However, with the creation of hypereutectic pistons, which use an aluminum/silicon alloy, the thermal expansion (and contraction) of the piston is greatly reduced. This means that piston-to-wall clearance could be reduced as well.
The biggest advantage here is the reduction in blow-by gasses.
A good example of this was Ford's 302 HO. Engines with the grey oil pan (87 to sometime early 91) had TRW forged pistons. Later (91+) engines, including the one found in the Explorer, had hypereutectic pistons (and a black oil pan). The former engines were desired for their ability to better handle boost. But the change was made for the ever advancing emissions standards, as the hypereutectic slugs made the engine "cleaner" with the reduction of blow-by.
OVERKILL
$100 Site Donor 2021
Originally Posted By: Quest
k...here's the scoop RE: piston to bore clearances.
Excessive bore-to-piston clearances, you'll not only get piston skirt rocking inside the bore (similar sounds as piston skirts slapping when cold due to excessive clearances), but you'll also get yourself onto trouble of possible piston seizure due to insufficient piston to bore contacts (yes, it does need to have some "touch" to help dissipate the heat from piston).
On 2T engines: excessive piston-to-bore clearances (typical shadetree mech tricks that still in-use today) will lead to piston seizure; too tight of the clearances may also lead to seizure also.
Optimal clearances have long been established in the area of IC engine designs, and just like piston ring-gap clearances: piston-to-bore clearances hasn't change much during the past 20 to 30 years and I believe these shall remain as-is until they go into the history book.
automotive engine R&D team constantly finding ways to reduce friction (energy saved in friction reduction in engine rotating components equates to fuel savings&/improved energy conversion). Thus the tricks of pulvrerized Moly on piston skirt coatings (Honda), reduction in Piston skirts area, and may other tricks that previously not used, or tricks that previously deemed too costly/unaware of.
Q.
Ask me how I knew this subject for I've done work on Suzuki engines (4cycle, overbore the cylinder bore, lead to cold piston slapping; air-cooled 2T engines overbored which lead to seizure, etc.)
Another manufacturer to use the coated skirts was Ford when they released the Modular family. Short-skirt pistons (compared to the Windsor) but with a moly or Teflon coating on them to reduce friction (and potential piston-slap noise).
k...here's the scoop RE: piston to bore clearances.
Excessive bore-to-piston clearances, you'll not only get piston skirt rocking inside the bore (similar sounds as piston skirts slapping when cold due to excessive clearances), but you'll also get yourself onto trouble of possible piston seizure due to insufficient piston to bore contacts (yes, it does need to have some "touch" to help dissipate the heat from piston).
On 2T engines: excessive piston-to-bore clearances (typical shadetree mech tricks that still in-use today) will lead to piston seizure; too tight of the clearances may also lead to seizure also.
Optimal clearances have long been established in the area of IC engine designs, and just like piston ring-gap clearances: piston-to-bore clearances hasn't change much during the past 20 to 30 years and I believe these shall remain as-is until they go into the history book.
automotive engine R&D team constantly finding ways to reduce friction (energy saved in friction reduction in engine rotating components equates to fuel savings&/improved energy conversion). Thus the tricks of pulvrerized Moly on piston skirt coatings (Honda), reduction in Piston skirts area, and may other tricks that previously not used, or tricks that previously deemed too costly/unaware of.
Q.
Ask me how I knew this subject for I've done work on Suzuki engines (4cycle, overbore the cylinder bore, lead to cold piston slapping; air-cooled 2T engines overbored which lead to seizure, etc.)
Another manufacturer to use the coated skirts was Ford when they released the Modular family. Short-skirt pistons (compared to the Windsor) but with a moly or Teflon coating on them to reduce friction (and potential piston-slap noise).
OVERKILL
$100 Site Donor 2021
Originally Posted By: 147_Grain
Are the Japan-built engines from Toyota, Honda, Subaru, and Nissan also benefitting from hypereutectic pistons with pulverized moly coatings?
Quite likely. They became popular in the late 80's, early 90's.
Are the Japan-built engines from Toyota, Honda, Subaru, and Nissan also benefitting from hypereutectic pistons with pulverized moly coatings?
Quite likely. They became popular in the late 80's, early 90's.
Consider the clearance on my Acura is .0008. This would be unheard of 30 yrs ago. Technology has come a long way, heck just holding a tolerance of under .001 required good equipment and skilled operators.
Originally Posted By: Smoky14
Consider the clearance on my Acura is .0008. This would be unheard of 30 yrs ago. Technology has come a long way, heck just holding a tolerance of under .001 required good equipment and skilled operators.
Perhaps you just made a case for the thinner 20-weight oils. Conversely, there are camshaft and valve spring issues to deal with on higher revving engines and bearing clearances as well.
Consider the clearance on my Acura is .0008. This would be unheard of 30 yrs ago. Technology has come a long way, heck just holding a tolerance of under .001 required good equipment and skilled operators.
Perhaps you just made a case for the thinner 20-weight oils. Conversely, there are camshaft and valve spring issues to deal with on higher revving engines and bearing clearances as well.
Originally Posted By: 147_Grain
Engine Design Question:
Have the piston to cylinder wall CLEARANCES in new engines changed over the past 20+ years?
No, and not significantly in the last FIFTY years. Well, right at 50 years... that's when thermally compensated pistons started replacing autothermic tin coated pistons in most north American mass-market engines.
The change to hypereutectic pistons in the 90s allowed some tightening of cold clearances, but not as much as the change that happened in the early 1960s. Mostly hypereutectic and eutectic piston alloys allowed re-centering the pin on the piston- the offset had been added to prevent cold engine piston slap. Of course we all know that it was less than perfectly successful in practice, given the surge in piston slap complaints that occurred and is still going on.
Engine Design Question:
Have the piston to cylinder wall CLEARANCES in new engines changed over the past 20+ years?
No, and not significantly in the last FIFTY years. Well, right at 50 years... that's when thermally compensated pistons started replacing autothermic tin coated pistons in most north American mass-market engines.
The change to hypereutectic pistons in the 90s allowed some tightening of cold clearances, but not as much as the change that happened in the early 1960s. Mostly hypereutectic and eutectic piston alloys allowed re-centering the pin on the piston- the offset had been added to prevent cold engine piston slap. Of course we all know that it was less than perfectly successful in practice, given the surge in piston slap complaints that occurred and is still going on.
Originally Posted By: 147_Grain
Question:
I've heard that Subaru's pistons and cylinders are a bit different than other manufactures.......anyone familiar with the differences? I love the torque and power of our 2013 Subaru Outback with the 3.6L 6-cylinder engine.
Subaru used short skirts and moly coating at least since 2000, most likely much earlier. They did have their share of piston slap.
Question:
I've heard that Subaru's pistons and cylinders are a bit different than other manufactures.......anyone familiar with the differences? I love the torque and power of our 2013 Subaru Outback with the 3.6L 6-cylinder engine.
Subaru used short skirts and moly coating at least since 2000, most likely much earlier. They did have their share of piston slap.
when i started reading about cars in the early 60s the inside engine dementions in books was shown in fractions. true
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