The pistons most definitely touch the cylinder wall. There is only a few thou clearance between the 2 and when the piston heats up it growsbjust a bit and gets really close and touches, the oil film is what keeps it from destroying itself. That's why there is skirt wear, it didn't come from rubbing air lol. Put a moly coated piston in and run it a few mins and take it out. Guaranteed to be missing some coating. 👍🏻 Everytime the piston changes direction the piston rocks a few thousands side to side, aka skirt wear, now the crown of the piston is a good bit smaller and should never touch unless the skirt wear is just horribly worn.
If the piston never touched the cylinder, we wouldn't need said oil (okay maybe for the ring, but you get the point) The idea of these oil films is to reduce that contact to a small amount as possible. Same thing with the cross hatching and surface finish.. that's to HOLD said oil. That contact to some degree is going to happen. Notice that an engine will run for beaucoup hours and be fine.. then it starts knocking. Why all of the sudden? The wear has accumulated to a point where the piston starts rocking and that oil film breaks down. It's one of those things where there is some level truth to what he is saying.. but from a perspective of physics it is more like the piston "barely" contacts the jug.. and at 10k rpm that "barely" is where the wear comes from. Going to have to get some of that husky chain.. that cuts nice!
The piston most definitely contacts the cylinder bore. The job of the ring(s) is to provide a gas seal. Pretty simple I think we all know this. Don’t really know what else to say.
I have some old Carlton semi chisel non safety chain , after a good file job and knocking the rakers down it cuts real close to some full chisel in oak, im liking it.
I agree Corey, I have always used husqvarna and origon semi non safety chains in the wood pile for over 30 years. Lately I'm using 8ten chains off Amazon, if you buy more than 3 good price point last good and sharpen well . Cheers brother.
Couple things to consider about piston contact... multi ring piston = less rocking in bore. Also, tightness of ring(s) in lands (groove) will affect the skirt clearance/contact. I flog the shit out of my saws without concern because I Know there is plenty of Good oil keeping things from melting 👍🏻
Agreed, there's definitely shifting but near constant contact between the piston skirt and cylinder, with only a thin boundary layer of oil to 'hopefully' prevent friction. Good to know the sp83 cuts decent👍🏻 actually better than I expected! Picked up a loop a couple months ago on a whim but have yet to use it.
Maybe somebody can call Wiseco or a piston manufacturer and then call an oil manufacturer tomorrow and get their answer on the piston and cyl question? From what I recall, on a microscopic level the oil acts like a bunch of loose ball bearings that cling to a surface. Neither surface is flat. Shaped more like little corrugated sheet metal but the oil fills your valleys between the peaks and the only metal contact is peak to peak between your surfaces. I agree on metal to metal, material wear being my evidence.
I will not bore everyone with my list of mechanical credentials but, I agree with you 100%. That is a nice Red Oak you are cutting cookies off of. Really enjoy your channel. Thanks for going to the trouble of making it and for sharing your knowledge with the rest of us.
In short I've been into saws in every way for 40 years and yes it definitely 100% makes contact with cylinder walls. How could it not at 13,000 rpms! Good work! So I finally figured out who you remind me of and it's Clint Bowyer to the T!!! Keep up the good work and thanks for all your info!!
I have been studying this chain for last couple of days, man your right on time, thanks again for your time and effort, 👍 your the only video on TH-cam on it.
Myself I would never run a full chisel in dirty wood I find they dull very quick vs a semi chisel. Maybe try 8ten chains nice price point and a decent chain to use and sharpen. Just my 2 cents worth. Keep on keeping on man. Cheers.
Nice channel👍only good stuffs to learn. Thank you. In Croatia we've got only x cut C85, while in Germany they have C85( full chisel) and also S85( semi chisel)- for dirty logs. So I' ve ordered some S85 chains.✌️❤️
I put C85 18' on Husqvarna 550mk2 and it is freakin awesome, because I wanted same chain on all my chainsaws. With Mk2 actually I work only smaller logs.
Same thing I have seen. Factory Poulan Pro chain Oregon semi chisel safety chain raker, versus a Oregon full chisel with safety chain raker, and the full chisel beat it in White Oak by 4 seconds. You are correct, Oregon runs a higher raker setup for hardwoods.
In a perfect world a thin layer of oil keeps the rings and piston from contacting the cylinder wall. The oil acts as a “cushion” and also helps seal. More oil technically the better seal and technically the more power (compression) you’ll have.
John Wilkins is absolutely correct. The piston does not come in contact with the cylinder wall. It truly does ride on a film of oil. If there were physical contact, pistons wouldn’t last very long. Also, looking at the construction of a 4 stroke piston the third set of rings in a ring pack, that third set is referred to as the “oil wiper”. It’s job is just that. To wipe that thin film of oil off on every stroke so it doesn’t build up too much. The rings are what contact the cylinder and have two jobs. To seal for compression, and to transfer heat from the piston crown to the cylinder walls. Cylinders are final machined to a given tolerance fit for its intended piston material and diameter and the piston grows into that tolerance as it heats up and there will be a minimal clearance to spare. That is where the oil film come it to play. When you have a non plated cylinder machined for piston fit, you need to specify whether you are machining for forged or cast pistons. They require different tolerances due to the forged having a higher silicone content, so they need a looser fit. They grow into,the bore as they heat up at a greater rate than cast. If machined properly, none of these examples will physically “touch” the cylinder. When you see an example of piston slap, it is cause by foreign object damage entering the air filter like wood fines. I’ve seen pistons with many hours of use on them and still see the machine lines.
I mentioned the oil film in either my first or second post. He was adamant. The piston never comes in contact with the wall, not because of the oil seal, but because the piston is smaller than the bore. He isn't taking into consideration that the piston rocks back and forth. This is not only on worn out pistons, this happens on a brand new factory spec piston. Go read our comments. He thinks the piston is balanced by the rings and that the rings are the only part that makes contact to the cylinder walls. This is incorrect. That piston is chattering about back and forth all around the cylinder. He doesn't believe this is happening. I know the oil film exists and is what prevents catastrophic failure over the life of the saw, but the piston rocks back and forth every time it goes up and down.
@@novicelumberjack I probably spoke without my complete version of what is happening in the cylinder. Yes, the piston physically does rock. And yes it’s oil film that creates a barrier between physical contact of the two metals to include the ring pack.
I'm not an engineer. I think they run on magic. You must be a powerful witch doctor because your spells really make them run. Especially with the NOS. I'm just being silly and enjoy watching your channel. I think maybe the piston does ride on the film of oil. The coatings make it slide better in the film. The oil film itself , no matter how slippery everything is will cause wear . Add the fine particles . And possibly to much heat at times to break down the film. I also agree with your thought that any piston traveling at 13,000 rpms as well as completely changing direction must make some kind of metal to metal contact. That means I'm taking your side and if I'm wrong I will admit it with you.
I would 💯 agree with you. It does make contact. Even if it rode on the rings, the ring would act like a pivot point and the piston would wobble in the bore. Even then, if there is proper ring gap, shouldn’t the rings compress just a small amount on the power stoke the piston make contact anyway?
Jiminey Christmas... ask any of the big names in porting- Egan, kunz, buxton, walker, Dyno Joe, briscoe, van layaway... they all have videos even showing piston wear and how machining marks disappear over time. That's flat out contact with another surface. It's especially recognizable in the newer Stihls- 461, 462, 661 etc... you'll see very obvious signs of it rubbing. Surely, there's no way he.... never mind I can't say it.
I had ah Yamaha 400it 1977 and it had so much piston slap it rattled the jug loose there's no way the piston was floating in the jug more like slapping front and rear witch mad the cylinder Bolt's were finger tight when I took it off being Enduro it had light and ah trip 1100km before it wouldn't motor ticky anymore loved that bike😜🌳❤👍
Design and theory of a piston engine would say that the piston does not touch the cylinder wall. It would always have a oil layer hydraulically supporting it. If you look at real world examples you can clearly see that doesn’t happen. By design I think the 2 stroke engine will always see more piston wear than a 4 stroke. But If someone asked me if they touched I would have to answer no. Because “technically” they shouldn’t be touching and in a 4 stroke I don’t think they do enough to have this type of discussion. In a 2 stoke your fighting a losing battle with an unfiltered oiling system and way less piston support because of all the ports in the cylinder walls. I think those 2 factors contribute to piston wear way more than the piston actually touching the wall.
Yeah that's crazy. Why would piston manufacturers put an anti wear coating on the skirts to reduce friction and noise on automobile pistons if they weren't making any contact?
I would reference NATEF/ASE. Short story long, you're right. You'd get a lot of piston slap on a cold start if the piston had enough room to travel freely in the cylinder bore regardless of application: aviation, diesel, gas in two/four stroke.
It's simple physics. There is nothing to stabilize the piston laterally, the ring to wrist pin distance especially on a single ring piston will far and away creates more side leverage than the ring can overcome. In a 4 cycle engine (automotive) There is a ring pack of several rings that will help minimize the skirts dragging but that is a completely different animal... I'm not saying the guy is dumb, I do think he is ignorant of the topic where 2 stroke engines are concerned
Why did you use a semi chisel safety chain ( low kick back) instead of a semi chisel vs full chisel ? They do make a semi that doesn't have the wood bumpers that run beside the rakers . I think that might be a test for another day .cheers man and keep on keeping on.
Question for you. My observation is that the Stihl full chisel chain seems to be the best out there for cutting speed. When I compare that to the Husqvarna chain.... the husky chain just feels like it comes up short. Needs to be sharpened sooner, and doesn't get as sharp. Is this your feeling too, or am I just not doing a good job with the file? Side note: your wind protector on your mic worked really well. Thanks for that.
The Husky chain is definitely superior to all others when it comes to out of the box cutting speed. However, once they dull, I have found it impossible to get it back to stock cutting speed. But I think they hold the edge just as well as anything else.
Is this other bloke talking about the piston sections between the rings?? I don’t think that should be touching, maybe I’m wrong, but the skirt of the piston does I think, I’ve never pulled a saw apart that far.
Skirt coating are for situations when lubrication is compromised. in normal oil film condition piston really doesnt touch walls. 2 stroke has holes in the walls and runs uneven temperatures and uneven lubrication all the time. other hand 4 strokes have too good lubrication in the walls so they use oil control rings to scrape oil away from cylinder walls. want touch the walls straight gas you 2 stroke,,,,,,,,,,,,,,,,,,
The conversation excluded the oil film. Yes, we all know about the oil film. Look at it this way...if you are wearing a condom, does that mean that your shaft isn't touching the vaginally walls and you are technically still a virgin? No. You still goat all up in that and were slamming around and up against the walls. The piston is SLAMMING hard against the walls, specifically on the intake side. That is why it is literally called the thrust side.
Just on the chains, I’m running a few Husqvarna saws, I’ve gone with 3/8 on the 592xp because my 576xp was 3/8 so I have a heap of chains and bars and assemble what I want for the job, but… these full chisel chains are good yes but one touch of the dirt and they’re dead, just no go. So does anyone else prefer the semi chisel? Sometimes I know I’m going to touch the dirt so I personally prefer the semi chisel, what is the best semi chisel chain for cutting up crappy logs? not the clean stuff. For me it’s about not needing to change saws, chains or sharpen every 20 minutes.
If the piston doesn’t touch the cylinder then how does the piston get wear on the skirt! That makes no sense the rings seal the bore carries oil but there deffintly is contact between the cylinder and piston that guy is wrong!!!! Also the further from dead center of the piston the wrist pin is the more cylinder piston contact you will get equals more skirt wear! Stick to your guns Boedy cause you’re 100% right!!
I'll have to go back and check in on it. Last I saw he started back tracking a bit and was talking about the oil film. I think I had mentioned that in either my very first or second post. He thinks it is balanced in the bore and does not rock back and forth.
The pistons most definitely touch the cylinder wall. There is only a few thou clearance between the 2 and when the piston heats up it growsbjust a bit and gets really close and touches, the oil film is what keeps it from destroying itself. That's why there is skirt wear, it didn't come from rubbing air lol. Put a moly coated piston in and run it a few mins and take it out. Guaranteed to be missing some coating. 👍🏻 Everytime the piston changes direction the piston rocks a few thousands side to side, aka skirt wear, now the crown of the piston is a good bit smaller and should never touch unless the skirt wear is just horribly worn.
If the piston never touched the cylinder, we wouldn't need said oil (okay maybe for the ring, but you get the point)
The idea of these oil films is to reduce that contact to a small amount as possible. Same thing with the cross hatching and surface finish.. that's to HOLD said oil. That contact to some degree is going to happen.
Notice that an engine will run for beaucoup hours and be fine.. then it starts knocking. Why all of the sudden? The wear has accumulated to a point where the piston starts rocking and that oil film breaks down.
It's one of those things where there is some level truth to what he is saying.. but from a perspective of physics it is more like the piston "barely" contacts the jug.. and at 10k rpm that "barely" is where the wear comes from.
Going to have to get some of that husky chain.. that cuts nice!
The piston most definitely contacts the cylinder bore. The job of the ring(s) is to provide a gas seal. Pretty simple I think we all know this. Don’t really know what else to say.
I have some old Carlton semi chisel non safety chain , after a good file job and knocking the rakers down it cuts real close to some full chisel in oak, im liking it.
I agree Corey, I have always used husqvarna and origon semi non safety chains in the wood pile for over 30 years. Lately I'm using 8ten chains off Amazon, if you buy more than 3 good price point last good and sharpen well . Cheers brother.
Couple things to consider about piston contact... multi ring piston = less rocking in bore. Also, tightness of ring(s) in lands (groove) will affect the skirt clearance/contact. I flog the shit out of my saws without concern because I Know there is plenty of Good oil keeping things from melting 👍🏻
That's the best protection from premature wear. Good oil and plenty of it. It will also keep 5 series Husqvarna saws from eating crank bearings.
That guys is probably talking about full size car/ truck engine that are designed to be guided by the piston rings and not contact the wall
That's my guess also because pistons in a car engine are absolutely not meant to touch
Agreed, there's definitely shifting but near constant contact between the piston skirt and cylinder, with only a thin boundary layer of oil to 'hopefully' prevent friction.
Good to know the sp83 cuts decent👍🏻 actually better than I expected! Picked up a loop a couple months ago on a whim but have yet to use it.
Maybe somebody can call Wiseco or a piston manufacturer and then call an oil manufacturer tomorrow and get their answer on the piston and cyl question?
From what I recall, on a microscopic level the oil acts like a bunch of loose ball bearings that cling to a surface. Neither surface is flat. Shaped more like little corrugated sheet metal but the oil fills your valleys between the peaks and the only metal contact is peak to peak between your surfaces.
I agree on metal to metal, material wear being my evidence.
YES.
Hope to see you do some more semi chisel stuff.
Seems a little lazy off throttle but pulls good in the wood. I really like those 630s.
I will not bore everyone with my list of mechanical credentials but, I agree with you 100%. That is a nice Red Oak you are cutting cookies off of. Really enjoy your channel. Thanks for going to the trouble of making it and for sharing your knowledge with the rest of us.
The cylinder and piston will wear from the contact of the piston rings and piston skirt on the cylinder. This wear is minimised by oil lubrication.
In short I've been into saws in every way for 40 years and yes it definitely 100% makes contact with cylinder walls. How could it not at 13,000 rpms! Good work! So I finally figured out who you remind me of and it's Clint Bowyer to the T!!! Keep up the good work and thanks for all your info!!
I have been studying this chain for last couple of days, man your right on time, thanks again for your time and effort, 👍 your the only video on TH-cam on it.
Yes it does Pistons definitely touch the cylinder walls
Yep piston touches but oil keeps them happy.
Myself I would never run a full chisel in dirty wood I find they dull very quick vs a semi chisel. Maybe try 8ten chains nice price point and a decent chain to use and sharpen. Just my 2 cents worth. Keep on keeping on man. Cheers.
Nice channel👍only good stuffs to learn. Thank you. In Croatia we've got only x cut C85, while in Germany they have C85( full chisel) and also S85( semi chisel)- for dirty logs. So I' ve ordered some S85 chains.✌️❤️
This chain is for the smaller saws. S85 is the semi chisel version of the C85. C85 and C83 is the same but one is 1.5mm and the other 1.3mm
This chain is for the smaller saws. S85 is the semi chisel version of the C85. C85 and C83 is the same but one is 1.5mm and the other 1.3mm
I put C85 18' on Husqvarna 550mk2 and it is freakin awesome, because I wanted same chain on all my chainsaws. With Mk2 actually I work only smaller logs.
Same thing I have seen. Factory Poulan Pro chain Oregon semi chisel safety chain raker, versus a Oregon full chisel with safety chain raker, and the full chisel beat it in White Oak by 4 seconds. You are correct, Oregon runs a higher raker setup for hardwoods.
Ever heard of piston slap, now that is point game set match.
In a perfect world a thin layer of oil keeps the rings and piston from contacting the cylinder wall. The oil acts as a “cushion” and also helps seal. More oil technically the better seal and technically the more power (compression) you’ll have.
John Wilkins is absolutely correct. The piston does not come in contact with the cylinder wall. It truly does ride on a film of oil. If there were physical contact, pistons wouldn’t last very long. Also, looking at the construction of a 4 stroke piston the third set of rings in a ring pack, that third set is referred to as the “oil wiper”. It’s job is just that. To wipe that thin film of oil off on every stroke so it doesn’t build up too much. The rings are what contact the cylinder and have two jobs. To seal for compression, and to transfer heat from the piston crown to the cylinder walls. Cylinders are final machined to a given tolerance fit for its intended piston material and diameter and the piston grows into that tolerance as it heats up and there will be a minimal clearance to spare. That is where the oil film come it to play. When you have a non plated cylinder machined for piston fit, you need to specify whether you are machining for forged or cast pistons. They require different tolerances due to the forged having a higher silicone content, so they need a looser fit. They grow into,the bore as they heat up at a greater rate than cast. If machined properly, none of these examples will physically “touch” the cylinder. When you see an example of piston slap, it is cause by foreign object damage entering the air filter like wood fines. I’ve seen pistons with many hours of use on them and still see the machine lines.
I mentioned the oil film in either my first or second post. He was adamant. The piston never comes in contact with the wall, not because of the oil seal, but because the piston is smaller than the bore. He isn't taking into consideration that the piston rocks back and forth. This is not only on worn out pistons, this happens on a brand new factory spec piston. Go read our comments. He thinks the piston is balanced by the rings and that the rings are the only part that makes contact to the cylinder walls. This is incorrect. That piston is chattering about back and forth all around the cylinder. He doesn't believe this is happening. I know the oil film exists and is what prevents catastrophic failure over the life of the saw, but the piston rocks back and forth every time it goes up and down.
@@novicelumberjack I probably spoke without my complete version of what is happening in the cylinder. Yes, the piston physically does rock. And yes it’s oil film that creates a barrier between physical contact of the two metals to include the ring pack.
I'm not an engineer. I think they run on magic. You must be a powerful witch doctor because your spells really make them run. Especially with the NOS. I'm just being silly and enjoy watching your channel. I think maybe the piston does ride on the film of oil. The coatings make it slide better in the film. The oil film itself , no matter how slippery everything is will cause wear . Add the fine particles . And possibly to much heat at times to break down the film. I also agree with your thought that any piston traveling at 13,000 rpms as well as completely changing direction must make some kind of metal to metal contact. That means I'm taking your side and if I'm wrong I will admit it with you.
I would 💯 agree with you. It does make contact. Even if it rode on the rings, the ring would act like a pivot point and the piston would wobble in the bore. Even then, if there is proper ring gap, shouldn’t the rings compress just a small amount on the power stoke the piston make contact anyway?
Jiminey Christmas... ask any of the big names in porting- Egan, kunz, buxton, walker, Dyno Joe, briscoe, van layaway... they all have videos even showing piston wear and how machining marks disappear over time. That's flat out contact with another surface. It's especially recognizable in the newer Stihls- 461, 462, 661 etc... you'll see very obvious signs of it rubbing. Surely, there's no way he.... never mind I can't say it.
I had ah Yamaha 400it 1977 and it had so much piston slap it rattled the jug loose there's no way the piston was floating in the jug more like slapping front and rear witch mad the cylinder Bolt's were finger tight when I took it off being Enduro it had light and ah trip 1100km before it wouldn't motor ticky anymore loved that bike😜🌳❤👍
Design and theory of a piston engine would say that the piston does not touch the cylinder wall. It would always have a oil layer hydraulically supporting it. If you look at real world examples you can clearly see that doesn’t happen. By design I think the 2 stroke engine will always see more piston wear than a 4 stroke. But If someone asked me if they touched I would have to answer no. Because “technically” they shouldn’t be touching and in a 4 stroke I don’t think they do enough to have this type of discussion. In a 2 stoke your fighting a losing battle with an unfiltered oiling system and way less piston support because of all the ports in the cylinder walls. I think those 2 factors contribute to piston wear way more than the piston actually touching the wall.
Yeah that's crazy. Why would piston manufacturers put an anti wear coating on the skirts to reduce friction and noise on automobile pistons if they weren't making any contact?
Mark your piston with a sharpie- front and rear. Won't take long for most of it to dissappear.
I would reference NATEF/ASE. Short story long, you're right. You'd get a lot of piston slap on a cold start if the piston had enough room to travel freely in the cylinder bore regardless of application: aviation, diesel, gas in two/four stroke.
If the piston doesn’t touch the cylinder wall? Than why does the piston sometimes have scoring on it?
It's simple physics. There is nothing to stabilize the piston laterally, the ring to wrist pin distance especially on a single ring piston will far and away creates more side leverage than the ring can overcome. In a 4 cycle engine (automotive) There is a ring pack of several rings that will help minimize the skirts dragging but that is a completely different animal... I'm not saying the guy is dumb, I do think he is ignorant of the topic where 2 stroke engines are concerned
Why did you use a semi chisel safety chain ( low kick back) instead of a semi chisel vs full chisel ? They do make a semi that doesn't have the wood bumpers that run beside the rakers . I think that might be a test for another day .cheers man and keep on keeping on.
Because modern safety chain isnt slower
Question for you. My observation is that the Stihl full chisel chain seems to be the best out there for cutting speed. When I compare that to the Husqvarna chain.... the husky chain just feels like it comes up short. Needs to be sharpened sooner, and doesn't get as sharp. Is this your feeling too, or am I just not doing a good job with the file?
Side note: your wind protector on your mic worked really well. Thanks for that.
The Husky chain is definitely superior to all others when it comes to out of the box cutting speed. However, once they dull, I have found it impossible to get it back to stock cutting speed. But I think they hold the edge just as well as anything else.
If the piston doesn't how would it block off ports
Stubby is looking good buddy
Is this other bloke talking about the piston sections between the rings?? I don’t think that should be touching, maybe I’m wrong, but the skirt of the piston does I think, I’ve never pulled a saw apart that far.
Has the dude ever wondered why pistons have skirts. With his theory nothing is needed after the last ring. That would be super sweet but impossible.
Skirt coating are for situations when lubrication is compromised. in normal oil film condition piston really doesnt touch walls.
2 stroke has holes in the walls and runs uneven temperatures and uneven lubrication all the time. other hand 4 strokes have too good lubrication in the walls so they use oil control rings to scrape oil away from cylinder walls. want touch the walls straight gas you 2 stroke,,,,,,,,,,,,,,,,,,
The conversation excluded the oil film. Yes, we all know about the oil film. Look at it this way...if you are wearing a condom, does that mean that your shaft isn't touching the vaginally walls and you are technically still a virgin? No. You still goat all up in that and were slamming around and up against the walls. The piston is SLAMMING hard against the walls, specifically on the intake side. That is why it is literally called the thrust side.
The first thing taught in engine building is "Bearing load"
Just on the chains, I’m running a few Husqvarna saws, I’ve gone with 3/8 on the 592xp because my 576xp was 3/8 so I have a heap of chains and bars and assemble what I want for the job, but… these full chisel chains are good yes but one touch of the dirt and they’re dead, just no go. So does anyone else prefer the semi chisel? Sometimes I know I’m going to touch the dirt so I personally prefer the semi chisel, what is the best semi chisel chain for cutting up crappy logs? not the clean stuff. For me it’s about not needing to change saws, chains or sharpen every 20 minutes.
👍🆙BigGuy
Do not under estimate the use of earplugs
If the piston doesn’t touch the cylinder then how does the piston get wear on the skirt! That makes no sense the rings seal the bore carries oil but there deffintly is contact between the cylinder and piston that guy is wrong!!!! Also the further from dead center of the piston the wrist pin is the more cylinder piston contact you will get equals more skirt wear! Stick to your guns Boedy cause you’re 100% right!!
The discussion continues in the comments of that video referenced here.
I'll have to go back and check in on it. Last I saw he started back tracking a bit and was talking about the oil film. I think I had mentioned that in either my very first or second post. He thinks it is balanced in the bore and does not rock back and forth.
Never heard of a SP83G. Dont you mean SP93G? Its also a 3/8 picco chain.
Piston block intake duct.How !!!