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Author Topic: Air cooled vs liquid cooled pistons  (Read 1134 times)

basanti

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Air cooled vs liquid cooled pistons
« on: January 05, 2013, 05:03:45 AM »
Is it possible to run a piston from a liquid cooled engine in an air cooled one?

I'm asking because i installed a piston for a Suzuki DRZ in my AVL engine and even though we maintain correct clearance (0.14mm for 90mm  bore), it still seized.

Just wondering if the piston is the issue or is it something else.

Thanks in advance.

dampking

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Re: Air cooled vs liquid cooled pistons
« Reply #1 on: January 05, 2013, 06:17:33 AM »
Similar issue was faced by a friend of mine. In his case it was not from a motorcyle but a car. It was an 85mm piston was pretty light but even then it gave up. I think watecooled engine pistons can't fight against the immense heat of air cooled.

ace.cafe

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Re: Air cooled vs liquid cooled pistons
« Reply #2 on: January 05, 2013, 12:19:04 PM »
Could be a lot of things.
The piston from a water cooled engine might work, as long as it only gets the heat and forces that it was designed to get, and it never saw any detonation or lean conditions or wrong timing.

However the other possibility is that with a 90mm bore, that is FAR too much bore size, and left you with a thin cylinder wall which probably severely distorted when it got hot, and no piston can run in a distorted bore.

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basanti

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Re: Air cooled vs liquid cooled pistons
« Reply #3 on: January 05, 2013, 03:39:08 PM »
Could be a lot of things.

 it never saw any detonation or lean conditions or wrong timing.

However the other possibility is that with a 90mm bore, that is FAR too much bore size, and left you with a thin cylinder wall which probably severely distorted when it got hot, and no piston can run in a distorted bore.

Timing was fine and I had jetted on the rich side.

We have had re-sleeved the barrel with a bigger sleeve before boring to 90 mm so had a minimum wall thickness of 4-4.5 mm. Here are some photos of the piston and barrel. It looks too symmetrical to seem like barrel distortion.


ace.cafe

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Re: Air cooled vs liquid cooled pistons
« Reply #4 on: January 05, 2013, 04:04:29 PM »
Well, that's a classic 4-point seizure.
Typically the sign of an overheated piston.
I don't see signs of any real blow-by, so I really can't say what overheated it.

After looking up the specs on the DRZ, it's a short stroke engine, that doesn't have nearly the side thrust issues that the long stroke Bullet has.
It's a pretty big stretch to expect a piston designed for a 62mm stroke to perform in an engine with a 90mm stroke.




« Last Edit: January 05, 2013, 04:35:13 PM by ace.cafe »
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basanti

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Re: Air cooled vs liquid cooled pistons
« Reply #5 on: January 05, 2013, 05:33:26 PM »
I not sure but I think I may have figured out why the DRZ  piston seized. I was comparing the JE piston and the DRZ piston and specifically looking at oil holes. On the JE piston there is an oil feeder line that goes from the oil ring groove to the gugeon pin bore thus lubricating the gugeon pin. There is no such lubrication system on the DRZ piston. Plus the oil holes on the oil ring groove are bigger on the JE piston.

This seems in accordance with a manual I came across that had a picture of the exact same seizure pattern as my piston and attributed it to the gugeon pin not getting lubrication and over heating thus leading to that type of seizure.

But then I wonder how does the DRZ engine get by.

ace.cafe

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Re: Air cooled vs liquid cooled pistons
« Reply #6 on: January 05, 2013, 05:44:39 PM »
The short stroke engine has much less pin movement and much less side thrust angle, which involve things in the piston design requirement.

Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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basanti

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Re: Air cooled vs liquid cooled pistons
« Reply #7 on: January 05, 2013, 06:31:41 PM »
The short stroke engine has much less pin movement and much less side thrust angle, which involve things in the piston design requirement.

Wow, imagine that! Everyday some thing new :)

Thank you for the answers,  Ace!

Arizoni

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Re: Air cooled vs liquid cooled pistons
« Reply #8 on: January 05, 2013, 07:44:00 PM »
I'm just guessing but the short piston shown in the photos looks like it is made for a short stroke engine.

Doing a bit more guessing, if I use the 90mm size as the diameter piston and the 398cc capacity I find listed for the Suzuki DRZ  that bikes engine would have a 62.6mm stroke (2.46 inches).

If this number crunching is right it may be that the 90mm (3.54") stroke the Royal Enfield has is too much for that short piston and is causing the Suzuki piston to rock about the wrist pin (gudgeon) which could create very heavy loads on the front and rear of the piston.
These heavy loads could wipe off the bores lubricating oil resulting in the galling shown in the photos.

As I say, I'm just guessing but I would expect to see a much longer skirted piston in a engine with the long stroke our RE's have.
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ace.cafe

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Re: Air cooled vs liquid cooled pistons
« Reply #9 on: January 05, 2013, 08:09:29 PM »
I'm just guessing but the short piston shown in the photos looks like it is made for a short stroke engine.

Doing a bit more guessing, if I use the 90mm size as the diameter piston and the 398cc capacity I find listed for the Suzuki DRZ  that bikes engine would have a 62.6mm stroke (2.46 inches).

If this number crunching is right it may be that the 90mm (3.54") stroke the Royal Enfield has is too much for that short piston and is causing the Suzuki piston to rock about the wrist pin (gudgeon) which could create very heavy loads on the front and rear of the piston.
These heavy loads could wipe off the bores lubricating oil resulting in the galling shown in the photos.

As I say, I'm just guessing but I would expect to see a much longer skirted piston in a engine with the long stroke our RE's have.

This is correct.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

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barenekd

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Re: Air cooled vs liquid cooled pistons
« Reply #10 on: January 05, 2013, 10:27:04 PM »
The internal bits always run a bit hotter than a watercooled engine, so a bit more piston clearance might help. However, if the piston is rocking too much, that can only get worse. Solution, find a longer piston and add a bit more clearance.
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basanti

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Re: Air cooled vs liquid cooled pistons
« Reply #11 on: January 06, 2013, 03:18:14 PM »
As I say, I'm just guessing but I would expect to see a much longer skirted piston in a engine with the long stroke our RE's have.
It's a pretty big stretch to expect a piston designed for a 62mm stroke to perform in an engine with a 90mm stroke.

You guys do have a point there. But my engine is destroked to 84mm. And I had measured the 2 pistons side by side: the JE piston skirt was 53 mm and the DRZ piston skirt was 46 mm. A difference of 6 mm which doesn't seem like much.


baird4444

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Re: Air cooled vs liquid cooled pistons
« Reply #12 on: January 06, 2013, 03:51:10 PM »
seems like I remember reading that an "Old school"
and very cheap way to go with a lighter piston is
to cut about 1/2'' off the skirt of stock job with a hacksaw....
   if so, how does this play into the discussion??
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ace.cafe

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Re: Air cooled vs liquid cooled pistons
« Reply #13 on: January 06, 2013, 05:14:31 PM »
You guys do have a point there. But my engine is destroked to 84mm. And I had measured the 2 pistons side by side: the JE piston skirt was 53 mm and the DRZ piston skirt was 46 mm. A difference of 6 mm which doesn't seem like much.

Well, you are now in "no-man's land" with a new engine design that has nothing in common with the original engine.

Good luck.


« Last Edit: January 06, 2013, 05:18:32 PM by ace.cafe »
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head . Pistons, cams, etc. Highest performance Bullet engine mods available .  AVL mods. Redditch 700/750 Twin mods. UCE kit soon.

Please visit my new website:
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